Genetika Sapi Kambing

8/12/2019 Genetika Sapi Kambing

1/20


2/20

planning stages. With the available genome information,however, there is an explosion of information in studiesrelating to genome variation and various aspects of disease,production, and adaptation. However, genome research inrelation to diseases in farm animals is less intense and alsodiffers in several respects from that in humans. The mainfocus of research into the genetic basis of animal diseasesis the prospect of increasing productivity for human benetor using such as models for human disease research. Theattention now is also being directed toward breeding fordisease resistance. Effective exploitation of disease-resis-tant livestock or complete elimination of diseased livestock must be backed by knowledge of the genes, the causalmutations, and interactions with other factors that conferresistance. Although diseases controlled by monogenic locitend to be eliminated through years of breeding from thestock, they still occur from time to time with associatedlosses. The specic mutations responsible for some of thesediseases with a simple Mendelian mode of inheritance stilleludes investigation and therefore still pose a great chal-lenge to geneticist. On the other hand, some of the mosteconomically important diseases of livestock are controlledby variations on many genes, further compounded by host9 pathogen 9 environment interactions. Elucidating thegenetic basis of such diseases has been most challengingand research efforts are intensifying in this regard. In thisreview, we shall attempt to summarize and analyze thetypes of reported mutations responsible for some animal(cattle, goat, pig and sheep) diseases in todays agriculture.

Functional consequences of DNA polymorphismsin single-locus-disease genes

About 200 diseases of cattle, goat, pig, and sheep are thoughtto be caused by sequence variations in single genes, of whichthe causal mutations in less than half of them have beenelucidated. The causal mutations are found in the coding andnoncoding regions with profound consequences on mRNAprocessing and stability of the protein product. Furtherinformation on animal diseases with a simple mode of inheritance can be seen at http://www.omia.angis.org.au /.Table 1 presents a summary of the genes and type of muta-tions implicated in several diseases of livestock.

Coding region disease variants and the consequencesfor causal mutations

The coding region is the portion of a gene that is tran-scribed and translated into proteins and does not includesuch regions as a recognition site, initiator sequence, ortermination sequence. All the different types of polymor-phisms have been reported in monogenic disease genes of

livestock. The majority of cases are caused by SNPs withvarying degrees of effects on gene action, such as substi-tuting one amino acid for another, duplications anddeletions that lead to frame shift and premature terminationof translation, and complete deletion of entire exon(s) orgene(s) in diseased individuals. These changes in codingregions have been recognized to inuence gene function byaffecting mRNA splicing patterns (Cartegni et al. 2002) orby altering protein function.

In a simple amino acid exchange caused by a SNP, onemay not expect much change in protein function or abun-dance becauseonly one amino acid out of hundreds of othershas been altered. However, the amino acid in question or thepart of the protein where the change takes place determinesthe effect of the mutation. In most reports, pathologicmutations are found to occur in functionally conservedregions of the protein, with effects ranging from reducedexpression of the mutant protein, to altered function, tocomplete abolition of expression. In a disease condition likecomplex vertebral malformation in cattle, Thomsen et al.(2006) found the causal mutation to be a substitution of thymine for guanine (nucleotide 559) of the SLC35A3 gene,which led to a change in amino acid 180, from valine tophenylalanine. This mutation results in abnormal nucleo-tide-sugar transport into the Golgi apparatus, thus disruptingnormal protein glycosylation. In bovine Ehlers-Danlossyndrome, Tajima et al. ( 1999) reported a SNP (G254A)that occurred in the serine-glycine dipeptide repeat region of the binding portion of DSPG3 gene. The G254A substitutionmight be considered a simple nucleotide change, but itcaused an amino acid change (serine to asparagine) that isresponsible for functional abnormality in cutaneous tissuesof carrier individuals. Another mutation, A383G orAsp128Gly, detected in a highly conserved region of theextracellular portion of the CD18 gene (codes for a glyco-protein), is responsible for leukocyte adhesion deciency(LAD) in Holstein cattle (Shuster et al. 1992). Shuster et al.(1992) estimated the carrier frequency of the Asp128Glyallele at about 15% in bulls of U.S. Holstein populations andat about 6% in cows. This mutation is also present in Hol-stein cattle throughout the world, making LAD one of themost common genetic diseases of Holstein cattle. Also,substitution of an evolutionarily conserved glutamic acid bylysine (p.Glu1200Lys), caused by a c.3598G [ A transitionin the FBN1 gene, results in bovine Marfan syndrome(Singleton et al. 2005). The glutamic acid residue is part of acalcium-binding epidermal growth factor-like molecule,which is also frequently altered in human Marfan syndrome(Rantamaki et al. 1999).

In some instances, different SNPs on the same gene areknown to be responsible for the same genetic disorder indifferent breeds. A good example is bovine lysosomala-mannosidosis whereby a T961C (or Phe321Leu) is

E. M. Ibeagha-Awemu et al.: Disease-associated DNA polymorphisms in farm animals 227

1 3
http://www.omia.angis.org.au/http://www.omia.angis.org.au/


3/20


4/20

T a

b l e 1 c o n t i n u e d

D i s e a s e / t r a i t

S p e c i e s

G e n e n a m e

G e n e s y m b o l V a r i a n t o r m u t a t i o n a

R e f e r e n c e

G e n e t i c t e s t

G l y c o g e n s t o r a g e d i s e a s e I I

C a t t l e

A c i d i c a l p h a - g l u c o s i d a s e A A G

( 1 ) D i n u c l e o t i d e d e l e t i o n i n e x o n 1 8 i n

S h o r t h o r n s ( 2 4 5 4 D C A ) l e a d s t o f r a m e s h i f t

a n d p r e m a t u r e t e r m i n a t i o n

D e n n i s e t a l . 2

0 0 0

Y e s , D

e n n i s e t a l . 2

0 0 0

( 2 ) D i n u c l e o t i d e d e l e t i o n i n e x o n 7 i n B r a h m a n

1 0 5 7 D T A ) l e a d s t o f r a m e s h i f t a n d p r e m a t u r e

t e r m i n a t i o n

( 3 ) 1 7 8 3 C ?

T i n e x o n 1 3 i n S h o r t h o r n s l e a d t o

A r g 5 9 5 X

G l y c o g e n s t o r a g e d i s e a s e V

C a t t l e

M y o p h o s p h o r y l a s e

P Y G M

C ?

T , 4

8 9 A r g ( C G G ) t o T r p ( T G G )

T s u i j i n o e t a l . 1

9 9 6

Y e s , T

s u i j i n o e t a l . 1

9 9 6 ;

B i l s t r o m e t a l . 1

9 9 8

S h e e p

M u s c l e g l y c o g e n

p h o s p h o r y l a s e

P Y G M

G ?

A s u b s t i t u t i o n a t t h e 3 0 s p l i c e s i t e o f i n t r o n

1 9 l e a d s t o a 8 - b p d e l e t i o n a t t h e 5

0

e n d o f

e x o n 2 0

, c r e a t i n g a f r a m e s h i f t a n d r e s u l t i n g i n

a p r e m a t u r e s t o p c o d o n

T a n e t a l . 1

9 9 7

Y e s , T

a n e t a l . 1

9 9 7

G o i t e r f a m i l i a l

C a t t l e

T h y r o g l o b u l i n

T G

C ?

T t r a n s i t i o n i n e x o n 9 c r e a t e s a s t o p c o d o n a t

p o s i t i o n 6 9 7

R i c k e t t s e t a l . 1

9 8 7

Y e s , R

i c k e t t s e t a l . 1

9 8 7

G o a t ( D u t c h )


T G

C ?

G i n e x o n 8 l e a d s t o p r e m a t u r e s t o p c o d o n

( T A C o r T y r ?

T A G o r s t o p c o d o n

V e e n b o e r a n d d e V i j l d e r

1 9 9 3

Y e s , V

e e n b o e r a n d d e V i j l d e r

1 9 9 3

A l s o C ?

T i n e x o n 5 l e a d s t o S e r ?

L e u

G o a t


T G

5 3 7 C ?

T i n e x o n 5 l e a d s t o 1 6 0 S e r ?

L e u , 3

6 0 -

b p i n s e r t i o n i n i n t r o n 5 , G ?

A / C ?

T i n

o p p o s i t e s t r a n d i n 3 0 U T R

v a n O m m e n e t a l . 1

9 8 9

H y p e r c h o l e s t e r o l e m i a

P i g

L o w - d e n s i t y l i p o p r o t e i n

r e c e p t o r

L D L R

2 5 0 C ?

T l e a d s t o 8 4 c g c t o t g c ( R 8 4 C

)

H a s l e r - R a p a c z e t a l .

1 9 9 8 ; G r u n w a l d e t a l .

1 9 9 9

T e s t , H a s l e r - R a p a c z e t a l . 1

9 9 8 ;

G r u n w a l d e t a l . 1

9 9 9

I m m o t i l e s h o r t - t a i l s p e r m

d e f e c t

P i g

K P L 2 p r o t e i n

K P L 2

I n s e r t i o n o f a 9 0 0 0 - b p r e t r o t r a n s p o s o n i n i n t r o n

3 0 l e a d s t o a b e r r a n t s p l i c i n g

S i r o n e n e t a l . ,

2 0 0 6

Y e s , S

i r o n e n e t a l . 2

0 0 6

L e t h a l t r a i t A 4 6

C a t t l e

S o l u t e - l

i n k e d c a r r i e r

3 9 A 4

S L C 3 9 A 4

G ?

A i n r s t n t . o

f i n t r o n 1 0 l e a d s t o d e l e t i o n o f

e x o n 1 0

Y u z b a s i y a n - G u r k a n a n d

B a r t l e t t 2 0 0 6

N o

M a l i g n a n t h y p e r t h e r m i a o r

p o r c i n e s t r e s s s y n d r o m

P i g

R y a n o d i n e r e c e p t o r 1

( s k e l e t a l m u s c l e )

R Y R 1

1 8 4 3 C ?

T l e a d s t o R 6 1 5 C

F u j i i e t a l . 1

9 9 1

L e e e t

a l . 2

0 0 2

M a p l e s y r u p u r i n e d i s e a s e

C a t t l e

B r a n c h e d - c h a i n k e t o a c i d

d e h y d r o g e n a s e E 1 -

a

B C K D H A

C 1 3 8 0 T l e a d s t o P r o 3 7 2 L e u i n P o l l S h o r t h o r n s Z h a n g e t a l . 1

9 9 0 ;

Y e s , D

e n n i s a n d H e a l y 1 9 9 9

C 2 4 8 T l e a d s t o G l u 6 X i n P o l l H e r e f o r d

D e n n i s a n d H e a l y

, 1 9 9 9

M a r f a n s y n d o m e

C a t t l e

F i b r i l l i n 1

F B N 1

c . 3 5 9 8 G [ A l e a d s t o p . E 1 2 0 0 K ( G A A

? A A A )

S i n g l e t o n e t a l . 2

0 0 5

Y e s , S

i n g l e t o n e t a l . 2

0 0 5

M u c o p o l y s a c c h a r i d o s i s I I I D

G o a t

G l u c o s a m i n e ( N - a c e t y l ) -

6 - s u l f a t a s e

G N S

C ?

T l e a d s t o C G A ?

U G A

, p r e m a t u r e s t o p

c o d o n a t p o s i t i o n 1 0 2

C a v a n a g h e t a l . 1

9 9 5

Y e s , H

o a r d e t a l . 1

9 9 8

M u l e f o o t d i s e a s e

( s y n d a c t y l y )

C a t t l e ( H o

l s t e i n )

L R P 4

C p G / A p T n o n c o n s e r v a t i v e s u b s t i t u t i o n i n e x o n

3 3 ( C 4 8 6 3 A

, G 4 8 6 4 T )

D u c h e s n e e t a l . 2

0 0 6

N o

C a t t l e ( A n g u s )

L R P 4

G ?

T i n r s t n t o f i n t r o n 3 7 p r e v e n t s

n o r m a l

s p l i c i n g

J o h n s o n e t a l . 2

0 0 6

N o


1 3


5/20

T a

b l e 1 c o n t i n u e d

D i s e a s e / t r a i t

S p e c i e s

G e n e n a m e

G e n e s y m b o l V a r i a n t o r m u t a t i o n a

R e f e r e n c e

G e n e t i c t e s t

M y o p a t h y o f t h e

d i a p h r a g m a t i c m u s c l e s

C a t t l e

H e a t s h o c k 7 0 - k

D a

p r o t e i n 2

H S P A 1 B

D e l e t i o n o f H S P A 1 B

S u g i m o t o e t a l . 2

0 0 3

N o

M y o t o n i a

G o a t

C h l o r i d e c h a n n e l 1

C L C N 1

G ?

C , l

e a d s t o 8 8 5 A l a ?

P r o ( G C C ? C C C )

B e c k e t a l . 1

9 9 6

N o

N e u r o n a l c e r o i d

l i p o f u s c i n o s i s

C a t t l e

C e r o i d - l i p o f u s c i n o s i s ,

n e u r o n a l 5

C L N 5

c . 6 6 2 d u p G l e a d s t o f r a m e s h i f t a n d p r e m a t u r e

t e r m i n a t i o n ( p

. A r g 2 2 1 G l y f s X 6 )

H o u w e l i n g e t a l . 2

0 0 6

Y e s , H

o u w e l i n g e t a l . 2

0 0 6

S h e e p

C a t h e p s i n D

C T S D

G ?

A l e a d s t o c o n v e r s i o n o f a n a c t i v e s i t e A s p

t o A s n t h a t r e s u l t s i n a n e n z y m a t i c a l l y

i n a c t i v e b u t s t a b l e p r o t e i n

T y y n e l a e t a l . 2

0 0 0

N o

N o n s h i v e r i n g t h e r m i o g e n e s i s P i g

U n c o u p l i n g p r o t e i n 1

U C P 1

D e l e t i o n o f e x o n s 3 , 4 , a n d 5 .

B e r g e t a l . 2

0 0 6

N o

P o l l e d i n t e r s e x s y n d r o m e

G o a t

P I S R T 1 /

F O X L 2 /

S R Y

D e l e t i o n o f 1 1

. 7 - k

b r e g u l a t o r y r e g i o n

i n c l u d i n g

t h e

P I S R T 1 a n d F O X L 2 g e n e s .

S R Y g e n e

i n h i b i t s P I S R T 1 a n d F O X L 2 g e n e s i n X Y

( n o r m a l ) m a l e s

P a i l h o u x e t a l . 2

0 0 1 ,

2 0 0 5

N o

P o r c i n e d e n s e d e p o s i t d i s e a s e

o r m e m b r a n o p r o l i f e r a t i v e

g l o m e r u l o n e p h r i t i s t y p e I I

P i g

F a c t o r H

T 3 6 1 0 G l e a d s t o I 1 1 6 6 R w h i c h c a u s e s a b l o c k

i n p r o t e i n r e l e a s e , r e s u l t i n g i n i n t r a c e l l u l a r

a c c u m u l a t i o n o f m u t a t e d p r o t e i n . A l s o ,

C 1 5 9 0 G l e a d s t o L 4 9 3 V

H e g a s y e t a l . 2

0 0 2

N o

P o r p h y r i a c u t a n e a t a r d a

S h e e p

U r o p o r p h y r i n o g e n

d e c a r b o x y l a s e

U R O D

C ?

T l e a d s t o L e u 1 3 1 P r o , l

o c a t e d w i t h i n t h e

a c t i v e c l e f t s i t e o f U R O D p r o t e i n

N e z a m z a d e h e t a l . 2

0 0 5

N o

P r o t o p o r p h y r i a

C a t t l e

F e r r o c h e l a t a s e

F E C H

1 2 5 0 G ?

T c h a n g e d s t o p c o d o n t o l e u c i n e

( X 4 1 7 L e u )

J e n k i n s e t a l . 1

9 9 8

Y e s , J

e n k i n s e t a l . 1

9 9 8

R e n a l t u b u l a r d y s p l a s i a

C a t t l e

C l a u d i n 1 6

C L D N 1 6

D e l e t i o n o f 3 7 - k

b r e g i o n i n c l u d i n g e x o n s 1 t o 4

( t y p e 1 m u t a t i o n ) .

O h b a e t a l . 2

0 0 0

Y e s . H

i r a n o e t a l . 2

0 0 2

5 6 - k

b d e l e t i o n c o n t a i n i n g e x o n s 1 t o 4 a n d 2 1 b p

o f e x o n 5 ( t y p e 2 m u t a t i o n ) .

H i r a n o e t a l . 2

0 0 2

S e x r e v e r s a l : X Y f e m a l e

C a t t l e

S e x d e t e r m i n i n g r e g i o n Y S R Y

P o s s i b l e d e l e t i o n o f

S R Y g e n e

K a w a k u r a e t a l . ,

1 9 9 6

Y e s , K

a w a k u r a e t a l . 1

9 9 6

S p h e r o c y t o s i s

C a t t l e

S o l u t e c a r r i e r f a m i l y 4 ,

a n i o n e x c h a n g e r ,

m e m b e r 1

S L C 4 A 1

C ?

T l e a d s t o C G A ?

T G A ( A r g ? S t o p i . e

.

R 6 6 4 X )

I n a b a e t a l . 1

9 9 6

Y e s , I

n a b a e t a l . 1

9 9 6 ;

K a g e y a m a e t a l . 2

0 0 6

V i t a m i n D - d e c i e n c y r i c k e t s ,

t y p e I .

P i g

C y t o c h r o m e P 4 5 0 C 1 o r

C Y P 2 7 B 1

P 4 5 0 C 1

1 7 3 o r 3 2 9 b p d e l e t i o n s i n v o l v i n g e x o n s 5 , 6 ,

a n d 7 l e a d s t o e x p r e s s i o n o f n o n s e n s e

p r o d u c t s

C h a v e z e t a l . 2

0 0 3

N o

a

V a r i a n t o r m u t a t i o n n o t a t i o n s a r e

a s u s e d i n t h e i r o r i g i n a l p u b l i c a t i o n s

230 E. M. Ibeagha-Awemu et al.: Disease-associated DNA polymorphisms in farm animals

1 3


6/20

responsible for the condition in Angus cattle, while G662A(or Arg221His) is the causal polymorphism in Gallowaycattle (Tollersrud et al. 1997). The amino acids substitutedin both cases are conserved among the a-mannosidaseclass-2 family, indicating important roles in protein func-tion. Their independent substitution therefore disrupted thefunction of the protein, to the same extent, leading to adeciency of lysosomal a-mannosidase. Molecular heter-ogeneity also exists in bovine maple syrup urine disease(MSUD) (Dennis and Healy 1999; Zhang et al. 1990) andglycogen storage disease II (Dennis et al. 2000). Zhanget al. (1990) investigated Polled Shorthorn with MSUDand found the causal mutation to be 248C ? T in exon 2 of the BCKDHA gene that is responsible for converting 6glutamine to a premature stop codon. In Polled Herefordsconversely, the same condition is caused by a 1380C ? T(Pro372Leu) mutation in the same gene (Dennis and Healy1999). In both cases an important functional part of thegene is either absent (premature stop codon) or altered(Pro372Leu). Further investigations with crosses of PolledHerefords and Polled Shorthorns with the disease showedheterozygosity for both mutations (Healy and Dennis1994).

SNPs that change an amino acid to a stop codon bringabout premature termination and, in some of the mono-genic-disease loci in livestock, lead to a completedisruption in protein synthesis or the production of shortertranscripts with decreased activity. Such conditions areusually responsible for nonsense-mediated mRNA decay(Culbertson 1999). Goiter in both cattle and goats developsfrom SNPs that cause premature termination of mRNAtranslation of the TG gene (Ricketts et al. 1987; Veenboerand de Vijlder 1993). A nonsense mutation (R238X) in theFMO3 gene that underlies shy off-avor in cows milk was shown to eliminate about 50% abundance of the genein heterozygous carriers (Lunden et al. 2002). Completelack of FMO3 activity, necessary for complete oxidation of trimethylamine to an odorless compound, may therefore bethe case in homozygous carriers of the condition. Pierceet al. (2001) observed that the molecular basis of bovinemyoclonus is the substitution of tyrosine by a terminationcodon (Tyr24X) in exon 2 of the Glra1 gene. The stopcodon results in a prematurely truncated protein that lacksligand-binding and membrane-spanning domains. Inbovine beta mannosidosis, the lack of 22 C-terminal aminoacids in mutant proteins, the result of a nonsense mutationin the MANBA gene, indicates their importance in thestability and proper functioning of the enzyme (Leipprandtet al. 1999). In the same condition in goats, an earliertermination of mRNA synthesis is brought about by asingle base deletion (1398delG) that results in a shift in thereading frame and production of a shorter peptide, 481amino acids compared with 879 amino acids of the normal

protein (Leipprandt et al. 1996). Deciency of uridinemonophosphate synthase in cattle also results from amutant protein lacking 76 C-terminal amino acids (Schw-enger et al. 1993). A rare situation occurs in bovineprotoporphyria where a SNP changes a stop codon to acoding amino acid (TGA to TTA or X417Leu) therebyadding 27 more amino acids to mutant proteins (Jenkinset al. 1998). This addition affects catalytic activity of theenzyme since it occurs in the carboxyl terminal, known toplay important roles in catalytic function.

Single-base-pair (bp) deletions or insertions to exonsand whole genes are also important players in alteringprotein function and causing disease conditions in farmanimals. In addition to the single-bp deletion that causedcaprine mannosidase beta described above, a 17-bp dele-tion in ADAMTS2 is responsible for Ehlers-Danlossyndrome type VII in cattle (Colige et al. 1999), while a20-bp deletion in CHRNE causes bovine congenital my-asthemic syndrome (Kraner et al. 2002). Larger deletionsinvolving whole exons are reported for genes causingbovine renal tubular dysplasia (Hirano et al. 2002; Ohbaet al. 2000) and porcine nonshivering thermiogenesis (Berget al. 2006). On a more dramatic note, whole genes aredeleted or suspected of being deleted in conditions likebovine myopathy of the diaphragmatic muscles (Sugimotoet al. 2003), sex reversal (XY female) in cattle (Kawakuraet al. 1996), and polled intersex syndrome in goats (Pail-houx et al. 2005). Reports of pathologic insertions rangefrom single bp to several hundred bp in conditions likebovine factor XI deciency and bovine neuronal ceroidlipofuscinosis (Houweling et al. 2006; Kunieda et al. 2005;Marron et al. 2004). The effects of these deletion/insertionmutations include shift in reading frame and prematuretermination and, in extreme cases like whole gene dele-tions, total absence of protein activity.

Consequences of causal SNPs in noncoding regions

The noncoding regions of genes constitute the promoter, 5 0

and 30 untranslated regions (UTRs), introns, and intergenicor large regions between genes. In these regions are foundregulatory sequences that affect gene splicing, transcrip-tion, and translation. Polymorphisms in these regions canalter gene expression as has been demonstrated as thegenetic basis of some animal diseases with a simple modeof inheritance.

Deletion of a 11.7-kb intergenic region on the Y chro-mosome triggers intersexuality and polledness in goats(Pailhoux et al. 2001). This region contains mainly repet-itive sequences and its deletion affects the transcription of two genes, namely, PISRT1 that encodes a 1.5-kb mRNAdevoid of open reading frame, and FOXL2 , known to beresponsible for blepharophimosis epicanthus inversus


1 3


7/20

syndrome in humans (Crisponi et al. 2001). The deletion,even though located 20 ( PISRT1 ) and 200 (FOXL2 ) kbaway from the genes, contains regulatory sequences whoseabsence has direct consequences on the transcription of both genes. In goats with XX sex-reversed gonads, theexpression of PISRT1 decreases between 36 days post-coitus (dpc) and 40 dpc accompanied with an increase inSOX9 expression (Pailhoux et al. 2001). SOX9 gene is animportant regulator of testis development that functions bytriggering AMH transcription (Arango et al. 1999; Koop-man 1999). On the other hand, FOXL2 is involved in earlyovarian differentiation and development, possibly by hav-ing a function in folliculogenesis (Crisponi et al. 2001;Pailhoux et al. 2001). In normal circumstances, therefore,PISRT1 functions by inhibiting SOX9 as an antitestis genewhile FOXL2 promotes ovarian development. In normalmales, another gene, SRY , has the inhibitory function of inactivating the transcription of both genes.

Intronic splice-site mutations are responsible for ovineglycogen storage disease, mule foot, lethal trait A46, andanhydrotic ectodermal dysplasia diseases of cattle(Drogenmu ller et al. 2002; Johnson et al. 2006; Tan et al.1997; Yuzbasiyan-Gurkan and Bartlett 2006). In ovineglycogen storage disease, a G ? A transition at the 3 0 splicesite of intron 19 of the PYGM gene causes a frame shift intranslation, resulting in a premature codon and the removalof the last 31 amino acid residues from the C-terminal of the protein in affected individuals (Tan et al. 1997). Con-sequently, there is a deciency of the muscle glycogenphosphorylase enzyme which is responsible for catalyzingbreakdown of muscle glycogen stores to glucose-1-phos-phate in affected individuals (Schmid and Mahler 1959).Another G ? A transition at the rst nucleotide of intron 37of the LRP4 gene completely disables this donor splice site,thereby abrogating the normal splicing of the gene (John-son et al. 2006). The effect of the mutation of this highlyconserved guanine base is the disruption of the normalfunctioning of the protein in affected individuals throughthe production of a dysfunctional membrane-anchoredreceptor lacking the normal cytoplasmic domain (Johnsonet al. 2006). There is reduced mobility accompanied bypainful fusion of hooves in affected subjects. A furthersplice-site variant, also a G ? A transition of the rstnucleotide of intron 10 ( SCL39A4 gene) leads to the out-splicing of the entire exon 10 in affected animals (Yuz-basiyan-Gurkan and Bartlett 2006). The resultant protein ispredicted to lack two critical motifs implicated in the for-mation of a pore responsible for impaired zinc absorptionin diseased individuals (Yuzbasiyan-Gurkan and Bartlett2006). Another splice-site donor variant involves a G ? Ttransversion located at the second position of intron 8 of the ED1 gene resulting in anhydrotic ectodermal dysplasiaphenotype in cattle (Drogenmu ller et al. 2002). The effect

of this mutation is a translated protein with a large deletionin the functionally important C-terminal tumor necrosisfactor-like domain. Recent ndings suggest that the ED1gene plays a role in the development of mucous glands,the absence of which resembles a feature of X-linkedanhydrotic ectodermal dysplasia in human patients(Seeliger et al. 2005).

A rare situation in causal SNPs in noncoding regions isthe insertion of a 9000-bp retrotransposon within intron 30of the KPL2 gene which causes immotile short-tail spermdefect in pig (Sironen et al. 2006). Interestingly, theinserted retrotransposon affects splicing of the KPL2transcript in two ways: it causes either skipping of anupstream exon or inclusion of an intronic sequence as wellas part of the insertion in the transcript. Both scenarios alterthe reading frame leading to premature termination of translation. Sironen et al. ( 2006) further demonstrated thatthe aberrantly spliced exon is expressed predominantly intesticular tissue, thus explaining the tissue specicity of theimmotile sperm defect and the importance of the KPL2gene in correct axoneme development.

Functional consequences of DNA variationsin multigenic-disease loci

Several economically important diseases of farm animals,including mastitis, transmissible spongiform encephalopa-thies (TSEs), brucellosis, dermatophilosis, trypanosomiasis,and tick resistance, pose a problem for satisfactory controlor complete eradication because of the complex interplay of factors that support their development, namely, the patho-gen, the environment, and animal-related factors. Initialmethods of control like changes in management, treatment,vaccination, pathogen control, movement control, slaughter,isolation, and quarantine of diseased animals are no longerattractive due to increased pathogen resistance to chemo-therapeutic and prophylactic drugs and antibiotic residues inthe environment and animal products, just to mention a few.The option of exploiting host genetic resistance to controlthese diseases does not suffer these drawbacks in the broadsense and is the key to cheap and effective control. Unfor-tunately, these diseases are under the interplay of many geneloci that must be identied and characterized before satis-factory control can be achieved. The search for disease-resistance markers involves screening for associationbetween disease resistance and a variety of polymorphismsin candidate genes and anonymous markers and mapping forquantitative trait loci (QTLs). In particular, genetic traits of innate and acquired immunity related to resistance havereceived considerable attention and there is now evidencelinking variations within some of these genes with resistanceto diseases.


1 3


8/20

In particular, genes of the major histocompatibilitycomplex (MHC) or BoLA system ( http://www.ebi.ac.uk/ ipd/mhc /) are thought to play a role in host resistance againstthe development of these diseases. In cattle, the BoLA sys-tem is located on chromosome 23 and includes three classesof loci: class I (locus A); class II, divided into IIa (includesloci DRA, DRB1-3, DQA, DQB, etc.) and IIb (includesDOB, DYA, DYB, DIB, etc.); and class III (includes TNF,21-OH, C4, BF, HSP70-1 and -2, EAM, PRL, etc.) (Roths-child et al. 2000; http://www.ebi.ac.uk/ipd/mhc /). The rsttwo groups of loci code for surface molecules relevant in theinduction and regulation of immune responses. Some of these genes are highlypolymorphic, with about 100differentalleles described for DRB3 exon 2 and about 39 for DQB(Maillard et al. 2001; da Mota et al. 2004; http://www.projects.roslin.ac.uk/bola /). Numerous lines of evidenceindicate that the extensive polymorphisms reported for thesemolecules are responsible for the differences among indi-viduals in immune responses to infectious agents. Some of the advances achieved so far for a few of these diseases andtheir associated resistant/susceptible polymorphisms willnow be examined individually.

Mastitis

Mastitis is one of the most frequent, complex, and costlydiseases of dairy cattle, goat, and sheep and its developmentis inuenced by many genes, the environment, and patho-gen factors. Host genes that are receiving attention areimmunity traits and mainly include antibody response andfunctionality of neutrophils whose presence and function-ality are essential in the innate defense against udderinfections. The genetic variability of the immune mecha-nisms underlying mastitis resistance, including such genesas CD14 , CD18 , lactofferin, lysozyme, and class I and classII genes of MHC, have been reviewed by Detilleux ( 2002),Paape et al. (2003), and Rupp and Boichard ( 2003) andcould therefore aid in selection for mastitis resistance.

In dairy cattle, most studies have focused on exon 2 of the class II BoLA DRB3 because of its high polymorphism.In an early study, Dietz et al. ( 1997) associatedDRB3.2*16 with an increased risk for acute intramammaryinfection (mastitis). In the same year, Kelm et al. ( 1997)associated the same allele with higher estimated breedingvalue (EBV) for somatic cell score, and also DRB3.2*8 , IgG2

b , and CD18 A1 with increased EBV for clinicalmastitis. On the contrary, Sharif et al. ( 1998) signicantlyassociated DRB3.2*16 with lower somatic score or lowerrisk of mastitis in Holsteins but reported signicantassociation of DRB2.3*23 with occurrence of severemastitis. The presence of glutamic acid at position b74, amotif present in DRB3.2*22, *23, and *24 alleles, wasrecently associated with occurrence of mastitis caused by

Staphylococcus spp. (Sharif et al. 2000). Similarly, thesame authors indicated that the presence of arginine orlysine at position 13 of a motif present on DRB3.2*23 and*8 alleles showed a tendency toward association with ahigher risk of clinical mastitis; likewise, with presence of arginine at position b71 (present in alleles *23 and *22).More recently, Rupp et al. ( 2007) associated DRB3.2*3and *11 with lower somatic cell counts (SCC), alleles *22and *23 with higher SCC, allele *3 with less clinicalmastitis, and *8 with a higher mastitis risk. For MHC ClassI molecules, several studies have reported a relationshipbetween different alleles with mastitis resistance or sus-ceptibility (Mallard et al. 1995; Mejdell et al. 1994).Conicting as some of these results may seem, most stillpoint to the fact that variations within the BoLA systemgenes predispose to mastitis.

On immune genes, CXCR2 , a chemokine receptorrequired for neutrophil migration to infection sites, con-tains a SNP (+ 777G ? C) (Grosse et al. 1999; GenBank No. U19947) that is located in a region involved inmediating calcium signaling and mobilization as well as G-protein binding. Youngerman et al. ( 2004) showed that the+777GG genotype was associated with decreased per-centages of subclinical mastitis, while genotype CC hadincreased percentages of subclinical mastitis in Holsteincows. No difference in clinical mastitis incidence wasobserved between genotypes. In the same light, cows with+777CC or CG genotype showed signicantly lower neu-trophil migration to recombinant human (rh) IL-8 thanthose of GG genotype (Rambeaud and Pighetti 2005).Furthermore, they also demonstrated that neutrophilmigration of +777CC genotype to zymosan-activatedserum was slower compared to the other genotypes, andupregulation of CD18 expression after stimulation withrhIL-8 was also decreased. Further to the search, Ram-beaud et al. (2006) reported a signicant increase insurvival of neutrophils from cows with genotype +777CCin response to IL-8 compared with genotype +777GG. Onthe other hand, they observed a signicant reduction inneutrophil reactive oxygen species (ROS) generation inresponse to phorbol-13-myristate-12 acetate by neutrophilsof +777CC than of +777GG, although no differences inbactericidal activity or glutathione levels were observedamong genotypes. These results indicate that neutrophilsfrom cows with different CXCR2 genotypes vary in theirability to suppress apoptosis and produce ROS and there-fore may partly explain the inter- and intraindividualvariations observed in the development of mastitis. InCCR2 , another chemokine receptor gene, Leyva-Baca et al.(2007) associated c.414C [ T with estimated breeding valuefor somatic cell score and udder depth in Canadian Hol-steins, which indicates possible relationships with mastitis-related traits and estimated breeding values.


1 3
http://www.ebi.ac.uk/ipd/mhchttp://www.ebi.ac.uk/ipd/mhchttp://www.ebi.ac.uk/ipd/mhchttp://www.projects.roslin.ac.uk/bolahttp://www.projects.roslin.ac.uk/bolahttp://www.projects.roslin.ac.uk/bolahttp://www.projects.roslin.ac.uk/bolahttp://www.ebi.ac.uk/ipd/mhchttp://www.ebi.ac.uk/ipd/mhchttp://www.ebi.ac.uk/ipd/mhc


9/20

Other attempts at nding markers responsible for mas-titis incidence/resistance include anonymous markers ingenome scan approaches (Van Tassel et al. 2000) andmapping of QTLs with effects on SCC and clinical mastitison the 29 autosomes of cattle (Khatar et al. 2004; Sugimotoet al. 2006). The mapping of a QTL to a particular locationof the genome points to the location where the actualgene(s)/mutations responsible for the effect in questionmay be located. As a result, genes in the vicinity of a QTLare targets for possible associations with the condition inquestion. For example, Sugimoto et al. ( 2006) sequencedthree genes in the vicinity of a QTL for SCC and reported athree-base insertion in the glycine-coding stretch of FEZL gene (a transcription factor with a role in neuronal devel-opment) that resulted in the extension of 12 glycine (12G)residues to 13 (13G). Further analysis indicated that 12GFEZL inuences resistance to mastitis. Their results alsoindicated that FEZL induced lower expression of SEMA5A(axon-attracting molecule semaphorin 5A) in susceptibleanimals (13G). Meanwhile, in resistant animals (12G),enhanced SEMA5A induced expression of at least ninegenes related to immune responses, including TNF- a and IL-8. The implication of their ndings is that susceptibilityto mastitis results from an impaired immune response dueto the lower transcription activity of FEZL .

Transmissible spongiform encephalopathies or priondiseases

Transmissible spongiform encephalopathies (TSEs), alsoknown as prion diseases, are caused by the conversion of thehost-encoded prion protein (PrP) or normal cellular prionprotein (PrP c ) into a misfolded abnormal form of the protein.The misfolded prion protein (PrP sc ) results from pointmutations at the PRNP locus. There is, however, recentevidence implicating other genes or agents involved in theetiologyof TSE(Diazet al. 2005; Lloyd et al. 2001; Marcos-Carcavilla et al. 2007) thus making it a polygenic trait whoseresistance/susceptibility is controlled by one major gene(PRNP ) and modulated by several other genes. For thisreason, we have decided to discuss TSE in this section.

TSEs may occur as genetic, infectious, or sporadic dis-orders in humans, cattle, sheep, goat, deer, and otherdomestic animals (reviews by Priola and Vorberg 2004;Doherr 2006). The most common forms of TSEs arescrapie in sheep and goats and bovine spongiformencephalopathy (BSE) in cattle. One human form of TSE,variant Creutzfeldt-Jacob disease, is thought to be causedby BSE through the consumption of beef (Scott et al.1999), making TSE elimination from the food chain a pri-ority by most governments.

In sheep, about 23 SNPs in the PRNP gene have beenreported, of which three SNPs causing amino acid changes

within the protein-coding sequence have been associatedwith scrapie development (incubation period, pathology,and clinical signs) (reviewed by Baylis and Goldmann2004). The most important SNPs in terms of scrapie sus-ceptibility/resistance are SNPs that lead to amino acidchanges at codons 136 (A ? V), 154 (R? H), and 171(Q? H or Q? R) (Belt et al. 1995; Goldmann et al. 1990).136V has been associated with scrapie susceptibility inboth natural and experimental conditions, while 171R isassociated with low incidence (Belt et al. 1995; Hunteret al. 1993; Maciulis et al. 1992). These common variants,however, dene ve PRNP haplotypes, namely, ARQ(A136 R154 Q171 ), ARR, ARH, AHQ, and VRQ, that result in15 genotype combinations, each with an associated degreeof risk (Table 2). For instance, animals homozygous forVRQ rapidly develop clinical signs of scrapie wheninfected and are considered highly susceptible, while ani-mals homozygous for ARR are resistant (Belt et al. 1995;Hunter et al. 1996). Susceptibility of the haplotypes ARQ,AHQ, ARH, and ARK is more complex and varies withbreed. For example, ARQ/ARQ is the common genotypefor scrapie cases in Suffolk sheep (Hunter et al. 1997a, b),while scrapie is rare in Texel sheep of this genotype(Dawson et al. 1998). Furthermore, 171R is dominant forincreased scrapie resistance, implying that ocks derivedfrom 171RR founder animals are expected to remain scra-pie-free, even under exposure. In a recent study, Green et al.(2006) reported 36 previously unreported polymorphisms inthe PRNP gene and further dened regions of strong linkagedisequilibrium with the common resistant/susceptiblehaplotypes. In their study, the amino acid residues A136,R154, and Q171 were found within nine larger haplotypesspanning the entire PRNP gene (promoter, 5 0UTR, codingregion, and 3 0UTR). Also, VRQ was observed on two of these larger haplotypes and ARR, ARH, and AHQ on oneeach. The signicance of these observations to scrapiesusceptibility, which may explain the variation observedwith some genotypes, remains to be elucidated.

QTLs involved in resistance/susceptibility to scrapie andother TSEs in a region close to IL1B and IL1RN genes onsheep chromosome 3 and mouse chromosome 2 (Lloydet al. 2001; Manolakou et al. 2001; Moreno et al. 2003a, b)and in cattle (Zhang et al. 2004) have been reported.Marcos-Carcavilla et al. ( 2007) recently characterized the IL1B and IL1RN genes in sheep and also reported,respectively, 29 SNPs and 1 insertion and 2 SNPs and a 14-bp deletion within the genes. Expression analysis of thetwo genes by real-time RT-PCR found a signicantincrease in mRNA concentration of the genes in the cere-bellum of scrapie-infected sheep but not in healthy sheep.Their ndings are in agreement with previous studies(Campbell et al. 1994; Cunningham et al. 2005) thatrevealed an altered proinamatory cytokines prole


1 3


10/20

associated with nervous tissues during scrapie infection.They concluded that the increase in the mRNA levels of thegenes in the cerebellum of infected sheep may explain theneurodegeneration associated with the disease and the

differences in susceptibility observed between individualsof the same scrapie PRNP -associated genotypes. Theseobservations thus make the genes good positional andfunctional candidates involved in the modulation of thescrapie incubation period in sheep. More insights into thesignicance of the identied polymorphisms are needed formeaningful conclusions to be drawn. The possible role of other genes within this QTL region may not be ruled out.Other agents causing unexplained types of scrapie oratypical scrapie rst reported in Norway in 1998 are nowwidespread (Benestad et al. 2003; Moum et al. 2005; Orgeet al. 2004), and, recently, Lu hken et al. (2007) have

associated microsatellites MCMA53 and MCMA16 onsheep chromosome 15 with susceptibility to atypical scra-pie. Other polymorphic microsatelittes also occur withinthe ovine and bovine PRNP gene (Geldermann et al. 2003)

In goats, polymorphisms involving amino acid changesat codons 21 (V ? A), 23 (L ? P), 37 (G ? V), 49 (G ? S),102 (W? G), 110 (T ? N o r T? P), 127 (G? S), 133(L ? Q), 137 (M? I), 142 (I? M), 143 (H? R), 146(N? S),154 (R ? H), 168 (P ? Q), 211 (R ? Q), 218 (I ? L),220 (Q ? H), 222 (Q ? K), and 240 (S ? P) of the caprine

PrP have been reported (Acutis et al. 2006; Agrimi et al.2003; Billinis et al. 2002; Goldmann et al. 1996). Resultsfollowing experimental challenge and natural infectionindicate that variations at some of these codons may be

relevant for scrapie susceptibility (Billinis et al. 2002;Goldmann et al. 1996, 1998). Variants associated withscrapie-affected goats include VV 21 , LL23 , GG49 , SS49 ,IM142 , HH143 , HR143 , RR154 , PP168 , PP240 , SP240 , and SS240(Billinis et al. 2002; Goldmann et al. 1996). In addition, allscrapie-affected animals in Billinis et al. ( 2002) carriedHH143 RR154 . Furthermore, they associated seven PrPhaplotypes with scrapie-affected goats and ve with heal-thy goats, while two genotypes were common to bothgroups. In another study, Agrimi et al. ( 2003) foundassociations between scrapie susceptibility and the distri-bution of genotypes at codons 37, 143, and 240 in the

Italian Ionica breed of goats.SNPs resulting in amino acid substitutions in the bovine

PRNP gene have not been found. However, silent muta-tions and a variable number of octapeptide repeats in thecoding region as well as three mutations in the untranslatedexon 1 and its 5 0 anking region have been reported(Goldmann et al. 1991; Humeny et al. 2002). Furthermore,no or few associations between PRNP polymorphisms andBSE incidence have been found (Neibergs et al. 1994;Sander et al. 2004). A polymorphism (T174M) in another

Table 2 A summary of prionprotein gene ( PRNP ) genotypesassociated with different scrapiephenotypes in sheep and goat

a ARQ are amino acids atcodons 136, 154, and 171,respectively

Species/ breed

PRNP genotype Scrapie phenotype Reference

Sheep ARR a Resistant genotype Belt et al. 1995VRQ Susceptible genotype Belt et al. 1995ARH May be neutral Dawson et al. 1998AHQ Associated with resistance in

some breeds but not in othersDawson et al. 1998

VRQ/VRQ Carriers develop rapid clinicalsigns of scrapie when infected

Belt et al. 1995; Hunteret al. 1996; Bayliset al. 2002

ARQ/ARQ Scrapie susceptible in somebreeds and not in others

Hunter et al. 1997a, b;Dawson et al. 1998

ARR/ARR Carriers are highly resistant Belt et al. 1995; Hunteret al. 1996; Bayliset al. 2002

Goat VV 21 , LL23 , GG49 , SS49 , HH143 ,HR143 , RR154 , PP168 , PP240 ,SP240 and SS240

Variants found in scrapieaffected goats

Billinis et al. 2002

R143 and H154 Moderately protective againstscrapie

Billinis et al. 2002

K222 Associated to healthy animals orscrapie resistance

Acutis et al. 2006;Vaccari et al. 2006

Q168 Associated with scrapiesusceptibility

Acutis et al. 2006

M142 Associated with prolongedincubation period of scrapieand BSE in goats

Goldmann et al. 1996


1 3


11/20

gene close to PRNP in humans, the anking prion doppelgene (PRND ), is involved in susceptibility to sporadicCreutzfeldt-Jacob disease (Croes et al. 2004; Jeong et al.2005). This gene was identied in a search for genesparalogous to PRNP in mouse and a linked expressionbetween the two genes has been demonstrated (Mooreet al. 1999). In contrast to the PRNP gene, SNPs in thebovine PRND gene have been observed to result in aminoacid substitutions (R50H, N110H, R132Q) (Cominciniet al. 2001; Luhrs et al. 2003). In addition, two synony-mous SNPs, C4819T and T5063A, have been reported inGerman cattle breeds (Balbus et al. 2005). Haplotype andgenotype analyses of BSE and control animals revealedsignicantly different distribution of C4815T and R13Qpolymorphisms in German Simmental, while no BSE sus-ceptibility was associated with R50H and A5063T (Balbuset al. 2005). Two synonymous SNPs are also known tooccur in the ovine PRND gene.

Brucellosis

Natural resistance to brucellosis has been reported in sev-eral species, including cattle and humans (Montaraz andWinter 1986; Templeton et al. 1990). Through breedingstudies with cattle, Templeton et al. ( 1990) reported thatnatural resistance to Brucella could be dramaticallyincreased by selective breeding. With initial evidencelinking the Nramp1 gene to resistance/susceptibility inmice (Vidal et al. 1993), a later survey of the genes of several bovid species and the mode of inheritance of bru-cellosis in cattle suggest that other genes are involved inthe development of this disease (Adams and Templeton1998). In addition to several host factors that are associatedwith innate immunity against Brucella abortus (reviews byBaldwin and Parent 2002; Wyckoff 2002), polymorphismswithin the Nramp1 gene in cattle are associated with nat-ural resistance to brucellosis (Adams and Templeton 1998;Barthel et al. 2001). Basically, these polymorphismsinvolve a (GT) n repeat microsatellite in the 3 0UTR of Nramp1 . Adams and Templeton ( 1998) associated theGT13 allele with resistance toward B. abortus and the otheralleles, GT 1416 , with susceptibility. In another study,Paixao et al. (2006) detected GT 13 in cattle genotypicallyresistant to brucellosis and detected GT 14 , GT13 /GT14 , orGT13 /GT15 in genotypically susceptible cattle. However, anumber of studies have found a lack of association of GT 13with resistance to bovine brucellosis (Kumar et al. 2005;Paixao et al. 2007). In humans, Bravo et al. ( 2006) foundno association of susceptibility to brucellosis with severalpolymorphisms of the Nramp1 gene, while signicantassociations have been reported in Koreans (Ryu et al.2000). A Nramp1 SNP that actually led to a change in anamino acid in mice (G169D, Vidal et al. 1993) has not

been detected in any other mammalian species, includingcattle. However, monocytes from naturally resistant cattlecan more efciently resist the intracellular growth of B.abortus than those from susceptible cattle (Qureshi et al.1996; Templeton et al. 1990). From these accounts, it isclear that host ability to control the development of bru-cellosis is under the control of more than one gene, manynot yet identied and characterized.

Trypanosomiasis

In many parts of Africa, Asia, and South America, try-panosomiasis is one of the main debilitating and limitingfactors to animal productivity, infecting about 50 millioncattle and costing producers and consumers about US$11.2billion in losses (Kristjanson et al. 1999). Present controlmeasures include limitation of the tsetse vector through thewidespread use of insecticides and the use of trypanocidaldrugs to treat sick animals. Theuseof insecticide comes withextra cost and associated environmental problems, whiletrypanocidal drugs are limited and resistance to them isgrowing steadily. However, some local breeds of cattle(NDama, Muturu, Namchi), sheep (West African Dwarf),and goats (West African Dwarf) in the central/west Africanregion show natural resistance to the disease (Agyemang2005). The ability to naturally resist trypanosome infections,also known as trypanotolerance, results from several bio-logical mechanisms under multigenic control (review byNaessens 2006). Understanding of the genes that control thetrypanotolerant trait may offer new, cheaper, and saferapproaches to improving productivity of animals in endemiczones.

To date, numerous studies have been conducted but thekey genes responsible for susceptibility/resistance have notbeen identied and characterized. The results of severalstudies have shown that trypanotolerant livestock have aremarkable capacity to control parasitemia and, thus, thedevelopment of severe anemia during infection (Dolan1987; Gibson 2001; Trail et al. 1991, 1992). In an analysisof Boran/NDama chimeric twins, Naessens et al. ( 2003)conrmed that trypanotolerance is mediated by two inde-pendent mechanisms, (1) a better capacity to controlparasitemia, which was suggested not to be due to differ-ences in immune responses, and (2) a better capacity tocontrol associated anemia, mediated by cells from thehemopoietic system. Therefore, two pools of genes areinvolved but none of the numerous studies, includingzootechnical surveys (dIeteren et al. 1998; Murray et al.1991), quantitative genetic studies (Trail et al. 1994),electrophoretic analysis of targeted proteins (Queval andBambara 1984; Queval and Petit 1982), and genotyping of genes of the MHC (Maillard et al. 1989), have been able toidentify trypanotolerance genes. Using the QTL approach,


1 3


12/20

Hanotte et al. ( 2003) analyzed 16 bovine phenotypes,including anemia, body weight, and parasitemia, andidentied 18 QTLs linked to trypanotolerance. Their studyfurther indicated that trypanotolerance is a highly poly-genic trait with each gene or locus explaining only about1012% of the phenotypic variance of the trait. Most of theidentied QTLs were linked to the control of anemia,suggesting that anemia control is complex and of majorsignicance, and only a few were linked to parasitemia.Some authors have recently used the serial analysis of geneexpression (SAGE) approach and have identied 187 genesthat changed their expression in NDama leukocytes afterinfection by T. congolense (Berthier et al. 2003; Maillardet al. 2004, 2005). In another study using SAGE, Berthieret al. (2006) have constructed four different mRNA tran-script libraries from the white blood cells of a NDamatrypanotolerant animal obtained at different stages of development of experimentally induced trypanosomiasis(by T. congolense ). The libraries contain about 75,000sequences, including several known genes, described orexpressed sequence tags, and completely new genes thatmay be functional in trypanotolerance. The availability of these libraries may now facilitate the identication of genesand the functional mutations responsible for trypanotoler-ance in cattle and therefore better options for control. Inhumans, on the other hand, Courtin et al. ( 2006) haveassociated two SNPs (IL10 592 C/A and TNF 308 G/A ) withthe development of African trypanosomiasis whereby theIL10 - 592 A allele was found to present a lower risk of disease while TNF - 308 A presented a higher risk of developing the disease early after exposure.

Dermatophilosis and other tick infections

Dermatophilosis, a severe skin disease of ruminants, iscaused by the lamentous actinomycete bacterium Der-matophilus congolensis and is aggravated by the presenceof the tick Amblyomma variegatum (Ambrose et al. 1999;Morrow and Compton 1991). It results in the death of up to15% of infected stock. Present control measures are ham-pered by the development of chemoresistance to acaricidesand antibiotics and there is little success in the develop-ment of a vaccine against the disease. However, eldstudies indicate differential breed response to the devel-opment of severe dermatophilosis, particularly a higherresistance by the west African NDama (taurine) breed,intermediate resistance by zebu breeds like the Sanga of Ghana and Gudali of Cameroon, and high susceptibility byimported (into tropical regions) breeds like Friesian (Ko-ney et al. 1994; Leroy and Marchot 1987; Mattioli et al.1995). Several studies on host immunity to dermatophilosissuggest two possible mechanisms of immunity: antibody-mediated prevention of the establishment of infection and

antibody- or cell-mediated clearance of infection (How andLloyd 1988; Martinez et al. 1993). Consequently, immunegenes of the MHC in cattle have been studied for their rolein the development of dermatophilosis. In a study onBrahman zebu cattle in Guadeloupe, classied according toabsence or presence of clinical signs into, respectively,dermatophilosis resistant or susceptible, Maillard et al.(1996) reported an amino acid sequence in exon 2 of BoLA DRB3 gene associated with a BoLA class I specicity as apossible genetic marker of resistance to dermatophilosis.The sequence EIAY, located at amino acid positions 66,67, 74, and 78 within the antigen recognition sites (ARS),was found in 12 animals classied as resistant, and 10 of them also displayed class I BoLA-A8 specicity. Further-more, only 3 of 18 susceptible animals showedsimultaneously the DRB3 EIAY sequence and BoLA-A8specicity. Also, they found a serine residue at position 30of the ARS of eight susceptible animals which was com-pletely absent in all resistant animals. Their results thusassociate MHC haplotypes, BoLA-A8 specicity and theBoLA-DRB3 EIAY, and lack of serine at position 30 withresistance to dermatophilosis. Other BoLA-DRB3 andBoLA-DQB alleles in relation to dermatophilosis havebeen characterized in cattle (Maillard et al. 1999, 2001;http://www.ri.bbsrc.ac.uk/bola /). One of the most signi-cant markers strongly associated with dermatophilosissusceptibility (96%) involves two linked alleles of exon 2DRB*09 (amino acid sequence C-E-S-F-L-QK-N in APSpositions 11-28-30-37-67-70/71-74, respectively) andDQB*1804 genes (Maillard et al. 2002). Elimination of animals possessing this haplotype by marker-assistedselection reduced the incidence of dermatophilosis from76% to 2% over a period of 5 years (Maillard et al. 2002).A recent study also found a MHC allele associated withhypersensitivity to dermatophilosis in previous studies of the Renitelo cattle of Madagascar (Razandraibe et al.2006). The DRB*09 marker sequence may be exposed toproteases possibly hindering recognition by a T cellreceptor (Maillard et al. 2003). In the Maillard et al. (2002)study, only about 30% of susceptible animals possessed theDRB*09/DQB*1804 marker, indicating the possibility of the involvement of other markers or minor players.

Like dermatophilosis, host ability to develop tick resis-tance has been recorded in ruminants and has also been asubject for study for many years. Tick infestations of several species, e.g., Boophilus microplus, B. decolorants, Amblyomma americanum, A. bebraeum, A. variegatum ,have received differential host responses by different cattlebreeds located in different regions. For example, theNDama (taurine) cattle of west Africa and many tropicalzebu breeds are known to have greater tolerance to tick infestations than taurine breeds of temperate regions ororigin (Latif et al. 1991; Mattioli et al. 1993; Rechav et al.


1 3
http://www.ri.bbsrc.ac.uk/bolahttp://www.ri.bbsrc.ac.uk/bola


13/20

1990). Thus, it is believed that tick resistance tends to beacquired with exposure (Latif et al. 1991). However, thereport by Kerr et al. ( 1994) about evidence of a major genefor tick resistance in cattle and evidence from previousreports (Stear et al. 1984, 1990) began the earnest searchfor the gene or genes that control genetic resistance to tick infestations. Several reports today have associated allelesof genes of the BoLA system with various aspects of resistance/susceptibility to tick infections in cattle. Initialreports of associations came from Stear et al. ( 1984, 1990)who related BoLA class I alleles w6.1 and w7 to tick protection. In a preliminary study, Martinez et al. ( 2004)found putative associations between tick counts and allelesBoLA-DRB3.2*10 and *42 and between warble counts andalleles *31 and *42 in cattle. In a more recent study,associations of BoLA alleles with lower tick number werefound for alleles DRB3.2*18, *20, and *27 and a weakerassociation with allele *26 (Martinez et al. 2006). Fromanother perspective, dermal mast cells (DMC) are alsothought to play a role in the hosts resistance to tick infestations. Some reports have indicated that zebu breedsknown to be highly resistant to ticks have twice the numberof DMC than taurine cattle (of temperate origin) in B.microplus -parasitized skin biopsies (Moraes et al. 1992).F2 crossbred Gir 9 Holstein cattle were recently demon-strated to acquire resistance against B. microplus , probablythe result of an increase in DMC (Engracia Filho et al.2006). The massive migration of mast cells to the dermisduring tick infestations is certainly under the control of yetunidentied genes. Given the above reports, it is clear thathost immune genes play a major role in developing resis-tance to tick infestations. The major challenge now is toidentify such genes and incorporate them into breedingprograms for the generation of resistant livestock.

Exploitation of genetic information and engineeringin controlling livestock diseases

The knowledge of the molecular genetic basis of livestock diseases has offered or is offering geneticists and breedersnew avenues of tackling these diseases safely and cheaply.It should be noted that conventional methods of controlsuch as change in management practices, culling, vacci-nations, antibiotics, and other types of medications havesucceeded to control many livestock diseases but with extracost and associated problems, including antibiotic resis-tance and residues in the environment, and thus are a majorcause of environmental and human health problems. Agenetic means of control is one route of action that mayprove benecial to the animals, producers, and consumers.Genetic control of diseases that are under the control of single genes, if known, is easily achievable. For example,

genetic tests (Table 1) exist for genotyping breeding ani-mals for disease-causing mutations and the elimination of carriers from the breeding herd, thus limiting the spread of disease. Using this method, several of these diseases havebeen successfully controlled or eliminated from the herd.However, the causal mutations of many more diseases of cattle, goat, pig, and sheep that are under the control of single genes are yet to be determined and effectivelycontrolled.

Diseases under multigenic control, which is complex,are not as easily determined and controlled as are thoseunder unigenic control. Also, the interaction of many hostgenes is further compounded by pathogenic and environ-mental factors. This does not, however, make geneticcontrol unattainable but calls for deeper knowledge of theinteracting factors. With classical methods of breeding,disease traits with high heritability have been used suc-cessfully to reduce the incidence of some infectiousdiseases of farm animals. However, the heritability of most disease traits is very low and genetic control is noteasily achievable through breeding. With the continuedadvancement in molecular genetic techniques and knowl-edge of the genome of farm animals, there is hope thatmolecular information can actually play a major role ineffectively controlling livestock diseases. Available gen-ome sequences and high-resolution molecular maps of some livestock species have opened new insights into thegenetic bases of infectious diseases (McKay et al. 2007).Location of signicant QTLs for some disease traits hasactually led to the identication of responsible genes andcausal SNPs and thus the possibility of disease control.

Apart from QTLs, genetic engineering through targeteddisruption or addition of genes may be one avenue of control. Recently, Wall et al. ( 2005) produced transgeniccows secreting lysostaphin in their milk and further dem-onstrated that the transgenic cows have enhancedresistance to Staphylococcus aureus mastitis. In this caseonly enhanced resistance and not complete control becauseof the effects of other genes and the presence of otherfactors prompted Donovan et al. ( 2005) to think aboutintroducing other genes or using other techniques like RNAinterference to deal with more mastitis pathogens and alsohandle potential resistance issues. For prion diseases,Denning et al. ( 2001) and Perrier et al. (2002) indicated thepossibility of a genetic engineering approach to controldiseases through their observations in sheep and mice,respectively. Recently, Richt et al. ( 2006), by the methodof sequential gene-targeting, produced cows decient innormal cellular prion protein (PrP c ); they were clinically,physiologically, histopathologically, immunologically, andreproductively normal thus opening an avenue for theproduction of cattle and products free of prion proteins.Theapplication of genetic engineering in controlling livestock


1 3


14/20

diseases is still at its infancy stage due to ethical issues andyet unidentied risk factors related to the technique.

Implications of current ndings and future perspectiveson farm animal disease control

Molecular markers have been used extensively to controldiseases and to map QTLs that control resistance to certaindiseases in farm animals, as exemplied in this review.However, much work is still required for many other dis-eases. To adequately control livestock diseases byexploiting genetic information, deeper knowledge of gen-ome variations is required. As exemplied in humans, thenear complete sequencing of human chromosomes hasfacilitated accurate characterization and assessment of allclasses of genomic variation, and with the application of genome-wide scanning technologies (e.g., microarray-based comparative genomic hybridization, genome-wideSNP platforms), a new, previously unrecognized degrees of larger-sized genomic variations have been detected. Theselarger-sized variations include copy number variants ( [ 1kb), large-sized inversions, insertions, deletions, and othercomplex rearrangements, most times not detectable bystandard DNA sequencing procedures and cytogenetics(Feuk et al. 2006). It has been well established in studies of monogenic, oligogenetic, and complex diseases of humansthat the study of such large-sized chromosomal rear-rangements can be the fastest approach to identifyingcandidate disease loci (variants) and genes (Lugtenberget al. 2006; Rosenberg et al. 2006; Vissers et al. 2005).Studies on such large-sized chromosomal rearrangementson livestock genomes could therefore facilitate detection of the genetic bases for some of those diseases (monogenicand complex) of livestock that still elude investigation.This implies that the genome sequences for these livestock species must rst be available before such studies can beundertaken. For the genome sequences, including candi-date genes and loci that are currently available, moredetailed studies involving all sections of candidate genesand more genes in the vicinity of a QTL have to be carriedout in order to identify candidate SNPs and copy numbervariants for more effective livestock disease control.

Furthermore, resistance or susceptibility to complexdiseases of livestock (e.g., mastitis) pose great challengesto research efforts in terms of developing new method-ologies for detection and integration of various geneticvariants. Much research on disease-resistance phenotypes,conserved sequence homologies, and conserved functionshas been done in human and mouse genes, and farmanimals should be used as excellent models for investi-gation. Development and application of microassay-basedtechniques for genomics (DNA and mRNA), proteomics

(protein), protein-protein interaction, and protein-DNAinteraction and the role of small functional RNAs will nodoubt facilitate our search for disease-resistance genes infarm animals. Furthermore, recent interest in and study of epigenetics in human medicine should greatly inuenceour research on disease resistance in farm animals. Epi-genetic disorders give rise to several signicant humandiseases (Eggar et al. 2004). Epigenetic inheritance is thetransmission of information from a one-cell or multicellorganism to its descendants without that informationbeing encoded in the nucleotide sequence of the gene.Epigenetic mechanisms such as DNA methylation, post-translational modications of histone proteins, remodelingof nucleosomes, and expression of small regulatory RNAsalso contribute to the regulation of gene expression,determination of cell and tissue specicity, and assuranceof inheritance of gene expression levels. All these couldaffect disease resistance. At this time, the epigeneticmechanisms underlining disease resistance in farm ani-mals are unclear.

It is apparent that we are just at the beginning of understanding the contributions of genetics and epigeneticsto diseases in farm animals. Despite many difcultiesahead of us, identication of the genes and mutationsresponsible for variation in disease resistance could greatlyenhance the efciency of breeding animals that possessinnate disease resistance. Furthermore, it will provide newtools to facilitate research into the mechanisms of infec-tion, possibly leading to additional pharmacologic andmanagement approaches for the control of disease trans-mission. Finally, genetic control of animal diseases canreduce the costs associated with diseases, improve animalwelfare, and provide healthy animal products to consum-ers, and it should be given more attention.

Generally, the less attention paid to research and controlof animal diseases compared to diseases in humans is not ahealthy trend of events. This is because an outbreak of alivestock disease can affect us directly or indirectly. Themore recent outbreaks of BSE in livestock has lead towidespread loss of income, at both the farm and the gov-ernment levels, and the Avian u virus has led to the loss of hundreds of human lives. In the last century, losses of human lives due to livestock disease outbreaks were evenmore dramatic. Therefore, controlling livestock diseasesshould not be considered any less important.

Conclusion

Different types of changes that describe genetic variationsof the genetic material have been implicated in one diseaseof livestock or another. These variations affect mRNAsplicing patterns and result in alteration or complete


1 3


15/20

elimination of protein function thereby leading to patho-logic conditions in farm animals. However, information ongenome variations involving large sections of the geneticmaterial, including complex chromosomal rearrangementsshown to explain some disease conditions in humans, is notavailable for livestock species. Knowledge of the geneticbases of some livestock diseases has led to control throughbreeding and is also opening new avenues of controlthrough genetic engineering. For diseases under multigeniccontrol, more research efforts have to be expended to fullyunderstand the roles of controlling genes and developeffective control measures. Also, more effort has to bemade in sequencing the genomes of the sheep, goat, andpig; this will provide the much needed baseline informationfor genetic studies into diseases. With increasing knowl-edge and advances in molecular biology, efforts atsearching for and characterizing genes that control live-stock diseases should intensify. The tool of geneticengineering should be ne tuned and safer alternatives toantibiotics and other therapeutic measures should bedeveloped. Finally, a better understanding of all thesefactors could be better harnessed to effectively identify andcontrol livestock diseases.

Acknowledgments Financial support was provided by McGillUniversitys James McGill Professorship Program to X Zhao.

Open Access This article is distributed under the terms of theCreative Commons Attribution Noncommercial License which per-mits any noncommercial use, distribution, and reproduction in anymedium, provided the original author(s) and source are credited.

References

Acutis PL, Bossers A, Priem J, Riina MV, Peletto S et al (2006)Identication of prion protein gene polymorphisms in goats fromItalian scrapie outbreaks. J Gen Virol 87:10291033

Adams LG, Templeton JW (1998) Genetic resistance to bacterialdiseases of animals. Rev Sci Tech 17:200219

Agrimi U, Conte M, Morelli L, Di Bari MA, Di Guardo G et al (2003)Animal transmissible spongiform encephalopathies and genetics.Vet Res Commun 27(Suppl 1):3138

Agyemang K (2005) Trypanotolerant livestock in the context of trypanosomiasis intervention strategies. PAAT Technical andScientic Series 7. FAO, Rome

Ambrose N, Lloyd D, Maillard J-C (1999) Immune responses to Dermatophilus congolensis infections. Parasitol Today 15:295300Arango NA, Lovell-Badge R, Behringer RR (1999) Targeted

mutagenesis of the endogenous mouse Mis gene promoter: invivo denition of genetic pathways of vertebrate sexual devel-opment. Cell 99:409419

Balbus N,HumenyA, KashkevichK, HenzI, FischerC et al(2005)DNApolymorphisms of the prion doppel gene region in four differentGerman cattle breeds and cows tested positive for bovine spongi-form encephalopathy. Mamm Genome 16:884892

Baldwin CL, Parent M (2002) Fundamentals of host immune responseagainst Brucella abortus : what the mouse model has revealedabout control of infection. Vet Microbiol 90:367382

Barthel R, Feng J, Piedrahita JA, McMurray DN, Templeton JA et al(2001) Stable transfection of bovine Nramp1 gene into murineRAW264.7 cells: Effect on Brucella abortus survival. InfectImmun 69:31103119

Baylis M, Goldmann W (2004) The genetics of scrapie in sheep andgoats. Curr Mol Med 4:385396

Baylis M, Goldmann W, Houston F, Cairns D, Chong A et al (2002)Scrapie epidemic in a fully PrP-genotyped sheep ock. J GenVirol 83:29072914

Beck CL, Fahlke C, George AL (1996) Molecular basis for decreasedmuscle chloride conductance in the myotonic goat. Proc NatlAcad Sci USA 93:1124811252

Beever JE, Smit MA, Meyers SN, Hadeld TS, Bottema C et al(2006) A single-base change in the tyrosine kinase II domain of ovine FGFR3 causes hereditary chondrodysplasia in sheep.Anim Genet 37:6671

Belt PBGM, Muileman IH, Schreuder BEC, Ruijter JBD, GielkensALJ et al (1995) Identication of ve allelic variants of thesheep PrP gene and their association with natural scrapie. J GenVirol 76:509517

Benestad SL, Thu B, Bratberg B, Sarradin P, Scho nheit J et al (2003)Cases of scrapie with unusual features in Norway and designa-tion of a new type, Nor98. Vet Rec 153:202208

Berg F, Gustafson U, Andersson L (2006) The uncoupling protein 1 gene(UCP1 ) is disrupted in the pig lineage: a genetic explanation forpoor thermoregulation in piglets. PLoS Genet 2:11781181

Berthier D, QuereR, Thevenon S,Belemsaga D, Piquemal D et al (2003)Serial analysis of gene expression (SAGE) in bovine trypanotoler-ance: preliminary results. Genet Sel Evol 35(Suppl 1):3547

Berthier D, Chantal I, Thevenon S, Marti J, Piquemal D et al (2006)Bovine transcriptome analysis by SAGE technology during anexperimental Trypanosoma congolense infection. Ann N Y AcadSci 1081:286299

Billinis C, Panagiotidis CH, Psychas V, Argyroudis S, Nicolaou Aet al (2002) Prion protein gene polymorphisms in natural goatscrapie. J Gen Virol 83:713721

Bilstrom JA, Valberg SJ, Bernoco D, Mickelson JR (1998) Genetictest for myophosphorylase deciency in Charolais cattle. Am JVet Res 59:267270

Bravo MJ, de Dios Colmenero J, Mart n J, Alonson A, Gonza lez AC(2006) Variation in the NRAMP1 genedoes not affect susceptibilityor protection in human brucellosis. Microb Infect 8:154156

Campbell IL, Eddleston M, Kemper P, Oldstone MB, Hobbs MV(1994) Activation of cerebral cytokine gene expression and itscorrelation with onset of reactive astrocyte and acute-phaseresponse gene expression in scrapie. J Virol 68:23832387

Cartegni L, Chew SL, Krainer AR (2002) Listening to silence andunderstanding nonsense: Exonic mutations that affect splicing.Nat Rev Genet 3:285298

Cavanagh KT, Leipprandt JR, Jones MZ, Friderici K (1995)Molecular defect of caprine N-acetylglucosamine-6-sulphatasedeciency. A single base substitution creates a stop codon in the50-region of the coding sequence. J Inherit Metab Dis 18:96

Chavez LS, Serda R, Choe S, Davidi L, Harmeyer J et al (2003)Molecular basis for pseudo vitamin D-deciency rickets in theHannover pig. J Nutr Biochem 14:378385

Check E (2005) Human genome: Patchwork people. Nature 437:10841086

Colige A, Sieron AL, Li SW, Schwarze U Petty E et al (1999) HumanEhlers-Danlos syndrome type VII C and bovine dermatosparaxisare caused by mutations in the Procollagen I N- Proteinase gene.Am J Hum Genet 65:308317

Comincini S, Foti MG, Tranulis MA, Hills D, Di Guardo G et al(2001) Genomic organization, comparative analysis, and geneticpolymorphisms of the bovine and ovine prion Doppel genes(PRND). Mamm Genome 12:729733


1 3


16/20

Courtin D, Argiro L, Jamonneau V, Ndri L, Nguessan P et al (2006)Interest of tumor necrosisfactor-alpha 308G/A and interleukin-10592C/A polymorphismsin human Africantrypanosomiasis.InfectGenet Evol 6 :123129

Crisponi L, Deiana M, Loi A, Chiappe F, Uda M et al (2001) Theputative forkhead transcription factor FOXL2 is mutated inblepharophimosis/epicanthus inversus syndrome. Nat Genet 27:159166

Croes EA, Alizadeh BZ, Bertoli-Avella AM, Rademaker T, Vergeer-Drop J et al (2004) Polymorphisms in the prion protein gene andin the doppel gene increase susceptibility for Creutzfeldt-Jakobdisease. Eur J Hum Genet 12:389394

Culbertson MR (1999) RNA surveillance. Unforeseen consequencesfor gene expression, inherited genetic disorders and cancer.Trends Genet 15:7480

Cunningham C, Wilcockson DC, Boche D, Perry VH (2005)Comparison of inammatory and acute-phase responses in thebrain and peripheral organs of the ME7 model of prion disease.J Virol 79:51745184

da Mota AF, Martinez ML, Coutinho LL (2004) Genotyping BoLA-DRB3 alleles in Brazilian dairy cattle ( Bos indicus ) by temper-ature gradient gel electrophoresis (TGGE) and direct sequencing.Eur J Immunogenet 31:3135

Dawson M, Hoinville LJ, Hosie BD, Hunter N (1998) Guidance onthe use of PrP genotyping as an aid to the control of clinicalscrapie. Vet Rec 142:623625

Denning C, Burl S, Ainslie A, Bracken J, Dinnyes A et al (2001)Deletion of the a (1,3) galactosyl transferase ( GGTA1 ) gene andthe prion protein ( PrP ) gene in sheep. Nat Biotech 19:559562

Dennis JA, Healy PJ (1999) Denition of the mutation responsible formaple syrup urine disease in poll shorthorns and genotyping pollshorthorns and pool herefords for maple syrup urine diseasealleles. Res Vet Sci 67:16

Dennis JA, Healy PJ, Beaudet al, Obrien WE (1989) Moleculardenition of bovine argininosuccinate synthetase deciency.Proc Natl Acad Sci USA 86:79477951

Dennis JA, Moran C, Healy PJ (2000) The bovine alpha-glucosidasegene: coding region, genomic structure, and mutations that causebovine generalized glycogenosis. Mamm Genome 11:206212

Detilleux JC (2002) Genetic factorsaffecting susceptibility of dairy cowsto udder pathogens. Vet Immunol Immunopathol 88:103110

Diaz C, Vitezica ZG, Rupp R, Andreoletti O, Elsen JM (2005)Polygenic variation and transmission factors involved in theresistance/susceptibility to scrapie in a Romanov ock. J GenVirol 86:849857

DIeteren GDM, Authie E, Wissocq N, Murray M (1998) Trypano-tolerance, an option for sustainable

Documents

Genetika Sapi Kambing