Genetica (1973) 44: 454-458

ACROMELANIC ALBINISM IN MAMMALS

ROY ROBINSON

St. Stephens Road Nursery, Ealing, London, England

Received and Accepted March 5. 1973

A mutation to acromelanic albinism (symbol ch) is reported for the Mongolian gerbil, Meviolzes unguiculatus (Milne-Edwards, 1867). A compari- son is made of the characteristics of acromelanic mutants in seven species of mammals. All are basically similar but differ in details.

Introduction

Two forms of albino mutants are recognized in mammalian colour genetics. The first is complete albinism, in which no pigmentation is formed in the hair, skin or deeper tissues of the body. The outcome is a pink-eyed animal with white fur. The second is acromelanic albinism, which is phenotypically similar to the above but with variable amounts of pigment on the extremities (nose, ears, feet and tail). The eyes are often pink, sometimes ruby, and, in one instance, blue.

Material and Observations

A mutation to acromelanic albinism was found in 1970 in Britain for the Mongolian gerbil, Merioaes ulzguiculatus (Milne-Edwards, 1867). Mutant nestlings never develop the black skin of the normal animal and, as juveniles, have pink eyes and snowy white fur. The pink eyes persist throughout life. The body fur also remains white but about three months of age, pigmented hairs commence to appear on the tail. These never become abundant but can be clearly seen. Only the guard hairs are pigmented, the down hairs in particular never become colour- ed. The pigmented hairs are distributed throughout the entire length of the tail. Although no direct test for allelism with complete albinism is possible at this time, there is no reason to suppose that the gene is not a homologue of acromelanic albino mutants in other species. The symbol ch is proposed for the gene.

The mutant is inherited as a simple autosomal recessive to normal.

TABL

E 1

OC

CU

RR

ENC

E O

F AC

RO

MEL

ANIC

AL

BIN

O

MU

TAN

TS

IN

MA

MM

ALS

Spec

ies

Eye

Extre

mitie

s Ag

e of

Expr

essio

n Ge

ne

Refer

ence

b

colou

r co

loure

d on

set

of ye

llow

Symb

ol g

pigme

nt

5 Ca

t (F

elis

catu

s)

Blue

Al

l 1-

2 da

ys

Abun

dant

c*

CAST

LE

(191

9)

E Gu

inea-

pig

z (C

avia

powe

llus)

Pi

nk

All

2-3

days

No

ne

ca

WRI

GHT

(191

5)

::

Hous

e Mo

use

E z (M

us

musc

ulus)

Pink

41

1 1

week

No

ne

ch

GRE

EN

(196

1)

G $ Mi

nk

(Mus

tela

Viso

n)

Pink

No

se,

tail

? ?

c” CA

STLE

&

MOO

RE

(194

6)

2

Mong

olian

Ge

rbil

(Mer

iones

un

guicu

latus

) Pi

nk

Tail

3 mo

nths

? Ch

Th

is pa

per

$ E

Rabb

it (Oryc

tolag

us

cunic

ulus)

Syria

n Ha

mster

(M

esoc

ricetu

s au

ra&s

)

Pink

Al

l

Pink

Ea

rs,

scrot

um

3-4

week

s

4 we

eks

Trac

e/non

e ?

z r ch

CA

STLE

(1

905)

v)

Cd

ROBI

NSON

(1

959)

456 ROY ROBINSON

The experimental data are as follows. Albino mutant x normal gave 15 normal offspring. Fi mated to albino gave 22 normal and 17 albino ; while Fi x Fi gave 35 normal and 9 albinos. Albino x albino has produced 34 albinos.

Discussion

Acromelanic mutants are definitely known for seven species of mammals and are surmised for a few others, in which they have been observed but not investigated genetically. It is a fair assumption that each mutant is a transpecies homologue at the same gene locus (SEARLE 1968; ROBINSON, 1970), namely, the mammalian albino locus c which is closely, if not directly, concerned in the formation of melanin pigment. It probably mediates the quantitative production of the enzyme tyrosinase, an essential catalyst in the chain of melanin synthesis (SEARLE, 1968).

There is a basic similarity of phenotype for all of these mutants which transcends species. At birth, no pigmentation is normally evident but as growth continues pigment is feebly produced in the extremities. Species divergences are encountered at this stage in the onset and rate of development of pigment. It is difficult, if not im- possible, to decide if these are due to minute differences between alleles or to the different genetic milieu provided by the species karyotype in which each allele finds itself.

The inter-species differences of expression are interesting enough to be briefly described. These stem primarily from the amount of pigment produced. In the cat, acromelanic albinism results in the well known Siamese pattern. This animal displays the greatest amount of pig- mentation as witnessed by the rapid onset of pigmentation, the blue eye (indicative of impaired pigmentation but considerably more than that found in other species which are either pink or rarely ruby), fully coloured limbs (in contrast to other species where the colour is mostly confined to the distal portion) and pale sepia body fur (instead of white).

Other species display idiosyncrasies of expression, mainly in the direction of less than typical manifestation. The “albino” mink has a smudge of colour on the nose and tail while the body fur is off-white (CASTLE & MOORE, 1946). The Syrian hamster mutant (dark eared

ACROMELANICALBINISMINMAMMALS 457

albino) develops pigment merely in the skin of the ear, perineal region and scrotum, These are the areas which are coloured in the normal animal. It is note-worthy, however, that no pigment forms in the hair of the albino at any time (ROBINSON, 1959). The eye colour may change to ruby in older individuals (indicating the slow accumulation of pigment; cf. KLEBERGER, 1960), a property shared by the Himalay- an mouse (GREEN, 1961). The Mongolian gerbil mutant is exceptional for the long interval between birth and the onset of pigmentation and the fact that the pigmentation is confined to one hair type of the tail. If the Siamese cat gene shows the greatest amount of pigmentation, the gerbil mutant would seem to show the least.

In the presence of the mutant gene for acromelanic albino, the synthesis of pigment is thermo-sensitive, pigment being formed below a physiological threshold but not above it. The acromelanism results from gradients between the surface temperature of the extremities and the body. The extremities are regularly cooler than the body and, perhaps by chance, the temperature difference straddles the threshold. This fact has been demonstrated on many occasions; mainly in the rabbit but also for the cat, guinea-pig and mouse (SCHULTZ, 1915; KAUFMAN, 1925; ILJIN, 1926a, b; ILJIN & ILJIN, I~~O;GREEN, 196 1). Lowering the skin temperature of the body will induce coloured hair while raising the temperature of the extremities will produce white hair.

It is characteristic of the albino locus that the various alleles cause a successive degradation of pigmentation. The yellow pigment is usually affected early, disappearing from the coat before the black is severely modified, which in turn becomes a sepia brown. The rabbit has a classic series of alleles displaying the phenomenon (ROBINSON, 1958). The acromelanic albino rarely manifests yellow and the expressed eumelanin is dark sepia rather than black. The Siamese allele of the cat is exceptional in that abundant yellow is produced in the extremities (LITTLE, 1957). This is in keeping with the fact that the cat gene is more productive of pigment generally than those of other species.

The maximum expression is shown when the acromelanic gene is combined with non-agouti (a). The wild type form has appreciably less pigment but there is no implication of an interaction between a and ch- type genes. Non-agouti is unknown at this time in the Syrian hamster and Mongolian gerbil, and it will be interesting to observe (hopefully,

458 ROY ROBINSON

in due course) if the non-agouti acromelanic albino animals of these two species develop more pigment, particularly, to demonstrate if the hamster mutant phenotype is able to produce pigmented hair.

REFERENCES

CASTLE, W. E. (1905). Heredity of coat characters in guinea-pigs and rabbits. Pubis Carnegie Instn Wash. No. 23.

CASTLE, W. E. (19 19). Siamese, an albinistic color variation in cats. Am. Nat. 53 : 265-268.

CASTLE, W. E. & L. MOORE (1946). Mutations of the mink under domestication. J. Hered. 37: 137-146.

GREEN, M. C. (1961). Himalayan, a new allele of albino in the mouse. J. Heved. 52 : 73-75.

ILJIN, N. A., (1926a). Morphogenetic analysis of the genetic constitution in albino guinea-pigs. Trans. Lab. Exp. Biol. Zoopk. Moscozv 1: 96-106.

ILJIN, N. A. (1926b). Investigation of the temperature on the Himalayan rabbit’s pigmentation. Trans. Lab. Exp. Biol. Zoopk. Moscow 1: 130-181.

ILJIN, N. A. & V. N. ILJIN (1930). Temperature effects on the color of the Siamese cat. J. Hered. 21: 309-318.

KAUFMAN, L. (1925), Experimental study in the partial albinism in Himalayan rabbits. Biologia gen. 1: 7-21.

KLEBERGER, E. (1960). Pigmentierung der Augen des partiellen Albino des Goldhamsters. Naturwissenschaften 47: 263-264.

LITTLE, C. C. (1957). The Yellow Siamese cat. J. Heved. 48: 57-58. ROBINSON, R. (1958). Genetic studies of the rabbit. Biblphia genet. 17: 229-558. ROBINSON, R. (1959). Genetic studies of the Syrian hamster. 11. Partial albinism.

Heredity 13: 165-177. ROBINSON, R. (1970). Homologous mutants in mammalian coat colour variation.

Symp. Zool. Sot. Lond. 26: 251-269. SCHULTZ, W. (1915). Schwarzfarburg weisser Haare durch Rasur und die Ent-

wicklungs-mechanik der Farben von Haaren und Federn. Arch. Entw. Mech. Org. 41: 535-557.

SEARLE, A. G. (1968). Comparative Genetics of Coat Colour in Mammals. London, Logos Press.

WRIGHT, S. (1915). The albino series of allelomorphs in guinea-pigs. Am. Nat. 49: 140-148.