Effects of thewhiteallele of themilocus on coat pigmentation in chimeric mice

Abstract

SummaryTo investigate the cellular action of theMiωhallele in the mouse with regard to its effects upon coat color patterns, we generated a series of aggregation chimeras, using embryos that differ in theirmilocus genotype. We have obtained 11 chimerasMiωh/ +C/C↔ + / +c/cand 8 chimeras + / +C/C↔ + / +c/c. Chimerism was determined by coat and retinal pigment epithelium mosaicism and by the electrophoretic analysis of GPI-1 isoenzymes. InMiωh/+C/C↔, +/+c/cmice white coat color prevailed due to the higher percentage of unpigmented areas and the higher percentage of unpigmented hairs in pigmented areas. Our data indicate that a singleMiωhgene dose decreases the melanoblast proliferative activity, causing the lightening of coat pigmentation. InMiωh/ +C/C↔+/+c/cmice a few pigmented hairs were often detected on the belly whereMiωh/ + mice always had a white spot. This suggests that in the chimeras the presence of some non-Miωhcells in the skin of the belly allows pigment cells to develop. Using embryos of two substrains ofMiωh/Miωhmice that differ in their Gpi-1 locus genotype we have produced 8Miωh/ + ↔Miωh/Miωhchimeras. In all these chimeras coat color patterns resembled those ofMiωh/ + heterozygotes despite the higher percentage of theMiwh/Miωhcomponent in three chimeras. Mosaic hairs were absent in the chimeras. This shows that the chimeras have only oneMiωh/ + melanoblast population which actively proliferates and colonizes almost all hair follicles. Thus theMiωh/Miωhdermis and epidermis do not suppress proliferation and differentiation of theMiωh/ + melanoblasts except the certain area on the belly.