A STUDY OF THE GENE WHITE EFFECTS ON THE COAT PIGMENTATION IN MOUSE AGGREGATION CHIMERAS

We obtained eight Mi(wh)/+ <--> Mi(wh)/Mi(wh) chimeras using embryos o f two mutant substrains of Mi(wh)/Mi(wh) mice with different isozymes Gpi-1aa and Gpi-1bb. Chimerism was determined by the mosaicism of reti nal pigment epithelium and electrophoretically different variants of g lucose phosphate isomerase. The patterns of coat pigmentation in all c himeras were similar to those in Mi(wh)/+ heterozygotes. Despite the h igh proportion of the parental Mi(wh)/Mi(wh) component in three chimer as, the phenotype of their coat pigmentation was also similar with tha t of Mi(wh)/+ mice. The chimeras lacked mosaic-pigmented hairs. These data suggest presence only one cell population of Mi(wh)/+ melanoblast s that actively proliferate and colonize almost all forming hair folli cles. Hence, the proliferation and/or differentiation of Mi(wh)/+ mela noblasts is not suppressed in the Mi(wh)/Mi(wh) dermis and epidermis. The Mi(wh) gene acting in melanoblasts leads to the block of their pro liferation at the early stages of development in the homozygotes.