[The effects of the white gene on coat pigmentation in mouse aggregation chimeras].

We obtained eight Mi(wh)/+<==>Mi(wh)/Mi(wh) chimeras using embryos of two mutant substrains of Mi(wh)/Mi(wh) mice with different isozymes Gpi-1(aa) and Gpi-1(bb). Chimerism was determined by the mosaicism of retinal pigment epithelium and electrophoretically different variants of glucose phosphate isomerase. The patterns of coat pigmentation in all chimeras were similar to those in Mi(wh)/+ heterozygotes. Despite the high proportion of the parental Mi(wh)/Mi(wh) component in three chimeras, the phenotype of their coat pigmentation was also similar with that of Mi(wh)/+ mice. The chimeras lacked mosaic-pigmented hairs. These data suggest presence only one cell population of Mi(wh)/+ melanoblasts that actively proliferate and colonize almost all forming hair follicles. Hence, the proliferation and/or differentiation of Mi(wh)/+ melanoblasts 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 proliferation at the early stages of development in the homozygotes.