A comparison of pigment cell development in albino, steel, and dominant-spotting mutant mouse embryos

The mutations albino, steel, and dominant-spotting were investigated through a method of introducing normal melanoblasts into skin from mutant embryos of various ages. The skin-melanoblast combinations were cultured in the chick embryo for 15 days, and the development of pigmentation in the grafted skin and host tissues was determined. Eleven-day embryonic albino skin combined with normal melanoblasts resulted in the appearance of pigment in the graft and host tissues. Thirteen day and older albino embryonic skin-melanoblast combinations yielded pigment only in the host tissues. Melanocytes were absent in the large majority of the grafts themselves. Thirteen- to 18-day W v W v embryonic skin-melanoblast combinations resulted in pigment formation in both the grafted skin and host tissues in all cases. Sl d Sl d skin-melanoblast combinations of 13–18 days resulted in pigment development in neither the grafted skin nor the host tissues in the large majority of the cases. These results demonstrated that the presence of amelanotic melanoblasts in albino skin at 13 days and older prevented the entrance of normal melanoblasts. The receptivity of W v W v skin to normal melanoblasts indicated that skin of this genotype did not possess melanoblasts in any form at the ages tested. W v W v melanoblasts either never entered the skin of prospective black-eyed white embryos, or they did not survive because of some intrinsic factor immediately after colonizing the skin. The skin of steel mice either prevented the differentiation of the normal melanoblasts or it inhibited their migration. This action of steel skin was rather potent, for the inhibition affected not only itself but the appearance of pigment in the host tissues as well.