Pigment cell migration in piebald mice

Abstract

White-spotting patterns in mice have been attributed alternatively to a selective migration of melanoblasts into certain regions of the skin, or to a failure of the melanoblasts to differentiate in the areas that remain pigment free. These two alternatives were tested experimentally in a series of grafting experiments in which embryonic 11-day mouse skin and 9-day neural tubes were grafted in combination to White Leghorn chick embryos. In one grafting series pigment production after 15 days of incubation was examined, and in the second series the migration of neural tube cells was followed using tritiated thymidine and autoradiographic techniques. Grafts of normal skin and normal neural tubes produced pigmented hair, and the tissues of the host were colonized by melanocytes in the operated region. The combination of piebald skin-piebald tube did not produce pigment in the host tissues, and a large majority of the grafted skin cases produced pigment-free hair. The fate of the melanoblasts in both grafting combinations was followed by labeling the neural tube cells prior to grafting. The pattern of migration of the labeled cells in the normal and in the piebald combination grafts was identical following incubation of 4 days. Labeled cells from normal neural tubes were identified in the same tissue environments where pigment was observed after 15 days of incubation. Piebald labeled cells were present in these same tissue locations, but the correlation with pigment development as in the normal series did not exist. These results favor the conclusion that the development of pigment-free areas under the conditions of these experiments may be attributed to a failure of melanoblasts to differentiate in certain tissue environments, not to a defect in migration. The hypothesis that white-spotting patterns of piebald mice develop by a similar mechanism preventing melanoblast differentiation in the prospective white-spotted regions is thereby supported.