Abstract
In spite of their different origin, both melanocytes and mast cells are deficient in the skin of mutant mice of the Sl/Sld genotype. Since the neural crest and the liver of Sl/Std embryos contain normal precursors of melanocytes and mast cells, respectively, the deficiency is attributed to a defect in tissue environment necessary for migration and/or differentiation of precursor cells. We investigated whether the tissue environment used for differentiation of melanocytes and mast cells was identical by producing aggregation chimaeras from Sl/Sld and +/ + embryos. Chimaeric mice with apparent pigmented and nonpigmented stripes were obtained. In the nonpigmented stripes of these Sl/Sld ↔ + / + chimaeras, melanocytes were not detectable in hair follicles but were detectable in the dermis. In contrast, melanocytes were detectable neither in hair follicles nor in the dermis of non-chimaeric Sl/Sl mice. Concentrations of mast cells were comparable in the pigmented and nonpigmented stripes of Sl/Sld ↔ + / + chimaeras, but the average concentration of mast cells significantly varied in the chimaeras (from 8 % to 74 % of the value observed in control +/+ mice). The present result suggests that mesodermal cells that support the migration and differentiation of both melanocyte precursors and mast-cell precursors mix homogeneously in the dermis and that ectodermal cells that influence the invasion of differentiating melanocytes into hair follicles make discrete patches.
