Special features of dermal melanocytes in white silky chicken embryos

In the hyperpigmented Silky (SK) chicken, melanoblasts are neural crest cells that emigrate from the neural tube, migrate dorsolaterally, close to the ectoderm and medioventrally, reaching visceral regions of the embryo, as well as populating the dermis. In this work, we analyzed the morphology and distribution of melanocytic lineage cells in white SK embryos at later stages of development (6 to 19 days of incubation) focusing in the dermis of dorsal skin to characterize this ectopically located population. Melanoblasts and immature melanocytes are seen at all analyzed stages, some of them clearly proliferative, suggesting a possibility of continued renewal of the population. Mature, fully differentiated melanocytes are elongated cells with many long cytoplasmic processes, forming a meshwork in superficial dermis, below a layer of collagen and elastic fibers that seems to prevent melanocytic lineage cells from reaching the epidermis at these later stages. SK chicken is the only Gallus gallus breed to display this arrangement of dermal melanocytes. The distribution of melanocytes below the collagen layer, observed in regions covered by feathers, is clearly not related with structural coloration as in areas of bare skin. Other functions for this conserved trait in SK must be investigated.