Richardson, Michael Keith; (1990) The formation of pigment patterns in bird embryos. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In bird embryos, melanin pigments in the feathers are made by melanocytes derived from the neural crest. I have examined the mechanisms by which these cells can give rise to pigment patterns. In the embryonic quail wing, most of the dorsal feather papillae are heavily pigmented, while many of those on the ventral surface are unpigmented. When quail neural crest cells were grafted to the chick, they gave rise to a pigment pattern which bore little or no resemblance to the donor. In contrast to the quail, the guinea fowl embryo has pigment in nearly all of its wing feathers, including those on the ventral surface. Chimaerae made from these species showed pigment patterns which, in most cases, corresponded to the genotype of the feathers and not that of the crest cells. Histological studies of the quail-chick chimaera showed that undifferentiated neural crest cells were present in unpigmented feathers. The same was shown to be true of the normal quail embryo: ectoderm was taken from unpigmented feathers and then grown in vitro. Melanocytes appeared in the culture after 3 days. Dihydroxyphenylalanlne (DOPA) was used to examine melanocyte differentiation. Pigmented feathers were DOPA-positive, while unpigmented feathers were DOPA-negative. A graft of polarizing region to the anterior margin of the quail wing produced a wing in which the cartilage, feather, and pigment patterns were all a mirror-image. The following model is proposed: pigment patterns arise from local cues In the feathers acting upon the differentiation of a uniformly distributed population of neural crest cells. These local cues constitute an Isomorphic prepattern, which may be specified by positional information.

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