Analysis of Some Phases of Melanoblast Migration in the Barred Plymouth Rock Embryos

Abstract

Systematic testing of epidermal areas of Barred Rock embryos by transplantation to White Leghorn embryos reveals an antero-posterior gradient in onset of migration of melanoblasts beneath the epidermis adjacent to neural tube. Characteristics of this gradient are explainable in terms of Holmdahl''s hypothesis of primary and secondary body development. Tardy establishment of melanoblasts in epidermis above the first 5 somites is associated with formation here of the head spot, an area of unpigmented or weakly pigmented down feathers. The migration of melanoblasts lateral to the somites is directed precociously towards the limb buds. Proximo-distal and dorso-ventral gradients of migration exist within the limb buds, the former associated with the unpigmented or weakly pigmented down feathers at the wing tips. The presence of melanophores in the coelomic lining and viscera of control embryos demonstrates that there is no selective migration of melanoblasts into the epidermis. Melanoblasts enter the mesonephroi at about 123 hrs. of incubation; although the testes frequently contain melanophores after the 14th day, melanoblasts could not be detected in the indifferent gonads by 167 hrs. of incubation. Hensen''s node and the definitive tail bud possess the capacity to yield melanophores when transplanted. The young, developing tail bud is unpredictable in this respect. Histological examination of nodal and tail bud grafts revealed no correlation between presence of nervous tissue and of melanophores in these grafts.