DISTRIBUTION PATTERNS OF NEURAL-CREST-DERIVED MELANOCYTE PRECURSOR CELLS IN THE QUAIL EMBRYO

Background: In vertebrate embryos, migration of trunk neural crest cel ls (NCC) proceeds mainly in two streams: a dorsoventral path between t he neural tube and somites, and a dorsolateral one between somites and ectoderm. This last pathway is taken by melanocyte precursor cells (M PC) homing the skin, while pigment cells seeding internal organs and t he peritoneal wall follow the dorsoventral pathway. Early routes taken by subpopulations of NCC have been well documented using the quail-ch ick chimaera system and monoclonal antibodies to NCC. However, very li ttle is known about the advanced migratory behavior of MPC, which dete rmines their late distribution patterns at different embryonic axial l evels. Methods: Histological sections of neck, thorax, and abdomen of 6.5 to 9 day quail embryos submitted to DOPA reaction (tyrosinase acti vity) were used. In four concentric areas-dorsal and ventrally subdivi ded-the relative density of MPC was determined by morphometric methods . Results: The relative regional density of MPC from their individuali zation as DOPA-positive putative pigment cells until their definitive seeding in the epidermis showed a progressively higher cell density fr om deeper to peripheral zones in all three levels studied, with peaks of cell density suggesting a centrifugal pattern occurring in at least ; two waves of migratory cells. Conclusions: The spatial distribution of the MPC varies according to both the axial level and the developmen tal stage of the embryo. Furthermore, the general pattern of centrifug al distribution observed might be attributed to a different timing of cell differentiation closely related to their migratory behavior. (C) 1998 Wiley-Liss, Inc.