THe acellular stroma of the chick cornea inhibits melanogenesis of the neural-crest-derived cells that colonize it.
Neural crest (NC) cells from the periorbital mesenchyme (POM) invade the acellular stroma of the chick cornea at stage 27 of development (approximately 6 days). The invading cells become collagen-producing fibroblasts while the NC cells remaining in the POM differentiate into a wide range of cell types, the most easily recognizable of which is the pigment-producing melanocyte. In this paper, we report observations on the differentiation in vitro of cells within and migrating from explants of corneal stroma and compare their behaviour with that of cells within and migrating from explants of the POM. In approximately 70% of cases, POM explants produced black, eumelanin pigmentation within 2-3 days in culture and gave rise to a mixed outgrowth of fibroblasts and melanoblasts that produced brown pigment. In no case, however, did a corneal explant produce black pigment (so demonstrating that any POM contamination was negligible). However, in 28% of cultures from stage-27 and -28 corneas, some of the cells in the outgrowth contained brown pigment indistinguishable from that produced by the POM control, although the majority of the cells in each case were fibroblasts. Two lines of investigation demonstrated that this pigment was melanin: first, transmission electron microscopy showed that the pigment organelles were incompletely melanized, granular melanosomes; second, tests designed to demonstrate the presence of lipofuscin, an alternative pigment, proved negative. Migrating cells from older corneas, in contrast, showed no evidence of even the first stages of melanogenesis. These results show, first, that some of the NC cells that invade the cornea are at least bipotent and hence representative of the POM population rather than being a unique subgroup and, second, that the acellular stroma of the cornea determines the state of differentiation of the NC cells that colonize it. The results thus provide an unequivocal demonstration that extracellular matrix can induce postmigratory NC cells to differentiate into fibroblasts.
D000818:Animals; D002454:Cell Differentiation; D002642:Chick Embryo; D003315:Cornea / Q000196:embryology* / Q000648:ultrastructure; D008543:Melanins / Q000096:biosynthesis*; D008544:Melanocytes / Q000648:ultrastructure; D008854:Microscopy, Electron; D008858:Microscopy, Phase-Contrast; D009432:Neural Crest / Q000166:cytology* / Q000378:metabolism; D010858:Pigmentation
D008543:Melanins