ABSTRACT
We have studied neural crest development in two teleost fish species, Xiphophorus maculatus (platyfish) and X. heUeri (swordtail), and found similarities to that in other vertebrates but also some important differences. Unlike in other vertebrates, segregation of neural crest cells occurs in masses or groups from the dorsal-lateral part of the neural keel (tube) except in the mesencephalon region, where neural crest cells segregate from the dorsal-midline and in the most anterior trunk region, where they segregate individually. However, the cells were found in the usual neural tube-somite and somite-ectoderm migration pathways. Notably numerous cells, presumed in part to be neural crest cells, were found in a third location, dorsally on the neural tube. These cells exhibit a series of morphological stages referred to as ‘covering’, ‘condensation’, and ‘differentiation’. A great amount of ECM was observed in these fish and can be temporally and regionally correlated with the appearance of the neural crest cells. No major differences could be detected between the two fish species with the exception that segregation and appearance of neural crest cells in various locations occur earlier in the platyfish. This time difference could lead to perturbations in neural crest cell development in certain platyfish-swordtail hybrids and may contribute to the formation of neural-crest-derived pigment cell tumours, melanomas, in these hybrids.
