Patterns of migration and regulation of trunk neural crest cells in Zebrafish (Danio rerio)

Regulation is the replacement of lost, undifferentiated embryonic cells by neighboring cells in response to environmental signals. Neural crest cells, embryonic cells unique to craniates, are good candidates for studies of re gulation because they are pluripotent, and thus might be able to alter thei r behavior in response to environmental signals. This study investigated re gulation for the loss of trunk neural crest (TNC) cells, specifically pigme nt derivatives, in the zebrafish, Danio rerio. The first part of the study clarifies and extends what has previously been described on normal patterns of TNC migration and differentiation. These data were then used to address the hypothesis that there is regulation for loss of TNC, and that regulati on would vary with the amount removed, the position or stage of removal. Ze brafish TNC cells are large and numerous. SEM and Dil labeling revealed tha t TNC cells undergo several successive waves of 'sheet' and 'segmental' mig ration, beginning as early as the 12 somite stage. Dil-labeled TNC cells of ten migrated several somite lengths anteriorly and posteriorly along the tr unk axis to form glial cells, ganglia, pigment, ectomesenchyme and tail ret icular cells. Regulation occurred on a sliding scale, ranging from complete to incomplete. Defects in development and/or pigmentation occurred if larg e regions of TNC cells were removed, or if cells were removed from anterior (cardiac) and posterior (tail) extremities of the trunk. Melanophores were the cell type most visibly affected by TNC extirpations. Otherwise, pigmen tation was remarkably normal. We propose that the completeness of regulatio n largely depends upon healing of the overlying epidermis.