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 regulation because they are pluripotent, and thus might be able to alter their behavior in response to environmental signals. This study investigated regulation for the loss of trunk neural crest (TNC) cells, specifically pigment 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 regulation would vary with the amount removed, the position or stage of removal. Zebrafish TNC cells are large and numerous. SEM and Dil labeling revealed that TNC cells undergo several successive waves of 'sheet' and 'segmental' migration, beginning as early as the 12 somite stage. Dil-labeled TNC cells often migrated several somite lengths anteriorly and posteriorly along the trunk axis to form glial cells, ganglia, pigment, ectomesenchyme and tail reticular cells. Regulation occurred on a sliding scale, ranging from complete to incomplete. Defects in development and/or pigmentation occurred if large 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, pigmentation was remarkably normal. We propose that the completeness of regulation largely depends upon healing of the overlying epidermis.