A role for semaphorin 3D, a secreted cell-signaling molecule, in zebrafish cranial neural crest cell delamination and migration

The appropriate migration of cranial neural crest cells is critical for the correct formation of the craniofacial skeleton and sensory ganglia of the head. Relatively little is known about the molecular factors regulating neural crest cell delamination from the neural keel and migration to the pharyngeal arches and sensory ganglia. sema3D mRNA is expressed in the dorsal region of the hindbrain and in specific clusters of neural crest cells, beginning at the onset of and continuing throughout neural crest cell migration. Based on this expression pattern, we hypothesize that Sema3D acts in a repulsive manner to promote delamination and to separate adjacent streams of migrating crest cells. Morpholino antisense-mediated knockdown of Sema3D expression results in a dose dependent decrease in a subpopulation of cranial neural crest cells that normally express sema3D. Furthermore, when morpholino injected embryos are observed later in development there is a significant disruption in the organization of the craniofacial cartilage. We are currently analyzing the dynamics of neural crest cell delamination using DIC microscopy and time-lapse video analysis in vivo. Preliminary results suggest that in morpholino-injected embryos fewer cells may be undergoing the epithelial to mesenchymal transformation necessary to initiate migration. We are also analyzing the pattern of migration to the pharyngeal arches using fluorescent tracer dyes and confocal imaging. Preliminary data from these experiments suggest that Sema3D may play a role in the structural organization of the pharyngeal arches.