Meeting Abstract
Cells expressing neural crest markers emerge from the trunk neural tube in the turtle Trachemys scripta in two migratory phases over a greatly extended period. The NCCs that emerge late (in stage G16-17 turtle embryos), well beyond the stage of neural crest emigration in chick or mouse embryos, appear to migrate ventrally to form an ectomesenchymal dermis that gives rise to the bones of the plastron. Transfection with a GFP-expressing plasmid has shown that the early phase of migration is still occurring in stage G10, but not stage G12 turtle embryos. The specification of premigratory NCCs, and the epithelial-mesenchymal transition that produces migratory NCCs, is controlled by a gene regulatory network. We are currently comparing the expression of markers of premigratory and early migratory NCCs in G10 and later turtle embryos to examine whether the premigratory NCC domain persists during the period between the early and late migratory phases. Preliminary results have demonstrated the expression of Cad6B protein in the dorsal neural tube of G12 turtle embryos, suggesting the maintenance of the premigratory NCC population between the two phases of NCC migration. We are using antibody staining and in situ hybridization to confirm and extend these findings to additional genes expressed in premigratory NCCs, including the transcription factors Snail2, Sox9, FoxD3. If the expression of premigratory NCC markers persists after the first wave of NCC migration, it will suggest that the premigratory NCC region is maintained longer than in other model amniotes, and that the lack of NCC migration in stage G11-15 turtle embryos may be due to the absence of a supportive environment.
