Early Neural Crest Specification, Induction and Competence

Citation

Basch, Martin Leandro (2004) Early Neural Crest Specification, Induction and Competence. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/9SPT-RS22. https://resolver.caltech.edu/CaltechETD:etd-02102004-172305

Abstract

The neural crest is a transient population of embryonic cells that originates at the border between the neural plate and the non-neural ectoderm. Near the time of neural tube closure, the neural crest go through an epithelial to mesenchymal transition and start an extensive migration throughout the embryo. During migration or shortly after they reached their final position, neural crest cells differentiate to form a wealth of derivatives. The mechanisms of migration and differentiation of neural crest have been vastly studied. Comparatively, much less is known about the embryological origins of the neural crest, and the nature of the interactions that generate them. To clarify the timing and nature of these inductive interactions, I examined the time of competence of the neural plate to become neural crest as well as the time of neural fold specification in chick embryos. The neural plate is competent to respond to inductive interactions with the non-neural ectoderm for a limited period, losing its responsive ability after stage 10. In contrast, non-neural ectoderm from numerous stages retains the potential to induce neural crest cells from competent neural plate. When I tested the ability of neural folds to produce neural crest, I found that folds derived from all rostrocaudal levels of the open neural plate of stage 10 embryos can generate neural crest when cultured in isolation. To further characterize the time of neural crest specification, I isolated regions of the epiblast from stages 3 and 4 embryos and identified a region that is already specified to adopt neural crest fates at the beginning of gastrulation. I describe the early expression pattern of the paired box transcription factor Pax-7, which correlates from stage 4+ onwards with the prospective neural crest forming region. Therefore, I propose that Pax-7 is the earliest neural crest marker described in chick. Furthermore, using a morpholino-based loss of function approach, I show that Pax-7 expression is required during neural crest development in chicks. Taken together, my results suggest that specification of the neural crest begins very early in development and it requires multiple and sustained signals and tissue intractions.

Thesis Files