The Bhh cell signaling pathway is involved in neural crest migration and craniofacial development

AGÜERO, TRISTAN H.; FERNÁNDEZ, JUAN P.; AYBAR, MANUEL J.

Buenos Aires, Argentina

Congreso; IV International Meeting of the Latinamerican Society of Developmental Biology; 2008

LASDB

The neural crest (NC) is a transient embryonic cell population found only in vertebrate embryos. These cells can migrate extensively and differentiate into diverse derivatives, ranging from neurons and glia of the sensory ganglia, to medullary secretory cells, melanocytes, and much of the facial skeleton. Several signals (BMP, Wnt, FGF, Notch/Delta, RA) are involved in the initial induction of this tissue; however the participation of other cell signaling pathways has not been established. The NC is first induced by a set of signaling events at the border between future neural and non-neural ectoderm. They concomitantly acquire migratory ability that allow them to respond properly to cell–cell interactions and environmental cues that influence their pathways of migration. This complex succession of events is guided by a gene regulatory network, from early induction, migration to distant locations, to differentiation. In Xenopus laevis there are three secreted morphogens of the hedgehog (Hh) family, sonic, cephalic and banded hedgehog (Bhh). These morphogens direct a wide range of developmental processes like cell fate determination, pattern formation and cell proliferation in many tissue types. The aim of our work is to study the role of the Bhh pathway in NC development. We have previously shown that Bhh and its transcription effector Gli3 expression patterns overlap with NC markers and functional experiments have shown that both genes participate in the NC induction. In this work, we focus our analysis in regulatory aspects of the pathway concerning to subsequent events in NC development, and we confine our discussion to the role of Bhh signaling in the NC migration and differentiation. In particular, we focus on how members of the Gli family of transcription factors act as effectors of Hh signalling in the NC development. We showed that specific morpholino oligonucleotide against Bhh and Gli3 reduced the migration of neural crest cells, indicating that this signaling is required for this process. Making transplant approaches of NC cells, we confirmed the requirement of the Bhh signal in the migration and cell fate determination. By in vitro analysis, using explants experiments in stages in which the migration is occurring, we confirm that this signaling is required during migration. We also observed that Bhh and Gli3 morpholinos were able to block the formation of craniofacial derivatives as facial abnormalities in tadpole-stage embryos were discovered. Carrying out rescue experiments, the inhibitory effects of morpholino approaches were suppressed by the coinjection of different constructs of Bhh and Gli3. Our results demonstrate that this pathway is required for normal development and provide new insights into the possible molecular regulation of Bhh pathway in the NC.