Genetic dissection of neural crest cell migration

Neural crest cells are a multipotent cell population unique to vertebrates that migrate long distances to give rise to variety of cell types. In the embryonic trunk, neural crest cells migrate in a segmentally restricted manner through a specific portion of the somite. Despite this being an evolutionary conserved process in vertebrates, signaling pathways critical for this segmental neural crest migration are only partially understood. Here I report the requirement of two signaling pathways in early segmental neural crest migration. I find that in zebrafish wnt11r and in MuSK mutants neural crest cells are no longer restricted to a central path but instead stream over the entire somite territory. Moreover, blocking non-canonical (PCP) wnt signaling in muscles recapitulates the aberrant neural crest cell migration observed in wnt11r or MuSK mutant embryo. In addition to the Wnt11r-MuSK-Dishevelled pathway, I report a second pathway consisting of Lh3, a glycosylating enzyme, and its presumptive substrate, Collagen XVIII, an extracellular matrix component. Loss of function studies show that this pathway acts to restrict neural crest stream formation to midsegmental sites. Together my data identifies two muscle cell derived and complementary pathways guiding neural crest cells along the somatic path: while non-canonical wnt signaling maintains segmental neural crest cell migration, Lh3 dependent ECM modifications are critical to initiate the transition from unsegemented to segmented migration. 
Finally, to understand how neural crest cells at late stages contribute to their target organ development, I have characterized a zebrafish mutant called rushhour isolated in a forwards genetic screen which shows defects in cardiac neural crest cell migration and in the atrio-ventricular (A-V) valve development. Currently I am using sequence enrichment method coupled with next generation sequencing to molecularly identify the rushhour gene.