Expression and function of netrin and its receptors in sea urchin embryos: implications for neural and ectoderm development




Juurinen, Andrew

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Functional and temporal-spatial studies of Netrin and its receptors have been reported in several species including, M. musculus, D. melanogaster and C. elegans. These studies indicate that Netrins are a family of evolutionarily conserved, secreted proteins that function to elicit the extension and turning responses of axons. Here, I describe the sequences for netrin and its receptors, unc5 and neogenin, in Strongylocentrotus purpuratus and show that the larval nervous system is patterned predictably with respect to cell body and axon location, early in its development. These findings led to a tentative hypothesis that Sp-Netrin functions to guide axonal growth in the larval nervous system. Quantitative PCR indicates that Sp-netrin and Sp-unc5 are expressed prior to neurogenesis, whereas Sp-neogenin is expressed close to the stage at which neurons differentiate. A polyclonal antibody to Sp-Netrin and in situ hybridizations reveal that Sp-Netrin is initially expressed in the vegetal plate, the archenteron and the protein is present on the basal surface of the oral ectoderm in early prism stage embryos. Suppression of Netrin expression, with a morpholino antisense oligonucleotide, results in loss of neurons, loss of ciliary band cells and loss of the oralectoderm markers, Chordin and Goosecoid. These findings suggest that Netrin is responsible for maintaining or differentiating oral and ciliary band ectoderm, which is necessary for neural specification or differentiation. Further study of this model is necessary to determine if Sp-Netrin retains a role in axon guidance.



Sea urchin, axon guidance, ectoderm regulation, neural development, Netrin, Unc5, Neogenin