N1-Src Kinase Is Required for Primary Neurogenesis in Xenopus tropicalis.

The presence of the neuronal-specific Nl-Src splice variant of the C-Src tyrosine kinase is conserved through vertebrate evolution, suggesting an important role in complex nervous systems. Alternative splicing involving an Nl-Src-specific microexon leads to a 5 or 6 aa insertion into the SH3 domain of Src. A prevailing model suggests that N1-Src regulates neuronal differentiation via cytoskeletal dynamics in the growth cone. Here we investigated the role of nl-src in the early development of the amphibian Xenopus tropicalis, and found that nl-src expression is regulated in entbryogenesis, with highest levels detected during the phases of primary and secondary neurogenesis. In situ hybridization analysis, using locked nucleic acid oligo probes complementary to the nl-src microexon, indicates that nl-src expression is highly enriched in the open neural plate during neurula stages and in the neural tissue of adult frogs. Given the nl-src expression pattern, we investigated a possible role for nl-src in neurogenesis. Using splice site-specific antisense morpholino oligos, we inhibited nl-src splicing, while preserving c-src expression. Differentiation of neurons in the primary nervous system is reduced in n 1-str-knockdown embryos, accompanied by a severely impaired touch response in later development. These data reveal an essential role for nl-src in amphibian neural development and suggest that alternative splicing of C-Src in the developing vertebrate nervous system evolved to regulate neurogenesis. [ABSTRACT FROM AUTHOR]