Characterization of rtSH3p13 gene encoding a development protein involved in vesicular traffic in spermiogenesis.

A cDNA, designated as rtSH3p13, was isolated from a rat testis cDNA library. It consists of 1463 bp nuclear acids, which encodes a protein of 312 amino acids and was assigned the GenBank accession number AF227439. The deduced rtSH3p13 protein is a truncated isoform of SH3p13 as a result of mRNA alternative splicing. It is mainly expressed in the rat testis, detected in spermatids at the steps 8-19 of spermiogenesis, and found around the acrosome. During postnatal development, rtSH3p13 appears on day 18 and reaches maximum on day 60. Further experimental results suggested that rtSH3p13 forms a complex with activated epidermal growth factor receptor (EGFR) and interacts with synaptojanin I. Surprisingly, similar to SH3 domain, the V region of rtSH3p13 also inhibits endocytosis in CHO cells. Our results reveal a link between an rtSH3p13-synaptojanin-clathrin complex-mediated formation of pits and the process of spermiogenesis.