Bull testicular haploid germ cells express a messenger encoding for a truncated form of the protein tyrosine kinase HCK

Protein tyrosine phosphorylation is a process that has been studied worldwide during sperm capacitation and acrosomal exocytosis events. Although few capacitation-induced phosphotyrosine-containing proteins have been identified, little is known about the tyrosine kinases directly involved in this post-translational modification. Different studies from our and other groups using tyrosine kinase inhibitors suggest the involvement of members of the family of src-related tyrosine kinases in the sperm capacitation associated increase in protein tyrosine phosphorylation. Using a molecular biology approach, we report for the first time messengers encoding for members from the src-related tyrosine kinase family in bovine spermatogenic cells. Degenerated primers were designed within a highly homologous region specific to the family of src tyrosine kinases, and RNAs coding for c-src, c-yes, lyn, lck, and hck were identified in bull testis and haploid germ cells by RT-PCR. We also report the presence of a messenger in haploid bull germ cells that could encode for a truncated isoform of the hck tyrosine kinase. This messenger was detected by screening of a haploid germ cells cDNA library using the RT-PCR product homologous to hck as a probe. The presence of this transcript in haploid germ cell RNA preparations was validated by RT-PCR, 3'RACE, 5'RACE as well as Northern blot. Such a truncated protein could function as an adaptor protein or as a competitive inhibitor in spermiogenesis or mature sperm functions.