EXPRESSION OF A NOVEL ISOFORM OF VAV, VAV-T, CONTAINING A SINGLE SRC HOMOLOGY-3 DOMAIN IN MURINE TESTICULAR GERM-CELLS

Vav is a signal transducing molecule containing C-terminal Src homolog y 3 (SH3)-SH2-SH3 domains, and has been thought to be expressed exclus ively in hematopoietic and trophoblastic cells, By Northern blot analy sis, vav transcripts of unique sizes, 4.8 kb and 1.0 kb, were detected in the testis among various tissues examined, From a mouse spermatocy te cDNA library, a novel isoform of vav (vav-T) was cloned, which corr esponded to a part of the 4.8 kb transcript, Vav-T had an alternative 5' sequence up to the middle of SH2-coding region, and encoded 163 ami no acids with a single SH3 domain, Northern blot analysis of fractiona ted testicular cells and in situ hybridization histochemistry demonstr ated that vav-T transcripts were expressed in the differentiating germ cells, especially spermatocytes. A 24 kD protein was detected by anti -Vav antibodies in the testis, but not in the spleen or bone marrow, T ranscripts of heterogeneous nuclear ribonucleoprotein K, known to asso ciate with the most C-terminal SH3 domain of Vav, were also detected i n the differentiating male germ cells, These results demonstrate expre ssion of previously nondescribed Vav-isoform in the testicular germ ce lls, and suggest that it interacts with RNA-binding proteins and plays an important role in spermatogenesis.