Expression of a novel isoform of Vav, Vav-T, containing a single Src homology 3 domain in murine testicular germ cells

Abstract

Vav is a signal transducing molecule containing Cterminal Src homology 3 (SH3)-SH2-SH3 domains, and has been thought to be expressed exclusively in hematopoietic and trophoblastic cells. By Northern blot analysis, vav transcripts of unique sizes, 4.8 kb and 1.0 kb, were detected in the testis among various tissues examined. From a mouse spermatocyte cDNA library, a novel isoform of vav (vav-T) was cloned, which corresponded 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 amino acids with a single SH3 domain. Northern blot analysis of fractionated testicular cells and in situ hybridization histochemistry demonstrated that vav-T transcripts were expressed in the dierentiating 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. Transcripts of heterogeneous nuclear ribonucleoprotein K, known to associate with the most C-terminal SH3 domain of Vav, were also detected in the dierentiating male germ cells. These results demonstrate expression of previously nondescribed Vav-isoform in the testicular germ cells, and suggest that it interacts with RNAbinding proteins and plays an important role in spermatogenesis.

Vav proteins, adaptors and cell signaling

“…The overexpression of these C-terminal domains leads to a dominant negative e ect in T-cells, mast cells, and ®broblasts, probably by blocking the interaction of the autophosphorylated kinases with the endogenous Vav proteins (Arudchandran et al, 2000;Wu et al, 1996;unpublished observations Figure 1a). Interestingly, the expression of these proteins does not overlap with the full length proteins (Okumura et al, 1997;Zeng et al, 2000). These results suggest these other versions of Vav proteins have functional roles of their own, probably by working as adaptor proteins in some speci®c pathways.…”

Cytoskeletal Reorganization by G Protein-Coupled Receptors Is Dependent on Phosphoinositide 3-Kinase γ, a Rac Guanosine Exchange Factor, and Rac

“…Since Vav-1 expression is restricted to hematopoietic cells, it cannot account for the activation of Rac in Cos-7SH cells when activated PI3-K ␥ is expressed alone. A nonhematopoietic Vav (Vav-2 or Vav-T) has recently been identified, although it is not known whether this has exchange activity for Rac (26). Certainly, the striking inhibition of actin reorganization seen when the inactive Vav variants are expressed implies that these variants are competing with an endogenous exchange factor with similar binding characteristics.…”

Constitutive Bcl-2 expression throughout the hematopoietic compartment affects multiple lineages and enhances progenitor cell survival

“…2A), hBcl-2 was abundant in the spleen and thymus, but none was evident in testis, brain, or muscle, nor in kidney (not shown). Although testis is known to contain a distinct Vav isoform (36), it would be undetectable by the Vav antibody used here, and no testicular hBcl-2 expression would be expected, because that isoform arises from a promoter not present in our transgene. Some hBcl-2 was present in lung and liver and a trace in small intestine, but these organs normally contain some hematopoietic cells, and the vav-bcl-2 mice often showed focal accumulations of lymphocytes in lung and liver (see below).…”