Identification of a rat testis-specific gene encoding a potential rat outer dense fibre protein

Screening of a rat testis expression library with an antiserum specific for an outer dense fibre (ODF) has led to the identification of a gene encoding for a putative protein previously unknown as a component of the sperm tail. This gene has been designated tpx-1 by virtue of its homology with the mouse and human gene of the same name (79 and 73%, respectively). The tpx-1-like gene encoded a 1.6-kb mRNA and a 243-amino-acid protein that had significant homology with members of the cysteine-rich secretory protein (CRISP) family and partial homology with several venom/allergen proteins from both plants and insects. During rat spermatogenesis, the tpx-1-like transcript was first detected by in situ hybridization in low levels in late pachytene spermatocytes. Low but detectable levels of expression continued up to step 5 round spermatids, after which expression levels increased dramatically to a maximum in step 11-12 spermatids. Progressively decreasing levels of expression were detected in up to step 17 elongating spermatids. Testicular somatic cells did not contain detectable tpx-1-like transcript. This pattern of expression is consistent with published data on the development of the ODF in spermatogenesis and, when taken together with a comparison of the predicted amino acid sequence of tpx-1 with the amino acid analysis of a 29-kDa rat ODF protein, suggests that the tpx-1-like gene may encode for this protein.