The novel, actin-like protein Tact3 is expressed in rodent testicular haploid germ cells.

Mouse testis actin-like proteins 1 and 2 (mTact1 and mTact2), which are expressed in murine haploid germ cells, have been described previously. Here, we report the cloning and characterization of a third actin-like protein from rat, rat testis actin-like protein 3 (rTact3). The complete cDNA of the rTact3 gene was approximately 3.7 kb in length, and its corresponding amino acid sequence consisted of 1219 amino acids. The rTact3 gene lacks introns, similar to mTact1 and mTact2. The 356 C-terminal amino acids of rTact3 showed 43% homology with mTact1, whereas the 863 N-terminal amino acids did not show any significant homology. Northern blot analysis revealed that rTact3 mRNA was expressed only in adult rat testes and not during the prepubescent stage. In situ hybridization revealed that rTact3 was expressed exclusively during round and elongated spermatids maturation stages in rat testes. Immunohistochemical experiments using antibodies raised against a synthetic peptide showed that the expression of the rTact3 protein was also restricted in round and elongated spermatids, specifically in the head and acrosome of mature rat sperm. The 5′-flanking region of the mTact3 gene was found to contain a TATA-box motif as well as two putative CREB/c-Jun and five C/EBP motifs. mTact3 promoter activity was enhanced in a dose-dependent manner by the transfection of CREB, c-Jun, or C/EBP in NIH3T3 cells. These results suggest that Tact3 proteins might play an important role in rodent germ-cell development.