CLONING AND CHARACTERIZATION OF A TESTIS-SPECIFIC THYMOSIN-BETA-10 CDNA - EXPRESSION IN POSTMEIOTIC MALE GERM-CELLS

Thymosin beta-10 is one of a small family of proteins closely related in sequence to thymosin beta-4, recently identified as an actin-sequestering protein. A single molecular weight species of thymosin beta-10 mRNA is present in a number of rat tissues. In adult rat testis, an additional thymosin beta-10 mRNA of higher molecular weight was identified. Nucleotide sequencing of cDNA clones complementary to the testis-specific thymosin mRNA indicated that this mRNA differed from the ubiquitous thymosin beta-10 mRNA only in its 5'-untranslated region, beginning 14 nucleotides upstream of the translation initiation codon. These results, together with primer extension experiments, suggest that the two thymosin beta-10 mRNAs are transcribed from the same gene through a combination of differential promoter utilization and alternative splicing. The novel thymosin beta-10 mRNA could be detected only in RNA isolated from sexually mature rat testis. Both mRNAs were present in pachytene spermatocytes; only the testis-specific mRNA was detected in postmeiotic haploid spermatids. Immunoblot analysis using specific antibodies showed that the thymosin beta-10 protein synthesized in adult testis was identical in size to that synthesized in brain. Immunohistochemical analysis showed that the protein was present in differentiating spermatids, suggesting that the testis-specific thymosin beta-10 mRNA is translated in haploid male germ cells.