Translational regulation of the novel haploid-specific transcripts for the c-abl proto-oncogene and a member of the 70 kDa heat-shock protein gene family in the male germ line

Expression of the c- abl proto-oncogene in the mouse testis is characterized by the production of a unique 4.7-kb transcript present in germ cells that have entered the haploid phase of spermatogenesis. A similar developmental stage specificity of expression is observed for a member of the 70-kDa heat-shock protein (hsp 70) gene family. A unique-sized hsp 70 transcript (T-hsp 70) is produced in haploid spermatids and is stable throughout spermatogenesis. In the present study, we examined the regulation of expression of these genes by examining their association with polyribosomes. The germ cell-specific c- abl and T-hsp 70 mRNA variants were both associated with the polysomal fractions of mouse testis cells, suggesting that they are functional mRNAs. However, both c- abl and T-hsp 70 mRNAs were also found in the ribonucleoprotein particle fractions. The distribution of these mRNAs in both the polysomal and nonpolysomal fractions is comparable to that seen for the mRNA of protamine-1, a gene whose expression in the testis is known to be regulated at the level of translation. In contrast, transcripts from the β-tubulin gene were seen predominantly in the polyribosomal fractions. These findings suggest that translation of the novel c- abl and T-hsp 70 transcripts is confined to subpopulations of testicular cells.