Systematic variation in mRNA 3\u27-processing signals during mouse spermatogenesis.

Gene expression and processing during mouse male germ cell maturation (spermatogenesis) is highly specialized. Previous reports have suggested that there is a high incidence of alternative 3\u27-processing in male germ cell mRNAs, including reduced usage of the canonical polyadenylation signal, AAUAAA. We used EST libraries generated from mouse testicular cells to identify 3\u27-processing sites used at various stages of spermatogenesis (spermatogonia, spermatocytes and round spermatids) and testicular somatic Sertoli cells. We assessed differences in 3\u27-processing characteristics in the testicular samples, compared to control sets of widely used 3\u27-processing sites. Using a new method for comparison of degenerate regulatory elements between sequence samples, we identified significant changes in the use of putative 3\u27-processing regulatory sequence elements in all spermatogenic cell types. In addition, we observed a trend towards truncated 3\u27-untranslated regions (3\u27-UTRs), with the most significant differences apparent in round spermatids. In contrast, Sertoli cells displayed a much smaller trend towards 3\u27-UTR truncation and no significant difference in 3\u27-processing regulatory sequences. Finally, we identified a number of genes encoding mRNAs that were specifically subject to alternative 3\u27-processing during meiosis and postmeiotic development. Our results highlight developmental differences in polyadenylation site choice and in the elements that likely control them during spermatogenesis