TauCstF-64 Mediates Correct mRNA Polyadenylation and Splicing of Activator and Repressor Isoforms of the Cyclic AMP-Responsive Element Modulator (CREM) in Mouse Testis1

Spermatogenesis is coordinated by the spatial and temporal expression of many transcriptional and posttranscriptional factors. The cyclic AMP-responsive element modulator (CREM) gene encodes both activator and repressor isoforms that act as transcription factors to regulate spermiogenesis. We found that the testis-expressed paralog of CstF-64, tauCstF-64 (gene symbol Cstf2t), is involved in a polyadenylation site choice switch of Crem mRNA and leads to an overall decrease of the Crem mRNAs that are generated from internal promoters in Cstf2t−/− mice. More surprisingly, loss of tauCstF-64 also leads to alternative splicing of Crem exon 4, which contains an important activation domain. Thus, testis-specific CREMtau2 isoform protein levels are reduced in Cstf2t−/− mice. Consequently, expression of 15 CREM-regulated genes is decreased in testes of Cstf2t−/− mice at 25 days postpartum. These effects might further contribute to the infertility phenotype of these animals. This demonstrates that tauCstF-64 is an important stage-specific regulator of Crem mRNA processing that modulates the spatial and temporal expression of downstream stage-specific genes necessary for the proper development of sperm in mice.