Functional Interaction between U1snRNP and Sam68 Insures Proper 3′ End Pre-mRNA Processing during Germ Cell Differentiation

Male germ cells express the widest repertoire of transcript variants in mammalian tissues. Nevertheless, factors and mechanisms underlying such pronounced diversity are largely unknown. The splicing regulator Sam68 is highly expressed in meiotic cells, and its ablation results in defective spermatogenesis. Herein, we uncover an extensive splicing program operated by Sam68 across meiosis, primarily characterized by alternative last exon (ALE) regulation in genes of functional relevance for spermatogenesis. Lack of Sam68 preferentially causes premature transcript termination at internal polyadenylation sites, a feature observed also upon depletion of the spliceosomal U1snRNP in somatic cells. Notably, Sam68-regulated ALEs are characterized by proximity between U1snRNP and Sam68 binding motifs. We demonstrate a physical association between Sam68 and U1snRNP and show that U1snRNP recruitment to Sam68-regulated ALEs is impaired in Sam68−/− germ cells. Thus, our study reveals an unexpected cooperation between Sam68 and U1snRNP that insures proper processing of transcripts essential for male fertility. [Display omitted] •Sam68 controls an extensive splicing program across meiosis in male germ cells•Sam68 prevents selection of premature alternative last exons•Proximity of Sam68 and U1snRNP motifs identifies Sam68 target last exons•Sam68 cooperates with U1snRNP in preventing premature transcript termination Naro et al. show that Sam68 regulates an extensive splicing program during male germ cell differentiation. Sam68 primarily regulates alternative last exon selection in genes with functional relevance for spermatogenesis by preventing premature transcript termination and conferring tissue specificity to the U1snRNP telescripting activity.