A not so minor role for the minor spliceosome in spermatogenesis

Minor introns have been highly conserved in the genome since their emergence in the last eukaryotic common ancestor and are found in genes related to proliferation, chromatin organization, transcription, and splicing. Here, we show that minor intron-containing genes (MIGs) involved in the gene expression landscape of mouse spermatogenesis are largely conserved in chordates as MIGs, which rely on the minor spliceosome (MiS) and its small nuclear RNAs (snRNAs) for their minor intron splicing. We show that MIGs are highly enriched in regulating, mitosis, meiosis and specifically sperm differentiation. Stra8-Cre mediated ablation of U11 snRNA inhibited the minor spliceosome in differentiating spermatogonia and spermatocytes, which resulted in both mitosis and meiosis defects that resulted in severe reduction of mature sperm in the seminiferous tubule leading to testicular defect. Increased death of spermatocytes was observed in mutants due to defective meiotic chromosome features including DNA damage repair, telomere morphology, synapsis of homologous chromosomes and XY-chromosome association. These phenotypes were underscored by the aberrant splicing and differential expression of core spermatogenesis genes, including Hfm1. In all, we position spermatogenesis as another selective pressure that ensured conservation and expansion of MIGs in the genome.