An ancient testis-specific IQ motif-containing H gene regulates specific transcript isoform expression during spermatogenesis

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Spermatogenic cells express more alternatively spliced RNAs than most whole tissues; however, the regulation of these events remains unclear. Here, we have characterized the function of a testis-specific IQ motif-containing H gene (Iqch) using a mutant mouse model. We found that Iqch is essential for the specific expression of RNA isoforms during spermatogenesis. Using immunohistochemistry of the testis, we noted that Iqch was expressed mainly in the nucleus of spermatocyte and spermatid, where IQCH appeared juxtaposed with SRRM2 and ERSP1 in the nuclear speckles, suggesting that interactions among these proteins regulate alternative splicing (AS). Using RNA-seq, we found that mutant Iqch produces alterations in gene expression, including the clear downregulation of testis-specific lncRNAs and protein-coding genes at the spermatid stage, and AS modifications - principally increased intron retention - resulting in complete male infertility. Interestingly, we identified previously unreported spliced transcripts in the wild-type testis, while mutant Iqch modified the expression and use of hundreds of RNA isoforms, favouring the expression of the canonical form. This suggests that Iqch is part of a splicing control mechanism, which is essential in germ cell biology.
This study was funded by the Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación (PID2021-122507OB-I00 and PID2020-117491GB-I00) and the European Union NextGenerationEU/PRTR. P.N.-L. was supported by a pre-doctoral fellowship from the Ministerio de Ciencia e Innovación (PRE2019-088813) and M.L. was supported by a Juan de la Cierva postdoctoral contract (FJC2019-040385-I) from the Ministerio de Ciencia e Innovación. Open access funding provided by Consejo Superior de Investigaciones Cientıficas. Deposited in PMC for immediate release.