Transcription factor-like 5 is a potential DNA- and RNA-binding protein essential for maintaining male fertility in mice.

Transcription factor-like 5 (TCFL5) is a testis-specific protein that contains the basic helix-loop-helix domain, but the in vivo functions of TCFL5 remain unknown. Herein, we generated CRISPR/Cas9-mediated knockout mice to dissect the function of TCFL5 in mouse testes. Surprisingly, we found that it was difficult to generate homozygous mice with the Tcfl5 deletion as the heterozygous males (Tcfl5+/-) were infertile. However, we did observe markedly abnormal phenotypes of spermatids and spermatozoa in the testes and epididymides of Tcfl5+/- mice. Mechanistically, we demonstrated that TCFL5 transcriptionally and post-transcriptionally regulated a set of genes participating in male germ cell development via TCFL5 ChIP-DNA and eCLIP-RNA high-throughput sequencing. We also identified a known RNA-binding protein, FXR1, as an interacting partner of TCFL5 that may coordinate the transition and localization of TCFL5 in the nucleus. Collectively, we herein report for the first time that Tcfl5 is haploinsufficient in vivo and acts as a dual-function protein that mediates DNA and RNA to regulate spermatogenesis. This article has an associated First Person interview with the first author of the paper.