Testis-specific gene C3ORF22/BC048671 is dispensable for spermiogenesis and male fertility.

Testicular tissue displays the most complex transcriptome across all tissues, with over 2000 genes exhibiting testis-enriched expression patterns. However, the functional ambiguity of such genes limits our understanding of spermatogenesis and male fertility. Here, we reanalyzed testicular gene expression profiles from patients with impaired spermatogenesis and identified that reduced expression of the testis-specific gene C3ORF22 was correlated with spermatogenic defects in humans. We showed that the murine ortholog BC048671 was predominant expressed in round spermatids, and its protein is present in spermatozoa. BC048671 knockout (KO) mice exhibited normal fertility, sperm morphology, and sperm motility. Intriguingly, RNA-Seq analysis revealed that BC048671 was the most markedly dysregulated gene in KO testes. Although proteomic analysis reveals the down-regulated ADAM family members (e.g., ADAM28 and ADAM2) in BC048671-null sperm, expression of the key downstream effector ADAM3 remained unaffected. These findings indicate that BC048671/C3ORF22 exhibits functional redundancy in spermatozoa. Although C3ORF22 is dispensable for male fertility, we consider it essential to report such negative results to guide researchers to prioritize efforts toward genes critical for human fertility.