The Dispensable Roles of X-Linked and Its Autosomal Counterpart in Spermatogenesis Represent a New Evolutionary Type of X-Derived Retrogenes.

X-derived retrogenes contribute to genetic diversity in evolution and are usually specifically expressed in testis and perform important functions during spermatogenesis. is an autosomal retrogene with testis-specific expression derived from , an X-linked housekeeping gene. In the current study, we performed phylogenetic analysis and revealed that and are subject to purifying selection and may have conserved functions in evolution. was knocked out in mice using CRISPR/Cas9 genome editing technology and interestingly, we found no alterations in reproductive parameters of male mice. To get insights into whether could compensate the absence of , we further obtained mice that lack both and , and the double knockout (dKO) mice also displayed normal spermatogenesis, showing that and are both dispensable for spermatogenesis. Thus, through the study of UBL4A and UBL4B, we provided a direct evidence for the first time that some X chromosome-derived autosomal retrogenes can be unfunctional in spermatogenesis, which represents an additional evolutionary type of X-derived retrogenes.