The Functional Role And Related Mechanism Of RPL10L,An X Chromosome Derived Retrogene,in Spermatogenesis

The mammalian sex chromosomes have undergone profound changes during their evolution from an ancestral pair of autosomes.For example,the X chromosome evolved dramatically after the divergence of eutherian and metatherian mammals,with two major bursts of gene origination events that resulted in a substantial increase in its contribution to the genome.Specifically,the X chromosome has acquired a paradoxical sex-biased function by redistributing gene contents and has generated a disproportionately high number of retrogenes that are located on autosomes and exhibit male-biased expression patterns.Concomitantly,most of these retrogenes exist in the eutherian and metatherian lineages.Several selection-based models have been proposed to explain this phenomenon,including sexual antagonism driving X inactivation(SAXI)model and meiotic sex chromosome inactivation(MSCI)-based compensatory mechanism.However,the function of only a small number of X-to-autosome retrogenes has been investigated,and insight into the forces that drive directional gene movement during mammalian evolution remains limited.RPL10L is testis-specifically expressed retrogene originated from RPL10,an ancient X-linked ribosomal protein encoding gene,shortly after the divergence of eutherian and metatherian lineages.In order to further understand the significance of X-derived retrogenes and its evolutionary mechanism,we selected the RPL10L and RPL10 as a model to investigate their gene expression patterns and functional roles,respectively.Firstly,we generated Rpl10l-deficient mice using CRISPR/Cas9 technology and found that deficiency of RpllOl prohibits the transition from prophase into metaphase of the first meiotic division,resulting in male infertility.Secondly,we showed that RPL10L is a ribosomal component in mouse spermatogenic cells,and deletion of it results in disturbance of ribosome biogenesis and content fluxes of a large number of proteins in pachytene and diplotene spermatocytes.Thirdly,Rpl10 exhibits a broad expression pattern in diffirent tissues mice and even early stage of spermatogenic cells(spermatogonia,preleptotene spermatocytes,leptotene and zygotene spermatocytes),but its expression is sharply reduced in pachytene,diplotene spermatocytes and round spermatids.Interestingly,Rpl10l expression compensates for the lack of Rpl10 caused by MSCI during spermatogenesis.Lastly,we found that knockdown of RPL10 results in disturbance of ribosome biogenesis and cell cycle arrest.Knockout of RPLIO results in cell proliferation failure and inviability,while ectopic expression of RPL10L prevents death of RPL10-deficient cells.More importantly,Rpl10l-promoter-driven transgenic expression of Rpl10 in spermatocytes restores spermatogenesis and fertility in Rpl10l-deficient mice.Our results demonstrate that Rpl10l plays an essential role during the meiotic stage of spermatogenesis by compensating for MSCI-mediated transcriptional silencing of Rpl10.These data provide direct evidence for the compensatory hypothesis and add novel insight into the evolution of X chromosome-derived autosomal retrogenes and their role in male fertility.