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Spermatogenesis involves coordinated processes, including meiosis, to produce functional gametes. We previously reportedTopaz1as a germ cell-specific gene highly conserved in vertebrates.Topaz1knockout males are sterile with testes that lack haploid germ cells because of meiotic arrest after prophase I. To better characterizeTopaz1–/–testes, we used RNA-sequencing analyses at two different developmental stages (P16 and P18). The absence of TOPAZ1 disturbed the expression of genes involved in microtubule and/or cilium mobility, biological processes required for spermatogenesis. Moreover, a quarter of P18 dysregulated genes are long non-coding RNAs (lncRNAs), and three of them are testis-specific and located in spermatocytes, their expression starting between P11 and P15. The suppression of one of them,4939463O16Rik, did not alter fertility although sperm parameters were disturbed and sperm concentration fell. The transcriptome of P18-4939463O16Rik–/–testes was altered and the molecular pathways affected included microtubule-based processes, the regulation of cilium movement and spermatogenesis. The absence of TOPAZ1 protein or4930463O16Rikproduced the same enrichment clusters in mutant testes despite a contrasted phenotype on male fertility. In conclusion, althoughTopaz1is essential for the meiosis in male germ cells and regulate the expression of numerous lncRNAs, these studies have identified aTopaz1regulated lncRNA (4930463O16Rik) that is key for both sperm production and motility.

Spermatogenesis comprises a coordinated process, including meiosis, to produce fertile male gametes. Previous study reported that Topaz1 is a germ cell specific gene highly conserved in vertebrates. Topaz1 knockout male mice are sterile. The mutant testes lack haploid germ cells and meiosis arrests at the first-division prophase-metaphase transition. Here, in order to better characterize the testicular phenotype of Topaz1-/- mice, we used RNA-seq analyses at two different developmental stages. At postnatal days 16 (P16), 205 genes were differentially expressed genes (DEGs) in Topaz1-/- testes. They suggest stress conditions in mutant testes. At P18, the number of DEGs was increased 10-fold and 90% were down-regulated. The absence of Topaz1 seems to disturb the expression of genes involved in microtubule and/or cilium mobility, spermatogenesis and first meiotic division during the transition from prophase to metaphase. This is consistent with the Topaz1-/- testis phenotype where microtubule networks and centrosomes are disrupted. Moreover, a quarter of P18-DEGs are long non-coding RNAs (lncRNAs). Three of them, down-regulated at P16 and P18, were studied. They are testis-specific, located in spermatocytes and their expression starts between P11 and P15. We report here the effects of the suppression of one of these lncRNAs, 4939463O16Rik. The mouse fertility is not affected although the sperm parameters are disturbed. Transcriptome of P18-4939463O16Rik-/- testes is altered and the affected molecular pathways include microtubule-based process, regulation of cilium movement, spermatogenesis, male gamete differentiation. The absence of TOPAZ1 protein or of 4930463O16Rik lncRNA showed the same enrichment clusters in mutant testes despite a contrasted phenotype on the male fertility. In conclusion, Topaz1 is an essential gene for male fertility in mice and seems to stabilize the expression of many lncRNAs. Its absence leads to meiotic arrest. Suppression of one lncRNA is dispensable for mouse fertility but is necessary during terminal differentiation of male gametes. Author SummaryThe Topaz1 gene was initially characterized during the meiotic initiation in the sheep fetal ovary. In order to determine its function, the KO of the murine gene was performed. In this species, only males are sterile and spermatogenesis is blocked before the first meiotic division. Here, we show that cytoskeletal elements are strongly disturbed in mutant testes, a sign that these elements take an important function in spermatogenesis. While the mitotic spindle of spermatogonia is normal, the meiotic spindle of spermatocytes is a hemispindle-shaped and the homologous chromosome pairs cannot position themselves on the equatorial plate. In addition, lncRNAs represent 25% of genes whose testis expression varies significantly due to the absence of Topaz1. This suggests a key role of these factors in spermatogenesis. Largely testis specific, they could be involved in spermatogenesis with a more or less critical role on the mouse fertility, probably also depending of their redundancies.