Deficiency of the onco-miRNA cluster, miR-106b∼25, causes oligozoospermia and the cooperative action of miR-106b∼25 and miR-17∼92 is required to maintain male fertility.

The identification of new genes involved in sexual development and gonadal function as potential candidates causing male infertility is important for both diagnostic and therapeutic purposes. Deficiency of the onco-miRNA cluster miR-17∼92 has been shown to disrupt spermatogenesis, whereas mutations in its paralog cluster, miR-106b∼25, that is expressed in the same cells, were reported to have no effect on testis development and function. The aim of this work is to determine the role of these two miRNA clusters in spermatogenesis and male fertility. For this, we analyzed miR-106b∼25 and miR-17∼92 single and double mouse mutants and compared them to control mice. We found that miR-106b∼25 knock out testes show reduced size, oligozoospermia and altered spermatogenesis. Transcriptomic analysis showed that multiple molecular pathways are deregulated in these mutant testes. Nevertheless, mutant males conserved normal fertility even when early spermatogenesis and other functions were disrupted. In contrast, miR-17∼92+/-; miR-106b∼25-/- double mutants showed severely disrupted testicular histology and significantly reduced fertility. Our results indicate that miR-106b∼25 and miR-17∼92 ensure accurate gene expression levels in the adult testis, keeping them within the required thresholds. They play a crucial role in testis homeostasis and are required to maintain male fertility. Hence, we have identified new candidate genetic factors to be screened in the molecular diagnosis of human males with reproductive disorders. Finally, considering the well-known oncogenic nature of these two clusters and the fact that patients with reduced fertility are more prone to testicular cancer, our results might also help to elucidate the molecular mechanisms linking both pathologies.

Complete male-to-female sex reversal in XY mice lacking the miR-17~92 cluster.

Mammalian sex determination is controlled by antagonistic gene cascades operating in embryonic undifferentiated gonads. The expression of the Y-linked gene SRY is sufficient to trigger the testicular pathway, whereas its absence in XX embryos leads to ovarian differentiation. Yet, the potential involvement of non-coding regulation in this process remains unclear. Here we show that the deletion of a single microRNA cluster, miR-17~92, induces complete primary male-to-female sex reversal in XY mice. Sry expression is delayed in XY knockout gonads, which develop as ovaries. Sertoli cell differentiation is reduced, delayed and unable to sustain testicular development. Pre-supporting cells in mutant gonads undergo a transient state of sex ambiguity which is subsequently resolved towards the ovarian fate. The miR-17~92 predicted target genes are upregulated, affecting the fine regulation of gene networks controlling gonad development. Thus, microRNAs emerge as key components for mammalian sex determination, controlling Sry expression timing and Sertoli cell differentiation.

Sox9 Is Required for Nail-Bed Differentiation and Digit-Tip Regeneration.

The nail organ is a specialized appendage in which several ectodermal tissues coordinately function to sustain nail growth, a process that is coupled to digit regeneration. In this study, we show that the transcription factor Sox9 is expressed in several cell populations in the mouse digit tip. We found a SOX9+ cell population in the nail bed, and genetic lineage tracing showed that this is a transient cell population differentiated from matrix nail stem cells. In the absence of Sox9, nail matrix stem cells fail to differentiate into epithelial nail-bed cells and proliferate, thus expanding distally and following the corneocyte fate, which results in outlandishly large fingernails. In addition, the tip of the underlying terminal phalanx undergoes bone regression. Sox9-lineage tracing also revealed the existence of a continuous cell supply from a Sox9-expressing population residing in the basal layers to the entire hyponychium epidermis. Furthermore, digit-tip regeneration is compromised in Sox9-knockout mice, revealing an essential role for the gene during this process. These results will contribute to understand the cellular and molecular basis of mammalian nail organ homeostasis and disease and digit-tip regeneration and will help to design new treatment strategies for patients with nail diseases or amputation.