MRNIP is essential for meiotic progression and spermatogenesis in mice

MRNIP limits ssDNA gaps during replication stress

Replication repriming by the specialized primase-polymerase PRIMPOL ensures the continuity of DNA synthesis during replication stress. PRIMPOL activity generates residual post-replicative single-stranded nascent DNA gaps, which are linked with mutagenesis and chemosensitivity in BRCA1/2-deficient models, and which are suppressed by replication fork reversal mediated by the DNA translocases SMARCAL1 and ZRANB3. Here, we report that the MRE11 regulator MRNIP limits the prevalence of PRIMPOL and MRE11-dependent ssDNA gaps in cells in which fork reversal is perturbed either by treatment with the PARP inhibitor Olaparib, or by depletion of SMARCAL1 or ZRANB3. MRNIP-deficient cells are sensitive to PARP inhibition and accumulate PRIMPOL-dependent DNA damage, supportive of a pro-survival role for MRNIP linked to the regulation of gap prevalence. In MRNIP-deficient cells, post-replicative gap filling is driven in S-phase by UBC13-mediated template switching involving REV1 and the TLS polymerase Pol-ζ. Our findings represent the first report of modulation of post-replicative ssDNA gap dynamics by a direct MRE11 regulator.

Protein disulfide isomerase is essential for spermatogenesis in mice

Spermatogenesis requires precise posttranslational control in the endoplasmic reticulum (ER), but the mechanism remains largely unknown. The protein disulfide isomerase (PDI) family is a group of thiol oxidoreductases responsible for catalyzing the disulfide bond formation of nascent proteins. In this study, we generated 14 strains of KO mice lacking the PDI family enzymes and found that only PDI deficiency caused spermatogenesis defects. Both inducible whole-body PDI-KO (UBC-Cre/Pdifl/fl) mice and premeiotic PDI-KO (Stra8-Cre/Pdifl/fl) mice experienced a significant decrease in germ cells, testicular atrophy, oligospermia, and complete male infertility. Stra8-Cre/Pdifl/fl spermatocytes had significantly upregulated ER stress-related proteins (GRP78 and XBP1) and apoptosis-related proteins (Cleaved caspase-3 and BAX), together with cell apoptosis. PDI deletion led to delayed DNA double-strand break repair and improper crossover at the pachytene spermatocytes. Quantitative mass spectrometry indicated that PDI deficiency downregulated vital proteins in spermatogenesis such as HSPA4L, SHCBP1L, and DDX4, consistent with the proteins' physical association with PDI in normal testes tissue. Furthermore, PDI served as a thiol oxidase for disulfide bond formation of SHCBP1L. Thus, PDI plays an essential role in protein quality control for spermatogenesis in mice.

Gold nanoparticles retrogradely penetrate through testicular barriers via Sertoli-cells mediated endocytosis/exocytosis and induce immune response in mouse

Despite the rapidly growing interest in nanoparticle-mediated controllable male contraception and recovery of male fertility, novel applications of nanoparticles in these processes are limited by a knowledge gap regarding their transport and distribution in the testes. Here, we investigated the fate of gold nanoparticles in the mouse testes using two injection methods, namely, interstitial testicular injection (IT-AuNPs, AuNPs exposure in the interstitial compartment of the testes) and rete testis injection (RT-AuNPs, AuNPs exposure in the adluminal compartment of the seminiferous tubules). In this study, we used 100 nm spherical AuNPs and microinjected with 5 μL AuNPs (30 mg/mL) for the experiments. For IT-AuNP injection, we found that AuNPs could not penetrate through the Sertoli cell-mediated blood-testis barrier (BTB) of the seminiferous tubules, and no male reproductive toxicity was observed. For RT-AuNP injection, AuNPs could be retrogradely transported from the adluminal compartment to the interstitial compartment of the testes via Sertoli cell-mediated endocytosis/exocytosis, resulting in damage and the release of inflammatory cytokines in the mouse testis. Our results highlight a retrograde nanoparticle transport function of Sertoli cells, thereby providing a mechanistic overview of the development and use of nanobiotechnology in male reproduction. SYNOPSIS: This study provides new insights into male reproductive immunotoxicity for AuNPs exposure and elucidates a mechanism via Sertoli cell-mediated endocytosis/exocytosis.

MRNIP interacts with sex body chromatin to support meiotic progression, spermatogenesis, and male fertility in mice

Meiosis has a principal role in sexual reproduction to generate haploid gametes in both sexes. During meiosis, the cell nucleus hosts a dynamic environment where some genes are transcriptionally activated, and some are inactivated at the same time. This becomes possible through subnuclear compartmentalization. The sex body, sequestering X and Y chromosomes during male meiosis and creating an environment for the meiotic sex chromosome inactivation (MSCI) is one of the best known and studied subnuclear compartments. Herein, we show that MRNIP forms droplet-like accumulations that fuse together to create a distinct subnuclear compartment that partially overlaps with the sex body chromatin during diplotene. We demonstrate that Mrnip-/- spermatocytes have impaired DNA double-strand break (DSB) repair, they display reduced sex body formation and defective MSCI. We show that Mrnip-/- undergoes critical meiocyte loss at the diplotene stage. Furthermore, we determine that DNA DSBs (induced by SPO11) and synapsis initiation (facilitated by SYCP1) precede Mrnip expression in testes. Altogether, our findings indicate that in addition to an emerging role in DNA DSB repair, MRNIP has an essential function in spermatogenesis during meiosis I by forming drop-like accumulations interacting with the sex body.

E3 ubiquitin ligase ASB17 is required for spermiation in mice

Background

A major goal of spermiation is to degrade the apical ectoplasmic specialization (ES) junction between Sertoli cells and elongating spermatids in preparation for the eventual disengagement of spermatids into the lumen. E3 ubiquitin ligases mediate the process of ubiquitination and the subsequent proteasomal degradation, but their specific role during spermiation remains largely unexplored.

Methods

Ankyrin repeat and SOCS box protein 17 (Asb17)-knockout mice were generated via a CRISPR/Cas9 approach. Epididymal sperm parameters were assessed by a computer-assisted sperm analysis (CASA) system, and morphological analysis of testicular tissues were performed based on histological and immunostaining staining, and transmission electron microscopy (TEM). The interactions between ASB17 and Espin (ESPN) were predicted by HawkDock server and validated through protein pull-down and immunoprecipitation assays.

Results

We report that ASB17, an E3 ligase, is required for the completion of spermiation and that mice lacking Asb17 are oligozoospermic owing to spermiation failure. ASB17-deficient mice are fertile; however, spermatids exhibit a disorganized ES junction, resulting in retention within the seminiferous epithelium. Mechanistically, ASB17 deficiency leads to excess accumulation of ESPN, an actin-binding essential structural component of the ES. We determined that ASB17 regulates the removal of the ES through ubiquitin mediated protein degradation of ESPN.

Conclusions

In summary, our study describes a role for ASB17 in the regulation of cell-cell junctions between germ cells and somatic cells in the testis. These findings establish a novel mechanism for the regulatory role of E3 ligases during spermatogenesis.