Conditional inactivation of the DNA damage response gene Hus1 in mouse testis reveals separable roles for components of the RAD9-RAD1-HUS1 complex in meiotic chromosome maintenance

Spermatocytes have the capacity to segregate chromosomes despite centriole duplication failure

Centrosomes are the canonical microtubule organizing centers (MTOCs) of most mammalian cells, including spermatocytes. Centrosomes comprise a centriole pair within a structurally ordered and dynamic pericentriolar matrix (PCM). Unlike in mitosis, where centrioles duplicate once per cycle, centrioles undergo two rounds of duplication during spermatogenesis. The first duplication is during early meiotic prophase I, and the second is during interkinesis. Using mouse mutants and chemical inhibition, we have blocked centriole duplication during spermatogenesis and determined that non-centrosomal MTOCs (ncMTOCs) can mediate chromosome segregation. This mechanism is different from the acentriolar MTOCs that form bipolar spindles in oocytes, which require PCM components, including gamma-tubulin and CEP192. From an in-depth analysis, we identified six microtubule-associated proteins, TPX2, KIF11, NuMA, and CAMSAP1-3, that localized to the non-centrosomal MTOC. These factors contribute to a mechanism that ensures bipolar MTOC formation and chromosome segregation during spermatogenesis when centriole duplication fails. However, despite the successful completion of meiosis and round spermatid formation, centriole inheritance and PLK4 function are required for normal spermiogenesis and flagella assembly, which are critical to ensure fertility.

Unlocking Genetic Mysteries during the Epic Sperm Journey toward Fertilization: Further Expanding Cre Mouse Lines

The spatiotemporal expression patterns of genes are crucial for maintaining normal physiological functions in animals. Conditional gene knockout using the cyclization recombination enzyme (Cre)/locus of crossover of P1 (Cre/LoxP) strategy has been extensively employed for functional assays at specific tissue or developmental stages. This approach aids in uncovering the associations between phenotypes and gene regulation while minimizing interference among distinct tissues. Various Cre-engineered mouse models have been utilized in the male reproductive system, including Dppa3-MERCre for primordial germ cells, Ddx4-Cre and Stra8-Cre for spermatogonia, Prm1-Cre and Acrv1-iCre for haploid spermatids, Cyp17a1-iCre for the Leydig cell, Sox9-Cre for the Sertoli cell, and Lcn5/8/9-Cre for differentiated segments of the epididymis. Notably, the specificity and functioning stage of Cre recombinases vary, and the efficiency of recombination driven by Cre depends on endogenous promoters with different sequences as well as the constructed Cre vectors, even when controlled by an identical promoter. Cre mouse models generated via traditional recombination or CRISPR/Cas9 also exhibit distinct knockout properties. This review focuses on Cre-engineered mouse models applied to the male reproductive system, including Cre-targeting strategies, mouse model screening, and practical challenges encountered, particularly with novel mouse strains over the past decade. It aims to provide valuable references for studies conducted on the male reproductive system.

GRAS-1 is a novel regulator of early meiotic chromosome dynamics in C. elegans

Chromosome movements and licensing of synapsis must be tightly regulated during early meiosis to ensure accurate chromosome segregation and avoid aneuploidy, although how these steps are coordinated is not fully understood. Here we show that GRAS-1, the worm homolog of mammalian GRASP/Tamalin and CYTIP, coordinates early meiotic events with cytoskeletal forces outside the nucleus. GRAS-1 localizes close to the nuclear envelope (NE) in early prophase I and interacts with NE and cytoskeleton proteins. Delayed homologous chromosome pairing, synaptonemal complex (SC) assembly, and DNA double-strand break repair progression are partially rescued by the expression of human CYTIP in gras-1 mutants, supporting functional conservation. However, Tamalin, Cytip double knockout mice do not exhibit obvious fertility or meiotic defects, suggesting evolutionary differences between mammals. gras-1 mutants show accelerated chromosome movement during early prophase I, implicating GRAS-1 in regulating chromosome dynamics. GRAS-1-mediated regulation of chromosome movement is DHC-1-dependent, placing it acting within the LINC-controlled pathway, and depends on GRAS-1 phosphorylation at a C-terminal S/T cluster. We propose that GRAS-1 coordinates the early steps of homology search and licensing of SC assembly by regulating the pace of chromosome movement in early prophase I.

YTHDC2 serves a distinct late role in spermatocytes during germ cell differentiation

Post-transcriptional regulation of gene expression by RNA-binding proteins helps facilitate fast, clean transitions from one cell state to the next during germ cell differentiation. Previously we showed that the RNA helicase YTHDC2 is required for germ cells to properly switch from mitosis to meiosis (Bailey et al., 2017). While YTHDC2 protein is first expressed as male germ cells enter meiosis, when it is needed to shut down the mitotic program, YTHDC2 expression continues to increase and reaches its highest levels later in meiotic prophase, in pachytene spermatocytes. Here we show that YTHDC2 has an additional essential role regulating meiotic progression in late spermatocytes during mouse germ cell differentiation. Inducing conditional knockout of Ythdc2 during the first wave of spermatogenesis, after the germ cells have already initiated meiotic prophase, allowed Ythdc2-deficient germ cells to successfully reach the pachytene stage and properly express many meiotic markers. However, instead of continuing through meiotic prophase and initiating the meiotic divisions, late pachytene spermatocytes failed to transition to the diplotene stage and quickly died. Loss of function of Ythdc2 in spermatocytes resulted in changes in transcript levels for a number of genes, some up-regulated and some down-regulated, compared to control mid-stage spermatocytes. YTHDC2 interacts with different proteins in early and late spermatocytes, with many of the interacting proteins involved in post-transcriptional RNA regulation and present in RNA granules, similar to YTHDC2. Our findings suggest that YTHDC2 facilitates proper progression of germ cells through multiple steps of meiosis, potentially via several mechanisms of post-transcriptional RNA regulation.

PLK1 depletion alters homologous recombination and synaptonemal complex disassembly events during mammalian spermatogenesis

Homologous recombination (HR) is an essential meiotic process that contributes to the genetic variation of offspring and ensures accurate chromosome segregation. Recombination is facilitated by the formation and repair of programmed DNA double-strand breaks. These DNA breaks are repaired via recombination between maternal and paternal homologous chromosomes and a subset result in the formation of crossovers. HR and crossover formation is facilitated by synapsis of homologous chromosomes by a proteinaceous scaffold structure known as the synaptonemal complex (SC). Recent studies in yeast and worms have indicated that polo-like kinases (PLKs) regulate several events during meiosis, including DNA recombination and SC dynamics. Mammals express four active PLKs (PLK1-4), and our previous work assessing localization and kinase function in mouse spermatocytes suggested that PLK1 coordinates nuclear events during meiotic prophase. Therefore, we conditionally mutated Plk1 in early prophase spermatocytes and assessed stages of HR, crossover formation, and SC processes. Plk1 mutation resulted in increased RPA foci and reduced RAD51/DMC1 foci during zygonema, and an increase of both class I and class II crossover events. Furthermore, the disassembly of SC lateral elements was aberrant. Our results highlight the importance of PLK1 in regulating HR and SC disassembly during spermatogenesis.

Multiple 9-1-1 complexes promote homolog synapsis, DSB repair, and ATR signaling during mammalian meiosis

DNA damage response mechanisms have meiotic roles that ensure successful gamete formation. While completion of meiotic double-strand break (DSB) repair requires the canonical RAD9A-RAD1-HUS1 (9A-1-1) complex, mammalian meiocytes also express RAD9A and HUS1 paralogs, RAD9B and HUS1B, predicted to form alternative 9-1-1 complexes. The RAD1 subunit is shared by all predicted 9-1-1 complexes and localizes to meiotic chromosomes even in the absence of HUS1 and RAD9A. Here, we report that testis-specific disruption of RAD1 in mice resulted in impaired DSB repair, germ cell depletion, and infertility. Unlike Hus1 or Rad9a disruption, Rad1 loss in meiocytes also caused severe defects in homolog synapsis, impaired phosphorylation of ATR targets such as H2AX, CHK1, and HORMAD2, and compromised meiotic sex chromosome inactivation. Together, these results establish critical roles for both canonical and alternative 9-1-1 complexes in meiotic ATR activation and successful prophase I completion.

Meiotic sex chromosome inactivation and the XY body: a phase separation hypothesis

In mammalian male meiosis, the heterologous X and Y chromosomes remain unsynapsed and, as a result, are subject to meiotic sex chromosome inactivation (MSCI). MSCI is required for the successful completion of spermatogenesis. Following the initiation of MSCI, the X and Y chromosomes undergo various epigenetic modifications and are transformed into a nuclear body termed the XY body. Here, we review the mechanisms underlying the initiation of two essential, sequential processes in meiotic prophase I: MSCI and XY-body formation. The initiation of MSCI is directed by the action of DNA damage response (DDR) pathways; downstream of the DDR, unique epigenetic states are established, leading to the formation of the XY body. Accumulating evidence suggests that MSCI and subsequent XY-body formation may be driven by phase separation, a physical process that governs the formation of membraneless organelles and other biomolecular condensates. Thus, here we gather literature-based evidence to explore a phase separation hypothesis for the initiation of MSCI and the formation of the XY body.

Discovery and Validation of Novel Methylation Markers in Helicobacter pylori-Associated Gastric Cancer

Previous studies have shown that abnormal methylation is an early key event in the pathogenesis of most human cancers, contributing to the development of tumors. However, little attention has been given to the potential of DNA methylation patterns as markers for Helicobacter pylori- (H. pylori-) associated gastric cancer (GC). In this study, an integrated analysis of DNA methylation and gene expression was conducted to identify some potential key epigenetic markers in H. pylori-associated GC. DNA methylation data of 28 H. pylori-positive and 168 H. pylori-negative GC samples were compared and analyzed. We also analyzed the gene expression data of 18 H. pylori-positive and 145 H. pylori-negative GC cases. Finally, the results were verified by in vitro and in vivo experiments. A total of 5609 differentially methylated regions associated with 2454 differentially methylated genes were identified. A total of 228 differentially expressed genes were identified from the gene expression data of H. pylori-positive and H. pylori-negative GC cases. The screened genes were analyzed for functional enrichment. Subsequently, we obtained 28 genes regulated by methylation through a Venn diagram, and we identified five genes (GSTO2, HUS1, INTS1, TMEM184A, and TMEM190) downregulated by hypermethylation. HUS1, GSTO2, and TMEM190 were expressed at lower levels in GC than in adjacent samples (P < 0.05). Moreover, H. pylori infection decreased HUS1, GSTO2, and TMEM190 expression in vitro and in vivo. Our study identified HUS1, GSTO2, and TMEM190 as novel methylation markers for H. pylori-associated GC.

CENP-V is required for proper chromosome segregation through interaction with spindle microtubules in mouse oocytes

Proper chromosome segregation is essential to avoid aneuploidy, yet this process fails with increasing age in mammalian oocytes. Here we report a role for the scarcely described protein CENP-V in oocyte spindle formation and chromosome segregation. We show that depending on the oocyte maturation state, CENP-V localizes to centromeres, to microtubule organizing centers, and to spindle microtubules. We find that Cenp-V-/- oocytes feature severe deficiencies, including metaphase I arrest, strongly reduced polar body extrusion, increased numbers of mis-aligned chromosomes and aneuploidy, multipolar spindles, unfocused spindle poles and loss of kinetochore spindle fibres. We also show that CENP-V protein binds, diffuses along, and bundles microtubules in vitro. The spindle assembly checkpoint arrests about half of metaphase I Cenp-V-/- oocytes from young adults only. This finding suggests checkpoint weakening in ageing oocytes, which mature despite carrying mis-aligned chromosomes. Thus, CENP-V is a microtubule bundling protein crucial to faithful oocyte meiosis, and Cenp-V-/- oocytes reveal age-dependent weakening of the spindle assembly checkpoint.

Aurora a kinase (AURKA) is required for male germline maintenance and regulates sperm motility in the mouse

Aurora A kinase (AURKA) is an important regulator of cell division and is required for assembly of the mitotic spindle. We recently reported the unusual finding that this mitotic kinase is also found on the sperm flagellum. To determine its requirement in spermatogenesis, we generated conditional knockout animals with deletion of the Aurka gene in either spermatogonia or spermatocytes to assess its role in mitotic and postmitotic cells, respectively. Deletion of Aurka in spermatogonia resulted in disappearance of all developing germ cells in the testis, as expected given its vital role in mitotic cell division. Deletion of Aurka in spermatocytes reduced testis size, sperm count, and fertility, indicating disruption of meiosis or an effect on spermiogenesis in developing mice. Interestingly, deletion of Aurka in spermatocytes increased apoptosis in spermatocytes along with an increase in the percentage of sperm with abnormal morphology. Despite the increase in abnormal sperm, sperm from spermatocyte Aurka knockout mice displayed increased progressive motility. In addition, sperm lysate prepared from Aurka knockout animals had decreased protein phosphatase 1 (PP1) activity. Together, our results show that AURKA plays multiple roles in spermatogenesis, from mitotic divisions of spermatogonia to sperm morphology and motility.

The combined action of CTCF and its testis-specific paralog BORIS is essential for spermatogenesis

CTCF is a key organizer of the 3D genome. Its specialized paralog, BORIS, heterodimerizes with CTCF but is expressed only in male germ cells and in cancer states. Unexpectedly, BORIS-null mice have only minimal germ cell defects. To understand the CTCF-BORIS relationship, mouse models with varied CTCF and BORIS levels were generated. Whereas Ctcf+/+Boris+/+, Ctcf+/-Boris+/+, and Ctcf+/+Boris-/- males are fertile, Ctcf+/-Boris-/- (Compound Mutant; CM) males are sterile. Testes with combined depletion of both CTCF and BORIS show reduced size, defective meiotic recombination, increased apoptosis, and malformed spermatozoa. Although CM germ cells exhibit only 25% of CTCF WT expression, chromatin binding of CTCF is preferentially lost from CTCF-BORIS heterodimeric sites. Furthermore, CM testes lose the expression of a large number of spermatogenesis genes and gain the expression of developmentally inappropriate genes that are "toxic" to fertility. Thus, a combined action of CTCF and BORIS is required to both repress pre-meiotic genes and activate post-meiotic genes for a complete spermatogenesis program.

Overlapping roles for PLK1 and Aurora A during meiotic centrosome biogenesis in mouse spermatocytes

The establishment of bipolar spindles during meiotic divisions ensures faithful chromosome segregation to prevent gamete aneuploidy. We analyzed centriole duplication, as well as centrosome maturation and separation during meiosis I and II using mouse spermatocytes. The first round of centriole duplication occurs during early prophase I, and then, centrosomes mature and begin to separate by the end of prophase I to prime formation of bipolar metaphase I spindles. The second round of centriole duplication occurs at late anaphase I, and subsequently, centrosome separation coordinates bipolar segregation of sister chromatids during meiosis II. Using a germ cell-specific conditional knockout strategy, we show that Polo-like kinase 1 and Aurora A kinase are required for centrosome maturation and separation prior to metaphase I, leading to the formation of bipolar metaphase I spindles. Furthermore, we show that PLK1 is required to block the second round of centriole duplication and maturation until anaphase I. Our findings emphasize the importance of maintaining strict spatiotemporal control of cell cycle kinases during meiosis to ensure proficient centrosome biogenesis and, thus, accurate chromosome segregation during spermatogenesis.

Four-pronged negative feedback of DSB machinery in meiotic DNA-break control in mice

In most taxa, halving of chromosome numbers during meiosis requires that homologous chromosomes (homologues) pair and form crossovers. Crossovers emerge from the recombination-mediated repair of programmed DNA double-strand breaks (DSBs). DSBs are generated by SPO11, whose activity requires auxiliary protein complexes, called pre-DSB recombinosomes. To elucidate the spatiotemporal control of the DSB machinery, we focused on an essential SPO11 auxiliary protein, IHO1, which serves as the main anchor for pre-DSB recombinosomes on chromosome cores, called axes. We discovered that DSBs restrict the DSB machinery by at least four distinct pathways in mice. Firstly, by activating the DNA damage response (DDR) kinase ATM, DSBs restrict pre-DSB recombinosome numbers without affecting IHO1. Secondly, in their vicinity, DSBs trigger IHO1 depletion mainly by another DDR kinase, ATR. Thirdly, DSBs enable homologue synapsis, which promotes the depletion of IHO1 and pre-DSB recombinosomes from synapsed axes. Finally, DSBs and three DDR kinases, ATM, ATR and PRKDC, enable stage-specific depletion of IHO1 from all axes. We hypothesize that these four negative feedback pathways protect genome integrity by ensuring that DSBs form without excess, are well-distributed, and are restricted to genomic locations and prophase stages where DSBs are functional for promoting homologue pairing and crossover formation.

Proteasome subunit α4s is essential for formation of spermatoproteasomes and histone degradation during meiotic DNA repair in spermatocytes

Meiosis, which produces haploid progeny, is critical to ensuring both faithful genome transmission and genetic diversity. Proteasomes play critical roles at various stages of spermatogenesis, including meiosis, but the underlying mechanisms remain unclear. The atypical proteasomes, which contain the activator PA200, catalyze the acetylation-dependent degradation of the core histones in elongated spermatids and DNA repair in somatic cells. We show here that the testis-specific proteasome subunit α4s/PSMA8 is essential for male fertility by promoting proper formation of spermatoproteasomes, which harbor both PA200 and constitutive catalytic subunits. Immunostaining of a spermatocyte marker, SYCP3, indicated that meiosis was halted at the stage of spermatocytes in the α4s-deficient testes. α4s stimulated the in vitro degradation of the acetylated core histones, instead of nonacetylated histones, by the PA200-proteasome. Deletion of α4s blocked degradation of the core histones at DNA damage loci in spermatocytes, leading to meiotic arrest at metaphase I. Thus, α4s is required for histone degradation at meiotic DNA damage loci, proper progression of meiosis, and fertility in males by promoting proper formation of spermatoproteasomes. These results are important for understanding male infertility and might provide potential targets for male contraception or treatment of male infertility.

A Genetically Engineered Mouse Model of Malignant Testicular Germ Cell Tumors

Testicular germ cell tumors (TGCTs) are among the most curable solid cancers and are typically highly responsive to conventional DNA-damaging chemotherapies, even in patients with metastatic disease. It has therefore been of great interest to understand the basis for the unique chemosensitivity of these cancers, which is linked to the DNA damage sensitivity of their cancer stem cells. TGCTs have been difficult to study in the mouse, however, since most of the existing mouse models develop benign teratomas that are unlike the malignant TGCTs that afflict most testicular cancer patients. We describe here methods for generating a TGCT mouse model that closely resembles the malignant, metastatic disease observed in men with testicular cancer, and additionally include methods for analyzing the cancer stems cells and responses to chemotherapeutics in these murine TGCTs.

Aurora B and C kinases regulate chromosome desynapsis and segregation during mouse and human spermatogenesis

Precise control of chromosome dynamics during meiosis is critical for fertility. A gametocyte undergoing meiosis coordinates formation of the synaptonemal complex (SC) to promote efficient homologous chromosome recombination. Subsequent disassembly of the SC occurs prior to segregation of homologous chromosomes during meiosis I. We examined the requirements of the mammalian Aurora kinases (AURKA, AURKB and AURKC) during SC disassembly and chromosome segregation using a combination of chemical inhibition and gene deletion approaches. We find that both mouse and human spermatocytes fail to disassemble SC lateral elements when the kinase activity of AURKB and AURKC are chemically inhibited. Interestingly, both Aurkb conditional knockout and Aurkc knockout mouse spermatocytes successfully progress through meiosis, and the mice are fertile. In contrast, Aurkb, Aurkc double knockout spermatocytes fail to coordinate disassembly of SC lateral elements with chromosome condensation and segregation, resulting in delayed meiotic progression. In addition, deletion of Aurkb and Aurkc leads to an accumulation of metaphase spermatocytes, chromosome missegregation and aberrant cytokinesis. Collectively, our data demonstrate that AURKB and AURKC functionally compensate for one another ensuring successful mammalian spermatogenesis.This article has an associated First Person interview with the first author of the paper.

Adaptation of the AID system for stem cell and transgenic mouse research

The auxin-inducible degron (AID) system is becoming a widely used method for rapid and reversible degradation of target proteins. This system has been successfully used to study gene and protein functions in eukaryotic cells and common model organisms, such as nematode and fruit fly. To date, applications of the AID system in mammalian stem cell research are limited. Furthermore, standard mouse models harboring the AID system have not been established. Here we have explored the utility of the H11 safe-harbor locus for integration of the TIR1 transgene, an essential component of auxin-based protein degradation system. We have shown that the H11 locus can support constitutive and conditional TIR1 expression in mouse and human embryonic stem cells, as well as in mice. We demonstrate that the AID system can be successfully employed for rapid degradation of stable proteins in embryonic stem cells, which is crucial for investigation of protein functions in quickly changing environments, such as stem cell proliferation and differentiation. As embryonic stem cells possess unlimited proliferative capacity, differentiation potential, and can mimic organ development, we believe that these research tools will be an applicable resource to a broad scientific audience.

ATR signaling in mammalian meiosis: From upstream scaffolds to downstream signaling

In germ cells undergoing meiosis, the induction of double strand breaks (DSBs) is required for the generation of haploid gametes. Defects in the formation, detection, or recombinational repair of DSBs often result in defective chromosome segregation and aneuploidies. Central to the ability of meiotic cells to properly respond to DSBs are DNA damage response (DDR) pathways mediated by DNA damage sensor kinases. DDR signaling coordinates an extensive network of DDR effectors to induce cell cycle arrest and DNA repair, or trigger apoptosis if the damage is extensive. Despite their importance, the functions of DDR kinases and effector proteins during meiosis remain poorly understood and can often be distinct from their known mitotic roles. A key DDR kinase during meiosis is ataxia telangiectasia and Rad3-related (ATR). ATR mediates key signaling events that control DSB repair, cell cycle progression, and meiotic silencing. These meiotic functions of ATR depend on upstream scaffolds and regulators, including the 9-1-1 complex and TOPBP1, and converge on many downstream effectors such as the checkpoint kinase CHK1. Here, we review the meiotic functions of the 9-1-1/TOPBP1/ATR/CHK1 signaling pathway during mammalian meiosis.

CHTF18 ensures the quantity and quality of the ovarian reserve†

The number and quality of oocytes, as well as the decline in both of these parameters with age, determines reproductive potential in women. However, the underlying mechanisms of this diminution are incompletely understood. Previously, we identified novel roles for CHTF18 (Chromosome Transmission Fidelity Factor 18), a component of the conserved Replication Factor C-like complex, in male fertility and gametogenesis. Currently, we reveal crucial roles for CHTF18 in female meiosis and oocyte development. Chtf18-/- female mice are subfertile and have fewer offspring beginning at 6 months of age. Consistent with age-dependent subfertility, Chtf18-/- ovaries contain fewer follicles at all stages of folliculogenesis than wild type ovaries, but the decreases are more significant at 3 and 6 months of age. By 6 months of age, both primordial and growing ovarian follicle pools are markedly reduced to near depletion. Chromosomal synapsis in Chtf18-/- oocytes is complete, but meiotic recombination is impaired resulting in persistent DNA double-strand breaks, fewer crossovers, and early homolog disjunction during meiosis I. Consistent with poor oocyte quality, the majority of Chtf18-/- oocytes fail to progress to metaphase II following meiotic resumption and a significant percentage of those that do progress are aneuploid. Collectively, our findings indicate critical functions for CHTF18 in ensuring both the quantity and quality of the mammalian oocyte pool.

PLK1 is required for chromosome compaction and microtubule organization in mouse oocytes

Errors during meiotic resumption in oocytes can result in chromosome missegregation and infertility. Several cell cycle kinases have been linked with roles in coordinating events during meiotic resumption, including polo-like kinases (PLKs). Mammals express four kinase-proficient PLKs (PLK1-4). Previous studies assessing the role of PLK1 have relied on RNA knockdown and kinase inhibition approaches, as Plk1 null mutations are embryonically lethal. To further assess the roles of PLK1 during meiotic resumption, we developed a Plk1 conditional knockout (cKO) mouse to specifically mutate Plk1 in oocytes. Despite normal oocyte numbers and follicle maturation, Plk1 cKO mice were infertile. From analysis of meiotic resumption, Plk1 cKO oocytes underwent nuclear envelope breakdown with the same timing as control oocytes. However, Plk1 cKO oocytes failed to form compact bivalent chromosomes, and localization of cohesin and condensin were defective. Furthermore, Plk1 cKO oocytes either failed to organize α-tubulin or developed an abnormally small bipolar spindle. These abnormalities were attributed to aberrant release of the microtubule organizing center (MTOC) linker protein, C-NAP1, and the failure to recruit MTOC components and liquid-like spindle domain (LISD) factors. Ultimately, these defects result in meiosis I arrest before homologous chromosome segregation.

Mouse dead end1 acts with Nanos2 and Nanos3 to regulate testicular teratoma incidence

Spontaneous testicular teratomas (STTs) derived from primordial germ cells (PGCs) in the mouse embryonic testes predominantly develop in the 129 family inbred strain. Ter (spontaneous mutation) is a single nucleotide polymorphism that generates a premature stop codon of Dead end1 (Dnd1) and increases the incidence of STTs in the 129 genetic background. We previously found that DND1 interacts with NANOS2 or NANOS3 and that these complexes play a vital role in male embryonic germ cells and adult spermatogonia. However, the following are unclear: (a) whether DND1 works with NANOS2 or NANOS3 to regulate teratoma incidence, and (b) whether Ter simply causes Dnd1 loss or produces a short mutant DND1 protein. In the current study, we newly established a conventional Dnd1-knockout mouse line and found that these mice showed phenotypes similar to those of Ter mutant mice in spermatogenesis, oogenesis, and teratoma incidence, with a slight difference in spermiogenesis. In addition, we found that the amount of DND1 in Dnd1+/Ter embryos decreased to half of that in wild-type embryos, while the expression of the short mutant DND1 was not detected. We also found that double mutants for Dnd1 and Nanos2 or Nanos3 showed synergistic increase in the incidence of STTs. These data support the idea that Ter causes Dnd1 loss, leading to an increase in STT incidence, and that DND1 acts with NANOS2 and NANOS3 to regulate the development of teratoma from PGCs in the 129 genetic background. Thus, our results clarify the role of Dnd1 in the development of STTs and provide a novel insight into its pathogenic mechanism.

Conditional genome engineering reveals canonical and divergent roles for the Hus1 component of the 9-1-1 complex in the maintenance of the plastic genome of Leishmania

Leishmania species are protozoan parasites whose remarkably plastic genome limits the establishment of effective genetic manipulation and leishmaniasis treatment. The strategies used by Leishmania to maintain its genome while allowing variability are not fully understood. Here, we used DiCre-mediated conditional gene deletion to show that HUS1, a component of the 9-1-1 (RAD9-RAD1-HUS1) complex, is essential and is required for a G2/M checkpoint. By analyzing genome-wide instability in HUS1 ablated cells, HUS1 is shown to have a conserved role, by which it preserves genome stability and also a divergent role, by which it promotes genome variability. These roles of HUS1 are related to distinct patterns of formation and resolution of single-stranded DNA and γH2A, throughout the cell cycle. Our findings suggest that Leishmania 9-1-1 subunits have evolved to co-opt canonical genomic maintenance and genomic variation functions. Hence, this study reveals a pivotal function of HUS1 in balancing genome stability and transmission in Leishmania. These findings may be relevant to understanding the evolution of genome maintenance and plasticity in other pathogens and eukaryotes.

A mutation in the endonuclease domain of mouse MLH3 reveals novel roles for MutLγ during crossover formation in meiotic prophase I

During meiotic prophase I, double-strand breaks (DSBs) initiate homologous recombination leading to non-crossovers (NCOs) and crossovers (COs). In mouse, 10% of DSBs are designated to become COs, primarily through a pathway dependent on the MLH1-MLH3 heterodimer (MutLγ). Mlh3 contains an endonuclease domain that is critical for resolving COs in yeast. We generated a mouse (Mlh3DN/DN) harboring a mutation within this conserved domain that is predicted to generate a protein that is catalytically inert. Mlh3DN/DN males, like fully null Mlh3-/- males, have no spermatozoa and are infertile, yet spermatocytes have grossly normal DSBs and synapsis events in early prophase I. Unlike Mlh3-/- males, mutation of the endonuclease domain within MLH3 permits normal loading and frequency of MutLγ in pachynema. However, key DSB repair factors (RAD51) and mediators of CO pathway choice (BLM helicase) persist into pachynema in Mlh3DN/DN males, indicating a temporal delay in repair events and revealing a mechanism by which alternative DSB repair pathways may be selected. While Mlh3DN/DN spermatocytes retain only 22% of wildtype chiasmata counts, this frequency is greater than observed in Mlh3-/- males (10%), suggesting that the allele may permit partial endonuclease activity, or that other pathways can generate COs from these MutLγ-defined repair intermediates in Mlh3DN/DN males. Double mutant mice homozygous for the Mlh3DN/DN and Mus81-/- mutations show losses in chiasmata close to those observed in Mlh3-/- males, indicating that the MUS81-EME1-regulated crossover pathway can only partially account for the increased residual chiasmata in Mlh3DN/DN spermatocytes. Our data demonstrate that mouse spermatocytes bearing the MLH1-MLH3DN/DN complex display the proper loading of factors essential for CO resolution (MutSγ, CDK2, HEI10, MutLγ). Despite these functions, mice bearing the Mlh3DN/DN allele show defects in the repair of meiotic recombination intermediates and a loss of most chiasmata.

TopBP1 deficiency impairs the localization of proteins involved in early recombination and results in meiotic chromosome defects during spermatogenesis

Topoisomerase IIβ-binding protein 1 (TopBP1) is BRCT domain-containing protein that is required for DNA double-strand break (DSB) repair and DNA damage responses; however, its function during the early stage of spermatogenesis is still unclear. To investigate the physiological role of TopBP1, we have generated germ cell-specific TopBP1-depleted mouse model. TopBP1-deleted mice were infertile, showed a loss of germ cells and had meiotic defects. Conditional TopBP1 deletion resulted in reduced testis size, reduced number of epididymal sperm, increased apoptosis, and severely compromised fertility. TopBP1 deficiency caused defects in DMC1 and Rad51 foci formation, abnormal synaptonemal complexes and meiotic chromosome defects. Collectively, these results suggest that TopBP1 deficiency during spermatogenesis impairs the localization of proteins involved in early recombination at DSBs, results in meiotic chromosome defects and leads to infertility.

Depletion of SMC5/6 sensitizes male germ cells to DNA damage

The structural maintenance of chromosomes complex SMC5/6 is thought to be essential for DNA repair and chromosome segregation during mitosis and meiosis. To determine the requirements of the SMC5/6 complex during mouse spermatogenesis we combined a conditional knockout allele for Smc5, with four germ cell–specific Cre-recombinase transgenes, Ddx4-Cre, Stra8-Cre, Spo11-Cre, and Hspa2-Cre, to mutate Smc5 in spermatogonia, in spermatocytes before meiotic entry, during early meiotic stages, and during midmeiotic stages, respectively. Conditional mutation of Smc5 resulted in destabilization of the SMC5/6 complex. Despite this, we observed only mild defects in spermatogenesis. Mutation of Smc5 mediated by Ddx4-Cre and Stra8-Cre resulted in partial loss of preleptotene spermatocytes; however, spermatogenesis progresses and mice are fertile. Mutation of Smc5 via Spo11-Cre or Hspa2-Cre did not result in detectable defects of spermatogenesis. Upon exposure to gamma irradiation or etoposide treatment, each conditional Smc5 mutant demonstrated an increase in the number of enlarged round spermatids with multiple acrosomes and supernumerary chromosome content. We propose that the SMC5/6 complex is not acutely required for premeiotic DNA replication and meiotic progression during mouse spermatogenesis; however, when germ cells are challenged by exogenous DNA damage, the SMC5/6 complex ensures genome integrity, and thus, fertility.

Defects in meiotic recombination delay progression through pachytene in Tex19.1-/- mouse spermatocytes

Recombination, synapsis, chromosome segregation and gene expression are co-ordinately regulated during meiosis to ensure successful execution of this specialised cell division. Studies with multiple mutant mouse lines have shown that mouse spermatocytes possess quality control checkpoints that eliminate cells with persistent defects in chromosome synapsis. In addition, studies on Trip13^mod/mod mice suggest that pachytene spermatocytes that successfully complete chromosome synapsis can undergo meiotic arrest in response to defects in recombination. Here, we present additional support for a meiotic recombination-dependent checkpoint using a different mutant mouse line, Tex19.1^-/-. The appearance of early recombination foci is delayed in Tex19.1^-/- spermatocytes during leptotene/zygotene, but some Tex19.1^-/- spermatocytes still successfully synapse their chromosomes and we show that these spermatocytes are enriched for early recombination foci. Furthermore, we show that patterns of axis elongation, chromatin modifications and histone H1t expression are also all co-ordinately skewed towards earlier substages of pachytene in these autosomally synapsed Tex19.1^-/- spermatocytes. We also show that this skew towards earlier pachytene substages occurs in the absence of elevated spermatocyte death in the population, that spermatocytes with features of early pachytene are present in late stage Tex19.1^-/- testis tubules and that the delay in histone H1t expression in response to loss of Tex19.1 does not occur in a Spo11 mutant background. Taken together, these data suggest that a recombination-dependent checkpoint may be able to modulate pachytene progression in mouse spermatocytes to accommodate some types of recombination defect.

Ubiquitin Ligase Huwe1 Modulates Spermatogenesis by Regulating Spermatogonial Differentiation and Entry into Meiosis

Spermatogenesis consists of a series of highly regulated processes that include mitotic proliferation, meiosis and cellular remodeling. Although alterations in gene expression are well known to modulate spermatogenesis, posttranscriptional mechanisms are less well defined. The ubiquitin proteasome system plays a significant role in protein turnover and may be involved in these posttranscriptional mechanisms. We previously identified ubiquitin ligase Huwe1 in the testis and showed that it can ubiquitinate histones. Since modulation of histones is important at many steps in spermatogenesis, we performed a complete characterization of the functions of Huwe1 in this process by examining the effects of its inactivation in the differentiating spermatogonia, spermatocytes and spermatids. Inactivation of Huwe1 in differentiating spermatogonia led to their depletion and formation of fewer pre-leptotene spermatocytes. The cell degeneration was associated with an accumulation of DNA damage response protein γH2AX, impaired downstream signalling and apoptosis. Inactivation of Huwe1 in spermatocytes indicated that Huwe1 is not essential for meiosis and spermiogenesis, but can result in accumulation of γH2AX. Collectively, these results provide a comprehensive survey of the functions of Huwe1 in spermatogenesis and reveal Huwe1’s critical role as a modulator of the DNA damage response pathway in the earliest steps of spermatogonial differentiation.

The Exonuclease Homolog OsRAD1 Promotes Accurate Meiotic Double-Strand Break Repair by Suppressing Nonhomologous End Joining

During meiosis, programmed double-strand breaks (DSBs) are generated to initiate homologous recombination, which is crucial for faithful chromosome segregation. In yeast, Radiation sensitive1 (RAD1) acts together with Radiation sensitive9 (RAD9) and Hydroxyurea sensitive1 (HUS1) to facilitate meiotic recombination via cell-cycle checkpoint control. However, little is known about the meiotic functions of these proteins in higher eukaryotes. Here, we characterized a RAD1 homolog in rice (Oryza sativa) and obtained evidence that O. sativa RAD1 (OsRAD1) is important for meiotic DSB repair. Loss of OsRAD1 led to abnormal chromosome association and fragmentation upon completion of homologous pairing and synapsis. These aberrant chromosome associations were independent of OsDMC1. We found that classical nonhomologous end-joining mediated by Ku70 accounted for most of the ectopic associations in Osrad1 In addition, OsRAD1 interacts directly with OsHUS1 and OsRAD9, suggesting that these proteins act as a complex to promote DSB repair during rice meiosis. Together, these findings suggest that the 9-1-1 complex facilitates accurate meiotic recombination by suppressing nonhomologous end-joining during meiosis in rice.

Functional compartmentalization of Rad9 and Hus1 reveals diverse assembly of the 9-1-1 complex components during the DNA damage response in Leishmania

The Rad9‐Rad1‐Hus1 (9‐1‐1) complex is a key component in the coordination of DNA damage sensing, cell cycle progression and DNA repair pathways in eukaryotic cells. This PCNA‐related trimer is loaded onto RPA‐coated single stranded DNA and interacts with ATR kinase to mediate effective checkpoint signaling to halt the cell cycle and to promote DNA repair. Beyond these core activities, mounting evidence suggests that a broader range of functions can be provided by 9‐1‐1 structural diversification. The protozoan parasite Leishmania is an early‐branching eukaryote with a remarkably plastic genome, which hints at peculiar genome maintenance mechanisms. Here, we investigated the existence of homologs of the 9‐1‐1 complex subunits in L. major and found that LmRad9 and LmRad1 associate with chromatin in response to replication stress and form a complex in vivo with LmHus1. Similar to LmHus1, LmRad9 participates in telomere homeostasis and in the response to both replication stress and double strand breaks. However, LmRad9 and LmHus1‐deficient cells present markedly opposite phenotypes, which suggest their functional compartmentalization. We show that some of the cellular pool of LmRad9 forms an alternative complex and that some of LmHus1 exists as a monomer. We propose that the diverse assembly of the Leishmania 9‐1‐1 subunits mediates functional compartmentalization, which has a direct impact on the response to genotoxic stress.

Direct Binding to Replication Protein A (RPA)-coated Single-stranded DNA Allows Recruitment of the ATR Activator TopBP1 to Sites of DNA Damage

A critical event for the ability of cells to tolerate DNA damage and replication stress is activation of the ATR kinase. ATR activation is dependent on the BRCT (BRCA1 C terminus) repeat-containing protein TopBP1. Previous work has shown that recruitment of TopBP1 to sites of DNA damage and stalled replication forks is necessary for downstream events in ATR activation; however, the mechanism for this recruitment was not known. Here, we use protein binding assays and functional studies in Xenopus egg extracts to show that TopBP1 makes a direct interaction, via its BRCT2 domain, with RPA-coated single-stranded DNA. We identify a point mutant that abrogates this interaction and show that this mutant fails to accumulate at sites of DNA damage and that the mutant cannot activate ATR. These data thus supply a mechanism for how the critical ATR activator, TopBP1, senses DNA damage and stalled replication forks to initiate assembly of checkpoint signaling complexes.

HUS1 regulates in vivo responses to genotoxic chemotherapies

Cells are under constant attack from genotoxins and rely on a multifaceted DNA damage response (DDR) network to maintain genomic integrity. Central to the DDR are the ATM and ATR kinases, which respond primarily to double-strand DNA breaks (DSBs) and replication stress, respectively. Optimal ATR signaling requires the RAD9A-RAD1-HUS1 (9-1-1) complex, a toroidal clamp that is loaded at damage sites and scaffolds signaling and repair factors. Whereas complete ATR pathway inactivation causes embryonic lethality, partial Hus1 impairment has been accomplished in adult mice using hypomorphic (Hus1(neo)) and null (Hus1(Δ1)) Hus1 alleles, and here we use this system to define the tissue- and cell type-specific actions of the HUS1-mediated DDR in vivo. Hus1(neo/Δ1) mice showed hypersensitivity to agents that cause replication stress, including the crosslinking agent mitomycin C (MMC) and the replication inhibitor hydroxyurea, but not the DSB inducer ionizing radiation. Analysis of tissue morphology, genomic instability, cell proliferation and apoptosis revealed that MMC treatment caused severe damage in highly replicating tissues of mice with partial Hus1 inactivation. The role of the 9-1-1 complex in responding to MMC was partially ATR-independent, as a HUS1 mutant that was proficient for ATR-induced checkpoint kinase 1 phosphorylation nevertheless conferred MMC hypersensitivity. To assess the interplay between the ATM and ATR pathways in responding to replication stress in vivo, we used Hus1/Atm double mutant mice. Whereas Hus1(neo/neo) and Atm(-/-) single mutant mice survived low-dose MMC similar to wild-type controls, Hus1(neo/neo)Atm(-/-) double mutants showed striking MMC hypersensitivity, consistent with a model in which MMC exposure in the context of Hus1 dysfunction results in DSBs to which the ATM pathway normally responds. This improved understanding of the inter-dependency between two major DDR mechanisms during the response to a conventional chemotherapeutic illustrates how inhibition of checkpoint factors such as HUS1 may be effective for the treatment of ATM-deficient and other cancers.

Genome Protection by the 9-1-1 Complex Subunit HUS1 Requires Clamp Formation, DNA Contacts, and ATR Signaling-independent Effector Functions

The RAD9A-HUS1-RAD1 (9-1-1) complex is a heterotrimeric clamp that promotes checkpoint signaling and repair at DNA damage sites. In this study, we elucidated HUS1 functional residues that drive clamp assembly, DNA interactions, and downstream effector functions. First, we mapped a HUS1-RAD9A interface residue that was critical for 9-1-1 assembly and DNA loading. Next, we identified multiple positively charged residues in the inner ring of HUS1 that were crucial for genotoxin-induced 9-1-1 chromatin localization and ATR signaling. Finally, we found two hydrophobic pockets on the HUS1 outer surface that were important for cell survival after DNA damage. Interestingly, these pockets were not required for 9-1-1 chromatin localization or ATR-mediated CHK1 activation but were necessary for interactions between HUS1 and its binding partner MYH, suggesting that they serve as interaction domains for the recruitment and coordination of downstream effectors at damage sites. Together, these results indicate that, once properly loaded onto damaged DNA, the 9-1-1 complex executes multiple, separable functions that promote genome maintenance.

DNA damage response clamp 9-1-1 promotes assembly of ZMM proteins for formation of crossovers and synaptonemal complex

Formation of crossovers between homologous chromosomes during meiosis is positively regulated by the ZMM proteins (also known as SIC proteins). DNA damage checkpoint proteins also promote efficient formation of interhomolog crossovers. Here, we examined, in budding yeast, the meiotic role of the heterotrimeric DNA damage response clamp composed of Rad17, Ddc1 and Mec3 (known as '9-1-1' in other organisms) and a component of the clamp loader, Rad24 (known as Rad17 in other organisms). Cytological analysis indicated that the 9-1-1 clamp and its loader are not required for the chromosomal loading of RecA homologs Rad51 or Dmc1, but are necessary for the efficient loading of ZMM proteins. Interestingly, the loading of ZMM proteins onto meiotic chromosomes was independent of the checkpoint kinase Mec1 (the homolog of ATR) as well as Rad51. Furthermore, the ZMM member Zip3 (also known as Cst9) bound to the 9-1-1 complex in a cell-free system. These data suggest that, in addition to promoting interhomolog bias mediated by Rad51-Dmc1, the 9-1-1 clamp promotes crossover formation through a specific role in the assembly of ZMM proteins. Thus, the 9-1-1 complex functions to promote two crucial meiotic recombination processes, the regulation of interhomolog recombination and crossover formation mediated by ZMM.

MIWI and piRNA-mediated cleavage of messenger RNAs in mouse testes

The piRNA machinery is known for its role in mediating epigenetic silencing of transposons. Recent studies suggest that this function also involves piRNA-guided cleavage of transposon-derived transcripts. As many piRNAs also appear to have the capacity to target diverse mRNAs, this raises the intriguing possibility that piRNAs may act extensively as siRNAs to degrade specific mRNAs. To directly test this hypothesis, we compared mouse PIWI (MIWI)-associated piRNAs with experimentally identified cleaved mRNA fragments from mouse testes, and observed cleavage sites that predominantly occur at position 10 from the 5' end of putative targeting piRNAs. We also noted strong biases for U and A residues at nucleotide positions 1 and 10, respectively, in both piRNAs and mRNA fragments, features that resemble the pattern of piRNA amplification by the 'ping-pong' cycle. Through mapping of MIWI-RNA interactions by CLIP-seq and gene expression profiling, we found that many potential piRNA-targeted mRNAs directly interact with MIWI and show elevated expression levels in the testes of Miwi catalytic mutant mice. Reporter-based assays further revealed the importance of base pairing between piRNAs and mRNA targets and the requirement for both the slicer activity and piRNA-loading ability of MIWI in piRNA-mediated target repression. Importantly, we demonstrated that proper turnover of certain key piRNA targets is essential for sperm formation. Together, these findings reveal the siRNA-like function of the piRNA machinery in mouse testes and its central requirement for male germ cell development and maturation.

The meiotic checkpoint network: step-by-step through meiotic prophase

The generation of haploid gametes by meiosis is a highly conserved process for sexually reproducing organisms that, in almost all cases, involves the extensive breakage of chromosomes. These chromosome breaks occur during meiotic prophase and are essential for meiotic recombination as well as the subsequent segregation of homologous chromosomes. However, their formation and repair must be carefully monitored and choreographed with nuclear dynamics and the cell division program to avoid the creation of aberrant chromosomes and defective gametes. It is becoming increasingly clear that an intricate checkpoint-signaling network related to the canonical DNA damage response is deeply interwoven with the meiotic program and preserves order during meiotic prophase. This meiotic checkpoint network (MCN) creates a wide range of dependent relationships controlling chromosome movement, chromosome pairing, chromatin structure, and double-strand break (DSB) repair. In this review, we summarize our current understanding of the MCN. We discuss commonalities and differences in different experimental systems, with a particular emphasis on the emerging design principles that control and limit cross talk between signals to ultimately ensure the faithful inheritance of chromosomes by the next generation.

The 9-1-1 checkpoint clamp stimulates DNA resection by Dna2-Sgs1 and Exo1

Single-stranded DNA (ssDNA) at DNA ends is an important regulator of the DNA damage response. Resection, the generation of ssDNA, affects DNA damage checkpoint activation, DNA repair pathway choice, ssDNA-associated mutation and replication fork stability. In eukaryotes, extensive DNA resection requires the nuclease Exo1 and nuclease/helicase pair: Dna2 and Sgs1^BLM. How Exo1 and Dna2-Sgs1^BLM coordinate during resection remains poorly understood. The DNA damage checkpoint clamp (the 9-1-1 complex) has been reported to play an important role in stimulating resection but the exact mechanism remains unclear. Here we show that the human 9-1-1 complex enhances the cleavage of DNA by both DNA2 and EXO1 in vitro, showing that the resection-stimulatory role of the 9-1-1 complex is direct. We also show that in Saccharomyces cerevisiae, the 9-1-1 complex promotes both Dna2-Sgs1 and Exo1-dependent resection in response to uncapped telomeres. Our results suggest that the 9-1-1 complex facilitates resection by recruiting both Dna2-Sgs1 and Exo1 to sites of resection. This activity of the 9-1-1 complex in supporting resection is strongly inhibited by the checkpoint adaptor Rad9^53BP1. Our results provide important mechanistic insights into how DNA resection is regulated by checkpoint proteins and have implications for genome stability in eukaryotes.

OsHUS1 facilitates accurate meiotic recombination in rice

Meiotic recombination normally takes place between allelic sequences on homologs. This process can also occur between non-allelic homologous sequences. Such ectopic interaction events can lead to chromosome rearrangements and are normally avoided. However, much remains unknown about how these ectopic interaction events are sensed and eliminated. In this study, using a screen in rice, we characterized a homolog of HUS1 and explored its function in meiotic recombination. In Oshus1 mutants, in conjunction with nearly normal homologous pairing and synapsis, vigorous, aberrant ectopic interactions occurred between nonhomologous chromosomes, leading to multivalent formation and subsequent chromosome fragmentation. These ectopic interactions relied on programed meiotic double strand breaks and were formed in a manner independent of the OsMER3-mediated interference-sensitive crossover pathway. Although early homologous recombination events occurred normally, the number of interference-sensitive crossovers was reduced in the absence of OsHUS1. Together, our results indicate that OsHUS1 might be involved in regulating ectopic interactions during meiosis, probably by forming the canonical RAD9-RAD1-HUS1 (9-1-1) complex.

Meiosis is a special type of cell division that generates gametes for sexual reproduction. During meiosis, recombination not only occurs between allelic sequences on homologs, but also between non-allelic homologous sequences at dispersed loci. Such ectopic recombination is the main cause of chromosomal alterations and accounts for numerous genomic disorders in humans. To ensure genomic integrity, those ectopic recombinations must be quickly resolved. Despite the importance of ectopic recombination suppression, the mechanism underlying this process still remains largely unknown. Here, using rice as a model system, we identified the rice HUS1 homolog, a member of the RAD9-RAD1-HUS1 (9-1-1) complex, and elucidated its roles in meiotic recombination. In Oshus1, vigorous ectopic interactions occur between nonhomologous chromosomes, and the number of crossovers is reduced. We suspect that OsHUS1 participates in regulating ectopic interactions during meiosis, probably by forming the canonical RAD9-RAD1-HUS1 (9-1-1) complex.

Mammalian CNTD1 is critical for meiotic crossover maturation and deselection of excess precrossover sites

Meiotic crossovers (COs) are crucial for ensuring accurate homologous chromosome segregation during meiosis I. Because the double-strand breaks (DSBs) that initiate meiotic recombination greatly outnumber eventual COs, this process requires exquisite regulation to narrow down the pool of DSB intermediates that may form COs. In this paper, we identify a cyclin-related protein, CNTD1, as a critical mediator of this process. Disruption of Cntd1 results in failure to localize CO-specific factors MutLγ and HEI10 at designated CO sites and also leads to prolonged high levels of pre-CO intermediates marked by MutSγ and RNF212. These data show that maturation of COs is intimately coupled to deselection of excess pre-CO sites to yield a limited number of COs and that CNTD1 coordinates these processes by regulating the association between the RING finger proteins HEI10 and RNF212 and components of the CO machinery.

Prepubertal mouse testis growth and maturation and androgen production are acutely sensitive to di-n-butyl phthalate

Phthalates are plasticizers with widespread industrial, domestic, and medical applications. Epidemiological data indicating increased incidence of testicular dysgenesis in boys exposed to phthalates in utero are reinforced by studies demonstrating that phthalates impair fetal rodent testis development. Because humans are exposed to phthalates continuously from gestation through adulthood, it is imperative to understand what threat phthalates pose at other life stages. To determine the impact during prepuberty, we assessed the consequences of oral administration of 1 to 500 mg di-n-butyl phthalate (DBP)/kg/d in corn oil to wild-type (C57BL/6J) male mice from 4 to 14 days of age. Dose-dependent effects on testis growth correlated with reduced Sertoli cell proliferation. Histological and immunohistochemical analyses identified delayed spermatogenesis and impaired Sertoli cell maturation after exposure to 10 to 500 mg DBP/kg/d. Interference with the hypothalamic-pituitary-gonadal axis was indicated in mice fed 500 mg DBP/kg/d, which had elevated circulating inhibin but no change in serum FSH. Increased immunohistochemical staining for inhibin-α was apparent at doses of 10 to 500 mg DBP/kg/d. Serum testosterone and testicular androgen activity were lower in the 500 mg DBP/kg/d group; however, reduced anogenital distance in all DBP-treated mice suggested impaired androgen action at earlier time points. Long-term effects were evident, with smaller anogenital distance and indications of disrupted spermatogenesis in adult mice exposed prepubertally to doses from 1 mg DBP/kg/d. These data demonstrate the acute sensitivity of the prepubertal mouse testis to DBP at doses 50- to 500-fold lower than those used in rat and identify the upregulation of inhibin as a potential mechanism of DBP action.

Clamping down on mammalian meiosis

The RAD9A-RAD1-HUS1 (9-1-1) complex is a PCNA-like heterotrimeric clamp that binds damaged DNA to promote cell cycle checkpoint signaling and DNA repair. While various 9-1-1 functions in mammalian somatic cells have been established, mounting evidence from lower eukaryotes predicts critical roles in meiotic germ cells as well. This was investigated in 2 recent studies in which the 9-1-1 complex was disrupted specifically in the mouse male germline through conditional deletion of Rad9a or Hus1. Loss of these clamp subunits led to severely impaired fertility and meiotic defects, including faulty DNA double-strand break repair. While 9-1-1 is critical for ATR kinase activation in somatic cells, these studies did not reveal major defects in ATR checkpoint pathway signaling in meiotic cells. Intriguingly, this new work identified separable roles for 9-1-1 subunits, namely RAD9A- and HUS1-independent roles for RAD1. Based on these studies and the high-level expression of the paralogous proteins RAD9B and HUS1B in testis, we propose a model in which multiple alternative 9-1-1 clamps function during mammalian meiosis to ensure genome maintenance in the germline.