Ku70 and non-homologous end joining protect testicular cells from DNA damage

Characterization of PRDM9 Multifunctionality in Yak Testes Through Protein Interaction Mapping

Meiotic recombination is initiated by the formation of programmed DNA double-strand breaks during spermatogenesis. PRDM9 determines the localization of recombination hotspots by interacting with several protein complexes in mammals. The function of PRDM9 is not well understood during spermatogenesis in mice or yaks. In this study, we applied yeast two-hybrid assays combined with next-generation sequencing techniques to screen the complete set of PRDM9-interacting proteins and explore its novel functions in yak spermatogenesis. Our results showed that 267 PRDM9-interacting proteins were identified. The gene ontology (GO) analysis of the interacting proteins revealed that the GO terms were primarily associated with spermatogenesis, positive regulation of double-strand break repair via homologous recombination, RNA splicing, the ubiquitin-dependent ERAD pathway, and other biological processes. MKX and PDCD5 were verified to be strongly interacting with PRDM9 and expressed in prophase I of meiosis in both mouse and yak testes. The localizations of RNA splicing genes including THOC5, DDX5, and XRCC6 were expressed in spermatocytes. Cattleyak is the hybrid offspring of a yak and a domestic cow, and the male offspring are sterile. The gene expression of the interacting proteins was also examined in the sterile male hybrid of yak and cattle. Among the 58 detected genes, 55 were downregulated in cattleyak. In conclusion, we established a complete PRDM9 interaction network, and a novel function of PRDM9 was identified, which will further promote our understanding of spermatogenesis. It also provides new insights for the study of hybrid male sterility.

Running the gauntlet: challenges to genome integrity in spermiogenesis

Species' continuity depends on gametogenesis to produce the only cell types that can transmit genetic information across generations. Spermiogenesis, which encompasses post-meiotic, haploid stages of male gametogenesis, is a process that leads to the formation of sperm cells well-known for their motility. Spermiogenesis faces three major challenges. First, after two rounds of meiotic divisions, the genome lacks repair templates (no sister chromatids, no homologous chromosomes), making it incredibly vulnerable to any genomic insults over an extended time (typically days-weeks). Second, the sperm genome becomes transcriptionally silent, making it difficult to respond to new perturbations as spermiogenesis progresses. Third, the histone-to-protamine transition, which is essential to package the sperm genome, counterintuitively involves DNA break formation. How spermiogenesis handles these challenges remains poorly understood. In this review, we discuss each challenge and their intersection with the biology of protamines. Finally, we discuss the implication of protamines in the process of evolution.

The crosstalk between telomeres and DNA repair mechanisms: an overview to mammalian somatic cells, germ cells, and preimplantation embryos

Telomeres are located at the ends of linear chromosomes and play a critical role in maintaining genomic stability by preventing premature activation of DNA repair mechanisms. Because of exposure to various genotoxic agents, telomeres can undergo shortening and genetic changes. In mammalian cells, the basic DNA repair mechanisms, including base excision repair, nucleotide excision repair, double-strand break repair, and mismatch repair, function in repairing potential damages in telomeres. If these damages are not repaired correctly in time, the unfavorable results such as apoptosis, cell cycle arrest, and cancerous transition may occur. During lifespan, mammalian somatic cells, male and female germ cells, and preimplantation embryos experience a number of telomeric damages. Herein, we comprehensively reviewed the crosstalk between telomeres and the DNA repair mechanisms in the somatic cells, germ cells, and embryos. Infertility development resulting from possible defects in this crosstalk is also discussed in the light of existing studies.

Testis-specific fascin component FSCN3 is dispensable for mouse spermatogenesis and fertility

BACKGROUND

Fascins belong to a family of actin-bundling proteins that are involved in a wide range of biological functions. FSCN3, a newly identified testis-specific actin-bundling protein, is specifically expressed in elongated spermatids. However, its in vivo function in mouse spermiogenesis remains unknown.

METHODS AND RESULTS

We generated Fscn3 knockout mice through CRISPR/Cas9 gene-editing technology. Fscn3^-/- mice displayed normal testis morphology and testis to bodyweight ratio, and sperm concentrations did not differ significantly between Fscn3^+/+ and Fscn3^-/- mice. Fertility assays consistently revealed that Fscn3^-/- mice are completely fertile and their reproductive status does not differ from that of wild-type. Moreover, hematoxylin and eosin staining of the testis sections of Fscn3^-/- mice detected various germ cells, ranging from spermatogonia to mature spermatozoa. Furthermore, the swimming velocity of the sperm of Fscn3^-/- mice was comparable to that of their wild-type littermates. Both Fscn3^+/+ and Fscn3^-/-mice had normal sperm morphology, indicating that the disruption of Fscn3 does not affect sperm morphology. The analysis of meiotic prophase I progression demonstrated normal prophase-I phases (leptonema to diplonema) in both Fscn3^+/+ and Fscn3^-/- mice, suggesting that Fscn3 is not essential for meiosis I.

CONCLUSION

Our study provides the first evidence that FSCN3 is a testis-specific actin-bundling protein that is not required for mouse spermatogenesis. Our results will help reproductive biologists focus their efforts on genes that are crucial for fertility and avoid research duplication.

A Brief Overview of Radiation-Induced Effects on Spermatogenesis and Oncofertility

Simple Summary

Spermatogenesis is one of the most important processes for the propagation of life; however, the testes’ ability to form sperm via this differentiation process is highly radiosensitive and easily impacted by exposure to environmental, occupational, or therapeutic radiation. Furthermore, the possibility that radiation effects on the gonads can be passed on from generation to generation should not be overlooked. This review focuses on the radiation-induced effects on spermatogenesis and the transgenerational effects. We also explore the potential of novel radiobiological approaches to improve male fertility preservation during radiotherapy.

Abstract

The genotoxicity of radiation on germ cells may be passed on to the next generation, thus its elucidation is not only a scientific issue but also an ethical, legal, and social issue in modern society. In this article, we briefly overview the effects of radiation on spermatogenesis and its associated genotoxicity, including the latest findings in the field of radiobiology. The potential role of transgenerational effects is still poorly understood, and further research in this area is desirable. Furthermore, from the perspective of oncofertility, we discuss the historical background and clinical importance of preserving male fertility during radiation treatment and the potential of microbeam radiotherapy. We hope that this review will contribute to stimulating further discussions and investigations for therapies for pediatric and adolescent/young adult patients.

Targeting DNA Repair Response Promotes Immunotherapy in Ovarian Cancer: Rationale and Clinical Application

Immune checkpoint inhibitors (ICI) have emerged as a powerful oncologic treatment modality for patients with different solid tumors. Unfortunately, the efficacy of ICI monotherapy in ovarian cancer is limited, and combination therapy provides a new opportunity for immunotherapy in ovarian cancer. DNA damage repair (DDR) pathways play central roles in the maintenance of genomic integrity and promote the progression of cancer. A deficiency in DDR genes can cause different degrees of DNA damage that enhance local antigen release, resulting in systemic antitumor immune responses. Thus, the combination of DDR inhibitors with ICI represents an attractive therapeutic strategy with the potential to improve the clinical outcomes of patients with ovarian cancer. In this review, we provide an overview of the interconnectivity between DDR pathway deficiency and immune response, summarize available clinical trials on the combination therapy in ovarian cancer, and discuss the potential predictive biomarkers that can be utilized to guide the use of combination therapy.

Liquid chromatography-tandem mass spectrometry reveals an active response to DNA damage in human spermatozoa

OBJECTIVE

To investigate how endogenously elevated DNA fragmentation alters the human sperm proteome, and whether this fragmentation contributes to genomic deletions.

DESIGN

Research study.

SETTING

Commercial fertility clinic.

PATIENT(S)

Men with low (0%-4%, n = 7) or high (≥16%, n = 6) sperm DNA fragmentation, as assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling assay.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Global sperm proteome, single-nucleotide polymorphism genotyping array.

RESULT(S)

A total of 78 significantly differentially abundant proteins (30 decreased, 48 increased) were observed in control vs. high DNA damage samples. DNA damage resulted in robust proteomic responses, including markers of oxidative stress and apoptosis, DNA damage repair proteins, and transcription/translation and protein turnover machinery. Several key sperm functional proteins were significantly decreased in ejaculates with high DNA damage. We were unable to substantiate a link between increased DNA fragmentation and genomic deletions in human spermatozoa.

CONCLUSION(S)

Developing human spermatozoa initiate an active transcriptional response to endogenous DNA damage, which manifests as alterations in the sperm proteome.

Genome diversity and instability in human germ cells and preimplantation embryos

Genome diversity is essential for evolution and is of fundamental importance to human health. Generating genome diversity requires phases of DNA damage and repair that can cause genome instability. Humans have a high incidence of de novo congenital disorders compared to other organisms. Recent access to eggs, sperm and preimplantation embryos is revealing unprecedented rates of genome instability that may result in infertility and de novo mutations that cause genomic imbalance in at least 70% of conceptions. The error type and incidence of de novo mutations differ during developmental stages and are influenced by differences in male and female meiosis. In females, DNA repair is a critical factor that determines fertility and reproductive lifespan. In males, aberrant meiotic recombination causes infertility, embryonic failure and pregnancy loss. Evidence suggest germ cells are remarkably diverse in the type of genome instability that they display and the DNA damage responses they deploy. Additionally, the initial embryonic cell cycles are characterized by a high degree of genome instability that cause congenital disorders and may limit the use of CRISPR-Cas9 for heritable genome editing.

Recruitment of MRE-11 to complex DNA damage is modulated by meiosis-specific chromosome organization

DNA double-strand breaks (DSBs) are one of the most dangerous assaults on the genome, and yet their natural and programmed production are inherent to life. When DSBs arise close together they are particularly deleterious, and their repair may require an altered form of the DNA damage response. Our understanding of how clustered DSBs are repaired in the germline is unknown. Using laser microirradiation, we examine early events in the repair of clustered DSBs in germ cells within Caenorhabditis elegans. We use precise temporal resolution to show how the recruitment of MRE-11 to complex damage is regulated, and that clustered DNA damage can recruit proteins from various repair pathways. Abrogation of non-homologous end joining or COM-1 attenuates the recruitment of MRE-11 through distinct mechanisms. The synaptonemal complex plays both positive and negative regulatory roles in these mutant contexts. These findings indicate that MRE-11 is regulated by modifying its accessibility to chromosomes.

Parp1-Dependent DNA Double-Strand Break Repair in Irradiated Late Pachytene Spermatocytes

Poly (ADP-ribose) polymerase-1 (Parp1) is a member of nuclear enzymes family involved in to the response to genotoxic stresses, DNA repair, and is critical for the maintenance of genome stability. During gametogenesis, genome stability is essential for inheritance and formation of healthy gametes. The latter involves DNA double-strand break (DSB)-driven pairing of homologous chromosomes in first meiotic prophase. By analysis of DSB repair kinetics in male meiotic prophase cells of homologous recombination (HR) and nonhomologous end joining (NHEJ)-deficient mouse models, we previously demonstrated an interplay between HR and the conventional NHEJ repair pathway. In the current work, we evaluate the relative contribution of Parp1-dependent NHEJ to the repair of ectopic ionizing radiation (IR)-induced DSBs in control and Parp1-inhibited mouse pachytene spermatocytes before and after the completion of meiotic recombination in stages VI-XI. The disappearance of large, exogenous DSB-related γ-H2AX foci was quantified 1 and 8 h after 1 Gy γ-irradiation of control and 3,4-dihydro-5-[4-(1-piperidinyl)butoxy]-1(2H)quinolinone (DPQ) Parp1-inhibited mice. Late pachytene control spermatocytes obtained 8 h after IR had repaired >80% of DSBs observed at 1 h after IR. However, only 64% of DSBs were repaired in late spermatocytes of DPQ-treated (Parp1-inhibited) mice. Thus, it appears that Parp1 contributes to the repair of a fraction of DSBs in late prophase I, providing further insights in DNA repair pathway choreography during spermatogenic differentiation.

Differential gene expression analysis and cytological evidence reveal a sexual stage of an amoeba with multiparental cellular and nuclear fusion

Sex is a hallmark of eukaryotes but its evolution in microbial eukaryotes is poorly elucidated. Recent genomic studies revealed microbial eukaryotes possess a genetic toolkit necessary for sexual reproduction. However, the mechanism of sexual development in a majority of microbial eukaryotes including amoebozoans is poorly characterized. The major hurdle in studying sex in microbial eukaryotes is a lack of observational evidence, primarily due to its cryptic nature. In this study, we used a tractable fusing amoeba, Cochliopodium, to investigate sexual development using stage-specific Differential Gene Expression (DGE) and cytological analyses. Both DGE and cytological results showed that most of the meiosis and sex-related genes are upregulated in Cochliopodium undergoing fusion in laboratory culture. Relative gene ontology (GO) category representations in unfused and fused cells revealed a functional skew of the fused transcriptome toward DNA metabolism, nucleus and ligases that are suggestive of a commitment to sexual development. However, the GO categories of unfused cells were dominated by metabolic pathways and other processes indicative of a vegetative phase. Our study provides strong evidence that the fused cells represent a sexual stage in Cochliopodium. Our findings have further implications in understanding the evolution and mechanism of inheritance involving multiparents in other eukaryotes with a similar reproductive strategy.

Skp2 regulates DNA damage repair and apoptosis via interaction with Ku70

PURPOSE

Skp2, an oncoprotein, regulates tumor proliferation, invasion and metastasis. Ku70 is a critical component of the non-homologous end-joining (NHEJ) process. Both Skp2 and Ku70 are positively associated in multiple cancers. However, there is no report about the relationship between Skp2 and Ku70 proteins.

METHODS

In this study, we carried out Bioinformatics and molecular biological methods to investigate the relationship between Skp2 and Ku70 proteins.

RESULTS

We first observed Skp2 and Ku70 mRNAs were significantly increased in cervical cancer tissues. And we identified Ku70 as a Skp2-binding protein and the binding site located in the C-terminal of Ku70 protein. We further found that Skp2 knockdown decreased the Ku70 protein level in cells, and increase the cellular apoptosis and DNA damage, suggesting Skp2 mediates the Ku70 protein stability and function via post-translational modification.

CONCLUSION

The direct interaction between Skp2 and Ku70 proteins mediates the DNA damage repair and cellular apoptosis by regulating Ku70 stability and function via post-translational modification. The molecular mechanisms how Skp2 stabilize Ku70 would be clarified in our following research work.

Role of HP1β during spermatogenesis and DNA replication

Heterochromatin protein 1β (HP1β), encoded by the Cbx1 gene, has been functionally linked to chromatin condensation, transcriptional regulation, and DNA damage repair. Here we report that testis-specific Cbx1 conditional knockout (Cbx1 cKO) impairs male germ cell development in mice. Depletion of HP1β negatively affected sperm maturation and increased seminiferous tubule degeneration in Cbx1 cKO mice. In addition, the spermatogonia have elevated γ-H2AX foci levels as do Cbx1 deficient mouse embryonic fibroblasts (MEFs) as compared to wild-type (WT) control MEFs. The increase in γ-H2AX foci in proliferating Cbx1 cKO cells indicates defective replication-dependent DNA damage repair. Depletion or loss of HP1β from human cells and MEFs increased DNA replication fork stalling and firing of new origins of replication, indicating defective DNA synthesis. Taken together, these results suggest that loss of HP1β in proliferating cells leads to DNA replication defects with associated DNA damage that impact spermatogenesis.

NHJ-1 Is Required for Canonical Nonhomologous End Joining in Caenorhabditis elegans

DNA double-strand breaks (DSBs) are a particularly lethal form of DNA damage that must be repaired to restore genomic integrity. Canonical nonhomologous end joining (NHEJ), is a widely conserved pathway that detects and directly ligates the broken ends to repair the DSB. These events globally require the two proteins that form the Ku ring complex, Ku70 and Ku80, and the terminal ligase LIG4. While the NHEJ pathway in vertebrates is elaborated by more than a dozen factors of varying conservation and is similarly complex in other eukaryotes, the entire known NHEJ toolkit in Caenorhabditis elegans consists only of the core components CKU-70, CKU-80, and LIG-4 Here, we report the discovery of the first accessory NHEJ factor in C. elegans Our analysis of the DNA damage response in young larvae revealed that the canonical wild-type N2 strain consisted of two lines that exhibited a differential phenotypic response to ionizing radiation (IR). Following the mapping of the causative locus to a candidate on chromosome V and clustered regularly interspaced short palindromic repeats-Cas9 mutagenesis, we show that disruption of the nhj-1 sequence induces IR sensitivity in the N2 line that previously exhibited IR resistance. Using genetic and cytological analyses, we demonstrate that nhj-1 functions in the NHEJ pathway to repair DSBs. Double mutants of nhj-1 and lig-4 or cku-80 do not exhibit additive IR sensitivity, and the post-IR somatic and fertility phenotypes of nhj-1 mimic those of the other NHEJ factors. Furthermore, in com-1 mutants that permit repair of meiotic DSBs by NHEJ instead of restricting their repair to the homologous recombination pathway, loss of nhj-1 mimics the consequences of loss of lig-4 Diakinesis-stage nuclei in nhj-1; com-1 and nhj-1; lig-4 mutant germlines exhibit increased numbers of DAPI-staining bodies, consistent with increased chromosome fragmentation in the absence of NHEJ-mediated meiotic DSB repair. Finally, we show that NHJ-1 and LIG-4 localize to somatic nuclei in larvae, but are excluded from the germline progenitor cells, consistent with NHEJ being the dominant DNA repair pathway in the soma. nhj-1 shares no sequence homology with other known eukaryotic NHEJ factors and is taxonomically restricted to the Rhabditid family, underscoring the evolutionary plasticity of even highly conserved pathways.

Abnormal methylation of spermatozoa induced by benzo(a)pyrene in rats

Epigenetic mutations caused by pollutants are possibly linked to many diseases. Benzo(a)pyrene (BaP) is one of the most representative air pollutants and has aroused wide concern because of its strong carcinogenicity. The reproductive toxicity induced by BaP has been identified, but little is known about the characteristics of the methylation changes induced by BaP. In this study, a methylated DNA immunoprecipitation sequencing method was used to detect the methylation of sperm DNA of rats exposed to BaP. Compared with the respective genes in normal rats, there were 3227 hypomethylated genes and 828 hypermethylated genes after BaP exposure. Gene ontology enrichment analysis reported that differentially methylated genes (DMGs) were enriched in the localization, single-multicellular organism process and plasma membrane. Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that the DMGs were significantly enriched in the Ras signalling pathway, Rap1 signalling pathway, pancreatic secretion and neuroactive ligand-receptor interaction. DisGeNET disease spectrum analysis showed that DMGs were associated with infertility and certain genetic diseases. Further research needs to be done to explore whether these abnormal methylation are transgenerational.

ATR is required to complete meiotic recombination in mice

Precise execution of recombination during meiosis is essential for forming chromosomally-balanced gametes. Meiotic recombination initiates with the formation and resection of DNA double-strand breaks (DSBs). Cellular responses to meiotic DSBs are critical for efficient repair and quality control, but molecular features of these remain poorly understood, particularly in mammals. Here we report that the DNA damage response protein kinase ATR is crucial for meiotic recombination and completion of meiotic prophase in mice. Using a hypomorphic Atr mutation and pharmacological inhibition of ATR in vivo and in cultured spermatocytes, we show that ATR, through its effector kinase CHK1, promotes efficient RAD51 and DMC1 assembly at RPA-coated resected DSB sites and establishment of interhomolog connections during meiosis. Furthermore, our findings suggest that ATR promotes local accumulation of recombination markers on unsynapsed axes during meiotic prophase to favor homologous chromosome synapsis. These data reveal that ATR plays multiple roles in mammalian meiotic recombination.

NHEJ Contributes to the Fast Repair of Radiation-induced DNA Double-strand Breaks at Late Prophase I Telomeres

Exposure of cells to ionizing radiation induces DNA double-strand breaks. To repair double-strand breaks correctly, cells must distinguish between the ends of chromosomes (telomeres) and DNA double-strand breaks within chromosomes. Double-strand breaks in telomeric DNA may lead to telomere shortening and mutagenesis. Eukaryotic cells repair double-strand breaks primarily by two mechanisms: error-free homologous recombination and error-prone nonhomologous end joining, of which homologous recombination is used in early meiotic prophase I to create recombined haploid gametes by two meiotic cell divisions lacking an intervening S-phase. Genotoxic exposures put meiosis at risk to transmit mutations, and ionizing radiation is known to induce large double-strand break-marking phospho (gamma)-H2AX foci along the cores and ends of mouse meiotic chromosomes. However, it remained unclear through which repair pathway the ionizing radiation-induced telomeric double-strand breaks are repaired in late prophase I spermatocytes. Using male wild-type and nonhomologous end joining-deficient (severe combined immunodeficient) mice, this study investigated the kinetics of in vivo double-strand break formation and repair at telomeres of late prophase I chromosomes up to 12 h after 0.5 Gy of whole-body gamma irradiation. Late pachytene and diplotene spermatocytes revealed overlapping gamma-H2AX and telomere repeat signal foci, indicating telomeric DNA damage. The comparison of double-strand break repair rates at telomeres and internal prophase chromosome sites revealed a more rapid double-strand break repair at wild-type telomeres during the first hour after irradiation. Increased double-strand break foci numbers at nonhomologous end joining-deficient telomeres and chromosomes and a slowed repair rate in this DNA-dependent protein kinase catalytic subunit mutant suggest that the fast repair of double-strand breaks in telomeric DNA repeats during late prophase I is largely mediated by canonical nonhomologous end joining.

The evolutionarily conserved genes: Tex37, Ccdc73, Prss55 and Nxt2 are dispensable for fertility in mice

There are more than 2300 genes that are predominantly expressed in mouse testes. The role of hundreds of these genes has been studied in mouse spermatogenesis but still there are many genes whose function is unknown. Gene knockout (KO) strategy in mice is widely used for in vivo study of gene function. The present study was designed to explore the function of the four genes: Tex37, Ccdc73, Prss55 and Nxt2, which were evolutionarily conserved in eutherians. We found that these genes had a testis-enriched expression pattern in mice except Nxt2. We knocked out these genes by CRISPR/Cas9 individually and found that all the KO mice had normal fertility with no detectable difference in testis/body weight ratios, epididymal sperm counts, as well as testicular and epididymal histology from wild type mice. Although these genes are evolutionarily conserved in eutherians including human and mouse, they are not individually essential for spermatogenesis, testis development and male fertility in mice in laboratory conditions. Our report of these fertile KO data could avoid the repetition and duplication of efforts which will help in prioritizing efforts to focus on genes that are indispensable for male reproduction.

Genes, Proteins, and Biological Pathways Preventing Chromothripsis

The highly complex structural genome variations chromothripsis, chromoanasynthesis, and chromoplexy are subsumed under the term chromoanagenesis, which means chromosome rebirth. Precipitated by numerous DNA double-strand breaks, they differ in number of and distances between breakpoints, associated copy number variations, order and orientation of segments, and flanking sequences at joining points. Results from patients with the autosomal dominant cancer susceptibility disorder Li-Fraumeni syndrome implicated somatic TP53 mutations in chromothripsis. TP53 participates in the G2/M phase checkpoint, halting cell cycling after premature chromosome compaction during the second half of the S phase, thus preventing chromosome shattering. By experimental TP53 ablation and micronucleus induction, one or a few isolated chromosomes underwent desynchronized replication and chromothripsis. Secondly, chromothripsis occurred after experimental induction of telomere crisis after which dicentric chromosomes sustained TREX1-mediated resolution of chromosome bridges and kataegis. Third, DNA polymerase Polθ-dependent chromothripsis has been documented. Finally, a family with chromothripsis after L1 element-dependent retrotransposition and Alu/Alu homologous recombination has been reported. Human chromosomal instability syndromes share defects in responses to DNA double-strand breaks, characteristic cell cycle perturbations, elevated rates of micronucleus formation, premature chromosome compaction, and apoptosis. They are also associated with elevated susceptibility to malignant disease, such as medulloblastomas and gliomas in ataxia-telangiectasia, leukemia and lymphoma in Bloom syndrome, and osteosarcoma and soft tissue sarcoma in Werner syndrome. The latter syndrome is characterized by a premature aging-like progressive decline of mesenchymal tissues. In all thus far studied cases, constitutional chromothripsis occurred in the male germline and male patients with defects in the double-strand break response genes ATM, MRE11, BLM, LIG4, WRN, and Ku70 show impaired fertility. Conceivably, chromothripsis may, in a stochastic rather than deterministic way, be implicated in germline structural variation, malignant disease, premature aging, genome mosaicism in somatic tissues, and male infertility.

Critical Role of Hepatic Cyp450s in the Testis-Specific Toxicity of (5R)-5-Hydroxytriptolide in C57BL/6 Mice

Low solubility, tissue accumulation, and toxicity are chief obstacles to developing triptolide derivatives, so a better understanding of the pharmacokinetics and toxicity of triptolide derivatives will help with these limitations. To address this, we studied pharmacokinetics and toxicity of (5R)-5-hydroxytriptolide (LLDT-8), a novel triptolide derivative immunosuppressant in a conditional knockout (KO) mouse model with liver-specific deletion of CYP450 reductase. Compared to wild type (WT) mice, after LLDT-8 treatment, KO mice suffered severe testicular toxicity (decreased testicular weight, spermatocytes apoptosis) unlike WT mice. Moreover, KO mice had greater LLDT-8 exposure as confirmed with elevated AUC and Cmax, increased drug half-life, and greater tissue distribution. γ-H2AX, a marker of meiosis process, its localization and protein level in testis showed a distinct meiosis block induced by LLDT-8. RNA polymerase II (Pol II), an essential factor for RNA storage and synapsis in spermatogenesis, decreased in testes of KO mice after LLDT-8 treatment. Germ-cell line based assays confirmed that LLDT-8 selectively inhibited Pol II in spermatocyte-like cells. Importantly, the analysis of androgen receptor (AR) related genes showed that LLDT-8 did not change AR-related signaling in testes. Thus, hepatic CYP450s were responsible for in vivo metabolism and clearance of LLDT-8 and aggravated testicular injury may be due to increased LLDT-8 exposure in testis and subsequent Pol II reduction.

The aldehyde group of gossypol induces mitochondrial apoptosis via ROS-SIRT1-p53-PUMA pathway in male germline stem cell

As a widely grown economic crop, cotton is the major oil and protein resource for human and livestock. But the highly toxic of gossypol in cottonseed severely restricts its effective utilization, consequently creating huge resource waste. Previous studies have shown the male germline stem cells were the most vulnerable cells in gossypol damages, but the mechanism was still unclear. We found gossypol induced cell viability decline resulted from apoptosis. And the increase of Caspase-9 activity in gossypol treatment hinted the mitochondrial apoptosis. So the mitochondrial dysfunction was confirmed by the decreased mitochondrial membrane potential and ATP concentration. We found the higher intracellular H₂O₂ level did not accompany with the O₂^·- associated increase in gossypol-treated, which indicated that gossypol obstructed the intracellular reactive oxygen species (ROS) elimination. Manipulated gossypol-induced H₂O₂ level by H₂O₂ and α-lipoic acid, we demonstrated that the mitochondrial dysfunction resulted from the excessive intracellular H₂O₂. Treated with Apogossypolone (ApoG2), an aldehyde group removed derivative of gossypol, the GSH/GSSG ratio and H₂O₂ did not decrease. ApoG2 also did not cause the mitochondrial apoptosis. So the aldehyde group is key factor in gossypol cytotoxicity. We respectively detected the NAD⁺/NADH ratio, SIRT1 activity, the relative protein level and apoptosis. Comparing with the specific inhibitors groups, the data illustrated that gossypol induced apoptosis through SIRT1-P53-PUMA pathway. This study helped to overcome barriers of gossypol cytotoxicity, which is crucial in feed and food use of cottonseed. This also provides a reference for the gossypol derivatives using in male contraception and anticancer.

Cell-type specific role of the RNA-binding protein, NONO, in the DNA double-strand break response in the mouse testes

The tandem RNA recognition motif protein, NONO, was previously identified as a candidate DNA double-strand break (DSB) repair factor in a biochemical screen for proteins with end-joining stimulatory activity. Subsequent work showed that NONO and its binding partner, SFPQ, have many of the properties expected for bona fide repair factors in cell-based assays. Their contribution to the DNA damage response in intact tissue in vivo has not, however, been demonstrated. Here we compare DNA damage sensitivity in the testes of wild-type mice versus mice bearing a null allele of the NONO homologue (Nono ^gt). In wild-type mice, NONO protein was present in Sertoli, peritubular myoid, and interstitial cells, with an increase in expression following induction of DNA damage. As expected for the product of an X-linked gene, NONO was not detected in germ cells. The Nono ^gt/0 mice had at most a mild testis developmental phenotype in the absence of genotoxic stress. However, following irradiation at sublethal, 2-4 Gy doses, Nono ^gt/0 mice displayed a number of indicators of radiosensitivity as compared to their wild-type counterparts. These included higher levels of persistent DSB repair foci, increased numbers of apoptotic cells in the seminiferous tubules, and partial degeneration of the blood-testis barrier. There was also an almost complete loss of germ cells at later times following irradiation, evidently arising as an indirect effect reflecting loss of stromal support. Results demonstrate a role for NONO protein in protection against direct and indirect biological effects of ionizing radiation in the whole animal.

Imaging of Chromosome Dynamics in Mouse Testis Tissue by Immuno-FISH

The mouse (Mus musculus) represents the central mammalian genetic model system for biomedical and developmental research. Mutant mouse models have provided important insights into chromosome dynamics during the complex meiotic differentiation program that compensates for the genome doubling at fertilization. Homologous chromosomes (homologues) undergo dynamic pairing and recombine during first meiotic prophase before they become partitioned into four haploid sets by two consecutive meiotic divisions that lack an intervening S-phase. Fluorescence in situ hybridization (FISH) has been instrumental in the visualization and imaging of the dynamic reshaping of chromosome territories and mobility during prophase I, in which meiotic telomeres were found to act as pacemakers for the chromosome pairing dance. FISH combined with immunofluorescence (IF) co-staining of nuclear proteins has been instrumental for the visualization and imaging of mammalian meiotic chromosome behavior. This chapter describes FISH and IF methods for the analysis of chromosome dynamics in nuclei of paraffin-embedded mouse testes. The techniques have proven useful for fresh and archived paraffin testis material of several mammalian species.

XRCC5 VNTR, XRCC6 -61C>G, and XRCC7 6721G>T Gene Polymorphisms Associated with Male Infertility Risk: Evidences from Case-Control and In Silico Studies

We evaluate the association between genetic polymorphisms of XRCC5 VNTR, XRCC6 -61C>G, and XRCC7 6721G>T with male infertility susceptibility. A total of 392 men including 178 infertile males (102 idiopathic azoospermia and 76 severe oligozoospermia) and 214 healthy controls were recruited. XRCC6 -61C>G and XRCC7 6721G>T genotyping was performed by PCR-RFLP whereas XRCC5 VNTR was performed by PCR. The 2R allele and 2R allele carriers of XRCC5 VNTR polymorphism significantly decreased risk of male infertility. The mutant GG genotypes and carriers of the CG and GG genotypes of XRCC6 -61C>G showed increased risk for the male infertility. Furthermore, the G allele of the XRCC6 -61C>G was correlated with increased susceptibility to male infertility. Likewise, the T allele of the XRCC7 6721G>T polymorphism was associated with increased susceptibility to male infertility in azoospermia. In silico analysis predicted that the presence of tandem repeats in XRCC5 gene prompter can be sequence to bind to more nuclear factors. Also, rs2267437 (C>G) variant was located in a well-conserved region in XRCC6 promoter and this variation might lead to differential allelic expression. The XRCC7 6721G>T gene polymorphism occurred in an acceptor-splicing site, but this polymorphism has no severe modification on XRCC7 mRNA splicing. Our results indicate the association of XRCC5 VNTR, XRCC6 -61C>G, and XRCC7 6721G>T gene polymorphisms with male infertility in Iranian men.

DNA repair kinetics in SCID mice Sertoli cells and DNA-PKcs-deficient mouse embryonic fibroblasts

Noncycling and terminally differentiated (TD) cells display differences in radiosensitivity and DNA damage response. Unlike other TD cells, Sertoli cells express a mixture of proliferation inducers and inhibitors in vivo and can reenter the cell cycle. Being in a G₁-like cell cycle stage, TD Sertoli cells are expected to repair DSBs by the error-prone nonhomologous end-joining pathway (NHEJ). Recently, we have provided evidence for the involvement of Ku-dependent NHEJ in protecting testis cells from DNA damage as indicated by persistent foci of the DNA double-strand break (DSB) repair proteins phospho-H2AX, 53BP1, and phospho-ATM in TD Sertoli cells of Ku70-deficient mice. Here, we analyzed the kinetics of 53BP1 foci induction and decay up to 12 h after 0.5 Gy gamma irradiation in DNA-PKcs-deficient (Prkdc ^scid ) and wild-type Sertoli cells. In nonirradiated mice and Prkdc ^scid Sertoli cells displayed persistent DSBs foci in around 12 % of cells and a fivefold increase in numbers of these DSB DNA damage-related foci relative to the wild type. In irradiated mice, Prkdc ^scid Sertoli cells showed elevated levels of DSB-indicating foci in 82 % of cells 12 h after ionizing radiation (IR) exposure, relative to 52 % of irradiated wild-type Sertoli cells. These data indicate that Sertoli cells respond to and repair IR-induced DSBs in vivo, with repair kinetics being slow in the wild type and inefficient in Prkdc ^scid . Applying the same dose of IR to Prdkc ^-/- and Ku ^-/- mouse embryonic fibroblast (MEF) cells revealed a delayed induction of 53BP1 DSB-indicating foci 5 min post-IR in Prdkc ^-/- cells. Inefficient DSB repair was evident 7 h post-IR in DNA-PKcs-deficient cells, but not in Ku ^-/- MEFs. Our data show that quiescent Sertoli cells repair genotoxic DSBs by DNA-PKcs-dependent NEHJ in vivo with a slower kinetics relative to somatic DNA-PKcs-deficient cells in vitro, while DNA-PKcs deficiency caused inefficient DSB repair at later time points post-IR in both conditions. These observations suggest that DNA-PKcs contributes to the fast and slow repair of DSBs by NHEJ.

DNA Double Strand Break Response and Limited Repair Capacity in Mouse Elongated Spermatids

Spermatids are extremely sensitive to genotoxic exposures since during spermiogenesis only error-prone non homologous end joining (NHEJ) repair pathways are available. Hence, genomic damage may accumulate in sperm and be transmitted to the zygote. Indirect, delayed DNA fragmentation and lesions associated with apoptotic-like processes have been observed during spermatid elongation, 27 days after irradiation. The proliferating spermatogonia and early meiotic prophase cells have been suggested to retain a memory of a radiation insult leading later to this delayed fragmentation. Here, we used meiotic spread preparations to localize phosphorylate histone H2 variant (γ-H2AX) foci marking DNA double strand breaks (DSBs) in elongated spermatids. This technique enabled us to determine the background level of DSB foci in elongated spermatids of RAD54/RAD54B double knockout (dko) mice, severe combined immunodeficiency SCID mice, and poly adenosine diphosphate (ADP)-ribose polymerase 1 (PARP1) inhibitor (DPQ)-treated mice to compare them with the appropriate wild type controls. The repair kinetics data and the protein expression patterns observed indicate that the conventional NHEJ repair pathway is not available for elongated spermatids to repair the programmed and the IR-induced DSBs, reflecting the limited repair capacity of these cells. However, although elongated spermatids express the proteins of the alternative NHEJ, PARP1-inhibition had no effect on the repair kinetics after IR, suggesting that DNA damage may be passed onto sperm. Finally, our genetic mutant analysis suggests that an incomplete or defective meiotic recombinational repair of Spo11-induced DSBs may lead to a carry-over of the DSB damage or induce a delayed nuclear fragmentation during the sensitive programmed chromatin remodeling occurring in elongated spermatids.

Cadmium delays non-homologous end joining (NHEJ) repair via inhibition of DNA-PKcs phosphorylation and downregulation of XRCC4 and Ligase IV

Although studies have shown that cadmium (Cd) interfered with DNA damage repair (DDR), whether Cd could affect non-homologous end joining (NHEJ) repair remains elusive. To further understand the effect of Cd on DDR, we used X-ray irradiation of Hela cells as an in vitro model system, along with γH2AX and 53BP1 as markers for DNA damage. Results showed that X-ray significantly increased γH2AX and 53BP1 foci in Hela cells (p < 0.01), all of which are characteristic of accrued DNA damage. The number of foci declined rapidly over time (1-8h postirradiation), indicating an initiation of NHEJ process. However, the disappearance of γH2AX and 53BP1 foci was remarkably slowed by Cd pretreatment (p < 0.01), suggesting that Cd reduced the efficiency of NHEJ. To further elucidate the mechanisms of Cd toxicity, several markers of NHEJ pathway including Ku70, DNA-PKcs, XRCC4 and Ligase IV were examined. Our data showed that Cd altered the phosphorylation of DNA-PKcs, and reduced the expression of both XRCC4 and Ligase IV in irradiated cells. These observations are indicative of the impairment of NHEJ-dependent DNA repair pathways. In addition, zinc (Zn) mitigated the effects of Cd on NHEJ, suggesting that the Cd-induced NHEJ alteration may partly result from the displacement of Zn or from an interference with the normal function of Zn-containing proteins by Cd. Our findings provide a new insight into the toxicity of Cd on NHEJ repair and its underlying mechanisms in human cells.

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.

Chromatin organization and remodeling of interstitial telomeric sites during meiosis in the Mongolian gerbil (Meriones unguiculatus)

Telomeric DNA repeats are key features of chromosomes that allow the maintenance of integrity and stability in the telomeres. However, interstitial telomere sites (ITSs) can also be found along the chromosomes, especially near the centromere, where they may appear following chromosomal rearrangements like Robertsonian translocations. There is no defined role for ITSs, but they are linked to DNA damage-prone sites. We were interested in studying the structural organization of ITSs during meiosis, a kind of cell division in which programmed DNA damage events and noticeable chromatin reorganizations occur. Here we describe the presence of highly amplified ITSs in the pericentromeric region of Mongolian gerbil (Meriones unguiculatus) chromosomes. During meiosis, ITSs show a different chromatin conformation than DNA repeats at telomeres, appearing more extended and accumulating heterochromatin markers. Interestingly, ITSs also recruit the telomeric proteins RAP1 and TRF1, but in a stage-dependent manner, appearing mainly at late prophase I stages. We did not find a specific accumulation of DNA repair factors to the ITSs, such as γH2AX or RAD51 at these stages, but we could detect the presence of MLH1, a marker for reciprocal recombination. However, contrary to previous reports, we did not find a specific accumulation of crossovers at ITSs. Intriguingly, some centromeric regions of metacentric chromosomes may bind the nuclear envelope through the association to SUN1 protein, a feature usually performed by telomeres. Therefore, ITSs present a particular and dynamic chromatin configuration in meiosis, which could be involved in maintaining their genetic stability, but they additionally retain some features of distal telomeres, provided by their capability to associate to telomere-binding proteins.