Chd5 orchestrates chromatin remodelling during sperm development

INO80 regulates chromatin accessibility to facilitate suppression of sex-linked gene expression during mouse spermatogenesis

The INO80 protein is the main catalytic subunit of the INO80-chromatin remodeling complex, which is critical for DNA repair and transcription regulation in murine spermatocytes. In this study, we explored the role of INO80 in silencing genes on meiotic sex chromosomes in male mice. INO80 immunolocalization at the XY body in pachytene spermatocytes suggested a role for INO80 in the meiotic sex body. Subsequent deletion of Ino80 resulted in high expression of sex-linked genes. Furthermore, the active form of RNA polymerase II at the sex chromosomes of Ino80-null pachytene spermatocytes indicates incomplete inactivation of sex-linked genes. A reduction in the recruitment of initiators of meiotic sex chromosome inhibition (MSCI) argues for INO80-facilitated recruitment of DNA repair factors required for silencing sex-linked genes. This role of INO80 is independent of a common INO80 target, H2A.Z. Instead, in the absence of INO80, a reduction in chromatin accessibility at DNA repair sites occurs on the sex chromosomes. These data suggest a role for INO80 in DNA repair factor localization, thereby facilitating the silencing of sex-linked genes during the onset of pachynema.

TMC7 deficiency causes acrosome biogenesis defects and male infertility in mice

Transmembrane channel-like (TMC) proteins are a highly conserved ion channel family consisting of eight members (TMC1-TMC8) in mammals. TMC1/2 are components of the mechanotransduction channel in hair cells, and mutations of TMC1/2 cause deafness in humans and mice. However, the physiological roles of other TMC proteins remain largely unknown. Here, we show that Tmc7 is specifically expressed in the testis and that it is required for acrosome biogenesis during spermatogenesis. Tmc7-/- mice exhibited abnormal sperm head, disorganized mitochondrial sheaths, and reduced number of elongating spermatids, similar to human oligo-astheno-teratozoospermia. We further demonstrate that TMC7 is colocalized with GM130 at the cis-Golgi region in round spermatids. TMC7 deficiency leads to aberrant Golgi morphology and impaired fusion of Golgi-derived vesicles to the developing acrosome. Moreover, upon loss of TMC7 intracellular ion homeostasis is impaired and ROS levels are increased, which in turn causes Golgi and endoplasmic reticulum stress. Taken together, these results suggest that TMC7 is required to maintain pH and ion homeostasis, which is needed for acrosome biogenesis. Our findings unveil a novel role for TMC7 in acrosome biogenesis during spermiogenesis.

INO80 regulates chromatin accessibility to facilitate suppression of sex-linked gene expression during mouse spermatogenesis

The INO80 protein is the main catalytic subunit of the INO80-chromatin remodeling complex, which is critical for DNA repair and transcription regulation in murine spermatocytes. In this study, we explored the role of INO80 in silencing genes on meiotic sex chromosomes in male mice. INO80 immunolocalization at the XY body in pachytene spermatocytes suggested a role for INO80 in the meiotic sex body. Subsequent deletion of Ino80 resulted in high expression of sex-linked genes. Furthermore, the active form of RNA polymerase II at the sex chromosomes of Ino80 -null pachytene spermatocytes indicates incomplete inactivation of sex-linked genes. A reduction in the recruitment of initiators of meiotic sex chromosome inhibition (MSCI) argues for INO80-facilitated recruitment of DNA repair factors required for silencing sex-linked genes. This role of INO80 is independent of a common INO80 target H2A.Z. Instead, in the absence of INO80, a reduction in chromatin accessibility at DNA repair sites occurs on the sex chromosomes. These data suggest a role for INO80 in DNA repair factor localization, thereby facilitating the silencing of sex-linked genes during the onset of pachynema.

Summary Statement

Chromatin accessibility and DNA repair factor localization at the sex chromosomes are facilitated by INO80, which regulates sex-linked gene silencing during meiotic progression in spermatocytes.

Evaluation of CHD5, H3K9me3, and H4K12ac in Human Testes with Spermatogenic Maturation Arrest: A Cross-Sectional Study

BACKGROUND

Spermatogenic maturation arrest is thought to be caused by epigenetic defects, specifically in chromatin remodeling and histone modification. This study evaluated the status of chromatin remodeling chromodomain helicase DNA binding protein 5 (CHD5) and histone modifications histone 4 lys-12 acetylation (H4K12ac) and histone 3 lys-9 trimethylation (H3K9me3) in human testicular biopsies, based on maturation arrest type.

MATERIALS AND METHODS

The cross-sectional study utilized 18 Bouin-fixed paraffin-embedded (BFPE) specimens prepared from residual tissue from routine laboratory tests of infertile patients. The expression of CHD5, H4K12ac, and H3K9me3 was examined through immunohistochemistry (IHC). The intensity was measured using ImageJ with IHC Profiler and StarDist plugins. Statistical analysis was performed using Python with Scipy.Stats module. The data were tested with Shapiro- Wilk for normality and Levene test for homogeneity. The differences in the intensity of spermatogenic cells were assessed using Kruskal-Wallis and Mann-Whitney tests. A difference was considered statistically significant if P<0.05.

RESULTS

We found three types of maturation arrest, including Sertoli cell only (n=5), spermatocyte arrest (n=4), and spermatid arrest (n=9). CHD5 was positive in spermatogonia and round spermatids but absent in spermatocytes. The mean grey value (MGV) of CHD5 in spermatogonia was generally weak in spermatocyte arrest (157.4 ± 16.6) and spermatid arrest (155.3 ± 16.8), and there was no significant difference between them [P=0.49, 95% confidence interval (CI): (-4.3, 6), effect size (r): 0.02]. Although there was a significant difference in the expression of H3K9me3 and H4K12ac (P<0.001), both histone modifications were found in all observed spermatogenic cells.

CONCLUSION

The expressions of CHD5, H3K9me3, and H4K12ac in different spermatogenic cell types produce similar results, indicating that they cannot be used as markers to determine the type of spermatogenic maturation arrest in humans. The significant finding in this research is the expression of CHD5 in human spermatogonia cells, which requires further study for elaboration.

Transcriptomic analysis of the HPG axis-related tissues reveals potential candidate genes and regulatory pathways associated with testicular size in Hu sheep

Testicular size is an excellent proxy for selecting high-fertility rams. The hypothalamus-pituitary-gonadal (HPG) axis plays an important role in regulating reproductive capacity in vertebrates, while key genes and regulatory pathways within the HPG axis associated with testicular size remain largely unknown in sheep. This study comprehensively compared the transcriptomic profiles in the hypothalamus, pituitary and testis of rams after sexual maturity between the large-testis group (LTG, testicular weight = 454.29 ± 54.24 g) and the small-testis group (STG, testicular weight = 77.29 ± 10.76 g). In total, 914, 795 and 10518 differentially expressed genes (DEGs) were identified in the hypothalamus, pituitary and testis between LTG and STG, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that these DEGs were mainly involved in the biological processes of reproduction, biological regulation, and development process. Notably, the neuroactive ligand-receptor interaction and cAMP signaling pathways, commonly enriched by the DEGs in the hypothalamus and pituitary between two groups, were considered as two key signal pathways regulating testicular development through the HPGs axis. Weighted gene co-expression network analysis (WGCNA) identified two modules that were significantly associated with testicular size, and 97 key genes were selected with high module membership (MM) and gene significance (GS) in these two modules. Finally, a protein-protein interaction (PPI) network was constructed, and ten genes with the highest degree were represented as hub genes, including FOS, NPY, SST, F2, AGT, NTS, OXT, EDN1, VIP and TAC1. Taken together, these results provide new insights into the molecular mechanism underlying the HPG axis regulating testicular size of Hu sheep.

Effect of smoking on methylation and semen parameters

One type of epigenetic modification is genomic DNA methylation, which is induced by smoking, and both are associated with male infertility. In this study, the relationship between smoking and CHD5 gene methylation and semen parameters in infertile men was determined. After the MS-PCR of blood in 224 samples, 103 infertile patients (62 smokers and 41 non-smokers) and 121 fertile men, methylation level changes between groups and the effect of methylation and smoking on infertility and semen parameters in infertile men were determined. The results showed that there is a significant difference in the methylation status (MM, MU, UU) of the CHD5 gene between the patient and the control group, and this correlation also exists for the semen parameters (p < .001). The average semen parameters in smokers decreased significantly compared to non-smokers and sperm concentration was (32.21 ± 5.27 vs. 55.27 ± 3.38), respectively. MM methylation status was higher in smokers (22.5%) compared to non-smokers (14.6%). Smoking components affect the methylation pattern of CHD5 gene, and smokers had higher methylation levels and lower semen parameters than non-smokers, which can be biomarkers for evaluating semen quality and infertility risk factors. Understanding the epigenetic effects of smoking on male infertility can be very useful for predicting negative consequences of smoking and providing therapeutic solutions.

Sperm chromatin accessibility's involvement in the intergenerational effects of stress hormone receptor activation

Dexamethasone is a stress hormone receptor agonist used widely in clinics. We and others previously showed that paternal administration of dexamethasone in mice affects the phenotype of their offspring. The substrate of intergenerational transmission of environmentally induced effects often involves changes in sperm RNA, yet other epigenetic modifications in the germline can be affected and are also plausible candidates. First, we tested the involvement of altered sperm RNAs in the transmission of dexamethasone induced phenotypes across generations. We did this by injecting sperm RNA into naïve fertilized oocytes, before performing metabolic and behavioral phenotyping of the offspring. We observed phenotypic changes in discordance with those found in offspring generated by in vitro fertilization using sperm from dexamethasone exposed males. Second, we investigated the effect of dexamethasone on chromatin accessibility using ATAC sequencing and found significant changes at specific genomic features and gene regulatory loci. Employing q-RT-PCR, we show altered expression of a gene in the tissue of offspring affected by accessibility changes in sperm. Third, we establish a correlation between specific DNA modifications and stress hormone receptor activity as a likely contributing factor influencing sperm accessibility. Finally, we independently investigated this dependency by genetically reducing thymine-DNA glycosylase levels and observing concomitant changes at the level of chromatin accessibility and stress hormone receptor activity.

Genetic variants underlying spermatogenic arrests in men with non-obstructive azoospermia

Spermatogenic arrest is a severe form of non-obstructive azoospermia (NOA), which occurs in 10-15% of infertile men. Interruption in spermatogenic progression at premeiotic, meiotic, or postmeiotic stage can lead to arrest in men with NOA. Recent studies have intensively focused on defining genetic variants underlying these spermatogenic arrests by making genome/exome sequencing. A number of variants were discovered in the genes involving in mitosis, meiosis, germline differentiation and other basic cellular events. Herein, defined variants in NOA cases with spermatogenic arrests and created knockout mouse models for the related genes are comprehensively reviewed. Also, importance of gene panel-based screening for NOA cases was discussed. Screening common variants in these infertile men with spermatogenic arrests may contribute to elucidating the molecular background and designing novel treatment strategies.

The DOT1L-MLLT10 complex regulates male fertility and promotes histone removal during spermiogenesis

Histone modifications regulate chromatin remodeling and gene expression in development and diseases. DOT1L, the sole histone H3K79 methyltransferase, is essential for embryonic development. Here, we report that DOT1L regulates male fertility in mouse. DOT1L associates with MLLT10 in testis. DOT1L and MLLT10 localize to the sex chromatin in meiotic and post-meiotic germ cells in an inter-dependent manner. Loss of either DOT1L or MLLT10 leads to reduced testis weight, decreased sperm count and male subfertility. H3K79me2 is abundant in elongating spermatids, which undergo the dramatic histone-to-protamine transition. Both DOT1L and MLLT10 are essential for H3K79me2 modification in germ cells. Strikingly, histones are substantially retained in epididymal sperm from either DOT1L- or MLLT10-deficient mice. These results demonstrate that H3K79 methylation promotes histone replacement during spermiogenesis.

DOT1L promotes spermatid differentiation by regulating expression of genes required for histone-to-protamine replacement

Unique chromatin remodeling factors orchestrate dramatic changes in nuclear morphology during differentiation of the mature sperm head. A crucial step in this process is histone-to-protamine exchange, which must be executed correctly to avoid sperm DNA damage, embryonic lethality and male sterility. Here, we define an essential role for the histone methyltransferase DOT1L in the histone-to-protamine transition. We show that DOT1L is abundantly expressed in mouse meiotic and postmeiotic germ cells, and that methylation of histone H3 lysine 79 (H3K79), the modification catalyzed by DOT1L, is enriched in developing spermatids in the initial stages of histone replacement. Elongating spermatids lacking DOT1L fail to fully replace histones and exhibit aberrant protamine recruitment, resulting in deformed sperm heads and male sterility. Loss of DOT1L results in transcriptional dysregulation coinciding with the onset of histone replacement and affecting genes required for histone-to-protamine exchange. DOT1L also deposits H3K79me2 and promotes accumulation of elongating RNA Polymerase II at the testis-specific bromodomain gene Brdt. Together, our results indicate that DOT1L is an important mediator of transcription during spermatid differentiation and an indispensable regulator of male fertility.

Single-cell RNA-seq uncovers dynamic processes orchestrated by RNA-binding protein DDX43 in chromatin remodeling during spermiogenesis

Mammalian spermatogenesis shows prominent chromatin and transcriptomic switches in germ cells, but it is unclear how such dynamics are controlled. Here we identify RNA helicase DDX43 as an essential regulator of the chromatin remodeling process during spermiogenesis. Testis-specific Ddx43 knockout mice show male infertility with defective histone-to-protamine replacement and post-meiotic chromatin condensation defects. The loss of its ATP hydrolysis activity by a missense mutation replicates the infertility phenotype in global Ddx43 knockout mice. Single-cell RNA sequencing analyses of germ cells depleted of Ddx43 or expressing the Ddx43 ATPase-dead mutant reveals that DDX43 regulates dynamic RNA regulatory processes that underlie spermatid chromatin remodeling and differentiation. Transcriptomic profiling focusing on early-stage spermatids combined with enhanced crosslinking immunoprecipitation and sequencing further identifies Elfn2 as DDX43-targeted hub gene. These findings illustrate an essential role for DDX43 in spermiogenesis and highlight the single-cell-based strategy to dissect cell-state-specific regulation of male germline development.

Single-cell transcriptome analysis and in vitro differentiation of testicular cells reveal novel insights into male sterility of the interspecific hybrid cattle-yak

BACKGROUND

Interspecific hybridization plays vital roles in enriching animal diversity, while male hybrid sterility (MHS) of the offspring commonly suffered from spermatogenic arrest constitutes the postzygotic reproductive isolation. Cattle-yak, the hybrid offspring of cattle (Bos taurus) and yak (Bos grunniens) can serve as an ideal MHS animal model. Although meiotic arrest was found to contribute to MHS of cattle-yak, yet the cellular characteristics and developmental potentials of male germline cell in pubertal cattle-yak remain to be systematically investigated.

RESULTS

Single-cell RNA-seq analysis of germline and niche cell types in pubertal testis of cattle-yak and yak indicated that dynamic gene expression of developmental germ cells was terminated at late primary spermatocyte (meiotic arrest) and abnormal components of niche cell in pubertal cattle-yak. Further in vitro proliferation and differentially expressed gene (DEG) analysis of specific type of cells revealed that undifferentiated spermatogonia of cattle-yak exhibited defects in viability and proliferation/differentiation potentials.

CONCLUSION

Comparative scRNA-seq and in vitro proliferation analysis of testicular cells indicated that not only meiotic arrest contributed to MHS of cattle-yak. Spermatogenic arrest of cattle-yak may originate from the differentiation stage of undifferentiated spermatogonia and niche cells of cattle-yak may provide an adverse microenvironment for spermatogenesis.

HBXIP blocks myosin-IIA assembly by phosphorylating and interacting with NMHC-IIA in breast cancer metastasis

Tumor metastasis depends on the dynamic balance of the actomyosin cytoskeleton. As a key component of actomyosin filaments, non-muscle myosin-IIA disassembly contributes to tumor cell spreading and migration. However, its regulatory mechanism in tumor migration and invasion is poorly understood. Here, we found that oncoprotein hepatitis B X-interacting protein (HBXIP) blocked the myosin-IIA assemble state promoting breast cancer cell migration. Mechanistically, mass spectrometry analysis, co-immunoprecipitation assay and GST-pull down assay proved that HBXIP directly interacted with the assembly-competent domain (ACD) of non-muscle heavy chain myosin-IIA (NMHC-IIA). The interaction was enhanced by NMHC-IIA S1916 phosphorylation via HBXIP-recruited protein kinase PKCβII. Moreover, HBXIP induced the transcription of PRKCB, encoding PKCβII, by coactivating Sp1, and triggered PKCβII kinase activity. Interestingly, RNA sequencing and mouse metastasis model indicated that the anti-hyperlipidemic drug bezafibrate (BZF) suppressed breast cancer metastasis via inhibiting PKCβII-mediated NMHC-IIA phosphorylation in vitro and in vivo. We reveal a novel mechanism by which HBXIP promotes myosin-IIA disassembly via interacting and phosphorylating NMHC-IIA, and BZF can serve as an effective anti-metastatic drug in breast cancer.

H3K36me2 methyltransferase NSD2 orchestrates epigenetic reprogramming during spermatogenesis

Spermatogenesis is precisely controlled by sophisticated gene expression programs and is driven by epigenetic reprogramming, including histone modification alterations and histone-to-protamine transition. Nuclear receptor binding SET domain protein 2 (Nsd2) is the predominant histone methyltransferase catalyzing H3K36me2 and its role in male germ cell development remains elusive. Here, we report that NSD2 protein is abundant in spermatogenic cells. Conditional loss of Nsd2 in postnatal germ cells impaired fertility owing to apoptosis of spermatocytes and aberrant spermiogenesis. Nsd2 deficiency results in dysregulation of thousands of genes and remarkable reduction of both H3K36me2 and H3K36me3 in spermatogenic cells, with H3K36me2 occupancy correlating positively with expression of germline genes. Nsd2 deficiency leads to H4K16ac elevation in spermatogenic cells, probably through interaction between NSD2 and PSMA8, which regulates acetylated histone degradation. We further reveal that Nsd2 deficiency impairs EP300-induced H4K5/8ac, recognized by BRDT to mediate the eviction of histones. Accordingly, histones are largely retained in Nsd2-deficient spermatozoa. In addition, Nsd2 deficiency enhances expression of protamine genes, leading to increased protamine proteins in Nsd2-deficient spermatozoa. Our findings thus reveal a previously unappreciated role of the Nsd2-dependent chromatin remodeling during spermatogenesis and provide clues to the molecular mechanisms in epigenetic abnormalities impacting male reproductive health.

The Art of Packaging the Sperm Genome: Molecular and Structural Basis of the Histone-To-Protamine Exchange

Male fertility throughout life hinges on the successful production of motile sperm, a developmental process that involves three coordinated transitions: mitosis, meiosis, and spermiogenesis. Germ cells undergo both mitosis and meiosis to generate haploid round spermatids, in which histones bound to the male genome are replaced with small nuclear proteins known as protamines. During this transformation, the chromatin undergoes extensive remodeling to become highly compacted in the sperm head. Despite its central role in spermiogenesis and fertility, we lack a comprehensive understanding of the molecular mechanisms underlying the remodeling process, including which remodelers/chaperones are involved, and whether intermediate chromatin proteins function as discrete steps, or unite simultaneously to drive successful exchange. Furthermore, it remains largely unknown whether more nuanced interactions instructed by protamine post-translational modifications affect chromatin dynamics or gene expression in the early embryo. Here, we bring together past and more recent work to explore these topics and suggest future studies that will elevate our understanding of the molecular basis of the histone-to-protamine exchange and the underlying etiology of idiopathic male infertility.

Mouse Chd4-NURD is required for neonatal spermatogonia survival and normal gonad development

Testis development and sustained germ cell production in adults rely on the establishment and maintenance of spermatogonia stem cells and their proper differentiation into spermatocytes. Chromatin remodeling complexes regulate critical processes during gamete development by restricting or promoting accessibility of DNA repair and gene expression machineries to the chromatin. Here, we investigated the role of Chd4 and Chd3 catalytic subunits of the NURD complex during spermatogenesis. Germ cell-specific deletion of chd4 early in gametogenesis, but not chd3, resulted in arrested early gamete development due to failed cell survival of neonate undifferentiated spermatogonia stem cell population. Candidate assessment revealed that Chd4 controls expression of dmrt1 and its downstream target plzf, both described as prominent regulators of spermatogonia stem cell maintenance. Our results show the requirement of Chd4 in mammalian gametogenesis pointing to functions in gene expression early in the process.

Transcriptional control of human gametogenesis

The pathways of gametogenesis encompass elaborate cellular specialization accompanied by precise partitioning of the genome content in order to produce fully matured spermatozoa and oocytes. Transcription factors are an important class of molecules that function in gametogenesis to regulate intrinsic gene expression programs, play essential roles in specifying (or determining) germ cell fate and assist in guiding full maturation of germ cells and maintenance of their populations. Moreover, in order to reinforce or redirect cell fate in vitro, it is transcription factors that are most frequently induced, over-expressed or activated. Many reviews have focused on the molecular development and genetics of gametogenesis, in vivo and in vitro, in model organisms and in humans, including several recent comprehensive reviews: here, we focus specifically on the role of transcription factors. Recent advances in stem cell biology and multi-omic studies have enabled deeper investigation into the unique transcriptional mechanisms of human reproductive development. Moreover, as methods continually improve, in vitro differentiation of germ cells can provide the platform for robust gain- and loss-of-function genetic analyses. These analyses are delineating unique and shared human germ cell transcriptional network components that, together with somatic lineage specifiers and pluripotency transcription factors, function in transitions from pluripotent stem cells to gametes. This grand theme review offers additional insight into human infertility and reproductive disorders that are linked predominantly to defects in the transcription factor networks and thus may potentially contribute to the development of novel treatments for infertility.

Citrylglutamate synthase deficient male mice are subfertile with impaired histone and transition protein 2 removal in late spermatids

Chromatin remodelling in spermatids is an essential step in spermiogenesis and involves the exchange of most histones by protamines, which drives chromatin condensation in late spermatids. The gene Rimklb encodes a citrylglutamate synthase highly expressed in testes of vertebrates and the increase of its reaction product, β-citrylglutamate, correlates in time with the appearance of spermatids. Here we show that deficiency in a functional Rimklb gene leads to male subfertility, which could be partially rescued by in vitro fertilization. Rimklb-deficient mice are impaired in a late step of spermiogenesis and produce spermatozoa with abnormally shaped heads and nuclei. Sperm chromatin in Rimklb-deficient mice was less condensed and showed impaired histone to protamine exchange and retained transition protein 2. These observations suggest that citrylglutamate synthase, probably via its reaction product β-citrylglutamate, is essential for efficient chromatin remodelling during spermiogenesis and may be a possible candidate gene for male subfertility or infertility in humans.

BAF-L Modulates Histone-to-Protamine Transition during Spermiogenesis

Maturing male germ cells undergo a unique developmental process in spermiogenesis that replaces nucleosomal histones with protamines, the process of which is critical for testicular development and male fertility. The progress of this exchange is regulated by complex mechanisms that are not well understood. Now, with mouse genetic models, we show that barrier-to-autointegration factor-like protein (BAF-L) plays an important role in spermiogenesis and spermatozoal function. BAF-L is a male germ cell marker, whose expression is highly associated with the maturation of male germ cells. The genetic deletion of BAF-L in mice impairs the progress of spermiogenesis and thus male fertility. This effect on male fertility is a consequence of the disturbed homeostasis of histones and protamines in maturing male germ cells, in which the interactions between BAF-L and histones/protamines are implicated. Finally, we show that reduced testicular expression of BAF-L represents a risk factor of human male infertility.

INO80 requires a polycomb subunit to regulate the establishment of poised chromatin in murine spermatocytes

INO80 is the catalytic subunit of the INO80-chromatin remodeling complex that is involved in DNA replication, repair and transcription regulation. Ino80 deficiency in murine spermatocytes (Ino80cKO) results in pachytene arrest of spermatocytes due to incomplete synapsis and aberrant DNA double-strand break repair, which leads to apoptosis. RNA-seq on Ino80cKO spermatocytes revealed major changes in transcription, indicating that an aberrant transcription program arises upon INO80 depletion. In Ino80WT spermatocytes, genome-wide analysis showed that INO80-binding sites were mostly promoter proximal and necessary for the regulation of spermatogenic gene expression, primarily of premeiotic and meiotic genes. Furthermore, most of the genes poised for activity, as well as those genes that are active, shared INO80 binding. In Ino80cKO spermatocytes, most poised genes demonstrated de-repression due to reduced H3K27me3 enrichment and, in turn, showed increased expression levels. INO80 interacts with the core PRC2 complex member SUZ12 and promotes its recruitment. Furthermore, INO80 mediates H2A.Z incorporation at the poised promoters, which was reduced in Ino80cKO spermatocytes. Taken together, INO80 is emerging as a major regulator of the meiotic transcription program by mediating poised chromatin establishment through SUZ12 binding.

Retinoblastoma-E2F Transcription Factor Interplay Is Essential for Testicular Development and Male Fertility

The retinoblastoma (RB) protein family members (pRB, p107 and p130) are key regulators of cell cycle progression, but also play crucial roles in apoptosis, and stem cell self-renewal and differentiation. RB proteins exert their effects through binding to E2F transcription factors, which are essential developmental and physiological regulators of tissue and organ homeostasis. According to the canonical view, phosphorylation of RB results in release of E2Fs and induction of genes needed for progress of the cell cycle. However, there are eight members in the E2F transcription factor family with both activator (E2F1-3a) and repressor (E2F3b-E2F8) roles, highlighting the functional diversity of RB-E2F pathway. In this review article we summarize the data showing that RB-E2F interaction is a key cell-autonomous mechanism responsible for establishment and maintenance of lifelong male fertility. We also review the expression pattern of RB proteins and E2F transcription factors in the testis and male germ cells. The available evidence supports that RB and E2F family members are widely and dynamically expressed in the testis, and they are known to have versatile roles during spermatogenesis. Knowledge of the function and significance of RB-E2F interplay for testicular development and spermatogenesis comes primarily from gene knock-out (KO) studies. Several studies conducted in Sertoli cell-specific pRB-KO mice have demonstrated that pRB-mediated inhibition of E2F3 is essential for Sertoli cell functional maturation and cell cycle exit, highlighting that RB-E2F interaction in Sertoli cells is paramount to male fertility. Similarly, ablation of either pRB or E2F1 in the germline results in progressive testicular atrophy due to germline stem cell (GSC) depletion, emphasizing the importance of proper RB-E2F interplay for germline maintenance and lifelong sperm production. In summary, while balanced RB-E2F interplay is essential for cell-autonomous maintenance of GSCs and, the pRB-E2F3 system in Sertoli cells is critical for providing GSC niche thus laying the basis for spermatogenesis.

Sentinels of chromatin: chromodomain helicase DNA-binding proteins in development and disease

Chromatin is highly dynamic, undergoing continuous global changes in its structure and type of histone and DNA modifications governed by processes such as transcription, repair, replication, and recombination. Members of the chromodomain helicase DNA-binding (CHD) family of enzymes are ATP-dependent chromatin remodelers that are intimately involved in the regulation of chromatin dynamics, altering nucleosomal structure and DNA accessibility. Genetic studies in yeast, fruit flies, zebrafish, and mice underscore essential roles of CHD enzymes in regulating cellular fate and identity, as well as proper embryonic development. With the advent of next-generation sequencing, evidence is emerging that these enzymes are subjected to frequent DNA copy number alterations or mutations and show aberrant expression in malignancies and other human diseases. As such, they might prove to be valuable biomarkers or targets for therapeutic intervention.

PHF7 Modulates BRDT Stability and Histone-to-Protamine Exchange during Spermiogenesis

Spermatogenesis is a complex process of sperm generation, including mitosis, meiosis, and spermiogenesis. During spermiogenesis, histones in post-meiotic spermatids are removed from chromatin and replaced by protamines. Although histone-to-protamine exchange is important for sperm nuclear condensation, the underlying regulatory mechanism is still poorly understood. Here, we identify PHD finger protein 7 (PHF7) as an E3 ubiquitin ligase for histone H3K14 in post-meiotic spermatids. Generation of Phf7-deficient mice and Phf7 C160A knockin mice with impaired E3 ubiquitin ligase activity reveals defects in histone-to-protamine exchange caused by dysregulation of histone removal factor Bromodomain, testis-specific (BRDT) in early condensing spermatids. Surprisingly, E3 ubiquitin ligase activity of PHF7 on histone ubiquitination leads to stabilization of BRDT by attenuating ubiquitination of BRDT. Collectively, our findings identify PHF7 as a critical factor for sperm chromatin condensation and contribute to mechanistic understanding of fundamental phenomenon of histone-to-protamine exchange and potential for drug development for the male reproduction system.

Infertility network and hub genes for nonobstructive azoospermia utilizing integrative analysis

Non-obstructive azoospermia (NOA) is the most severe form of male infertility owing to the absence of sperm during ejaculation as a result of failed spermatogenesis. The molecular mechanisms of NOA have not been well studied. Here, we revealed the dysregulated differentially expressed genes in NOA and related signaling pathways or biological processes. Cluster features of biological processes include spermatogenesis, fertilization, cilium movement, penetration of zona pellucida, sperm chromatin condensation, and being significantly enriched metabolic pathways in proximal tubule bicarbonate reclamation, aldosterone synthesis and secretion, glycolysis and glycogenesis pathways in NOA using Gene Ontology analysis and pathway enrichment analysis. The NOA gene co-expression network was constructed by weighted gene co-expression network analysis to identify the hub genes (CHD5 and SPTBN2). In addition, we used another Gene Expression Omnibus dataset (GSE45887) to validate these hub genes. Furthermore, we used the Seurat package to classify testicular tissue cells from NOA patients and to characterize the differential expression of hub genes in different cell types from different adult males based on the scRNA-seq dataset (GSE106487). These results provide new insights into the pathogenesis of NOA. Of particular note, CHD5 and SPTBN2 may be potential biomarkers for the diagnosis and treatment of NOA.

Identification of Potential Genes in Pathogenesis and Diagnostic Value Analysis of Partial Androgen Insensitivity Syndrome Using Bioinformatics Analysis

BACKGROUND

Androgen insensitivity syndrome (AIS) is a rare X-linked genetic disease and one of the causes of 46,XY disorder of sexual development. The unstraightforward diagnosis of AIS and the gender assignment dilemma still make a plague for this disorder due to the overlapping clinical phenotypes.

METHODS

Peripheral blood mononuclear cells (PBMCs) of partial AIS (PAIS) patients and healthy controls were separated, and RNA-seq was performed to investigate transcriptome variance. Then, tissue-specific gene expression, functional enrichment, and protein-protein interaction (PPI) network analyses were performed; and the key modules were identified. Finally, the RNA expression of differentially expressed genes (DEGs) of interest was validated by quantitative real-time PCR (qRT-PCR).

RESULTS

In our dataset, a total of 725 DEGs were captured, with functionally enriched reproduction and immune-related pathways and Gene Ontology (GO) functions. The most highly specific systems centered on hematologic/immune and reproductive/endocrine systems. We finally filtered out CCR1, PPBP, PF4, CLU, KMT2D, GP6, and SPARC by the key gene clusters of the PPI network and manual screening of tissue-specific gene expression. These genes provide novel insight into the pathogenesis of AIS in the immune system or metabolism and bring forward possible molecular markers for clinical screening. The qRT-PCR results showed a consistent trend in the expression levels of related genes between PAIS patients and healthy controls.

CONCLUSION

The present study sheds light on the molecular mechanisms underlying the pathogenesis and progression of AIS, providing potential targets for diagnosis and future investigation.

CFAP43-mediated intra-manchette transport is required for sperm head shaping and flagella formation

Mutation in CFAP43 leads to severe asthenozoospermia and multiple morphological abnormalities of the sperm flagellum (MMAF) in both human and mouse. Previous studies have shown that disruption of intra-manchette transport (IMT) caused failure of flagellum assembly and sperm head shaping. In a previous study, therefore, we postulated that disruption of IMT may contribute to the failure of sperm flagellum formation and result in MMAF, however the mechanisms underlying these defects are still poorly understood. Cfap43-deficient mice were studied here to reveal the cellular mechanisms of abnormal sperm head morphology and MMAF. Depletion of Cfap43 led to abnormal spermiogenesis and caused MMAF, sperm head abnormality and oligozoospermia. Furthermore, both abnormal manchette and disorganized ectoplasmic specialization (ES) could be observed at the elongated spermatids in Cfap43-deficient mice. Therefore, our findings demonstrated that, in mice, CFAP43-mediated IMT is essential for sperm head shaping and sperm flagellum formation.

Whole-exome sequencing of a large Chinese azoospermia and severe oligospermia cohort identifies novel infertility causative variants and genes

Rare coding variants have been proven to be one of the significant factors contributing to spermatogenic failure in patients with non-obstructive azoospermia (NOA) and severe oligospermia (SO). To delineate the molecular characteristics of idiopathic NOA and SO, we performed whole-exome sequencing of 314 unrelated patients of Chinese Han origin and verified our findings by comparing to 400 fertile controls. We detected six pathogenic/likely pathogenic variants and four variants of unknown significance, in genes known to cause NOA/SO, and 9 of which had not been earlier reported. Additionally, we identified 20 novel NOA candidate genes affecting 25 patients. Among them, five (BRDT, CHD5, MCM9, MLH3 and ZFX) were considered as strong candidates based on the evidence obtained from murine functional studies and human single-cell (sc)RNA-sequencing data. These genetic findings provide insight into the aetiology of human NOA/SO and pave the way for further functional analysis and molecular diagnosis of male infertility.

Gene expression regulation by the Chromodomain helicase DNA-binding protein 9 (CHD9) chromatin remodeler is dispensable for murine development

Chromodomain helicase DNA-binding (CHD) chromatin remodelers regulate transcription and DNA repair. They govern cell-fate decisions during embryonic development and are often deregulated in human pathologies. Chd1-8 show upon germline disruption pronounced, often developmental lethal phenotypes. Here we show that contrary to Chd1-8 disruption, Chd9-/-animals are viable, fertile and display no developmental defects or disease predisposition. Germline deletion of Chd9 only moderately affects gene expression in tissues and derived cells, whereas acute depletion in human cancer cells elicits more robust changes suggesting that CHD9 is a highly context-dependent chromatin regulator that, surprisingly, is dispensable for mouse development.

Insight Into the Ontogeny of GnRH Neurons From Patients Born Without a Nose

CONTEXT

The reproductive axis is controlled by a network of gonadotropin-releasing hormone (GnRH) neurons born in the primitive nose that migrate to the hypothalamus alongside axons of the olfactory system. The observation that congenital anosmia (inability to smell) is often associated with GnRH deficiency in humans led to the prevailing view that GnRH neurons depend on olfactory structures to reach the brain, but this hypothesis has not been confirmed.

OBJECTIVE

The objective of this work is to determine the potential for normal reproductive function in the setting of completely absent internal and external olfactory structures.

METHODS

We conducted comprehensive phenotyping studies in 11 patients with congenital arhinia. These studies were augmented by review of medical records and study questionnaires in another 40 international patients.

RESULTS

All male patients demonstrated clinical and/or biochemical signs of GnRH deficiency, and the 5 men studied in person had no luteinizing hormone (LH) pulses, suggesting absent GnRH activity. The 6 women studied in person also had apulsatile LH profiles, yet 3 had spontaneous breast development and 2 women (studied from afar) had normal breast development and menstrual cycles, suggesting a fully intact reproductive axis. Administration of pulsatile GnRH to 2 GnRH-deficient patients revealed normal pituitary responsiveness but gonadal failure in the male patient.

CONCLUSIONS

Patients with arhinia teach us that the GnRH neuron, a key gatekeeper of the reproductive axis, is associated with but may not depend on olfactory structures for normal migration and function, and more broadly, illustrate the power of extreme human phenotypes in answering fundamental questions about human embryology.

How defective spermatogenesis affects sperm DNA integrity

Spermatogenesis is the essential process to maintain and promote male fertility. It is extraordinarily complex with many regulatory elements and numerous steps. The process involves several cell types, regulatory molecules, repair mechanisms and epigenetic regulators. Evidence has shown that fertility can be negatively impacted by reduced sperm DNA integrity. Sources of sperm DNA damage include replication errors and causes of DNA fragmentation which include abortive apoptosis, defective maturation and oxidative stress. This review outlines the process of spermatogenesis, spermatogonial regulation and sperm differentiation; additionally, DNA damage and currently studied DNA repair mechanisms in spermatozoon are also covered.

The potential impact of tumor suppressor genes on human gametogenesis: a case-control study

PURPOSE

To study the incidence of tumor suppressor gene (TSG) mutations in men and women with impaired gametogenesis.

METHODS

Gene association analyses were performed on blood samples in two distinct patient populations: males with idiopathic male infertility and females with unexplained diminished ovarian reserve (DOR). The male study group consisted of men with idiopathic azoospermia, oligozoospermia, asthenozoospermia, or teratozoospermia. Age-matched controls were men with normal semen analyses. The female study group consisted of women with unexplained DOR with anti-Müllerian hormone levels ≤ 1.1 ng/mL. Controls were age-matched women with normal ovarian reserve (> 1.1 ng/mL).

RESULTS

Fifty-seven male cases (mean age = 38.4; mean sperm count = 15.7 ± 12.1; mean motility = 38.2 ± 24.7) and 37 age-matched controls (mean age = 38.0; mean sperm count = 89.6 ± 37.5; mean motility = 56.2 ± 14.3) were compared. Variants observed in CHD5 were found to be enriched in the study group (p = 0.000107). The incidence of CHD5 mutation c.*3198_*3199insT in the 3'UTR (rs538186680) was significantly higher in cases compared to controls (p = 0.0255). 72 DOR cases (mean age = 38.7; mean AMH = 0.5 ± 0.3; mean FSH = 11.7 ± 12.5) and 48 age-matched controls (mean age = 37.6; mean AMH = 4.1 ± 3.0; mean FSH = 7.1 ± 2.2) were compared. Mutations in CHD5 (c.-140A>C), RB1 (c.1422-18delT, rs70651121), and TP53 (c.376-161A>G, rs75821853) were found at significantly higher frequencies in DOR cases compared to controls (p ≤ 0.05). In addition, 363 variants detected in the DOR patients were not present in the control group.

CONCLUSION

Unexplained impaired gametogenesis in both males and females may be associated with genetic variation in TSGs. TSGs, which play cardinal roles in cell-cycle control, might also be critical for normal spermatogenesis and oogenesis. If validated in larger prospective studies, it is possible that TSGs provide an etiological basis for some patients with impaired gametogenesis.

The arginine methyltransferase CARM1 represses p300•ACT•CREMτ activity and is required for spermiogenesis

CARM1 is a protein arginine methyltransferase (PRMT) that has been firmly implicated in transcriptional regulation. However, the molecular mechanisms by which CARM1 orchestrates transcriptional regulation are not fully understood, especially in a tissue-specific context. We found that Carm1 is highly expressed in the mouse testis and localizes to the nucleus in spermatids, suggesting an important role for Carm1 in spermiogenesis. Using a germline-specific conditional Carm1 knockout mouse model, we found that it is essential for the late stages of haploid germ cell development. Loss of Carm1 led to a low sperm count and deformed sperm heads that can be attributed to defective elongation of round spermatids. RNA-seq analysis of Carm1-null spermatids revealed that the deregulated genes fell into similar categories as those impacted by p300-loss, thus providing a link between Carm1 and p300. Importantly, p300 has long been known to be a major Carm1 substrate. We found that CREMτ, a key testis-specific transcription factor, associates with p300 through its activator, ACT, and that this interaction is negatively regulated by the methylation of p300 by Carm1. Thus, high nuclear Carm1 levels negatively impact the p300•ACT•CREMτ axis during late stages of spermiogenesis.

Mammalian SWI/SNF collaborates with a polycomb-associated protein to regulate male germline transcription in the mouse

A deficiency in BRG1, the catalytic subunit of the SWI/SNF chromatin remodeling complex, results in a meiotic arrest during spermatogenesis. Here, we explore the causative mechanisms. BRG1 is preferentially enriched at active promoters of genes essential for spermatogonial pluripotency and meiosis. In contrast, BRG1 is also associated with the repression of somatic genes. Chromatin accessibility at these target promoters is dependent upon BRG1. These results favor a model in which BRG1 coordinates spermatogenic transcription to ensure meiotic progression. In spermatocytes, BRG1 interacts with SCML2, a testis-specific PRC1 factor that is associated with the repression of somatic genes. We present evidence to suggest that BRG1 and SCML2 concordantly regulate genes during meiosis. Furthermore, BRG1 is required for the proper localization of SCML2 and its associated deubiquitylase, USP7, to the sex chromosomes during pachynema. SCML2-associated mono-ubiquitylation of histone H2A lysine 119 (H2AK119ub1) and acetylation of histone lysine 27 (H3K27ac) are elevated in Brg1cKO testes. Coincidentally, the PRC1 ubiquitin ligase RNF2 is activated while a histone H2A/H2B deubiquitylase USP3 is repressed. Thus, BRG1 impacts the male epigenome by influencing the localization and expression of epigenetic modifiers. This mechanism highlights a novel paradigm of cooperativity between SWI/SNF and PRC1.

Genetic Factors Affecting Sperm Chromatin Structure

Spermatozoa genome has unique features that make it a fascinating field of investigation: first, because, with oocyte genome, it can be transmitted generation after generation; second, because of genetic shuffling during meiosis, each spermatozoon is virtually unique in terms of genetic content, with consequences for species evolution; and finally, because its chromatin organization is very different from that of somatic cells or oocytes, as it is not based on nucleosomes but on nucleoprotamines which confer a higher order of packaging. Histone-to-protamine transition involves many actors, such as regulators of spermatid gene expression, components of the nuclear envelop, histone-modifying enzymes and readers, chaperones, histone variants, transition proteins, protamines, and certainly many more to be discovered.In this book chapter, we will present what is currently known about sperm chromatin structure and how it is established during spermiogenesis, with the aim to list the genetic factors that regulate its organization.

The evolution and patterning of male gametophyte development

The reproductive adaptations of land plants have played a key role in their terrestrial colonization and radiation. This encompasses mechanisms used for the production, dispersal and union of gametes to support sexual reproduction. The production of small motile male gametes and larger immotile female gametes (oogamy) in specialized multicellular gametangia evolved in the charophyte algae, the closest extant relatives of land plants. Reliance on water and motile male gametes for sexual reproduction was retained by bryophytes and basal vascular plants, but was overcome in seed plants by the dispersal of pollen and the guided delivery of non-motile sperm to the female gametes. Here we discuss the evolutionary history of male gametogenesis in streptophytes (green plants) and the underlying developmental biology, including recent advances in bryophyte and angiosperm models. We conclude with a perspective on research trends that promise to deliver a deeper understanding of the evolutionary and developmental mechanisms of male gametogenesis in plants.

Chromatin-mediated translational control is essential for neural cell fate specification

Neural cell fate specification is a multistep process in which stem cells undergo sequential changes in states, giving rise to particular lineages such as neurons and astrocytes. This process is accompanied by dynamic changes of chromatin and in transcription, thereby orchestrating lineage-specific gene expression programs. A pressing question is how these events are interconnected to sculpt cell fate. We show that altered chromatin due to loss of the chromatin remodeler Chd5 causes neural stem cell activation to occur ahead of time. This premature activation is accompanied by transcriptional derepression of ribosomal subunits, enhanced ribosome biogenesis, and increased translation. These untimely events deregulate cell fate decisions, culminating in the generation of excessive numbers of astrocytes at the expense of neurons. By monitoring the proneural factor Mash1, we further show that translational control is crucial for appropriate execution of cell fate specification, thereby providing new insight into the interplay between transcription and translation at the initial stages of neurogenesis.

Deficient LRRC8A-dependent volume-regulated anion channel activity is associated with male infertility in mice

Ion channel-controlled cell volume regulation is of fundamental significance to the physiological function of sperm. In addition to volume regulation, LRRC8A-dependent volume-regulated anion channel (VRAC) activity is involved in cell cycle progression, insulin signaling, and cisplatin resistance. Nevertheless, the contribution of LRRC8A and its dependent VRAC activity in the germ cell lineage remain unknown. By utilizing a spontaneous Lrrc8a mouse mutation (c.1325delTG, p.F443*) and genetically engineered mouse models, we demonstrate that LRRC8A-dependent VRAC activity is essential for male germ cell development and fertility. Lrrc8a-null male germ cells undergo progressive degeneration independent of the apoptotic pathway during postnatal testicular development. Lrrc8a-deficient mouse sperm exhibit multiple morphological abnormalities of the flagella (MMAF), a feature commonly observed in the sperm of infertile human patients. Importantly, we identified a human patient with a rare LRRC8A hypomorphic mutation (c.1634G>A, p.Arg545His) possibly linked to Sertoli cell-only syndrome (SCOS), a male sterility disorder characterized by the loss of germ cells. Thus, LRRC8A is a critical factor required for germ cell development and volume regulation in the mouse, and it might serve as a novel diagnostic and therapeutic target for SCOS patients.

Identification of a complex population of chromatin-associated proteins in the European sea bass (Dicentrarchus labrax) sperm

A very common conception about the function of the spermatozoon is that its unique role is to transmit the paternal genome to the next generation. Most of the sperm genome is known to be condensed in many species by protamines, which are small and extremely positively charged proteins (50-70% arginine) with the functions of streamlining the sperm cell and protecting its DNA. However, more recently, it has been shown in mammals that 2-10% of its mature sperm chromatin is also associated to a complex population of histones and chromatin-associated proteins differentially distributed in the genome. These proteins are transferred to the oocyte upon fertilization and may be involved in the epigenetic marking of the paternal genome. However, little information is so far available on the additional potential sperm chromatin proteins present in other protamine-containing non-mammalian vertebrates detected through high-throughput mass spectrometry. Thus, we started the present work with the goal of characterizing the mature sperm proteome of the European sea bass, with a particular focus on the sperm chromatin, chosen as a representative of non-mammalian vertebrate protamine-containing species. Proteins were isolated by acidic extraction from purified sperm cells and from purified sperm nuclei, digested with trypsin, and subsequently the peptides were separated using liquid chromatography and identified through tandem mass spectrometry. A total of 296 proteins were identified. Of interest, the presence of 94 histones and other chromatin-associated proteins was detected, in addition to the protamines. These results provide phylogenetically strategic information, indicating that the coexistence of histones, additional chromatin proteins, and protamines in sperm is not exclusive of mammals, but is also present in other protamine-containing vertebrates. Thus, it indicates that the epigenetic marking of the sperm chromatin, first demonstrated in mammals, could be more fundamental and conserved than previously thought. Abbreviations: AU-PAGE: acetic acid-urea polyacrylamide gel electrophoresis; CPC: chromosomal passenger complex; DTT: dithiothreitol; EGA: embryonic genome activation; FDR: false discovery rate; GO: Gene Ontology; IAA: iodoacetamide; LC: liquid chromatography; LC-MS/MS: liquid chromatography coupled to tandem mass spectrometry; MS: mass spectrometry; MS/MS: tandem mass spectrometry; MW: molecular weight; PAGE: polyacrylamide gel electrophoresis; PBS: phosphate buffered saline; SDS: sodium dodecyl sulfate; SDS-PAGE: sodium dodecyl sulfate polyacrylamide gel electrophoresis; TCA: trichloroacetic acid.

A Decade of Exploring the Mammalian Sperm Epigenome: Paternal Epigenetic and Transgenerational Inheritance

The past decade has seen a tremendous increase in interest and progress in the field of sperm epigenetics. Studies have shown that chromatin regulation during male germline development is multiple and complex, and that the spermatozoon possesses a unique epigenome. Its DNA methylation profile, DNA-associated proteins, nucleo-protamine distribution pattern and non-coding RNA set up a unique epigenetic landscape which is delivered, along with its haploid genome, to the oocyte upon fertilization, and therefore can contribute to embryogenesis and to the offspring health. An emerging body of compelling data demonstrates that environmental exposures and paternal lifestyle can change the sperm epigenome and, consequently, may affect both the embryonic developmental program and the health of future generations. This short review will attempt to provide an overview of what is currently known about sperm epigenome and the existence of transgenerational epigenetic inheritance of paternally acquired traits that may contribute to the offspring phenotype.

Sperm DNA fragmentation in donors and normozoospermic patients attending for a first spermiogram: Static and dynamic assessment

Static assessment of sperm DNA Fragmentation (SDF at the time of ejaculation or sperm thawing when cryopreserved) and the dynamic assessment of SDF (SDF assessed after T2 hr, T6 hr and T24 hr of sperm thawing) were used to establish cut-off values associated with sperm donors when compared with closely related normozoospermic patients. Cryopreserved samples from donors revealed SDF levels two times lower in comparison with the patients. Donor sperm DNA exhibited a 2.5 times higher longevity when compared with the patients. Static values of SDF after thawing of approximately 11% identify the donors with a 71% of sensitivity and 84% specificity. With respect to the dynamic assessment, SDF increases of 2.3 per hr during the first 2 hr of incubation identify the donors with 70% of sensitivity and 66% of specificity. Creating the Rate of Combined Damage (RCD) defined as the product of SDF-T0 by the increase in the damage registered during the first 2 hr of incubation (r-SDF-T0-2 ), an index of RCD = 22.2 units has an identification capacity of donors with a 78% sensitivity and 77% specificity. Such cut-off values could be used to characterise donors with high chromatin resistance to damage when meeting the above-established criteria.

Role of microRNAs in epigenetic silencing of the CHD5 tumor suppressor gene in neuroblastomas

Neuroblastoma (NB), a tumor of the sympathetic nervous system, is the most common extracranial solid tumor of childhood. We and others have identified distinct patterns of genomic change that underlie diverse clinical behaviors, from spontaneous regression to relentless progression. We first identified CHD5 as a tumor suppressor gene that is frequently deleted in NBs. Mutation of the remaining CHD5 allele is rare in these tumors, yet expression is very low or absent, so expression is likely regulated by epigenetic mechanisms. In order to understand the potential role of miRNA regulation of CHD5 protein expression in NBs, we examined all miRNAs that are predicted to target the 3′-UTR using miRanda, TargetScan and other algorithms. We identified 18 miRNAs that were predicted by 2 or more programs: miR-204, -211, -216b, -17, -19ab, -20ab, -93, -106ab, -130ab, -301ab, -454, -519d, -3666. We then performed transient transfections in two NB cell lines, NLF (MYCN amplified) and SY5Y (MYCN non-amplified), with the reporter plasmid and miRNA mimic, as well as appropriate controls. We found seven miRNAs that significantly downregulated CHD5 expression in NB: miR-211, 17, -93, -20b, -106b, -204, and -3666. Interestingly, MYCN upregulates several of the candidates we identified: miR-17, -93, -106b & -20b. This suggests that miRNAs driven by MYCN and other genes represent a potential epigenetic mechanism to regulate CHD5 expression.

ATP-dependent chromatin remodeling during mammalian development

Precise gene expression ensures proper stem and progenitor cell differentiation, lineage commitment and organogenesis during mammalian development. ATP-dependent chromatin-remodeling complexes utilize the energy from ATP hydrolysis to reorganize chromatin and, hence, regulate gene expression. These complexes contain diverse subunits that together provide a multitude of functions, from early embryogenesis through cell differentiation and development into various adult tissues. Here, we review the functions of chromatin remodelers and their different subunits during mammalian development. We discuss the mechanisms by which chromatin remodelers function and highlight their specificities during mammalian cell differentiation and organogenesis.

Mice lacking the chromodomain helicase DNA-binding 5 chromatin remodeler display autism-like characteristics

Although autism spectrum disorders (ASDs) share a core set of nosological features, they exhibit substantial genetic heterogeneity. A parsimonious hypothesis posits that dysregulated epigenetic mechanisms represent common pathways in the etiology of ASDs. To investigate this hypothesis, we generated a novel mouse model resulting from brain-specific deletion of chromodomain helicase DNA-binding 5 (Chd5), a chromatin remodeling protein known to regulate neuronal differentiation and a member of a gene family strongly implicated in ASDs. RNA sequencing of Chd5-/- mouse forebrain tissue revealed a preponderance of changes in expression of genes important in cellular development and signaling, sociocommunicative behavior and ASDs. Pyramidal neurons cultured from Chd5-/- cortex displayed alterations in dendritic morphology. Paralleling ASD nosology, Chd5-/- mice exhibited abnormal sociocommunicative behavior and a strong preference for familiarity. Chd5-/- mice further showed deficits in responding to the distress of a conspecific, a mouse homolog of empathy. Thus, dysregulated chromatin remodeling produces a pattern of transcriptional, neuronal and behavioral effects consistent with the presentation of ASDs.

SLY regulates genes involved in chromatin remodeling and interacts with TBL1XR1 during sperm differentiation

Sperm differentiation requires unique transcriptional regulation and chromatin remodeling after meiosis to ensure proper compaction and protection of the paternal genome. Abnormal sperm chromatin remodeling can induce sperm DNA damage, embryo lethality and male infertility, yet, little is known about the factors which regulate this process. Deficiency in Sly, a mouse Y chromosome-encoded gene expressed only in postmeiotic male germ cells, has been shown to result in the deregulation of hundreds of sex chromosome-encoded genes associated with multiple sperm differentiation defects and subsequent male infertility. The underlying mechanism remained, to date, unknown. Here, we show that SLY binds to the promoter of sex chromosome-encoded and autosomal genes highly expressed postmeiotically and involved in chromatin regulation. Specifically, we demonstrate that Sly knockdown directly induces the deregulation of sex chromosome-encoded H2A variants and of the H3K79 methyltransferase DOT1L. The modifications prompted by loss of Sly alter the postmeiotic chromatin structure and ultimately result in abnormal sperm chromatin remodeling with negative consequences on the sperm genome integrity. Altogether our results show that SLY is a regulator of sperm chromatin remodeling. Finally we identified that SMRT/N-CoR repressor complex is involved in gene regulation during sperm differentiation since members of this complex, in particular TBL1XR1, interact with SLY in postmeiotic male germ cells.

TSSK6 is required for γH2AX formation and the histone-to-protamine transition during spermiogenesis

Spermiogenesis includes transcriptional silencing, chromatin condensation and extensive morphological changes as spermatids transform into sperm. Chromatin condensation involves histone hyperacetylation, transitory DNA breaks, histone H2AX (also known as H2AFX) phosphorylation at Ser139 (γH2AX), and replacement of histones by protamines. Previously, we have reported that the spermatid protein kinase TSSK6 is essential for fertility in mice, but its specific role in spermiogenesis is unknown. Here, we show that TSSK6 expression is spatiotemporally coincident with γH2AX formation in the nuclei of developing mouse spermatids. RNA-sequencing analysis demonstrates that genetic ablation of Tssk6 does not impact gene expression or silencing in spermatids. However, loss of TSSK6 blocks γH2AX formation, even though the timing and level of the transient DNA breaks is unaltered. Further, Tssk6-knockout sperm contained increased levels of histones H3 and H4, and protamine 2 precursor and intermediate(s) indicative of a defective histone-to-protamine transition. These results demonstrate that TSSK6 is required for γH2AX formation during spermiogenesis, and also link γH2AX to the histone-to-protamine transition and male fertility.

The Chromodomain Helicase DNA-Binding Chromatin Remodelers: Family Traits that Protect from and Promote Cancer

A plethora of mutations in chromatin regulators in diverse human cancers is emerging, attesting to the pivotal role of chromatin dynamics in tumorigenesis. A recurrent theme is inactivation of the chromodomain helicase DNA-binding (CHD) family of proteins-ATP-dependent chromatin remodelers that govern the cellular machinery's access to DNA, thereby controlling fundamental processes, including transcription, proliferation, and DNA damage repair. This review highlights what is currently known about how genetic and epigenetic perturbation of CHD proteins and the pathways that they regulate set the stage for cancer, providing new insight for designing more effective anti-cancer therapies.