Chromatin remodelers are ATP-hydrolyzing machines specialized to restructure, mobilize or eject nucleosomes, allowing regulated exposure of DNA in chromatin. Recently, remodelers have been analyzed ...using single-molecule techniques in real time, revealing them to be complex DNA-pumping machines. The results both support and challenge aspects of current models of remodeling, supporting the idea that the remodeler translocates or pumps DNA loops into and around the nucleosome, while also challenging earlier concepts about loop formation, the character of the loop and how it propagates. Several complex behaviors were observed, such as reverse translocation and long translocation bursts of the remodeler, without appreciable DNA twist. This review presents and discusses revised models for nucleosome sliding and ejection that integrate this new information with the earlier biochemical studies.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Because nucleosomes are widely replaced by protamine in mature human sperm, the epigenetic contributions of sperm chromatin to embryo development have been considered highly limited. Here we show ...that the retained nucleosomes are significantly enriched at loci of developmental importance, including imprinted gene clusters, microRNA clusters, HOX gene clusters, and the promoters of stand-alone developmental transcription and signalling factors. Notably, histone modifications localize to particular developmental loci. Dimethylated lysine 4 on histone H3 (H3K4me2) is enriched at certain developmental promoters, whereas large blocks of H3K4me3 localize to a subset of developmental promoters, regions in HOX clusters, certain noncoding RNAs, and generally to paternally expressed imprinted loci, but not paternally repressed loci. Notably, trimethylated H3K27 (H3K27me3) is significantly enriched at developmental promoters that are repressed in early embryos, including many bivalent (H3K4me3/H3K27me3) promoters in embryonic stem cells. Furthermore, developmental promoters are generally DNA hypomethylated in sperm, but acquire methylation during differentiation. Taken together, epigenetic marking in sperm is extensive, and correlated with developmental regulators.
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Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Objective To evaluate whether male fertility status and/or embryo quality during in vitro fertilization (IVF) therapy can be predicted based on genomewide sperm deoxyribonucleic acid (DNA) ...methylation patterns. Design Retrospective cohort study. Setting University-based fertility center. Patient(s) Participants were 127 men undergoing IVF treatment (where any major female factor cause of infertility had been ruled out), and 54 normozoospermic, fertile men. The IVF patients were stratified into 2 groups: patients who had generally good embryogenesis and a positive pregnancy (n = 55), and patients with generally poor embryogenesis (n = 72; 42 positive and 30 negative pregnancies) after IVF. Intervention(s) Genomewide sperm DNA methylation analysis was performed to measure methylation at >485,000 sites across the genome. Main Outcome Measure(s) A comparison was made of DNA methylation patterns of IVF patients vs. normozoospermic, fertile men. Result(s) Predictive models proved to be highly accurate in classifying male fertility status (fertile or infertile), with 82% sensitivity, and 99% positive predictive value. Hierarchic clustering identified clusters enriched for IVF patient samples and for poor-quality–embryo samples. Models built to identify samples within these groups, from neat samples, achieved positive predictive value ≥94% while identifying >one fifth of all IVF patient and poor-quality–embryo samples in each case. Using density gradient prepared samples, the same approach recovered 46% of poor-quality–embryo samples with no false positives. Conclusion(s) Sperm DNA methylation patterns differ significantly and consistently for infertile vs. fertile, normozoospermic men. In addition, DNA methylation patterns may be predictive of embryo quality during IVF.
The RSC complex remodels chromatin structure and regulates gene transcription. We used cryo-electron microscopy to determine the structure of yeast RSC bound to the nucleosome. RSC is delineated into ...the adenosine triphosphatase motor, the actin-related protein module, and the substrate recruitment module (SRM). RSC binds the nucleosome mainly through the motor, with the auxiliary subunit Sfh1 engaging the H2A-H2B acidic patch to enable nucleosome ejection. SRM is organized into three substrate-binding lobes poised to bind their respective nucleosomal epitopes. The relative orientations of the SRM and the motor on the nucleosome explain the directionality of DNA translocation and promoter nucleosome repositioning by RSC. Our findings shed light on RSC assembly and functionality, and they provide a framework to understand the mammalian homologs BAF/PBAF and the Sfh1 ortholog INI1/BAF47, which are frequently mutated in cancers.
The RSC chromatin remodeler slides and ejects nucleosomes, utilizing a catalytic subunit (Sth1) with DNA translocation activity, which can pump DNA around the nucleosome. A central question is ...whether and how DNA translocation is regulated to achieve sliding versus ejection. Here, we report the regulation of DNA translocation efficiency by two domains residing on Sth1 (Post-HSA and Protrusion 1) and by actin-related proteins (ARPs) that bind Sth1. ARPs facilitated sliding and ejection by improving “coupling”—the amount of DNA translocation by Sth1 relative to ATP hydrolysis. We also identified and characterized Protrusion 1 mutations that promote “coupling,” and Post-HSA mutations that improve ATP hydrolysis; notably, the strongest mutations conferred efficient nucleosome ejection without ARPs. Taken together, sliding-to-ejection involves a continuum of DNA translocation efficiency, consistent with higher magnitudes of ATPase and coupling activities (involving ARPs and Sth1 domains), enabling the simultaneous rupture of multiple histone-DNA contacts facilitating ejection.
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•Actin-related proteins and the P1 domain regulate Sth1 DNA translocation efficiency•The Post-HSA domain regulates Sth1 ATPase activity and DNA translocation speed•A blend of moderate-to-high ATPase activity and efficiency enable nucleosome ejection•Strong upregulation of DNA translocation confers chromatin changes and cell lethality
Clapier et al. establish that the chromatin remodeling complex RSC conducts regulated ATP-dependent DNA translocation. Distinct domains and actin-related proteins separately regulate ATPase activity and DNA translocation efficiency. These parameters combine to tune nucleosome sliding, and at higher levels, to cause the simultaneous rupture of multiple histone-DNA contacts, enabling ejection.
The human testis undergoes dramatic developmental and structural changes during puberty, including proliferation and maturation of somatic niche cells, and the onset of spermatogenesis. To ...characterize this understudied process, we profiled and analyzed single-cell transcriptomes of ∼10,000 testicular cells from four boys spanning puberty and compared them to those of infants and adults. During puberty, undifferentiated spermatogonia sequentially expand and differentiate prior to the initiation of gametogenesis. Notably, we identify a common pre-pubertal progenitor for Leydig and myoid cells and delineate candidate factors controlling pubertal differentiation. Furthermore, pre-pubertal Sertoli cells exhibit two distinct transcriptional states differing in metabolic profiles before converging to an alternative single mature population during puberty. Roles for testosterone in Sertoli cell maturation, antimicrobial peptide secretion, and spermatogonial differentiation are further highlighted through single-cell analysis of testosterone-suppressed transfemale testes. Taken together, our transcriptional atlas of the developing human testis provides multiple insights into developmental changes and key factors accompanying male puberty.
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•A transcriptional single-cell atlas of the developing testes during human puberty•Distinctive phases of germ cell differentiation occur during puberty•Identification of a common progenitor for Leydig and myoid cells prior to puberty•Partial reversal of Sertoli and germ cell maturation upon testosterone suppression
Guo et al. provide a transcriptional cell atlas of the developing human testis during puberty, revealing dramatic developmental changes in both germ and somatic niche cell lineages. Furthermore, germ cells and Sertoli cells from testosterone-suppressed transfemale testes display partial developmental reversal, revealing critical roles for testosterone in maintaining testis maturation.
Objective To evaluate the associations between proper protamine incorporation and DNA methylation at imprinted loci. Design Experimental research study. Setting Research laboratory. Patient(s) Three ...populations were tested—abnormal protamine patients, oligozoospermic patients, and fertile donors. Intervention(s) The CpG methylation patterns were examined at seven imprinted loci sequenced: LIT1, MEST, SNRPN, PLAGL1, PEG3, H19, and IGF2. Main Outcome Measure(s) The DNA methylation patterns were analyzed using bisulfite sequencing. The percentage of methylation was compared between fertile and infertile patients displaying abnormal protamination. Result(s) At six of the seven imprinted genes, the overall DNA methylation patterns at their respective differentially methylated regions were significantly altered in both infertile patient populations. When comparing the severity of methylation alterations among infertile patients, the oligozoospermic patients were significantly affected at mesoderm-specific transcript ( MEST), whereas abnormal protamine patients were affected at KCNQ1, overlapping transcript 1 (LIT1), and at small nuclear ribonucleoprotein polypeptide N (SNRPN). Conclusion(s) Patients with male factor infertility had significantly increased methylation alteration at six of seven imprinted loci tested, with differences in significance observed between oligozoospermic and abnormal protamine patients. This could suggest that risk of transmission of epigenetic alterations may be different with diagnoses. However, this study does not provide a causal link for epigenetic inheritance of imprinting diseases, but does show significant association between male factor infertility and alterations in sperm DNA methylation at imprinted loci.
Human adult spermatogonial stem cells (hSSCs) must balance self-renewal and differentiation. To understand how this is achieved, we profiled DNA methylation and open chromatin (ATAC-seq) in SSEA4+ ...hSSCs, analyzed bulk and single-cell RNA transcriptomes (RNA-seq) in SSEA4+ hSSCs and differentiating c-KIT+ spermatogonia, and performed validation studies via immunofluorescence. First, DNA hypomethylation at embryonic developmental genes supports their epigenetic “poising” in hSSCs for future/embryonic expression, while core pluripotency genes (OCT4 and NANOG) were transcriptionally and epigenetically repressed. Interestingly, open chromatin in hSSCs was strikingly enriched in binding sites for pioneer factors (NFYA/B, DMRT1, and hormone receptors). Remarkably, single-cell RNA-seq clustering analysis identified four cellular/developmental states during hSSC differentiation, involving major transitions in cell-cycle and transcriptional regulators, splicing and signaling factors, and glucose/mitochondria regulators. Overall, our results outline the dynamic chromatin/transcription landscape operating in hSSCs and identify crucial molecular pathways that accompany the transition from quiescence to proliferation and differentiation.
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•Open chromatin in hSSCs correlates with pioneer factors and hormone receptors•hSSC differentiation involves four sequential cellular/developmental states•Key transitions involve the cell cycle, transcription factors, signaling, and metabolism
Cairns and colleagues show that human spermatogonial stem cells (hSSCs) bear unique DNA methylation and open chromatin landscapes, which may enable proper development, niche responsiveness, and “poised” pluripotency. Interestingly, single-cell transcriptome and immunofluorescence analyses reveal four cellular states, spanning from quiescent hSSCs to proliferating, metabolically active, differentiating spermatogonia.
Evidence for active DNA demethylation in vertebrates is accumulating, but the mechanisms and enzymes remain unclear. Using zebrafish embryos we provide evidence for 5-methylcytosine (5-meC) removal ...in vivo via the coupling of a 5-meC deaminase (AID, which converts 5-meC to thymine) and a G:T mismatch-specific thymine glycosylase (Mbd4). The injection of methylated DNA into embryos induced a potent DNA demethylation activity, which was attenuated by depletion of AID or the non enzymatic factor Gadd45. Remarkably, overexpression of the deaminase/glycosylase pair AID/Mbd4 in vivo caused demethylation of the bulk genome and injected methylated DNA fragments, likely involving a G:T intermediate. Furthermore, AID or Mbd4 knockdown caused the remethylation of a set of common genes. Finally, Gadd45 promoted demethylation and enhanced functional interactions between deaminase/glycosylase pairs. Our results provide evidence for a coupled mechanism of 5-meC demethylation, whereby AID deaminates 5-meC, followed by thymine base excision by Mbd4, promoted by Gadd45.
Chromatin remodellers are specialized multi-protein machines that enable access to nucleosomal DNA by altering the structure, composition and positioning of nucleosomes. All remodellers have a ...catalytic ATPase subunit that is similar to known DNA-translocating motor proteins, suggesting DNA translocation as a unifying aspect of their mechanism. Here, we explore the diversity and specialization of chromatin remodellers, discuss how nucleosome modifications regulate remodeller activity and consider a model for the exposure of nucleosomal DNA that involves the use of directional DNA translocation to pump 'DNA waves' around the nucleosome.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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