Project description:The conversion of male germ cell chromatin to a nucleoprotamine structure is fundamental to the life cycle yet the underlying molecular details remain obscure. Here we show that an essential step is the genome-wide incorporation of TH2B, a histone H2B variant of hitherto unknown function. Using mouse models in which TH2B is depleted or C-terminally modified we show that TH2B directs the final transformation of dissociating nucleosomes into protamine-packed structures. Depletion of TH2B induces compensatory mechanisms that permit histone removal by up-regulating H2B and programming nucleosome instability through targeted histone modifications, including lysine crotonylation and arginine methylation. Furthermore, after fertilization, TH2B re-assembles onto the male genome during protamine-to-histone exchange. Thus, TH2B is a unique histone variant, which plays a key role in the histone-to-protamine packing of the male genome and guides genome-wide chromatin transitions that both precede and follow transmission of the male genome to the egg. Examination of TH2B binding on chromatin in meiotic (spermatocytes) and post-meiotic (round spermatids) male germ cells from adult Th2b+/tag mice (TH2B C-terminally fused to three consecutive affinity tags: His, Flag and Ha). Examination of TH2B (wild type) binding on chromatin in male germ cells from adult wt mice.
Project description:The conversion of male germ cell chromatin to a nucleoprotamine structure is fundamental to the life cycle yet the underlying molecular details remain obscure. Here we show that an essential step is the genome-wide incorporation of TH2B, a histone H2B variant of hitherto unknown function. Using mouse models in which TH2B is depleted or C-terminally modified we show that TH2B directs the final transformation of dissociating nucleosomes into protamine-packed structures. Depletion of TH2B induces compensatory mechanisms that permit histone removal by up-regulating H2B and programming nucleosome instability through targeted histone modifications, including lysine crotonylation and arginine methylation. Furthermore, after fertilization, TH2B re-assembles onto the male genome during protamine-to-histone exchange. Thus, TH2B is a unique histone variant, which plays a key role in the histone-to-protamine packing of the male genome and guides genome-wide chromatin transitions that both precede and follow transmission of the male genome to the egg.
Project description:The conversion of male germ cell chromatin to a nucleoprotamine structure is fundamental to the life cycle yet the underlying molecular details remain obscure. Here we show that an essential step is the genome-wide incorporation of TH2B, a histone H2B variant of hitherto unknown function. Using mouse models in which TH2B is depleted or C-terminally modified we show that TH2B directs the final transformation of dissociating nucleosomes into protamine-packed structures. Depletion of TH2B induces compensatory mechanisms that permit histone removal by up-regulating H2B and programming nucleosome instability through targeted histone modifications, including lysine crotonylation and arginine methylation. Furthermore, after fertilization, TH2B re-assembles onto the male genome during protamine-to-histone exchange. Thus, TH2B is a unique histone variant, which plays a key role in the histone-to-protamine packing of the male genome and guides genome-wide chromatin transitions that both precede and follow transmission of the male genome to the egg.
Project description:The conversion of male germ cell chromatin to a nucleoprotamine structure is fundamental to the life cycle yet the underlying molecular details remain obscure. Here we show that an essential step is the genome-wide incorporation of TH2B, a histone H2B variant of hitherto unknown function. Using mouse models in which TH2B is depleted or C-terminally modified we show that TH2B directs the final transformation of dissociating nucleosomes into protamine-packed structures. Depletion of TH2B induces compensatory mechanisms that permit histone removal by up-regulating H2B and programming nucleosome instability through targeted histone modifications, including lysine crotonylation and arginine methylation. Furthermore, after fertilization, TH2B re-assembles onto the male genome during protamine-to-histone exchange. Thus, TH2B is a unique histone variant, which plays a key role in the histone-to-protamine packing of the male genome and guides genome-wide chromatin transitions that both precede and follow transmission of the male genome to the egg. Total RNA were obtained from testes from meiotic (spermatocytes) and post-meiotic (round spermatids) male germ cells from adult wt and Th2b+/tag mice (experiment 1: 6 biological replicates for each condition) and adult wt and th2bkd mice (experiment 2: 5 biological replicates for each condition). In each experiment, 5 or 6 replicates of each genotype and each cell type were used. Th2b+/tag mice expressed TH2B C-terminally fused to three consecutive affinity tags: His, Flag and Ha. Th2bkd mice did not express any TH2B.
Project description:The testis-specific histone variant of H2B, TH2B, is enriched in the oocytes, sperm and early embryos, with levels decreasing as the embryos differentiate into pre-gastrula stages. However, the involvement of TH2B in epigenetic reprogramming in the preimplantation embryos is largely unknown. The current study mapped the genome-wide epigenetics of TH2B in MII oocytes and early embryos using ultra-low-input ChIP-seq (ULI-ChIP). We demonstrate that TH2B deposition varies greatly between gametes; however, following fertilization, TH2B from gametes is swiftly redistributed in 2-cell embryos. A considerable enrichment of TH2B at the transcription start site (TSS) was identified in sperm chromatin compared to that in oocytes. We also found some overlap between the dynamics of the sperm and the 2 cell, which contain genes related to transcription regulation. Additionally, TH2B was enriched at zygotic genome activation (ZGA) genes. H2A.Z and TH2B were associated, as was discovered in the presence of H2AK119ub1. The correct execution of ZGA and other developmental programs, such as timing the expression or repression of particular genes, may involve TH2B along with H2A.Z, and H2AK119ub1, the latter two regulating the aforementioned processes. Also, early embryos had H3K9me3 deposited at TH2B-bound loci, which is a sign of heterochromatin and functions in regulating retrotransposons. In our study, we found that TH2B was enriched in LTRs. Thus, TH2B chromatin in gametes and preimplantation embryos has distinctive properties, as highlighted by our study, and they also present fresh opportunities to investigate the epigenetic dynamics in murine preimplantation embryos.
Project description:In this study, chromatin immunoprecipitated sequencing was done for testis specific histone variants of H2B and H2A, TH2B and TH2A to understand the epigenomics of these retained histones, using murine caudal sperm.Our in silico analysis has attributed a myriad of novel functions to sperm retained TH2B with respect to embryo development and spermatogenesis.Also, based on genomic regions, TH2B was observed to be associated with spindle assembly and various meiosis-specific genes, which is an important finding as TH2A/TH2B DKO mice have been reported to have defective cohesin release.We also observed a degree of evolutionary conservation between the TH2B-DNA linkage across human and mouse.This overlap included genes important for embryogenesis. Most importantly, heterogeneity in the epigenetic landscape of TH2A and TH2B was seen which is intriguing as TH2B and TH2A are well reported to be present in the same nucleosomes to promote open chromatin. Additionally, unlike TH2B, TH2A was enriched on the mitochondrial chromosome. We presume that TH2A is associated with mitochondrial DNA inserted in the nuclear DNA and this observation needs further validation.. A comprehensive analysis of these observations indicates novel functions for the sperm retained TH2B and TH2A.
Project description:Spermatogenesis is the process by which spermatogonial stem cells differentiate into haploid spermatozoa. During this process, multiple testis-specific histone variants are involved in the dynamic chromatin transitions. H2BFWT is a testis-specific H2B variant only found in primates, and several reports showed that single-nucleotide polymorphisms (SNPs) of H2BFWT are associated with male non-obstructive infertility. Different from another testis-specific variant TH2B, H2BFWT is preferentially localized in sub-telomeric regions and the promoter regions of testicular high expression genes during the transition from differentiated spermatogonia to early spermatocytesspermatogenesis. Cryo-EM structural analysis shows that the H2BFWT nucleosome is defined by weakened interactions between H2A-H2BFWT dimer and H4, and between the histone octamer and DNA. WIn addition, we found that the shape of the H2A L1 loops was also changed by the presence of H2BFWT. Furthermore, our structural model shows that H2BFWTH100R, which is one of the SNPs associated with infertility, further destabilizes the nucleosome and increases the nucleosome unwrapping rate by interfering with the interaction with H4K91. Taken together, our results suggest that H2BFWT may be necessary for the regulation of spermatogenesis-related genes transcription in spermatogonia by decreasing RNA polymerase II transcription barriers, and that the H100R mutation overdrives its nucleosome-destabilizing effects which likely explain how it causes infertility.
Project description:Introgressed variants from other species can be an important source of genetic variation because they may arise rapidly, can include multiple mutations on a single haplotype, and have often been pretested by selection in the species of origin. Although introgressed alleles are generally deleterious, several studies have reported introgression as the source of adaptive alleles-including the rodenticide-resistant variant of Vkorc1 that introgressed from Mus spretus into European populations of Mus musculus domesticus. Here, we conducted bidirectional genome scans to characterize introgressed regions into one wild population of M. spretus from Spain and three wild populations of M. m. domesticus from France, Germany, and Iran. Despite the fact that these species show considerable intrinsic postzygotic reproductive isolation, introgression was observed in all individuals, including in the M. musculus reference genome (GRCm38). Mus spretus individuals had a greater proportion of introgression compared with M. m. domesticus, and within M. m. domesticus, the proportion of introgression decreased with geographic distance from the area of sympatry. Introgression was observed on all autosomes for both species, but not on the X-chromosome in M. m. domesticus, consistent with known X-linked hybrid sterility and inviability genes that have been mapped to the M. spretus X-chromosome. Tract lengths were generally short with a few outliers of up to 2.7 Mb. Interestingly, the longest introgressed tracts were in olfactory receptor regions, and introgressed tracts were significantly enriched for olfactory receptor genes in both species, suggesting that introgression may be a source of functional novelty even between species with high barriers to gene flow.