Three-dimensional genome structures of single mammalian sperm [scHi-C]
Ontology highlight
ABSTRACT: The three-dimensional (3D) organization of chromosomes is crucial for packaging a large mammalian genome into a confined nucleus and ensuring proper nuclear functions in somatic cells. However, the packaging of the much more condensed sperm genome is fundamentally different and not as well understood. In this study, we resolved the 3D whole-genome structures of a single mammalian sperm cell using an enhanced chromosome conformation capture assay. The reconstructed genome structures accurately delineate the species-specific nuclear morphologies for both human and mouse sperm. We discovered that sperm genomes are divided into chromosomal territories and A/B compartments, similarly as somatic cells. However, neither human nor mouse sperm chromosomes contain topologically associating domains or chromatin loops. These results suggest that the fine-scale chromosomal organization of mammalian sperm fundamentally differs from that of somatic cells.
Project description:The three-dimensional (3D) organization of chromosomes is crucial for packaging a large mammalian genome into a confined nucleus and ensuring proper nuclear functions in somatic cells. However, the packaging of the much more condensed sperm genome is fundamentally different and not as well understood. In this study, we resolved the 3D whole-genome structures of a single mammalian sperm cell using an enhanced chromosome conformation capture assay. The reconstructed genome structures accurately delineate the species-specific nuclear morphologies for both human and mouse sperm. We discovered that sperm genomes are divided into chromosomal territories and A/B compartments, similarly as somatic cells. However, neither human nor mouse sperm chromosomes contain topologically associating domains or chromatin loops. These results suggest that the fine-scale chromosomal organization of mammalian sperm fundamentally differs from that of somatic cells.
Project description:The three-dimensional (3D) organization of chromosomes is crucial for packaging a large mammalian genome into a confined nucleus and ensuring proper nuclear functions in somatic cells. However, the packaging of the much more condensed sperm genome is fundamentally different and not as well understood. In this study, we resolved the 3D whole-genome structures of a single mammalian sperm cell using an enhanced chromosome conformation capture assay. The reconstructed genome structures accurately delineate the species-specific nuclear morphologies for both human and mouse sperm. We discovered that sperm genomes are divided into chromosomal territories and A/B compartments, similarly as somatic cells. However, neither human nor mouse sperm chromosomes contain topologically associating domains or chromatin loops. These results suggest that the fine-scale chromosomal organization of mammalian sperm fundamentally differs from that of somatic cells.
Project description:Chromatin conformation capture assays, such as 3C and Hi-C, allow for studies of three-dimensional (3D) genome structures in bulk samples through proximity ligation of DNA. However, the difference between cells can only be observed by single-cell measurements that avoid ensemble averaging3, 4,5. To study 3D chromatin organization and dynamics before and after fertilization in flowering plants, we analyzed the 3D genomes of rice egg, sperm, and unicellular zygote as well as shoot cells. We show that chromatin architectures of rice egg and sperm are comparable to that of somatic cells and are reorganized after fertilization in unicellular zygote. The rice single cell 3D genomes display specific features of chromosome compartments and configuration of telomeres/centromeres compared to those shown in mammalian single cells. Active and silent chromatin domains gather to form multiple foci in the nuclear space. Notably, the 3D genomes of egg, unicellular zygote, and shoot cells contain a compact silent center (CSC), which is absent in sperm. CSC is dynamically reorganized after fertilization and is likely to be involved in gene regulation related to zygotic genome activation (ZGA). Our results reveal specific 3D genome features of plant gametes and unicellular zygote and provide a spatial chromatin basis for ZGA and gene expression in plant.
Project description:Anticancer drug therapy generally elicits the drug tolerance after long-term treatment. Recent studies suggested that 3D chromatin structures of cancer cells were intimately linked to drug resistance. However, 3D chromatin structures in drug-tolerant cancer cells at single-cell resolution haven’t been elucidated. Here we performed single-cell Hi-C (scHi-C) analysis to examine the 3D chromatin structures in three stages of breast cancer cells.
Project description:Genetic variation and 3D chromatin structure have major roles in gene regulation. Structural differences between genotypically different chromosomes and their effects on gene expression remain ill understood, due to challenges in mapping 3D genome structure with allele-specific resolution. Here, we applied Genome Architecture Mapping (GAM) to a hybrid mouse embryonic stem cell (ESC) line with high SNP density. Given the high efficiency of GAM in haplotype phasing, we could resolve allele-specific 3D genome structures with high sensitivity. We discovered extensive genotype-specific folding of chromosomes in compartments, topologically associating domains (TADs), long-range enhancer-promoter contacts and CTCF loops, often coinciding with allele-specific gene expression in association with Polycomb repression. We show that histone genes are expressed with allelic imbalance in ESCs, and involved in allele-specific chromatin contacts marked by H3K27me3. Functional analysis through conditional Ezh2- or Ring1b-knockdown shows a role for Polycomb repression in tuning histone protein levels. Our work reveals that the homologous chromosomes have highly distinct 3D folding structures, and their intricate relationships with gene-specific mechanisms of allelic expression imbalance.
Project description:Transposable elements (TEs) are major contributors of genetic material in mammalian genomes. These often include binding sites for architectural proteins, including the multifarious master protein, CTCF, which shapes the 3D genome by creating loops, domains, compartment borders and RNA-DNA interactions, all of which play a role in the compact packaging of DNA and have the potential to facilitate regulatory function. In this study, we explore the widespread contribution of TEs to mammalian 3D genomes by quantifying the extent to which they give rise to loops and domain border differences across various cell types and species using several 3D genome mapping technologies. We show that specific (sub-)families of TEs have contributed to lineage-specific 3D chromatin structures across mammalian species. In many cases, these loops may facilitate interaction between distant cis-regulatory elements and target genes, and domains may segregate chromatin state to impact gene expression in a lineage-specific manner. An experimental validation of our analytical findings using CRISPR-Cas9 to delete a candidate TE resulted in disruption of species-specific 3D chromatin structure. Taken together, we comprehensively quantify and selectively validate our finding that TEs contribute to 3D genome organization and may, in some cases, impact gene regulation during the course of mammalian evolution.
Project description:Vertebrate sperm genome differs from somatic cells and undergoes dramatic transformation after fertilization. However, the functional implications of the sperm genome structures have not been fully investigated. Here we show, in the sperms of Xenopus tropicalis, tens of genomic regions harbor multi-megabases, super-sized clustered loops (SSCLs) whose anchors are enriched with Helitrons, the only group of rolling-circle transposons. SSCL anchors are inaccessible and absent of active histone modifications, implying that SSCLs are repressive in nature. Moreover, genes associated with SSCL anchors express late during development, suggesting 3D structure in sperm may associate with gene expression control during embryo development. The absence of CTCF and RNAPII at SSCL anchors argues against CTCF-mediated or transcription-related looping for the SSCLs establishment. Furthermore, our molecular simulation excludes looping and supports a phase separation model through which SSCLs may form. Taken together, our work reveals a previously undiscovered, repressive 3D structure in sperm that may mediate intergenerational gene regulation.
Project description:Vertebrate sperm genome differs from somatic cells and undergoes dramatic transformation after fertilization. However, the functional implications of the sperm genome structures have not been fully investigated. Here we show, in the sperms of Xenopus tropicalis, tens of genomic regions harbor multi-megabases, super-sized clustered loops (SSCLs) whose anchors are enriched with Helitrons, the only group of rolling-circle transposons. SSCL anchors are inaccessible and absent of active histone modifications, implying that SSCLs are repressive in nature. Moreover, genes associated with SSCL anchors express late during development, suggesting 3D structure in sperm may associate with gene expression control during embryo development. The absence of CTCF and RNAPII at SSCL anchors argues against CTCF-mediated or transcription-related looping for the SSCLs establishment. Furthermore, our molecular simulation excludes looping and supports a phase separation model through which SSCLs may form. Taken together, our work reveals a previously undiscovered, repressive 3D structure in sperm that may mediate intergenerational gene regulation.
Project description:Vertebrate sperm genome differs from somatic cells and undergoes dramatic transformation after fertilization. However, the functional implications of the sperm genome structures have not been fully investigated. Here we show, in the sperms of Xenopus tropicalis, tens of genomic regions harbor multi-megabases, super-sized clustered loops (SSCLs) whose anchors are enriched with Helitrons, the only group of rolling-circle transposons. SSCL anchors are inaccessible and absent of active histone modifications, implying that SSCLs are repressive in nature. Moreover, genes associated with SSCL anchors express late during development, suggesting 3D structure in sperm may associate with gene expression control during embryo development. The absence of CTCF and RNAPII at SSCL anchors argues against CTCF-mediated or transcription-related looping for the SSCLs establishment. Furthermore, our molecular simulation excludes looping and supports a phase separation model through which SSCLs may form. Taken together, our work reveals a previously undiscovered, repressive 3D structure in sperm that may mediate intergenerational gene regulation.