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Dekker, J.

Publications and source records attributed to Dekker, J..

At least 37 records · Page 2Linked to original sources

Protein arginine methyltransferase 5 (Prmt5) localizes to chromatin loop anchors and modulates expression of genes at TAD boundaries during early adipogenesis

Protein arginine methyltransferase 5 (Prmt5) is an essential regulator of embryonic development and adult progenitor cell functions. Prmt5 expression is mis-regulated in many cancers, and the development of Prmt5 inhibitors as cancer therapeutics is an active area of research. Prmt5 functions via effects on gene expression, splicing, DNA repair, and other critical cellular processes. We examined whether Prmt5 functions broadly as a genome-wide regulator of gene transcription and higher-order chromatin interactions during the initial stages of adipogenesis using ChIP-Seq, RNA-seq, and Hi-C using 3T3-L1 cells, a frequently utilized model for adipogenesis. We observed robust genome-wide Prmt5 chromatin-binding at the onset of differentiation. Prmt5 localized to transcriptionally active genomic regions, acting as both a positive and a negative regulator. A subset of Prmt5 binding sites co-localized with mediators of chromatin organization at chromatin loop anchors. Prmt5 knockdown decreased insulation strength at the boundaries of topologically associating domains (TADs) adjacent to sites with Prmt5 and CTCF co-localization. Genes overlapping such weakened TAD boundaries showed transcriptional dysregulation. This study identifies Prmt5 as a broad regulator of gene expression, including regulation of early adipogenic factors, and reveals an unappreciated requirement for Prmt5 in maintaining strong insulation at TAD boundaries and overall chromatin organization.

genomics↗

High number of HPAI H5 Virus Infections and Antibodies in Wild Carnivores in the Netherlands, 2020-2022

In October 2020, a new lineage of clade 2.3.4.4b HPAI virus of the H5 subtype emerged in Europe, resulting in the largest global outbreak of HPAI to date, with unprecedented mortality in wild birds and poultry. The virus appears to have become enzootic in birds, continuously yielding novel HPAI virus variants. The recently increased abundance of infected birds worldwide increases the probability of bird-mammal contact, particularly in wild carnivores. Here, we performed molecular and serological screening of over 500 dead wild carnivores for H5 HPAI virus infection and sequencing of positive materials. We show virological evidence for HPAI H5 virus infection in 0.8%, 1.4% and 9.9% of animals tested in 2020, 2021 and 2022 respectively, with the highest proportion of positives in foxes, polecats and stone martens. We obtained near full genome sequences for seven viruses and detected PB2 amino acid substitutions known to play a role in mammalian adaptation in three of these. Infections were also found in animals without associated neurological signs or mortality. Serological evidence for infection was detected in 20% of the study population. These findings suggest that a higher number of wild carnivores are infected but undetected in current surveillance programs. We recommend increased surveillance in susceptible mammals, irrespective of the presence of neurological signs or encephalitis.

microbiology↗

The search behavior of terrestrial mammals

Animals moving through landscapes need to strike a balance between finding sufficient resources to grow and reproduce while minimizing encounters with predators 1,2. Because encounter rates are determined by the average distance over which directed motion persists 1,3-5, this trade-off should be apparent in individuals movement. Using GPS data from 1,396 individuals across 62 species of terrestrial mammals, we show how predators maintained directed motion ~7 times longer than for similarly-sized prey, revealing how prey species must trade off search efficiency against predator encounter rates. Individual search strategies were also modulated by resource abundance, with prey species forced to risk higher predator encounter rates when resources were scarce. These findings highlight the interplay between encounter rates and resource availability in shaping broad patterns mammalian movement strategies.

ecology↗

Revisiting chromatin packaging in mouse sperm

Mammalian sperm exhibit an unusual and heavily-compacted genomic packaging state. In addition to its role in organizing the compact and hydrodynamic sperm head, it has been proposed that sperm chromatin architecture helps to program gene expression in the early embryo. Scores of genome-wide surveys in sperm have reported patterns of chromatin accessibility, histone localization, histone modification, and chromosome folding. Here, we revisit these studies in light of recent reports that sperm obtained from the mouse epididymis are contaminated with low levels of cell-free chromatin. In the absence of proper sperm lysis we readily recapitulate multiple prominent genome-wide surveys of sperm chromatin, suggesting that these profiles primarily reflect contaminating cell-free chromatin. Removal of cell-free DNA, along with appropriate lysis conditions, are required to reveal a sperm chromatin state distinct from most previous reports. Using ATAC-Seq to explore relatively accessible genomic loci, we identify a landscape of open loci associated with early development and transcriptional control. Histone modification and chromosome folding studies also strongly support the hypothesis that prior studies suffer from contamination, but technical challenges associated with reliably preserving the architecture of the compacted sperm head prevent us from confidently assaying true localization patterns for these epigenetic marks. Together, our studies strongly argue that our knowledge of mammalian chromosome packaging remains largely incomplete, and motivate future efforts to more accurately characterize genome organization in mature sperm.

molecular biology↗

Mitotic chromosomes scale to nucleo-cytoplasmic ratio and cell size in Xenopus

During the rapid and reductive cleavage divisions of early embryogenesis, subcellular structures such as the nucleus and mitotic spindle scale to decreasing cell size. Mitotic chromosomes also decrease in size during development, presumably to coordinately scale with mitotic spindles, but underlying mechanisms are unclear. Here we combine in vivo and in vitro approaches using eggs and embryos from the frog Xenopus laevis to show that mitotic chromosome scaling is mechanistically distinct from other forms of subcellular scaling. We found that mitotic chromosomes scale continuously with cell, spindle and nuclear size in vivo. However, unlike for spindles and nuclei, mitotic chromosome size cannot be re-set by cytoplasmic factors from earlier developmental stages. In vitro, increasing nucleo-cytoplasmic (N/C) ratio is sufficient to recapitulate mitotic chromosome scaling, but not nuclear or spindle scaling, through differential loading of maternal factors during interphase. An additional pathway involving importin scales mitotic chromosomes to cell surface area/volume (SA/V) during metaphase. Finally, single-chromosome immunofluorescence and analysis of Hi-C data suggest that mitotic chromosomes scale through decreased recruitment of condensin I, resulting in major rearrangements of DNA loop architecture to accommodate the same amount of DNA on a shorter axis. Together, our findings demonstrate how mitotic chromosome size is set by spatially and temporally distinct developmental cues in the early embryo.

cell biology↗

Chromosome decompaction and cohesin direct Topoisomerase II activity to establish and maintain an unentangled interphase genome

The topological state of chromosomes determines their mechanical properties, dynamics, and function. Recent work indicated that interphase chromosomes are largely free of entanglements. Here, we use Hi-C, polymer simulations and multi-contact 3C, and propose that, in contrast, mitotic chromosomes are self-entangled. We explore how a mitotic self-entangled state is converted into an unentangled interphase state during mitotic exit. Most mitotic entanglements are removed during anaphase/telophase, with remaining ones removed during early G1, in a Topoisomerase II-dependent process. Polymer models suggest a two-stage disentanglement pathway: first, decondensation of mitotic chromosomes with remaining condensin loops produces entropic forces that bias Topoisomerase II activity towards decatenation. At the second stage, the loops are released, and formation of new entanglements is prevented by lower Topoisomerase II activity, allowing the establishment of unentangled and territorial G1 chromosomes. When mitotic entanglements are not removed, in experiment and models, a normal interphase state cannot be acquired.

genomics↗

Mechanisms of insertions at a DNA double-strand break

Insertions and deletions (indels) are common sources of structural variation, and insertions originating from spontaneous DNA lesions are frequent in cancer. We developed a highly sensitive assay in human cells (Indel-Seq) to monitor rearrangements at the TRIM37 acceptor locus which reports indels stemming from experimentally-induced and spontaneous genome instability. Templated insertions derive from sequences genome-wide and are enriched within 100 kb of donor regions flanking a DSB. Insertions require contact between donor and acceptor loci as well as DNA-PK catalytic activity. Notably, these templated insertions originate from actively transcribed loci, underscoring transcription as a critical source of spontaneous genome instability. Transcription-coupled insertions involve a DNA/RNA hybrid intermediate and are stimulated by DNA end-processing. Using engineered Cas9 breaks, we establish that ssDNA overhangs at the acceptor site greatly stimulate insertions. Indel-Seq revels that insertions are generated via at least three distinct pathways. Our studies indicate that insertions result from movement and subsequent contact between acceptor and donor loci followed invasion or annealing, then by non-homologous end-joining at the acceptor site.

molecular biology↗

Clarifying space use concepts in ecology: range vs. occurrence distributions

Quantifying animal movements is necessary for answering a wide array of research questions in ecology and conservation biology. Consequently, ecologists have made considerable efforts to identify the best way to estimate an animals home range, and many methods of estimating home ranges have arisen over the past half century. Most of these methods fall into two distinct categories of estimators that have only recently been described in statistical detail: those that measure range distributions (methods such as Kernel Density Estimation that quantify the long-run behavior of a movement process that features restricted space use) and those that measure occurrence distributions (methods such as Brownian Bridge Movement Models and the Correlated Random Walk Library that quantify uncertainty in an animal movement path during a specific period of observation). In this paper, we use theory, simulations, and empirical analysis to demonstrate the importance of applying these two classes of space use estimators appropriately and distinctly. Conflating range and occurrence distributions can have serious consequences for ecological inference and conservation practice. For example, in most situations, home-range estimates quantified using occurrence estimators are too small, and this problem is exacerbated by ongoing improvements in tracking technology that enable more frequent and more accurate data on animal movements. We encourage researchers to use range estimators to estimate the area of home ranges and occurrence estimators to answer other questions in movement ecology, such as when and where an animal crosses a linear feature, visits a location of interest, or interacts with other animals. Open Research StatementTracking data on Aepyceros melampus, Beatragus hunteri, Bycanistes bucinator, Cerdocyon thous, Eulemur rufifrons, Glyptemys insculpta, Gyps coprotheres, Madoqua guentheri, Ovis canadensis, Propithecus verreauxi, Sus scrofa, and Ursus arctos are publicly archived in the Dryad repository (Noonan et al. 2018; https://doi.org/10.5061/dryad.v5051j2), as are data from Procapra gutturosa (Fleming et al. 2014a; https://doi.org/10.5061/dryad.45157). Data on Panthera onca were taken from (Morato et al. 2018). Additional data are publicly archived in the Movebank repository under the following identifiers: Canis latrans, 8159699; Canis lupus, 8159399; Chrysocyon brachyurus, 18156143; Felis silvestris, 40386102; Gyps africanus, 2919708; Lepus europaeus, 25727477; Martes pennanti, 2964494; Panthera leo, 220229; Papio cynocephalus, 222027; Syncerus caffer, 1764627; Tapirus terrestris, 443607536; Torgos tracheliotus, 2919708; and Ursus americanus, 8170674.

ecology↗

The little skate genome and the evolutionary emergence of wing-like fin appendages

Skates are cartilaginous fish whose novel body plan features remarkably enlarged wing-like pectoral fins that allow them to thrive in benthic environments. The molecular underpinnings of this unique trait, however, remain elusive. Here we investigate the origin of this phenotypic innovation by developing the little skate Leucoraja erinacea as a genomically enabled model. Analysis of a high-quality chromosome-scale genome sequence for the little skate shows that it preserves many ancestral jawed vertebrate features compared with other sequenced genomes, including numerous ancient microchromosomes. Combining genome comparisons with extensive regulatory datasets in developing fins - gene expression, chromatin occupancy and three-dimensional (3D) conformation - we find skate-specific genomic rearrangements that alter the 3D regulatory landscape of genes involved in the planar cell polarity (PCP) pathway. Functional inhibition of PCP signaling resulted in marked reduction of anterior fin size, confirming this pathway as a major contributor of batoid fin morphology. We also identified a fin-specific enhancer that interacts with 3 HOX genes, consistent with the redeployment of Hox gene expression in anterior pectoral fins, and confirmed the potential of this element to activate transcription in the anterior fin using zebrafish reporter assays. Our findings underscore the central role of genome reorganizations and regulatory variation in the evolution of phenotypes, shedding light on the molecular origin of an enigmatic trait.

evolutionary biology↗

Multi-omics comparison of malignant and normal uveal melanocytes reveals novel molecular features of uveal melanoma.

Uveal Melanoma (UM) is a rare cancer resulting from transformation of melanocytes residing in the uveal tract. Integrative analysis has identified four molecular and clinical subsets in UM. To improve our molecular understanding of UM we performed extensive multi-omics characterization comparing two aggressive UM patient-derived xenograft models with normal choroidal melanocytes, including DNA optical mapping, specific histone modifications, and DNA topology analysis by Hi-C. Our gene expression and cytogenetic analyses suggest that genomic instability is a hallmark of UM. We also identified a recurrent deletion in the BAP1 promoter resulting in loss of expression and associated with high risk of metastases in UM patients. Hi-C revealed chromatin topology changes associated with up-regulation of PRAME, an independent prognostic biomarker in UM and potential therapeutic target. Our findings illustrate how multi-omics approaches can improve the understanding of tumorigenesis and reveals two novel mechanisms of gene expression dysregulation in UM.

genomics↗

Chromosome-level reference genomes for two strains of Caenorhabditis briggsae: an improved platform for comparative genomics

The publication of the Caenorhabditis briggsae reference genome in 2003 enabled the first comparative genomics studies between C. elegans and C. briggsae, shedding light on the evolution of genome content and structure in the Caenorhabditis genus. However, despite being widely used, the currently available C. briggsae reference genome is substantially less complete and structurally accurate than the C. elegans reference genome. Here, we used high-coverage Oxford Nanopore long-read and chromosome conformation capture data to generate chromosomally resolved reference genomes for two C. briggsae strains: QX1410, a new reference strain closely related to the laboratory AF16 strain, and VX34, a highly divergent strain isolated in China. We also sequenced 99 recombinant inbred lines (RILs) generated from reciprocal crosses between QX1410 and VX34 to create a recombination map and identify chromosomal domains. Additionally, we used both short- and long-read RNA sequencing (RNA-seq) data to generate high-quality gene annotations. By comparing these new reference genomes to the current reference, we reveal that hyper-divergent haplotypes cover large portions of the C. briggsae genome, similar to recent reports in C. elegans and C. tropicalis. We also show that the genomes of selfing Caenorhabditis species have undergone more rearrangement than their outcrossing relatives, which has biased previous estimates of rearrangement rate in Caenorhabditis. These new genomes provide a substantially improved platform for comparative genomics in Caenorhabditis and narrow the gap between the quality of genomic resources available for C. elegans and C. briggsae.

genomics↗

ARP2/3- and resection-coupled genome reorganization facilitates translocations

DNA end-resection and nuclear actin-based movements orchestrate clustering of double-strand breaks (DSBs) into homology-directed repair (HDR) domains. Here, we analyze how actin nucleation by ARP2/3 affects damage-dependent and -independent 3D genome reorganization and facilitates pathologic repair. We observe that DNA damage, followed by ARP2/3-dependent establishment of repair domains enhances local chromatin insulation at a set of damage-proximal boundaries and affects compartment organization genome-wide. Nuclear actin polymerization also promotes interactions between DSBs, which in turn facilitates aberrant intra- and inter-chromosomal rearrangements. Notably, BRCA1 deficiency, which decreases end-resection, DSB mobility, and subsequent HDR, nearly abrogates recurrent translocations between AsiSI DSBs. In contrast, loss of functional BRCA1 yields unique translocations genome-wide, reflecting a critical role in preventing spontaneous genome instability and subsequent rearrangements. Our work establishes that the assembly of DSB repair domains is coordinated with multiscale alterations in genome architecture that enable HDR despite increased risk of translocations with pathologic potential.

molecular biology↗

Biochemically distinct cohesin complexes mediate positioned loops between CTCF sites and dynamic loops within chromatin domains

The ring-like cohesin complex mediates sister chromatid cohesion by encircling pairs of sister chromatids. Cohesin also extrudes loops along chromatids. Whether the two activities involve similar mechanisms of DNA engagement is not known. We implemented an experimental approach based on isolated nuclei carrying engineered cleavable RAD21 proteins to precisely control cohesin ring integrity so that its role in chromatin looping could be studied under defined experimental conditions. This approach allowed us to identify cohesin complexes with distinct biochemical, and possibly structural properties, that mediate different sets of chromatin loops. When RAD21 is cleaved and the cohesin ring is opened, cohesin complexes at CTCF sites are released from DNA and loops at these elements are lost. In contrast, cohesin-dependent loops within chromatin domains and that are not anchored at CTCF sites are more resistant to RAD21 cleavage. The results show that the cohesin complex mediates loops in different ways depending on genomic context and suggests that it undergoes structural changes as it dynamically extrudes and encounters CTCF sites.

genomics↗

Loops, TADs, Compartments, and Territories are Elastic and Robust to Dramatic Nuclear Volume Swelling

Layers of genome organization are becoming increasingly better characterized, but less is known about how these structures respond to perturbation or shape changes. Low-salt swelling of isolated chromatin fibers or nuclei has been used for decades to investigate the structural properties of chromatin. But, visible changes in chromatin appearance have not been linked to known building blocks of genome structure or features along the genome sequence. We combine low-salt swelling of isolated nuclei with genome-wide chromosome conformation capture (Hi-C) and imaging approaches to probe the effects of chromatin extension genome-wide. Photoconverted patterns on nuclei during expansion and contraction indicate that global genome structure is preserved after dramatic nuclear volume swelling, suggesting a highly elastic chromosome topology. Hi-C experiments before, during, and after nuclear swelling show changes in average contact probabilities at short length scales, reflecting the extension of the local chromatin fiber. But, surprisingly, during this large increase in nuclear volume, there is a striking maintenance of loops, TADs, active and inactive compartments, and chromosome territories. Subtle differences after expansion are observed, suggesting that the local chromatin state, protein interactions, and location in the nucleus can affect how strongly a given structure is maintained under stress. From these observations, we propose that genome topology is robust to extension of the chromatin fiber and isotropic shape change, and that this elasticity may be beneficial in physiological circumstances of changes in nuclear size and volume.

genomics↗

Heterochromatin diversity modulates genome compartmentalization and loop extrusion barriers

Two dominant processes organizing chromosomes are loop extrusion and the compartmental segregation of active and inactive chromatin. The molecular players involved in loop extrusion during interphase, cohesin and CTCF, have been extensively studied and experimentally validated. However, neither the molecular determinants nor the functional roles of compartmentalization are well understood. Here, we distinguish three inactive chromatin states using contact frequency profiling, comprising two types of heterochromatin and a previously uncharacterized inactive state exhibiting a neutral interaction preference. We find that heterochromatin marked by long continuous stretches of H3K9me3, HP1 and HP1{beta} correlates with a conserved signature of strong compartmentalization and is abundant in HCT116 colon cancer cells. We demonstrate that disruption of DNA methyltransferase activity dramatically remodels genome compartmentalization as a consequence of the loss of H3K9me3 and HP1 binding. Interestingly, H3K9me3-HP1/{beta} is replaced by the neutral inactive state and retains late replication timing. Furthermore, we show that H3K9me3-HP1/{beta} heterochromatin is permissive to loop extrusion by cohesin but refractory to CTCF, explaining a paucity of visible loop extrusion-associated patterns in Hi-C. Accordingly, CTCF loop extrusion barriers are reactivated upon loss of H3K9me3-HP1/{beta}, not as a result of canonical demethylation of the CTCF binding motif but due to an intrinsic resistance of H3K9me3-HP1/{beta} heterochromatin to CTCF binding. Together, our work reveals a dynamic structural and organizational diversity of the inactive portion of the genome and establishes new connections between the regulation of chromatin state and chromosome organization, including an interplay between DNA methylation, compartmentalization and loop extrusion. HighlightsO_LIThree inactive chromatin states are distinguishable by long-range contact frequencies in HCT116, respectively associated with H3K9me3, H3K27me3 and a H3K9me2 state with neutral contact preferences. C_LIO_LIH3K9me3-HP1/{beta} heterochromatin has a high degree of homotypic affinity and is permissive to loop extrusion but depleted in extrusion barriers. C_LIO_LIDisrupting DNA methylation causes widespread loss of H3K9me3-HP1/{beta} and dramatic remodeling of genome compartmentalization. C_LIO_LIH3K9me3-HP1/{beta} is replaced by the neutral inactive state, which gains CTCF loop extrusion barriers and associated contact frequency patterns. C_LIO_LIDNA methylation suppresses CTCF binding via two distinct mechanisms. C_LI

genomics↗

A cohesin traffic pattern genetically linked to gene regulation

Cohesin-mediated loop extrusion folds interphase chromosomes at the ten to hundreds kilobases scale. This process produces structural features such as loops and topologically associating domains. We identify three types of cis-elements that define the chromatin folding landscape generated by loop extrusion. First, CTCF sites form boundaries by stalling extruding cohesin, as shown before. Second, transcription termination sites form boundaries by acting as cohesin unloading sites. RNA polymerase II contributes to boundary formation at transcription termination sites. Third, transcription start sites form boundaries that are mostly independent of cohesin, but are sites where cohesin can pause. Together with cohesin loading at enhancers, and possibly other cis-elements, these loci create a dynamic pattern of cohesin traffic along the genome that guides enhancer-promoter interactions. Disturbing this traffic pattern, by removing CTCF barriers, renders cells sensitive to knock-out of genes involved in transcription initiation, such as the SAGA and TFIID complexes, and RNA processing such DEAD-Box RNA helicases. In the absence of CTCF, several of these factors fail to be efficiently recruited to active promoters. We propose that the complex pattern of cohesin movement along chromatin contributes to appropriate promoter-enhancer interactions and localization of transcription and RNA processing factors to active genes. HIGHLIGHTSO_LIAt least three types of chromatin boundaries regulate a cohesin traffic pattern. C_LIO_LIThe cohesin traffic pattern guides enhancer-promoter interactions. C_LIO_LIRemoving CTCF renders cells sensitive to deletion of RNA processing and gene regulation genes. C_LIO_LIDepleting CTCF affects localization of RNA processing and gene regulatory proteins. C_LI

genomics↗

Cohesin-mediated loop anchors confine the location of human replication origins

DNA replication occurs through an intricately regulated series of molecular events and is fundamental for genome stability across dividing cells in metazoans. It is currently unknown how the location of replication origins and the timing of their activation is determined in the human genome. Here, we dissect the role for G1 phase topologically associating domains (TADs), subTADs, and loops in the activation of replication initiation zones (IZs). We identify twelve subtypes of self-interacting chromatin domains distinguished by their degree of nesting, the presence of corner dot structures indicative of loops, and their co-localization with A/B compartments. Early replicating IZs localize to boundaries of nested corner-dot TAD/subTADs anchored by high density arrays of co-occupied CTCF+cohesin binding sites with divergently oriented motifs. By contrast, late replicating IZs localize to weak TADs/subTAD boundaries devoid of corner dots and most often anchored by singlet CTCF+cohesin sites. Upon global knock-down of cohesin-mediated loops in G1, early wave focal IZs replicate later in S phase and convert to diffuse placement along the genome. Moreover, IZs in mid-late S phase are delayed to the final minutes before entry into G2 when cohesin-mediated dot-less boundaries are ablated. We also delete a specific loop anchor and observe a sharp local delay of an early wave IZ to replication in late S phase. Our data demonstrate that cohesin-mediated loops at genetically-encoded TAD/subTAD boundaries in G1 phase are an essential determinant of the precise genomic placement of human replication origins in S phase.

genomics↗

Systematic evaluation of chromosome conformation capture assays

Chromosome conformation capture (3C)-based assays are used to map chromatin interactions genome-wide. Quantitative analyses of chromatin interaction maps can lead to insights into the spatial organization of chromosomes and the mechanisms by which they fold. A number of protocols such as in situ Hi-C and Micro-C are now widely used and these differ in key experimental parameters including cross-linking chemistry and chromatin fragmentation strategy. To understand how the choice of experimental protocol determines the ability to detect and quantify aspects of chromosome folding we have performed a systematic evaluation of experimental parameters of 3C-based protocols. We find that different protocols capture different 3D genome features with different efficiencies. First, the use of cross-linkers such as DSG in addition to formaldehyde improves signal-to-noise allowing detection of thousands of additional loops and strengthens the compartment signal. Second, fragmenting chromatin to the level of nucleosomes using MNase allows detection of more loops. On the other hand, protocols that generate larger multi-kb fragments produce stronger compartmentalization signals. We confirmed our results for multiple cell types and cell cycle stages. We find that cell type-specific quantitative differences in chromosome folding are not detected or underestimated by some protocols. Based on these insights we developed Hi-C 3.0, a single protocol that can be used to both efficiently detect chromatin loops and to quantify compartmentalization. Finally, this study produced ultra-deeply sequenced reference interaction maps using conventional Hi-C, Micro-C and Hi-C 3.0 for commonly used cell lines in the 4D Nucleome Project.

genomics↗