Project description:Chromatin accessibility, a crucial component of genome regulation, has mostly been studied in homogenous and simple systems, such as isolated cell populations or early development models. Whether it can sensitively be assessed in complex, dynamic systems in vivo remains largely unexplored. In this study, we identify chromatin accessibility changes in a whole organism from embryogenesis to adulthood, using C. elegans as a model. Chromatin accessibility changes between developmental stages are highly reproducible, recapitulate histone modification changes, and reveal key regulatory aspects of the epigenomic landscape throughout organismal development. Even when derived from the chromatin of a whole organism, dynamic regions of chromatin accessibility are capable of identifying novel cell-type- and temporal-specific enhancers, which we functionally validate in vivo. Furthermore, by integrating transcription factor binding motifs into a machine-learning framework, we identify EOR-1 as a potential early regulator of chromatin accessibility changes. Our study provides a unique resource for C. elegans, a system in which the prevalence and importance of enhancers remains poorly characterized, and demonstrates the power of using whole organism chromatin accessibility to identify novel regulatory regions in complex systems.
Project description:Recently developed single cell technologies allow researchers to characterize cell states at ever greater resolution and scale. C. elegans is a particularly tractable system for studying development, and recent single cell RNA-seq studies characterized the gene expression patterns for nearly every cell type in the embryo and at the second larval stage (L2). Gene expression patterns are useful for learning about gene function and give insight into the biochemical state of different cell types; however, in order to understand these cell types, we must also determine how these gene expression levels are regulated. We present the first single cell ATAC-seq study in C. elegans. We collected data in L2 larvae to match the available single cell RNA-seq data set, and identify tissue-specific chromatin accessibility patterns that align well with existing data, including the L2 single cell RNA-seq results. Using a novel implementation of the Latent Dirichlet Allocation algorithm, our chromatin accessibility data provide new insights into which genomic loci may be participating in cell type-specific gene regulation, with promise for better understanding of cellular differentiation and gene regulation in the worm.
Project description:Background: The force generating mechanism of muscle is evolutionarily ancient; the fundamental structural and functional components of the sarcomere are common to motile animals throughout phylogeny. Recent evidence suggests that the transcription factors that regulate muscle development are also conserved. Thus, a comprehensive description of muscle gene expression in a simple model organism should define a basic muscle transcriptome that is also expressed in animals with more complex body plans. To this end, we have applied Micro-Array Profiling of Caenorhabditis elegans Cells (MAPCeL) to muscle cell populations extracted from developing Caenorhabditis elegans embryos. Results: Fluorescence Activated Cell Sorting (FACS) was used to isolate myo-3::GFP-positive muscle cells, and their cultured derivatives, from dissociated early Caenorhabditis elegans embryos. Microarray analysis identified 6,693 expressed genes, 1,305 of which are enriched in the myo-3::GFP positive cell population relative to the average embryonic cell. The muscle-enriched gene set was validated by comparisons to known muscle markers, independently derived expression data, and GFP reporters in transgenic strains. These results confirm the utility of MAPCeL for cell type-specific expression profiling and reveal that 60% of these transcripts have human homologs. Conclusions: This study provides a comprehensive description of gene expression in developing Caenorhabditis elegans embryonic muscle cells. The finding that over half of these muscle-enriched transcripts encode proteins with human homologs suggests that mutant analysis of these genes in Caenorhabditis elegans could reveal evolutionarily conserved models of muscle gene function with ready application to human muscle pathologies. Keywords: embryonic muscle, myo-3::GFP
Project description:Deep sequencing of size-selected DNaseI-treated chromatin (DNase-seq) allows high resolution measurement of chromatin accessibility to DNaseI cleavage, permitting identification of de novo active cis regulatory modules (CRMs) and individual transcription factor (TF) binding sites. We adapted DNase-seq to nuclei isolated from C. elegans embryos and L1 arrest larvae to generate high-resolution maps of TF binding. Over half of embryonic DNaseI hypersensitive sites (DHS) were annotated in noncoding sequences, with 23% in intergenic, 11% promoter regions and 21% in introns, with similar statistics in data collected from L1 arrest larvae. Noncoding DHS exhibit high evolutionary sequence conservation and are enriched in marks of enhancer activity and transcription. We validated noncoding DHS against a previously investigated set of enhancers from myo-2, myo-3, hlh-1, elt-2 and lin-26/lir-1 gene loci and recapitulated 15 of 17 known enhancers in these loci. We then mined the DNase-seq data to identify putative active CRMs and TF footprints. Our DNase-seq data could also be used to improve predictions of tissue-specific expression compared to motifs alone. In a pilot functional test, 10 of 15 DHS from pha-4, icl-1 and ceh-13 drove reporter gene expression in transgenic C. elegans. Overall, we provide experimental annotation of 26,644 putative CRMs in the embryo containing 55,890 TF footprints, and 15,841 putative CRMs in the L1 arrest larvae containing 32,685 TF footprints.
Project description:Gene regulation in mammals involves a complex interplay between promoter and distal regulatory elements that function in concert to drive precise spatio-temporal gene expression programs. However, the dynamics of distal gene regulatory elements and its function in transcriptional reprogramming that underlies neurogenesis and neuronal activity remain largely unknown. Here we use a combinatorial analysis of genomewide datasets for chromatin accessibility (FAIRE-Seq) and enhancer mark H3K27ac to reveal a highly dynamic nature of chromatin accessibility during neurogenesis that gets restricted to certain genomic regions as neurons acquire a post-mitotic, terminally differentiated state. We further reveal that the distal open regions serve as target sites of distinct transcription factors that function in a stage-specific manner to contribute to the transcriptional program underlying neuronal commitment and maturation. A prolonged NMDA-driven neural activity results in epigenetic reprogramming at a large number of distal regulatory elements as well as dramatic reorganization of super-enhancers that in turn mediate critical transcriptional responses. Taken together, these findings reveal dynamics of distal regulatory landscape during neurogenesis and uncover novel regulatory elements that function in concert with epigenetic mechanisms and transcription factors to generate transcriptome underlying neuronal development and function. FAIRE-Seq and H3K27ac profiles for three stages on neuronal differentation viz. neuronal progenitors, day 1 neurons and day 10 neurons, were generated to understand the dynamics of accessible and ehancer chromatin landscape. Along with this we also generated RNASeq and H3K27ac profiles for day 10 neurons upon control and NMDA treatment.