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Spatially uniform establishment of chromatin accessibility in the early Drosophila embryo

ABSTRACT: As the Drosophila embryo transitions from the use of maternal RNAs to zygotic transcription, domains of “open” chromatin, with relatively low nucleosome density and specific histone marks, are established at promoters and enhancers involved in patterned embryonic transcription. However it remains unclear whether open chromatin is a product of activity - transcription at promoters and patterning transcription factor binding at enhancers - or whether it is established by independent mechanisms. Recent work has implicated the ubiquitously expressed maternal factor Zelda in this process. To assess the relative contribution of activity in the establishment of open chromatin , we have probed chromatin accessibility across the anterior-posterior axis of early Drosophila melanogaster embryos by applying a transposon based assay for chromatin accessibility (ATAC-seq) to anterior and posterior halves of hand-dissected, cellular blastoderm embryos. We find that genome-wide chromatin accessibility is remarkably similar between the two halves. Promoters and enhancers that are active in exclusively one half of the embryo have open chromatin in the other half, demonstrating that chromatin accessibility is not a direct result of activity. However there is a small skew at enhancers that drive transcription exclusively in either the anterior or posterior half of the embryo, with greater accessibility in the region of activity. Taken together these data support a model in which regions of chromatin accessibility are defined and established by ubiquitous factors, and fine tuned subsequently by activity.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE104957 | GEO | 2017/10/30

SECONDARY ACCESSION(S): PRJNA414230

REPOSITORIES: GEO

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Project description:To glean an appreciation of the holistic genetic activity in the gastrulating mouse embryo, we performed a genome-wide spatial transcriptome analysis (Stereo-seq), using a low-cell number sequencing protocol on laser microdissected samples of epiblast cells with retained positional address. The 3D transcriptome reveals that (i) the epiblast is partitioned into transcription domains corresponding to regions of epiblast where cells are endowed specifically with ectoderm and mesendoderm potency, (ii) novel lineage markers are identified as genes expressed in epiblast domains populated by cells displaying different lineage fates, (iii) functionally related gene regulatory circuitry and signaling pathways are acting in concert in the transcriptional domains, and (iv) the spatial information provides reference zipcodes for mapping the prospective address of cell samples from different embryos and stem cell lines. The quantified expression data can also be visualized as â3D digitized whole mount in situ hybridizationâ of all the expressed transcripts in the epiblast. (i) By using laser-microdissection, we carried out transcriptome profiling on embryo sections at a high resolution of ~20 cells per sample with the spatial information preserved. We then constructed a comprehensive spatial transcriptome map in the mid-gastrulation embryo that is visualized in a 3D embryonic model based on the sequencing data. Embryo position (A/L/P/R) and section (1-11) descriptors: A stands for laser capture microdissected samples from the anterior epiblast of the embryo; P for posterior; L for the left lateral epiblast of the embryo; R for the right lateral. The section is collected from distal to proximal, and the section 1 to 11 is the cryosection order, covering the whole embryonic part of a late mid-streak embryo. Section 1 is the most distal section and 11 is the most proximal section. (ii) Additional samples are RNA-seq data of 70 single cells from E7.0 mouse embryo. These 70 samples were randomly picked from the anterior or posterior embryonic half.

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Spatially uniform establishment of chromatin accessibility in the early Drosophila embryo

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