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The evolutionary emergence of the rac3b/rfng/sgca regulatory cluster refined mechanisms for hindbrain boundaries formation

ABSTRACT: Developmental programs often rely on parallel morphogenetic mechanisms that guarantee precise tissue architecture. While redundancy constitutes an obvious selective advantage, little is known on how novel morphogenetic mechanisms emerge during evolution. In zebrafish, rhombomeric boundaries behave as an elastic barrier, preventing cell intermingling between adjacent compartments. Here, we identify the fundamental role of the small-GTPase Rac3b in actomyosin cables assembly at hindbrain boundaries. We show the novel rac3b/rfng/sgca regulatory cluster, which is specifically expressed at the boundaries, emerged in the Ostariophysi superorder by chromosomal rearrangement that generated new cis-regulatory interactions. By combining 4C-seq, ATAC-seq, transgenesis and CRISPR-induced deletions, we characterized this regulatory domain, identifying hindbrain boundaries-specific cis-regulatory elements. Our results suggest that the capacity of boundaries to act as an elastic mesh for segregating rhombomeric cells evolved by cooption of critical genes to a novel regulatory block, refining the mechanisms for hindbrain segmentation.

ORGANISM(S): Danio rerio

PROVIDER: GSE109219 | GEO | 2018/04/25

REPOSITORIES: GEO

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Project description:Genetic variants altering cis-regulation of normal gene expression (cis-eQTLs) have been extensively mapped in human cells and tissues, but the extent to which environmental perturbation influences such traits has not been studied to date. We carried out large-scale induction experiments using primary human bone cells derived from 113 unrelated donors of Swedish origin harvested under 18 different conditions (seven treatments, two vehicles, each assessed at two time points). The treatments with the largest impact on the transcriptome, verified on two independent expression arrays, included BMP-2 (t=2h), dexamethasone (DEX) (t=24h), and PGE2 (t=24h). Using these treatments, we performed expression profiling for 18,144 RefSeq transcripts applying biological replicates of the complete study cohort (ntotal=782) and combined it with genome-wide SNP-genotyping data in order to map treatment-specific cis-eQTLs. We found that 93% of cis-eQTLs at 1% FDR were replicated in at least one additional treatment and in fact, on average only 1.4% of the cis-eQTLs were considered as treatment-specific at high confidence. The relative invariability of cis-regulation following perturbation was reiterated independently by genome-wide allelic expression tests where only a small proportion of variance could be attributed to treatment, though treatment-specific cis-regulatory effects were 2-6-fold more abundant among up-or downregulated genes. We further followed-up and validated the DEX-specific cis-regulation of the MYO6 and TNC loci and found top cis-regulatory variants located 180 and 250kb upstream of the transcription start sites, respectively. Our results suggest that, as opposed to tissue-specificity of cis-eQTLs, the interaction between cellular environment and cis-variants are relatively rare (~1.5%), but that detection of such specific interactions can be achieved by combination of functional genomic tools. Total RNA from cultured trabecular bone cells obtained from ~100 unrelated Caucasian donors treated under multiple different conditions and timepoints. Each sample represented by two or three biological replicates. This dataset includes samples treated with bone morphogenetic protein 2 (BMP2) for 2 hours.

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The evolutionary emergence of the rac3b/rfng/sgca regulatory cluster refined mechanisms for hindbrain boundaries formation

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