Identification of a novel long-range enhancer driving Sonic Hedgehog expression in neural progenitor cells
Ontology highlight
ABSTRACT:
ORGANISM(S): Mus musculus
PROVIDER: GSE84168 | GEO | 2017/01/01
SECONDARY ACCESSION(S): PRJNA328173
REPOSITORIES: GEO
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Project description:Enhancers can regulate their target promoters over large genomic distances for which spatial proximity between these elements is assumed to be necessary. Topologically Associating Domains (TADs) are thought to provide such a spatial environment for regulatory domains harboring multiple enhancers driving complex expression of developmental genes. However, how enhancer position within the TAD affects its function in vivo is not known. Here, we address this question by generating a series of genome-engineered mouse lines in which we systematically reposition the limb enhancer of Sonic hedgehog (Shh), ZRS, to various positions within and outside of its TAD to analyze positional effects on gene expression, chromatin folding, and limb phenotype. We find that the enhancer activates Shh only when located within the same TAD, however, its activity varies across intra-TAD positions. ZRS-driven Shh expression drops rapidly with increasing distance from the promoter but eventually plateaus irrespective of linear distance. Moreover, engineering of 3D enhancer-promoter contacts through integration of different CTCF sites reveals that increased contact frequencies do not directly translate into increased transcriptional output and may cause undesired consequences in vivo due to detrimental effects on Shh expression in other tissues. Finally, we show a selective ability of the ZRS enhancer to activate non-target genes in ectopic TADs. Our work highlights the importance of genomic context within TADs for enhancer function and our limited understanding of the interplay between regulatory sequences within these domains.
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Project description:Cilia assembly, maintenance and the localization of signal-transduction proteins necessitate a functioning intraflagellar transport (IFT). The IFT machinery moves cargo along a microtubule scaffold from the proximal to the distal end of the cilium. This anterograde transport is facilitated by a large multiprotein complex IFT-B, which consists of 16 proteins in total and recruits motor protein Kinesin-2 for active movement. TTC30A and TTC30B are integral components of this complex and were shown before to have redundant function in context of IFT. One paralogue could compensate the loss of the other, preventing the disruption of IFT-B and thus a severe ciliogenesis defect with no formation of the cilium. Affinity-based protein complex analysis of endogenously tagged cells, generated via CRISPR/Cas9 system as described before, revealed paralogue specific protein interactors proposing the involvement of TTC30A or TTC30B in other ciliary functions, particularly Sonic hedgehog signaling (Shh). Defects in this ciliary signaling pathway are often correlated to synpolydactyly, which intriguingly is also linked to a rare TTC30 variant. In this study we focus on the so far unknown interaction of TTC30A with protein kinase A catalytic subunit α PRKACA, which is a negative regulator of Shh pathway. For an in-depth analysis of this unique interaction and the influence on Shh, we used previously, via the CRISPR/Cas9 system, generated TTC30A or B single- and double-knockout hTERT-RPE1 cells as well as rescue cells harboring the TTC30 mutation. Our systematic approach revealed the paralogue specific influence of TTC30A KO and mutated TTC30A on the activity of PRKACA as well as the uptake of Smoothened into the cilium resulting in a downregulation of Sonic hedgehog signaling. Affinity-based protein complex analysis of wildtype versus mutated TTC30A or TTC30B uncovered differences in interaction pattern. These interactome alterations combined with Shh downregulation suggest a possible mechanism of how mutant TTC30A and respectively TTC30A KO are linked to synpolydactyly.
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Project description:The expression of genes with key roles in development is under very tight spatial and temporal control, mediated by enhancers. A classic example of this is the sonic hedgehog gene (Shh), which plays a pivotal role in the proliferation, differentiation and survival of neural progenitor cells both in vivo and in vitro. Shh expression in the brain is tightly controlled by several known enhancers that have been identified through genetic, genomic and functional assays. Using chromatin profiling during the differentiation of embryonic stem cells to neural progenitor cells, here we report the identification of a novel long-range enhancer for Shh-Shh-brain-enhancer-6 (SBE6)-that is located 100 kb upstream of Shh and that is required for the proper induction of Shh expression during this differentiation programme. This element is capable of driving expression in the vertebrate brain. Our study illustrates how a chromatin-focused approach, coupled to in vivo testing, can be used to identify new cell-type specific cis-regulatory elements, and points to yet further complexity in the control of Shh expression during embryonic brain development.
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Project description:Cancer genomics has illuminated a wide spectrum of genes and core molecular processes contributing to human malignancy. Still, the genetic and molecular basis of many cancers remains only partially explained. Genetic predisposition accounts for 5-10% of cancer diagnoses and genetic events cooperating with known somatic driver events are poorly understood. Analyzing established cancer predisposition genes in medulloblastoma (MB), a malignant childhood brain tumor, we recently identified pathogenic germline variants that account for 5% of all MB patients. Here, by extending our previous analysis to include all protein-coding genes, we discovered and replicated rare germline loss-of-function (LoF) variants across Elongator Complex Protein 1 (ELP1) on 9q31.3 in 15% of pediatric MBSHH cases, thus implicating ELP1 as the most common MB predisposition gene and increasing genetic predisposition to 40% for pediatric MBSHH. Inheritance was verified based on parent-offspring and pedigree analysis, which identified two families with a history of pediatric MB. ELP1-associated MBs were restricted to the molecular SHH subtype and were characterized by universal biallelic inactivation of ELP1 due to somatic loss of chromosome 9q. The majority of ELP1-associated MBs exhibited co-occurring somatic PTCH1 (9q22.32) alterations, suggesting that ELP1-deficiency predisposes to tumor development in combination with constitutive activation of SHH signaling. ELP1 is an essential subunit of the evolutionary conserved Elongator complex, whose primary function is to enable efficient translational elongation through tRNAs modifications at the wobble (U34) position. Biochemical, transcriptional, and proteomic analyses revealed that ELP1-associated MBSHH are characterized by a destabilized core Elongator complex, loss of Elongator-dependent tRNA modifications, codon-dependent translational reprogramming, and induction of the unfolded protein response (UPR), consistent with deregulation of protein homeostasis due to Elongator-deficiency in model systems. Our findings suggest that genetic predisposition to proteome instability is a previously underappreciated determinant in the pathogenesis of pediatric brain cancer. These results provide strong rationale for further investigating the role of protein homeostasis in other pediatric and adult cancer types and potential opportunities for novel therapeutic interference.
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