Systematic perturbation of retroviral LTRs reveals widespread long-range effects on human gene regulation [ChIP-seq]
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ABSTRACT: Recent work suggests extensive adaptation of transposable elements (TEs) for host gene regulation. However, high numbers of integrations typical of TEs, coupled with sequence divergence within families, have made systematic interrogation of the regulatory contributions of TEs challenging. Here, we employ CARGO, our recent method for CRISPR gRNA multiplexing, to facilitate targeting of LTR5HS, a higher primate-specific class of HERVK (HML-2) LTRs that is active during early development and present in ~700 copies throughout the human genome. We combine CARGO with CRISPR activation or interference to, respectively, induce or silence LTR5HS en masse, and demonstrate that this system robustly targets the vast majority of LTR5HS insertions. Remarkably, activation/silencing of LTR5HS is associated with reciprocal up- and down-regulation of hundreds of human genes. These effects require presence of retroviral sequences, but occur over long genomic distances, consistent with a pervasive function of LTR5HS elements as early embryonic enhancers in higher primates.
Project description:Recent work suggests extensive adaptation of transposable elements (TEs) for host gene regulation. However, high numbers of integrations typical of TEs, coupled with sequence divergence within families, have made systematic interrogation of the regulatory contributions of TEs challenging. Here, we employ CARGO, our recent method for CRISPR gRNA multiplexing, to facilitate targeting of LTR5HS, a higher primate-specific class of HERVK (HML-2) LTRs that is active during early development and present in ~700 copies throughout the human genome. We combine CARGO with CRISPR activation or interference to, respectively, induce or silence LTR5HS en masse, and demonstrate that this system robustly targets the vast majority of LTR5HS insertions. Remarkably, activation/silencing of LTR5HS is associated with reciprocal up- and down-regulation of hundreds of human genes. These effects require presence of retroviral sequences, but occur over long genomic distances, consistent with a pervasive function of LTR5HS elements as early embryonic enhancers in higher primates.
Project description:Recent work suggests extensive adaptation of transposable elements (TEs) for host gene regulation. However, high numbers of integrations typical of TEs, coupled with sequence divergence within families, have made systematic interrogation of the regulatory contributions of TEs challenging. Here, we employ CARGO, our recent method for CRISPR gRNA multiplexing, to facilitate targeting of LTR5HS, a higher primate-specific class of HERVK (HML-2) LTRs that is active during early development and present in ~700 copies throughout the human genome. We combine CARGO with CRISPR activation or interference to, respectively, induce or silence LTR5HS en masse, and demonstrate that this system robustly targets the vast majority of LTR5HS insertions. Remarkably, activation/silencing of LTR5HS is associated with reciprocal up- and down-regulation of hundreds of human genes. These effects require presence of retroviral sequences, but occur over long genomic distances, consistent with a pervasive function of LTR5HS elements as early embryonic enhancers in higher primates.
Project description:Craniofacial development and neural crest specification are evolutionarily conserved processes, yet subtle modifications to their gene regulatory networks drive species-specific craniofacial diversity. Transposable elements (TEs) are increasingly recognized as contributors to genome evolution, but their role in shaping neural crest regulatory programs remains underexplored. Here, we investigate the domestication of hominoid-specific TEs as enhancers during cranial neural crest cell (CNCC) specification, a process critical for vertebrate head development. Using human iPSC-derived CNCCs, we identified ~250 human-specific TEs, half of which human-specific, acting as active enhancers. These TEs were predominantly LTR5Hs and, to a lesser extent, SVAs. We demonstrate that these elements have been co-opted through the acquisition of a conserved CNCC coordinator motif and are bound by the CNCC signature factor TWIST1, and that their co-option is largely specific to the CNCC cell type. To assess their functional relevance, we used CRISPR-interference to repress ~75% of all the LTR5Hs and SVAs active in CNCCs, leading to widespread transcriptional changes in genes associated with neural crest migration, a process essential for CNCCs to populate the embryo and form craniofacial structures. Using functional assays, we showed that CNCC migration was significantly impaired by CRISPR-mediated TE repression. We further demonstrated that genes near human-specific TEs are more highly expressed in human CNCCs relative to chimpanzee, but TE repression returns their expression to chimpanzee levels. These findings reveal how TEs have been repeatedly co-opted to fine-tune CNCC regulatory networks, shaping lineage-specific craniofacial traits. By integrating evolutionary and developmental perspectives, our study highlights how TEs contribute to regulatory innovations in an otherwise deeply conserved developmental program.
Project description:dCas9KRAB and gRNA targeting HERVK TEs were used to repress the TEs in stem cells (hiPS) and in differentiated induced neurons (iN). As control, dCas9KRAB alone without gRNA was used.
Project description:It has been claimed previously that loss of (cytosine-5) DNA methylation in Dnmt2 mutant embryos affected the establishment of silent chromatin at Invader4 LTRs (Phalke et al., 2009). The inability of Dnmt2 mutants to control TE expression after heat shock (GSE40432) raised the possibility that DNA methylation could be required for control of Invader 4 during the heat shock response. We used DNA bisulfite sequencing at Inv4 LTRs that were previously suggested to be methylated (Phalke et al., 2009).
Project description:In this study, we analyzed the DNA methylation levels of 4799 IAP LTRs in three murine cell types: AB2.2 ES cells, somatic cells and a neuroblastoma cell line Neuro2A. According to the results, half of the IAP LTR retrotransposons show constant methylation patterns between the three cell types whereas the remaining half display variable levels of methylation. About half of the variably methylated IAP LTRs tend to be hypomethylated in ES cells, and nearly all of this group are hypomethylated in Neuro2A cells. Interestingly, the observed hypomethylation in both cell types occur in a non-uniform, locus-specific manner and to various degrees of severity, with some of them being easily detectible by COBRA. Overall, this study demonstrates the feasibility of HT-TREBS to study alterations in DNA methylation at retrotransposons in a locus-specific manner in multiple cell types and further suggests the potential utility of this technique in developing epigenetic biomarkers for tracking disease progression. HT-TREBS has been used with the Ion Torrent PGM platform to analyze the DNA methylation of 4799 IAP LTRs in a locus-specific manner in 3 cell types: somatic cells (previously submitted under GEO Accession GSE49222), AB2.2 ES cells and Neuro2A cells
Project description:Transposable elements (TEs) are key to the evolutionary turnover of regulatory sequences. How they can play such an essential role in spite of their genotoxic potential is unknown. Here, we demonstrate that KRABcontaining zinc finger proteins control the timely and pleiotropic engagement of TE-derived cis-regulators of transcription. We first observed that evolutionary recent TEs of the SVA, HERVK and HERVH subgroups are major contributors to chromatin opening during human embryonic genome activation and act as KLF-stimulated enhancers in naïve embryonic stem cells. We then found that KZFPs of corresponding evolutionary ages are simultaneously induced and repress the transcriptional activity of these TEs. We finally determined that the same KZFP-controlled TE-based enhancers later serve as developmental and tissue-specific regulators of gene expression. Thus, by taming the transcriptional impact of TEs during early embryogenesis, KZFPs allow for their genome-wide incorporation into transcriptional networks, thereby contributing to the species-specificity of human genome regulation.
Project description:Transposable elements (TEs) are key to the evolutionary turnover of regulatory sequences. How they can play such an essential role in spite of their genotoxic potential is unknown. Here, we demonstrate that KRABcontaining zinc finger proteins control the timely and pleiotropic engagement of TE-derived cis-regulators of transcription. We first observed that evolutionary recent TEs of the SVA, HERVK and HERVH subgroups are major contributors to chromatin opening during human embryonic genome activation and act as KLF-stimulated enhancers in naïve embryonic stem cells. We then found that KZFPs of corresponding evolutionary ages are simultaneously induced and repress the transcriptional activity of these TEs. We finally determined that the same KZFP-controlled TE-based enhancers later serve as developmental and tissue-specific regulators of gene expression. Thus, by taming the transcriptional impact of TEs during early embryogenesis, KZFPs allow for their genome-wide incorporation into transcriptional networks, thereby contributing to the species-specificity of human genome regulation.
Project description:Transposable elements (TEs) are key to the evolutionary turnover of regulatory sequences. How they can play such an essential role in spite of their genotoxic potential is unknown. Here, we demonstrate that KRABcontaining zinc finger proteins control the timely and pleiotropic engagement of TE-derived cis-regulators of transcription. We first observed that evolutionary recent TEs of the SVA, HERVK and HERVH subgroups are major contributors to chromatin opening during human embryonic genome activation and act as KLF-stimulated enhancers in naïve embryonic stem cells. We then found that KZFPs of corresponding evolutionary ages are simultaneously induced and repress the transcriptional activity of these TEs. We finally determined that the same KZFP-controlled TE-based enhancers later serve as developmental and tissue-specific regulators of gene expression. Thus, by taming the transcriptional impact of TEs during early embryogenesis, KZFPs allow for their genome-wide incorporation into transcriptional networks, thereby contributing to the species-specificity of human genome regulation.