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Genome-wide mapping of i-Motifs reveals their association with transcription regulation in live human cells [CUT&Tag]

ABSTRACT: i-Motifs (iMs) are four-stranded DNA structures that form at cytosine (C)-rich sequences and in acidic conditions in vitro. However, their formation and distribution in cells is still under debate. Here we performed CUT&Tag sequencing using the anti-iM antibody iMab and showed that iMs form within the human genome in live cells. We mapped native iMs in two different human cell lines and recovered C-rich sequences that were confirmed to fold into iMs in vitro. We found that iMs in cells are mainly present at actively transcribing gene promoters and that their abundance and distribution are specific to each cell type. iMs with both long and short C-tracts were recovered, further extending the relevance of iMs throughout the genome. By simultaneously mapping G-quadruplexes (G4s), four-stranded structures that form at guanine-rich regions, and comparing the results with iMs, we proved that the two structures can form in independent genomic regions; however, when both iMs and G4s are present in the same genomic tract, their formation is favored. Our findings support the in vivo formation of iM structures and provide new insights into their interplay with G4s as new regulatory elements in the human genome.

ORGANISM(S): Homo sapiens

PROVIDER: GSE220878 | GEO | 2023/08/02

REPOSITORIES: GEO

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Genome-wide mapping of i-Motifs reveals their association with transcription regulation in live human cells [RNA-seq]

Project description:i-Motifs (iMs) are four-stranded DNA structures that form at cytosine (C)-rich sequences and in acidic conditions in vitro. However, their formation and distribution in cells is still under debate. Here we performed CUT&Tag sequencing using the anti-iM antibody iMab and showed that iMs form within the human genome in live cells. We mapped native iMs in two different human cell lines and recovered C-rich sequences that were confirmed to fold into iMs in vitro. We found that iMs in cells are mainly present at actively transcribing gene promoters and that their abundance and distribution are specific to each cell type. iMs with both long and short C-tracts were recovered, further extending the relevance of iMs throughout the genome. By simultaneously mapping G-quadruplexes (G4s), four-stranded structures that form at guanine-rich regions, and comparing the results with iMs, we proved that the two structures can form in independent genomic regions; however, when both iMs and G4s are present in the same genomic tract, their formation is favored. Our findings support the in vivo formation of iM structures and provide new insights into their interplay with G4s as new regulatory elements in the human genome.

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Project description:I-motifs (iMs) are four-stranded non-B DNA structures containing C-rich DNA sequences, which can be formed under various pH conditions. DNA methylation exhibits complex impacts on iM formation in vitro. However, how DNA methylation differentially affects pH dependent iM formation on a genome wide scale is completely uncharacterized in both humans and plants. To this end, we conducted iM-IP-seq under pH 5.5 and 7.0 conditions using CK and hyper/hypomethylated DNA in combination with BS-seq in rice. We found that pH 7.0 and 5.5 biased iMs had distinct genomic features and differential DNA methylation levels, the former having higher DNA methylation levels than the latter. Moreover, DNA demethylation and hyper methylation had more impacts on a subset of iM formation under pH 7.0 and 5.5, respectively, indicating that DNA de/hyper-methylation exhibits pH dependent impacts on iM formation. Importantly, we found that CG hypo-DMRs and CHH hyper-DMRs alone or coordinated with CG/CHG hyper-DMRs may play determinant roles in the regulation of iM formation under pH 5.5 and 7.0. Thus, our study shows that intrinsic DNA sequences alone or in combination with DNA methylation play vital roles in determining pH-dependent formation of iMs. It will contribute to in-depth understanding of DNA methylation in the modulation of pH dependent dynamics of iM conformation, therefore broadening its biological implications and practical application ranges.

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