Abstract
Nuclear noncoding RNAs (ncRNAs) are key regulators of gene expression and chromatin organization. The progress in studying nuclear ncRNAs depends on the ability to identify the genome-wide spectrum of contacts of ncRNAs with chromatin. To address this question, a panel of RNADNA proximity ligation techniques has been developed. However, neither of these techniques examines proteins involved in RNAchromatin interactions. Here, we introduce RedChIP, a technique combining RNADNA proximity ligation and chromatin immunoprecipitation for identifying RNAchromatin interactions mediated by a particular protein. Using antibodies against architectural protein CTCF and the EZH2 subunit of the Polycomb repressive complex 2, we identify a spectrum of cis- and trans-acting ncRNAs enriched at Polycomb- and CTCF-binding sites in human cells, which may be involved in Polycomb-mediated gene repression and CTCF-dependent chromatin looping. By providing a protein-centric view of RNADNA interactions, RedChIP represents an important tool for studies of nuclear ncRNAs.
The majority of the eukaryotic genome is transcribed into coding and noncoding RNAs (ncRNAs). ncRNAs fulfill various functions both in the cytoplasm and the cell nucleus. Nuclear ncRNAs are attracted to different genomic regions and mediate the activation or repression of genes located in these regions and are also implicated in the genome three-dimensional organization (1, 2). In particular, recent studies indicate that RNA is essential for the chromatin targeting of Polycomb repressive complexes (3) and the organization of CTCF-dependent chromatin loops (4). However, these studies do not show which particular RNAs are involved.
Helpful in studying nuclear functions of ncRNAs are methods that map the sites of ncRNA associations with the genome. Initially developed for probing genomic interactions of one particular RNA, these methods are now available in an all-vs.-all version allowing simultaneous detection of the sites of chromosomal locations for all RNA molecules present in the nucleus (reviewed in ref. 1). An important drawback of these techniques, however, is that they do not disclose the proteins involved in RNADNA interactions.
To identify RNAs that could be involved in the functioning of DNA-bound proteins, we developed a hybrid approachRedChIPcombining an RNADNA proximity ligation technique [Red-C (5)] with chromatin immunoprecipitation (ChIP). Using antibodies against CTCF and EZH2, we identified various ncRNAs interacting with DNA at the sites of deposition of the above-mentioned proteins.
The RedChIP experimental procedure is analogous to HiChIP used for protein-centric mapping of DNADNA interactions (6), with the difference being that RNADNA interactions are analyzed instead of DNADNA interactions. Briefly, RNAproteinDNA complexes are cross-linked in living cells, and RNA and DNA fragments are ligated in situ using a bridge adapter. Ligated complexes are solubilized by sonication and subjected to IP using antibodies against a protein of interest. RNADNA chimeric molecules are then purified and sequenced, thus reporting RNADNA interactions that may be mediated by a particular protein and proteinDNA interactions that may be mediated by various RNAs (Fig. 1A). An aliquot of the material (input fraction) is processed without an IP step to record the total set of RNADNA interactions mediated by any proteins, as in a regular Red-C experiment.
RedChIP technique. (A) Outline of the experimental procedure. (B) A region of Chr17 encompassing Hoxb genes showing distribution of DNA and RNA portions in IP (RedChIP) and input (RedC) fractions from experiments with EZH2 and CTCF antibodies. Shown alongside are ChIP-seq peaks of EZH2 in H1-hESCs (human embryonic stem cells) and ChIP-seq peaks of CTCF in K562 cells as well as total RNA-seq profiles for H1-hESCs and K562 cells (from ENCODE). (C) Distribution of DNA portions around EZH2 peaks in hESCs and CTCF peaks in K562. (D) Ratio of the number of RNA contacts detected in different chromatin types in IP fraction to the number of RNA contacts detected in the same chromatin types in input fraction.
We used antibodies against EZH2, a catalytic subunit of the PRC2 complex, to study the Polycomb-dependent RNADNA interactome in human embryonic stem cells. We also used antibodies against CTCF to study the CTCF-dependent RNADNA interactome in human K562 cells. DNA portions of the chimeric molecules showed a clear preference for the binding sites of corresponding proteins in the IP fraction (Fig.1 B and C), indicating successful IP. Accordingly, we observed an enrichment of DNA portions in chromatin types typical for poised promoters and Polycomb-repressed regions in the IP fraction from the EZH2 experiment and an enrichment of DNA portions in chromatin types typical for insulators and promoters in the IP fraction from the CTCF experiment (Fig. 1D). Meanwhile, RNA portions of the chimeric molecules showed correlation with RNA-sequencing (RNA-seq) profiles both in IP and input fractions (Fig. 1B), reflecting the origination of RNA portions from various transcripts. We combined the contacts of RNA portions originating from a single gene, thus obtaining a whole-genome contact profile for each annotated RNA.
We then focused on the analysis of contacts of individual RNAs in the experiment with EZH2 antibodies. We first aimed to identify cis-acting RNAs that fulfill their functions in the vicinity of an encoding gene. For each RNA, we selected a fraction of cis contacts established with DNA regions surrounding the gene (1 Mb of gene boundaries including the gene) and compared the number of cis contacts between EZH2-precipitated and input fractions. We found that the degree of enrichment in the IP fraction correlated with the percentage of contacts detected in Polycomb-specific and poised promoter-specific chromatin types but not any other chromatin types in the area under study (Fig. 2A). We identified 10 long intergenic ncRNAs (lincRNAs) with a fold enrichment of >1.3 in both replicates (Fig. 2C). Among the identified RNAs is Kcnq1ot1 (fold change = 1.5), a well-known example of antisense lincRNA involved in the Polycomb-mediated silencing of several genes in the same locus (7). High fold enrichment was also observed for AC078778, antisense lincRNAs from the HOXC locus. Notably, antisense RNAs, on average, demonstrate higher fold enrichment than other lincRNAs and mRNAs of protein-coding genes (Fig. 2G), indicating the enrichment of the group of antisense RNAs with RNAs that may mediate Polycomb targeting.
Identification of ncRNAs associated with genomic regions occupied by EZH2 in hESCs and by CTCF in K562 cells. (A) Ratio of the number of cis contacts of individual RNAs between EZH2-precipitated and input fractions (x axis) vs. the percentage of cis contacts detected in different chromatin types in EZH2-precipitated fraction (y axis). (B) The same as A for CTCF-precipitated fraction. (C and D) Ratio of the number of cis (C) or trans (D) contacts of individual RNAs between EZH2-precipitated and input fractions for rep1 and rep2. (E and F) Ratio of the number of cis (E) or trans (F) contacts of individual RNAs between CTCF-precipitated and input fractions for rep1 and rep2. (G) Distribution of fold changes from C for different RNA biotypes (antisense, n = 44; linc, n = 162; protein coding, n = 4,184). *P < 0.05, ***P < 0.001. (H) Intersection of RNAs enriched in RedChIP and fRIP-seq.
At the final step of the analysis, we searched for trans-acting RNAs that could participate in Polycomb functioning genome-wide. We compared the number of trans contacts (contacts with nonparental chromosomes) for each RNA between EZH2-precipitated and input fractions and looked for RNAs showing an elevated number of contacts in the IP fraction. The highest enrichment was observed for antisense RNA KIF5C-AS1, snRNA RNU5B-1, and SNORD3a RNA (Fig. 2D). These RNAs are good candidates to act as global mediators of Polycomb activity.
The above types of analysis were then performed for the data from the experiment with CTCF antibodies. In the analysis of cis-acting RNAs, we observed a correlation of RNA enrichment in the CTCF-precipitated fraction with the percentage of contacts detected in promoter-, enhancer-, and insulator-specific chromatin type (Fig. 2B). We identified seven lincRNAs with a fold enrichment of >1.3 in both replicates (Fig. 2E). These lincRNAs might participate in loading CTCF to its DNA sites and organization of promoter-enhancer specific and other chromatin loops within genomic loci from where lincRNAs are produced. In the analysis of trans-acting RNAs, the highest fold enrichment was observed for snRNA RNU12 (Fig. 2F). Notably, U12 RNA is the second top by the total number of contacts among all RNAs in K562 cells (1.1% of all contacts). The potential involvement of RNU12 RNA in the functions of CTCF requires further experimental evidence.
Remarkably, the set of RNAs enriched in RedChIP significantly intersects the set of RNAs enriched in RNA IP (formaldehyde RNA IP-sequencing, fRIP-seq) experiments (Fig. 2H). Importantly, 18 of 22 ncRNAs overrepresented in CTCF- and EZH2-RedChIP samples are fRIP-positive, indicating these ncRNAs indeed interact with the studied proteins.
Collectively, the present study results demonstrate the utility of the RedChIP protocol for identifying RNAs that may target nonhistone proteins to various locations on chromosomes or mediate interactions of these proteins with DNA. The identification of RNAs that are known to target Polycomb complexes to repressed genomic domains strongly supports the validity of the experimental approach, whereas identifying a set of RNAs possessing similar characteristics will stimulate studies of their possible role in Polycomb and CTCF functioning. The RedChIP technique can be used for identifying RNAs associated with genomic regions occupied by any protein of interest.
Cells are fixed with formaldehyde, DNA is fragmented with NlaIII restriction enzyme, and the ends are blunted and A-tailed. RNA 3 ends are ligated to a biotinylated bridge adapter followed by ligation of the opposite ends of the bridges with DNA ends in spatial proximity. Ligated complexes are solubilized by sonication, immunoprecipitated, and washed. RNADNA chimeras are purified, and DNA is digested with MmeI restriction enzyme. After biotin pull-down, reverse transcription is initiated from the bridge with template switching at the RNA 5 end, allowing for the incorporation of an Illumina adapter. Another Illumina adapter is ligated to DNA ends, and the chimeras are amplified and paired-end sequenced. The detailed protocol and sequencing data processing are described in SI Appendix. For sample processing statistics, refer to Dataset S1. For read processing statistics, refer to Dataset S2.
Raw fastq reads and processed TSV files with contacts are available at Gene Expression Omnibus (accession no. GSE174474). The code for read processing is available as RedClib on GitHub: https://github.com/agalitsyna/RedClib.
This work was supported by the Russian Science Foundation (21-64-00001) and by the Russian Ministry of Science and Higher Education (075-15-2021-1062).
Author contributions: A.A. Gavrilov, E.L.A., and S.V.R. designed research; A.A. Gavrilov and E.B.D. performed research; A.A. Gavrilov, R.I.S., M.D.M., and A.A. Galitsyna analyzed data; and A.A. Gavrilov and S.V.R. wrote the paper.
The authors declare no competing interest.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2116222119/-/DCSupplemental.
- Copy number variation of the restorer Rf4 underlies human selection ... - Nature.com - November 15th, 2023 [November 15th, 2023]
- NYU Langone Health in the NewsThursday, November 9, 2023 - NYU Langone Health - November 15th, 2023 [November 15th, 2023]
- Eugenics: Plaguing scientific community with dark history | Opinion ... - The Arkansas Traveler - November 15th, 2023 [November 15th, 2023]
- Cranberries can bounce, float and pollinate themselves: The saucy ... - Japan Today - November 15th, 2023 [November 15th, 2023]
- Government Housing Assistance Linked to Increased Cancer ... - HealthDay - November 15th, 2023 [November 15th, 2023]
- Rate of New Lung Cancer Cases Has Decreased Over Last Five Years - HealthDay - November 15th, 2023 [November 15th, 2023]
- Clinically relevant antibiotic resistance genes are linked to a limited ... - Nature.com - November 15th, 2023 [November 15th, 2023]
- Disparities in Guideline-Concordant Care Found for Black CRC ... - HealthDay - November 15th, 2023 [November 15th, 2023]
- Mathematician Heather Harrington is new director at the Max Planck ... - EurekAlert - November 15th, 2023 [November 15th, 2023]
- New study finds genetic testing can effectively identify patients with ... - EurekAlert - November 15th, 2023 [November 15th, 2023]
- STK11 loss leads to YAP1-mediated transcriptional activation in ... - Nature.com - November 15th, 2023 [November 15th, 2023]
- CRISPR-broad: combined design of multi-targeting gRNAs and ... - Nature.com - November 15th, 2023 [November 15th, 2023]
- Master regulator of the dark genome greatly improves cancer T-cell ... - Science Daily - November 15th, 2023 [November 15th, 2023]
- Omega Therapeutics Showcases Bidirectional and Multiplexed ... - BioSpace - November 15th, 2023 [November 15th, 2023]
- Today is International 15q Day - ASBMB Today - November 15th, 2023 [November 15th, 2023]
- Evolution of taste: Sharks were already able to perceive bitter ... - EurekAlert - November 15th, 2023 [November 15th, 2023]
- Stanford Scientists Uncover New Indicators of Health, Disease, and ... - SciTechDaily - October 16th, 2023 [October 16th, 2023]
- NHGRI Director Eric Green elected to the National Academy of ... - National Human Genome Research Institute - October 16th, 2023 [October 16th, 2023]
- Monkey survives for two years after gene-edited pig-kidney transplant - Nature.com - October 16th, 2023 [October 16th, 2023]
- Opinion: Interest in RNA Editing Accelerates as Therapies Approach ... - BioSpace - October 16th, 2023 [October 16th, 2023]
- Regulation of dermal fibroblasts by human neutrophil peptides ... - Nature.com - October 16th, 2023 [October 16th, 2023]
- Consistent effects of the genetics of happiness across the lifespan ... - Nature.com - October 16th, 2023 [October 16th, 2023]
- Storytelling through the looking glass of genetics The Stute - The Stute - October 16th, 2023 [October 16th, 2023]
- Pet dogs shed light on human health, researchers say - UPI News - October 16th, 2023 [October 16th, 2023]
- Native microbiome dominates over host factors in shaping the ... - Nature.com - October 16th, 2023 [October 16th, 2023]
- Illinois-led project to sequence soybean genomes, improve future ... - Herald-Whig - October 16th, 2023 [October 16th, 2023]
- Unrealized targets in the discovery of antibiotics for Gram-negative ... - Nature.com - October 16th, 2023 [October 16th, 2023]
- How Biotech And AI Are Transforming The Human - Noema Magazine - October 16th, 2023 [October 16th, 2023]
- The Many Lives of Alexandria Forbes - BioSpace - October 16th, 2023 [October 16th, 2023]
- CEP20 promotes invasion and metastasis of non-small cell lung ... - Nature.com - October 16th, 2023 [October 16th, 2023]
- Genotyping, sequencing and analysis of 140,000 adults from Mexico ... - Nature.com - October 16th, 2023 [October 16th, 2023]
- The role and impact of alternative polyadenylation and miRNA ... - Nature.com - October 16th, 2023 [October 16th, 2023]
- Human - Simple English Wikipedia, the free encyclopedia - January 30th, 2023 [January 30th, 2023]
- Deep Dive Ties Together Dog Genetics, Brain Physiology and Behavior to Explain Why Collies Are Different from Terriers - Scientific American - December 12th, 2022 [December 12th, 2022]
- How oxytocin drives connections of newly integrated adult-born neurons: Research - Hindustan Times - December 12th, 2022 [December 12th, 2022]
- Alzheimer's Disease Genetics Fact Sheet - National Institute on Aging - December 2nd, 2022 [December 2nd, 2022]
- Human genetic clustering - Wikipedia - November 23rd, 2022 [November 23rd, 2022]
- Human Genome Project Fact Sheet - November 23rd, 2022 [November 23rd, 2022]
- Abstracts | International Congress of Human Genetics 2023 - November 23rd, 2022 [November 23rd, 2022]
- Ancient DNA and Neanderthals | The Smithsonian Institution's Human ... - November 16th, 2022 [November 16th, 2022]
- Biological Influences on Human Behavior: Genetics & Environment - November 16th, 2022 [November 16th, 2022]
- Fluent BioSciences showcasing breakthrough solutions to enable unprecedented scale, cost-efficiency and access for single-cell RNA sequencing at the... - October 28th, 2022 [October 28th, 2022]
- Human behaviour genetics - Wikipedia - October 23rd, 2022 [October 23rd, 2022]
- Nucleome Therapeutics raises oversubscribed 37.5 million Series A financing to decode the dark matter of the human genome and deliver first-in-class... - October 19th, 2022 [October 19th, 2022]
- Gladstone data scientist elected to the National Academy of Medicine - EurekAlert - October 19th, 2022 [October 19th, 2022]
- Ocugen to Host R&D Day in New York City on Tuesday, November 1, 2022 - Yahoo Finance - October 19th, 2022 [October 19th, 2022]
- Pharmacy researcher earns $2.3 million NIH award to study opioid addiction - EurekAlert - October 19th, 2022 [October 19th, 2022]
- Study shows age often plays a bigger role than genetics in gene expression and susceptibility to disease - Anti Aging News - October 19th, 2022 [October 19th, 2022]
- CSRWire - Direct Relief, Amgen and C/Can Team Up To Improve Access to Breast Cancer Diagnostics and Treatment in Paraguay - CSRwire.com - October 19th, 2022 [October 19th, 2022]
- Maze Therapeutics Appoints Harold Bernstein, M.D., Ph.D., as President, Research and Development and Chief Medical Officer - Business Wire - October 19th, 2022 [October 19th, 2022]
- New Rare Disease Therapy Effectively Lowers Plasma Phe in Patients with PKU - MD Magazine - October 19th, 2022 [October 19th, 2022]
- GSK : announces expanded collaboration with Tempus in precision medicine to accelerate R&D - Marketscreener.com - October 19th, 2022 [October 19th, 2022]
- Famous Scientific Discoveries That Changed the Course of History - 24/7 Wall St. - October 19th, 2022 [October 19th, 2022]
- Construction workers seek fulfilment of their demands - Star of Mysore - October 19th, 2022 [October 19th, 2022]
- Genetics | The Smithsonian Institution's Human Origins Program - October 13th, 2022 [October 13th, 2022]
- Genetics - Wikipedia - October 13th, 2022 [October 13th, 2022]
- Study looking at human genetics and Covid vaccine immune responses - Science Media Centre - October 13th, 2022 [October 13th, 2022]
- ASHG 2022 in Los Angeles brings together researchers from around the world to advance discoveries in genetics, genomics research - EurekAlert - October 13th, 2022 [October 13th, 2022]
- Maze Therapeutics Appoints Harold Bernstein, M.D., Ph.D., as President, Research and Development and Chief Medical Officer - Yahoo Finance - October 13th, 2022 [October 13th, 2022]
- The Age of the Pangenome Dawns - DNA Science - PLOS - October 13th, 2022 [October 13th, 2022]
- Influence of the microbiome, diet and genetics on inter-individual variation in the human plasma metabolome - Nature.com - October 13th, 2022 [October 13th, 2022]
- Genome editing technologies: final conclusions of the re-examination of Article 13 of the Oviedo Convention - Council of Europe - October 13th, 2022 [October 13th, 2022]
- Global Biobank Meta-analysis Initiative making genome-wide association studies more diverse and representative - EurekAlert - October 13th, 2022 [October 13th, 2022]
- New NHS genetic testing service could save thousands of children in England - The Guardian - October 13th, 2022 [October 13th, 2022]
- Covid protection may be boosted by genes, study shows - Yahoo News Australia - October 13th, 2022 [October 13th, 2022]
- Genomics in Cancer Care Market is estimated to be US$ 72.61 billion by 2032 with a CAGR of 16.3% during the forecast period 2032 - By PMI -... - October 13th, 2022 [October 13th, 2022]
- Identification of hub genes and candidate herbal treatment in obesity through integrated bioinformatic analysis and reverse network pharmacology |... - October 13th, 2022 [October 13th, 2022]
- Our *Homo sapiens* ancestors shared the world with Neanderthals, Denisovans and other types of humans whose DNA lives on in our genes -... - October 8th, 2022 [October 8th, 2022]
- Blue Eyed People Have a Single Ancestor | History of Yesterday - History of Yesterday - October 6th, 2022 [October 6th, 2022]
- Heart infection could be cause of death of Polish, US hero - ABC News - October 6th, 2022 [October 6th, 2022]
- 23andMe Announces Trials-in-Progress Poster Presentation on 23ME-00610, An Investigational Antibody Targeting CD200R1, at The Society for... - October 6th, 2022 [October 6th, 2022]
- The Genetic Drivers Of Longevity In Mice, Humans And Worms - Science 2.0 - October 6th, 2022 [October 6th, 2022]
- ANGPTL7, a therapeutic target for increased intraocular pressure and glaucoma | Communications Biology - Nature.com - October 6th, 2022 [October 6th, 2022]
- 'Neanderthal Man' Nobel Prize winner Svante Pbo revolutionized anthropology. Here is a look back at his groundbreaking 2014 memoir - Genetic Literacy... - October 6th, 2022 [October 6th, 2022]
- Understanding Human Genetic Variation - NCBI Bookshelf - September 14th, 2022 [September 14th, 2022]
- Genetics - National Institute of General Medical Sciences (NIGMS) - September 14th, 2022 [September 14th, 2022]
- People with ME invited to take part in major genetic study - The Independent - September 14th, 2022 [September 14th, 2022]
- Ketamine Promising for Rare Condition Linked to Autism - Medscape - September 14th, 2022 [September 14th, 2022]
- How a small, unassuming fish helps reveal gene adaptations - University of Wisconsin-Madison - September 14th, 2022 [September 14th, 2022]
- How Nutrigenomics Explores Links Between Nutrition And Genes - Health Digest - September 14th, 2022 [September 14th, 2022]