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ChIP-seq

4 studies

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ChIP-seq stands for chromatin immunoprecipitation followed by sequencing. It uses an antibody to enrich DNA fragments associated with a chosen protein or histone modification, then sequences those fragments to map enrichment across the genome.

Epigenetics papers use ChIP-seq when they need to know where a histone mark or factor sits and how that occupancy changes with stress or cell type. It answers 'where is this modification, and does it track transcription?' The main limitation is that occupancy resemblance (for example Kcr looking like H3K9ac) is not a functional requirement, and several papers here use ChIP, CasIP, or methylation arrays rather than histone ChIP-seq.

What can a ChIP-seq peak establish about gene regulation?

Start with the findings and their cited studies, then compare the boundaries below.

  • Rice histone lysine butyrylation and crotonylation were mapped by mass spectrometry and ChIP-seq and compared with H3K9ac and stress transcriptomes. Many Kcr sites sit on H3/H4; Kbu/Kcr resemble acetylation distribution and change with metabolic stress. The maps do not prove every site is required for a specific stress phenotype.

    Histone acylations respond to plant stress

  • FECR1 was identified by dCas9 chromatin immunoprecipitation (CasIP) of RNAs at the FLI1 promoter in MDA-MB231 cells, then shown to activate FLI1 epigenetically via TET1/DNMT1 and to promote invasion, with FLI1 higher in tumour than adjacent tissue. CasIP is occupancy of RNA at a locus, not a histone-mark ChIP-seq atlas, and human data are observational.

    FLI1 circRNA FECR1 drives metastasis

Before applying these findings

Compare the antibody, controls, and assay before comparing peaks. Binding or enrichment alone does not establish a causal effect on gene expression.

A tension to inspect

Only the rice histone-acylation paper is clearly genome-wide ChIP-seq of chromatin marks (Kbu/Kcr versus H3K9ac under stress). Foxp3 work is candidate-locus ChIP; FECR1 is CasIP of promoter RNAs; Yoruba data are 27K methylation arrays. Treating them as one ChIP-seq method overstates shared technology.

Use the Claims tab to inspect each claim and its supporting, challenging, or qualifying studies.

Inspect source passages

Histone acylations respond to plant stress

These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.

Rice (and related plants for detection).

Background Post-translational modifications of histones affect chromatin state and gene expression.

Histone lysine butyrylation and crotonylation.

Histone acetylation/deacetylation is an essential process in the epigenetic regulation of diverse biological processes, including environmental stress responses in plants [–].
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Inspect source passages

FLI1 circRNA FECR1 drives metastasis

These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.

1% formaldehyde used to fix CasIP complexes.

After puromycin selection, stable cells were treated with 1% formaldehyde to fix the dCas9-gRNA- FLI1 promoter chromatin complex.

FECR1 identity?

FECR1, a FLI1 exonic circular RNA that binds to the FLI1 promoter
Read passages in the original paper

This is a selected set of studies, not an exhaustive literature review. A watch follows covered updates in PaperFren.

How does ChIP-seq work?
Researchers prepare and fragment chromatin, use an antibody to isolate fragments associated with the target, purify and sequence the DNA, and align the reads to a reference genome. Enrichment is assessed against a suitable control and checked across biological replicates.
What does a ChIP-seq peak tell you?
A peak marks a genomic region enriched for fragments associated with the target relative to background. It does not by itself establish direct binding, a change in gene expression, or a causal role for the target.
How is ChIP-seq different from RNA-seq?
ChIP-seq maps DNA associated with a selected protein or histone mark. RNA-seq measures RNA abundance. Comparing them can relate occupancy to transcription, but correlation alone does not prove regulation.

Method references: ENCODE experiment guidelines · ENCODE histone ChIP-seq standards

Keep up with this explanation

Watch changes to PaperFren’s ChIP-seq explanation and its linked findings. The four studies on this page include related assays; only the rice histone-acylation study is described here as genome-wide histone ChIP-seq. This watch covers this page, rather than every new ChIP-seq publication.

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Studies

4

Findings

4

4 supporting · 0 challenging · 0 qualifying citations

Open tensions

2

Currently

What we know

  1. Rice histone lysine butyrylation and crotonylation were mapped by mass spectrometry and ChIP-seq and compared with H3K9ac and stress transcriptomes. Many Kcr sites sit on H3/H4; Kbu/Kcr resemble acetylation distribution and change with metabolic stress. The maps do not prove every site is required for a specific stress phenotype.
  2. FECR1 was identified by dCas9 chromatin immunoprecipitation (CasIP) of RNAs at the FLI1 promoter in MDA-MB231 cells, then shown to activate FLI1 epigenetically via TET1/DNMT1 and to promote invasion, with FLI1 higher in tumour than adjacent tissue. CasIP is occupancy of RNA at a locus, not a histone-mark ChIP-seq atlas, and human data are observational.
  3. Foxp3 locus ChIP plus bisulphite sequencing compared natural Tregs, thymocytes and TGF-β–induced Foxp3+ cells: a TSDR-like element is demethylated in stable Tregs, and weak demethylation predicts unstable induced Foxp3. This 2007 design is locus-specific ChIP and methylation, mostly in mouse, not a genome-wide ChIP-seq of histone marks.
  4. Illumina 27K methylation in 77 Yoruba LCLs related to genotypes and RNA-seq: inter-individual methylation variation tracks genetics and correlates with expression. That is a methylation array plus RNA-seq, not ChIP-seq; LCLs may differ from primary tissues.

Largest unresolved question

Only the rice histone-acylation paper is clearly genome-wide ChIP-seq of chromatin marks (Kbu/Kcr versus H3K9ac under stress). Foxp3 work is candidate-locus ChIP; FECR1 is CasIP of promoter RNAs; Yoruba data are 27K methylation arrays. Treating them as one ChIP-seq method overstates shared technology.

Procedure

How it works

The main stages of the method. Specific protocols and analysis choices vary between studies.

  1. Crosslink the cells

    Crosslinked protocols use fixation to preserve protein–DNA associations before chromatin preparation. Native ChIP can omit fixation, particularly for histone targets; the protocol affects what the experiment captures.

  2. Fragment the chromatin

    Sonication or enzymatic digestion breaks chromatin into fragments. Fragment size and preparation affect resolution and background, so protocols and controls matter when comparing maps.

  3. Immunoprecipitate the target

    An antibody enriches fragments associated with the chosen protein or histone modification. Antibody specificity and validation are essential: enrichment can reflect off-target binding as well as the intended target.

  4. Reverse the crosslinks and purify

    Heat and protease undo the fixation and strip the protein away, leaving the DNA that was bound. What gets sequenced from here on is ordinary DNA — the protein identity survives only as the reason those particular fragments were enriched.

  5. Sequence and align to the genome

    The enriched library is sequenced and the reads are mapped back to a reference genome, turning the pulled-down fragments into read depth at genomic coordinates. Repetitive regions where reads cannot be placed uniquely stay dark.

  6. Call peaks against a control

    Compare aligned read enrichment with a matched control and evaluate reproducibility across biological replicates. Peaks or broad enriched regions indicate target-associated signal above background; they do not establish that the target causes a nearby gene’s behavior.

Common misconceptions

  • If Kcr ChIP-seq peaks match H3K9ac, crotonylation has been shown to be required for the stress transcriptome.

    Many Kcr sites on H3/H4 resemble acetylation distribution and change with metabolic stress. Resemblance and dynamics are not proof that every site is required for a named stress phenotype.

  • Foxp3 protein in TGF-β–induced cells means the locus has the same chromatin lock as natural Tregs.

    ChIP and bisulphite sequencing show a TSDR-like element demethylated in stable Tregs; weak demethylation predicts unstable induced Foxp3. Protein-positive is not the lock.

  • A 27K methylation array in LCLs is ChIP-seq of transcription-factor binding.

    The Yoruba study measured Illumina 27K methylation versus genotypes and RNA-seq in 77 lines. It does not map protein occupancy by ChIP-seq, and transformed LCLs may differ from primary tissues.

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