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bio-epitranscriptomics-modification-visualization

Create metagene plots and browser tracks for RNA modification data. Use when visualizing m6A distribution patterns around genomic features like stop codons.

personAuthor: jakexiaohubgithub
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Version Compatibility

Reference examples tested with: Guitar 2.18+ (Bioconductor), MetaPlotR (GitHub, unversioned), deepTools 3.5+, ggcoverage 1.4+, pyGenomeTracks 3.8+, Gviz 1.46+, ComplexHeatmap 2.18+, ggseqlogo 0.2+, ggplot2 3.5+, rtracklayer 1.62+, GenomicFeatures 1.54+, BSgenome.Hsapiens.UCSC.hg38 1.4+, TxDb.Hsapiens.UCSC.hg38.knownGene 3.18+, ChIPseeker 1.38+.

Before using code patterns, verify installed versions match. If versions differ:

  • R: packageVersion('Guitar') then ?GuitarPlot to verify parameters
  • CLI: <tool> --help; deepTools <tool> --help

If R throws unused argument or argument is missing, the API moved between Bioconductor minor releases. Guitar's older API used txdb= while newer uses txTxdb=; verify with ?GuitarPlot. deepTools bamCompare --operation log2 is the modern syntax (older --ratio log2 is being phased out).

RNA Modification Visualisation

"Make the canonical m6A metagene plot for my paper" -> Render the 5'UTR / CDS / 3'UTR transcript-feature metagene with stop-codon enrichment for visual confirmation of the canonical m6A topology (THE smoke test that the antibody-IP captured real m6A), the peak-feature-distribution stacked bar ("where do my peaks land?" Figure 1), peak-centred heatmaps clustered by condition, IP-over-Input paired browser tracks at specific loci, the DRACH sequence logo as a sanity check on antibody specificity, and the volcano / MA plots for differential modification. CRITICAL: the stop-codon enrichment plot is a biological-QC anchor — a MeRIP dataset that does NOT show enrichment at and around the stop codon indicates IP failure, wrong antibody, wrong protocol, or the assay captured a different modification (e.g., m1A is centred at TSS, not stop). Build this plot FIRST as a smoke test BEFORE any downstream visualisation.

  • R: Guitar::GuitarPlot(peakBedFiles, txTxdb=...) -- canonical transcript-feature metagene (THE field-standard plot)
  • CLI: deeptools computeMatrix scale-regions ... + plotProfile -- genome-coordinate metagene
  • R: ComplexHeatmap::Heatmap() on peak-centred signal matrix -- peak-centred heatmap clustered by condition
  • CLI: pyGenomeTracks --tracks tracks.ini --region chr:start-end -- multi-track browser plot
  • R: ggcoverage::ggcoverage(data=track, mark.region=peaks) + geom_gene() -- ggplot2-based browser tracks
  • R: ggseqlogo::ggseqlogo(seqs) -- DRACH sequence logo from peak-centre 5-mers
  • R: ChIPseeker::annotatePeak() + ggplot2 stacked bar -- 5'UTR / CDS / 3'UTR feature distribution

The Single Most Important Modern Insight -- Stop-codon enrichment in the metagene plot is the biological QC anchor — a MeRIP dataset without it is suspect

Dominissini 2012 Nature 485:201 and Meyer 2012 Cell 149:1635 — concurrent papers from different labs using different protocols (MeRIP-seq and m6A-seq, respectively) — both independently showed m6A enrichment at and around the stop codon (3'UTR-proximal end of the CDS). This is the most robust biological signal in MeRIP-seq, reproduced across cell types, conditions, and decades. A metagene plot from a MeRIP library that does NOT show stop-codon enrichment indicates: (1) IP failure (antibody did not bind), (2) wrong antibody, (3) wrong protocol (e.g., the assay actually captured a different modification — m1A is centred at TSS, not stop), or (4) sample-RNA degradation. Build the Guitar metagene plot FIRST after peak calling, BEFORE any downstream visualisation, as a smoke test. The corollary: the 5'UTR / CDS / 3'UTR feature-distribution stacked bar (the "where do m6A peaks land?" Figure 1) should always be PAIRED with the metagene plot, because the stacked bar can look right (peaks land in 3'UTR / stop area) while the metagene is off (peak DENSITY not concentrated at the codon itself), or vice versa. The two plots are complementary biology-QC anchors, not redundant.

Algorithmic Taxonomy

| Tool / plot | Mechanism | Inputs | Output | Strength | Fails when | |-------------|-----------|--------|--------|----------|------------| | Guitar GuitarPlot (Cui 2016 Biomed Res Int 2016:8367534) | Per-peak distance computation relative to TSS / start / stop / TES; feature-scaled rendering | BED + TxDb | PDF + per-feature density | THE field-standard m6A metagene; transcript-feature-aware | Older / newer API uses txdb= vs txTxdb= argument | | MetaPlotR (Olarerin-George 2017 Bioinformatics 33:1563) | Alternative metagene approach with different segment-rescaling | BED + GTF | PDF | Alternative segment rescaling philosophy | GitHub-only; less actively maintained | | deepTools computeMatrix + plotProfile (Ramírez 2016 NAR 44:W160) | Genome-coordinate signal aggregation over scaled gene regions | bigWig + BED | PDF + matrix | Fast; flexible region/anchor choice; well-tested ChIP-seq lineage | Not transcript-feature-aware; misses 5'UTR / CDS / 3'UTR distinction | | deepTools plotHeatmap | Same matrix as plotProfile; rendered as heatmap with row clustering | bigWig matrix | PDF | Standard peak-centred heatmap | Single-condition view (use ComplexHeatmap for multi-condition clustering) | | ComplexHeatmap (Gu 2016 Bioinformatics 32:2847) | General-purpose heatmap with multi-dimensional clustering | numeric matrix | PDF / interactive | Multi-condition cluster + annotation; publication-quality | Requires pre-computed signal matrix | | pyGenomeTracks (Lopez-Delisle 2021 Bioinformatics 37:422) | Config-file (INI) driven multi-track browser plot | bigWig / bed / GTF + INI config | PDF / PNG | Reproducible browser figures via config; multi-track stacking | INI config syntax error-prone for new users | | ggcoverage (Song & Wang 2023 BMC Bioinformatics 24:309) | ggplot2-native track plotting | bigWig / BAM + GTF | ggplot2 object | ggplot2 syntax; combinable with annotation layers | Newer tool; smaller user base than Gviz | | Gviz (Hahne & Ivanek 2016 Methods Mol Biol 1418:335) | R/Bioconductor general genome track | bigWig / BAM / GRanges + TxDb | PDF / R plot | Most flexible R-native; long Bioconductor history | Heavier than ggcoverage; steeper learning curve | | IGV / IGV.js (Robinson 2011 Nat Biotechnol 29:24) | Interactive browser via Java / JS | bigWig / BAM / bed | interactive | Standard for ad-hoc inspection | Not reproducible for figure generation | | UCSC Track Hubs | UCSC genome browser display | bigWig + hub.txt + genomes.txt | URL | Public-display standard | Setup overhead for short projects | | ggseqlogo (Wagih 2017 Bioinformatics 33:3645) | Sequence-logo rendering in ggplot2 | character vector of equal-length sequences | ggplot2 object | Native ggplot2; method='bits' or 'probability' | Requires equal-length sequences | | MEME-ChIP (Machanick & Bailey 2011 Bioinformatics 27:1696) | Motif discovery + logo | BED + genome | HTML + PWM | Comprehensive motif suite; gold standard | Heavier than ggseqlogo for simple visualisation | | HOMER findMotifsGenome.pl (Heinz 2010 Mol Cell 38:576) | Motif discovery via cumulative hypergeometric on shuffled background | BED + genome | HTML + motif files | Battle-tested; RNA mode via -rna | Less flexible output formatting than MEME |

Decision Tree by Scenario

| Scenario | Recommended | Why wrong choices fail | |----------|-------------|------------------------| | Canonical Figure 1 metagene plot for m6A paper | Guitar GuitarPlot with TxDb -- transcript-feature scaled | deepTools computeMatrix is genome-coordinate only; misses 5'UTR / CDS / 3'UTR distinction | | QC: does my MeRIP show stop-codon enrichment? | Guitar GuitarPlot FIRST -- the canonical biological-QC anchor | Skipping this and rushing to peak counting is the most common QC failure | | Browser-track Figure for a specific locus | pyGenomeTracks (config-file driven; reproducible) OR ggcoverage (ggplot2-native) | IGV is interactive but not reproducible for figures | | Multi-condition peak-centred heatmap with clustering | ComplexHeatmap; row-cluster k-means; annotate by condition | deepTools plotHeatmap is single-condition view | | DRACH sequence logo from peak centres | ggseqlogo on resized peak ranges (width=5, fix='center') | MEME-ChIP heavier than needed for visualisation only | | Differential m6A volcano plot | ggplot2 native (see m6a-differential) -- modification-visualization should NOT duplicate | Duplicating volcano recipe across skills inflates content | | Genome-coordinate metagene over custom features | deepTools computeMatrix scale-regions; plotProfile | Guitar restricted to transcript features; doesn't scale to arbitrary BED | | Cross-sample paired IP/input track display | bamCompare -> log2 bigWig; pyGenomeTracks multi-track | Single bigWig hides the IP/input pairing structure | | 5'UTR / CDS / 3'UTR stacked bar | ChIPseeker annotatePeak -> ggplot2 stacked bar | Manual annotation error-prone; ChIPseeker handles edge cases | | Reproducing Dominissini 2012 / Meyer 2012 stop-codon plot | Guitar GuitarPlot; the canonical recipe | Other tools produce similar but not identical plots |

Methodology evolves; before high-stakes figure generation, web-search "Guitar Bioconductor release notes" and "pyGenomeTracks vs ggcoverage" for current best practice.

Guitar Transcript-Feature Metagene (THE Canonical Plot)

Goal: Render the canonical m6A metagene plot showing peak density along scaled transcript features (5'UTR, CDS, 3'UTR), with the stop-codon-proximal enrichment that is the field's biological QC anchor.

Approach: Load called peaks from BED; pass to GuitarPlot with the matched TxDb; export per-feature density and the PDF.

library(Guitar)
library(TxDb.Hsapiens.UCSC.hg38.knownGene)
library(rtracklayer)

txdb <- TxDb.Hsapiens.UCSC.hg38.knownGene

# Older Guitar versions: argument is `txdb=`; newer: `txTxdb=`. Verify with ?GuitarPlot.
GuitarPlot(
    txTxdb           = txdb,
    stBedFiles       = list('exomepeak2_output/m6a_run1/peaks.bed'),
    miscOutFilePrefix = 'figures/m6a_metagene',
    enableCI         = FALSE,
    saveToPDFprefix  = 'figures/m6a_metagene'
)

If txTxdb= is rejected, fall back to txdb= and consult ?GuitarPlot. The expected output: stop-codon-proximal enrichment, with peak density rising toward and peaking near the stop codon in the 3'UTR. If the plot does NOT show this pattern, do not proceed to downstream visualisation — investigate IP / antibody / protocol failure in merip-preprocessing.

deepTools Genome-Coordinate Metagene

Goal: Render a genome-coordinate metagene over scaled gene regions using deepTools, useful when transcript-feature scaling is not needed or when the regions of interest are not standard genes (custom BED).

Approach: Build a signal matrix with computeMatrix scale-regions from a bigWig (typically IP-over-Input log2 from merip-preprocessing); render as profile plot + heatmap.

mkdir -p figures

computeMatrix scale-regions \
    --regionsFileName refs/protein_coding.bed \
    --scoreFileName tracks/IP_rep1_over_Input_rep1.bw \
    --regionBodyLength 2000 \
    --upstream 500 \
    --downstream 500 \
    --skipZeros \
    --numberOfProcessors 8 \
    --outFileName figures/m6a_matrix.gz

plotProfile \
    --matrixFile figures/m6a_matrix.gz \
    --outFileName figures/m6a_profile.pdf \
    --plotTitle 'm6A IP over Input metagene' \
    --plotType lines

plotHeatmap \
    --matrixFile figures/m6a_matrix.gz \
    --outFileName figures/m6a_heatmap.pdf \
    --colorMap RdBu_r \
    --plotTitle 'm6A IP over Input heatmap'

scale-regions is the right mode for gene-body metagene (5'-end-to-3'-end scaled to common length); reference-point is for peak-centred plots. For peak-centred, see the next section.

Peak-Centred Heatmap

Goal: Render a peak-centred heatmap of IP-over-Input signal at +/-window around each peak, clustered by condition or by signal pattern, for cross-condition comparison.

Approach: Use deepTools computeMatrix reference-point --referencePoint center for the matrix; ComplexHeatmap for the clustered render.

computeMatrix reference-point \
    --regionsFileName exomepeak2_output/m6a_run1/peaks.bed \
    --scoreFileName tracks/IP_rep1_over_Input_rep1.bw tracks/IP_rep2_over_Input_rep2.bw tracks/IP_rep3_over_Input_rep3.bw \
    --referencePoint center \
    --upstream 500 \
    --downstream 500 \
    --binSize 25 \
    --skipZeros \
    --numberOfProcessors 8 \
    --outFileName figures/peak_centred_matrix.gz \
    --outFileNameMatrix figures/peak_centred_matrix.tab

plotHeatmap \
    --matrixFile figures/peak_centred_matrix.gz \
    --outFileName figures/peak_centred_heatmap.pdf \
    --kmeans 3 \
    --colorMap viridis \
    --plotTitle 'm6A signal centred at peaks'

For multi-condition heatmap with annotations, parse the matrix into R and use ComplexHeatmap:

library(ComplexHeatmap)
library(circlize)

# deepTools --outFileNameMatrix has a 3-line JSON-style header before per-bin numeric columns.
raw <- read.delim('figures/peak_centred_matrix.tab', skip=3, header=FALSE)
mat <- as.matrix(raw[, -(1:6)])

col_fun <- colorRamp2(c(-2, 0, 2), c('blue', 'white', 'red'))

Heatmap(
    mat,
    name              = 'log2 IP / Input',
    col               = col_fun,
    cluster_columns   = FALSE,
    cluster_rows      = TRUE,
    row_km            = 3,
    show_row_names    = FALSE,
    show_column_names = FALSE,
    column_title      = 'Peak-centred (+/- 500 bp)'
)

IP-vs-Input Paired Browser Tracks via pyGenomeTracks

Goal: Render publication-quality genome-browser tracks at a specific locus showing paired IP / Input bigWig tracks, the IP/input log2 ratio, peak calls, and gene annotation; reproducible via INI config.

Approach: Build a tracks.ini config file listing each track type (bigwig, bed, gtf); invoke pyGenomeTracks --tracks tracks.ini --region chr:start-end.

[x-axis]
where = top
fontsize = 12

[IP rep1]
file = tracks/IP_rep1.bw
title = IP rep1
color = #d62728
height = 2
min_value = 0

[Input rep1]
file = tracks/Input_rep1.bw
title = Input rep1
color = #1f77b4
height = 2
min_value = 0

[IP / Input log2]
file = tracks/IP_rep1_over_Input_rep1.bw
title = log2 IP / Input
color = #2ca02c
height = 2

[spacer]

[m6A peaks]
file = exomepeak2_output/m6a_run1/peaks.bed
title = m6A peaks (exomePeak2)
color = #ff7f0e
height = 1
labels = false

[genes]
file = refs/annotation.gtf
title = GENCODE genes
height = 2
prefered_name = gene_name
merge_transcripts = true

pyGenomeTracks \
    --tracks tracks.ini \
    --region chr19:54,792,000-54,799,000 \
    --outFileName figures/browser_metti3_locus.pdf \
    --width 14 \
    --plotWidth 12

ggcoverage ggplot2-Native Browser Track

Goal: Render genome-browser tracks in ggplot2 syntax for combining with other ggplot2 layers (annotations, peak highlights, custom theming).

Approach: LoadTrackFile() parses a bigWig / bigBed / BAM input into the dataframe ggcoverage expects; chain ggcoverage() with geom_gene() for transcript annotation; mark.region requires columns start, end, and label.

library(ggcoverage)
library(rtracklayer)

peaks <- as.data.frame(import('exomepeak2_output/m6a_run1/peaks.bed'))

track.df <- LoadTrackFile(
    track.file = 'tracks/IP_rep1_over_Input_rep1.bw',
    format     = 'bw',
    region     = 'chr19:54792000-54799000'
)

mark.df <- data.frame(
    start = peaks$start,
    end   = peaks$end,
    label = peaks$name
)

ggcoverage(
    data        = track.df,
    color       = 'auto',
    mark.region = mark.df
) +
    geom_gene(gtf.file = 'refs/annotation.gtf') +
    ggplot2::theme_classic()

DRACH Sequence Logo

Goal: Render a sequence logo of peak-centre 5-mers as a sanity check that the called peak set is enriched for the DRACH consensus motif.

Approach: Resize peak GRanges to fixed 5-nt centred windows; extract genomic sequences; pass to ggseqlogo with method='probability'.

library(Biostrings)
library(BSgenome.Hsapiens.UCSC.hg38)
library(ggseqlogo)
library(rtracklayer)

peaks <- import('exomepeak2_output/m6a_run1/peaks.bed')

peak_centres <- resize(peaks, width=5, fix='center')

genome <- BSgenome.Hsapiens.UCSC.hg38
seqs <- as.character(getSeq(genome, peak_centres))

ggseqlogo(seqs, method='probability') +
    ggplot2::labs(title='Peak-centre 5-mer (DRACH consensus expected)',
                  subtitle='Sanity check on antibody specificity — NOT a per-peak filter')

The expected output: a logo showing approximately D-R-A-C-H consensus (D=A/G/U, R=A/G, A=methylated, C, H=A/C/U) with A clearly dominating position 3. If the logo does NOT show DRACH-like enrichment, the IP failed OR the wrong antibody was used.

5'UTR / CDS / 3'UTR Stacked Bar

Goal: Render the Figure 1 "where do my peaks land?" stacked bar showing the fraction of peaks in 5'UTR vs CDS vs 3'UTR vs intron, paired with the metagene to confirm canonical m6A topology.

Approach: Use ChIPseeker annotatePeak() with a matched TxDb; aggregate to per-feature counts; render as ggplot2 stacked bar.

library(ChIPseeker)
library(TxDb.Hsapiens.UCSC.hg38.knownGene)
library(rtracklayer)
library(ggplot2)
library(dplyr)

txdb <- TxDb.Hsapiens.UCSC.hg38.knownGene
peaks <- import('exomepeak2_output/m6a_run1/peaks.bed')

peak_anno <- annotatePeak(peaks, TxDb=txdb, level='transcript', verbose=FALSE)
anno_df <- as.data.frame(peak_anno@anno)

anno_df$feature <- gsub(' \\(.*\\)', '', anno_df$annotation)

feature_counts <- anno_df %>%
    group_by(feature) %>%
    summarise(n=n()) %>%
    mutate(fraction=n/sum(n)) %>%
    arrange(desc(fraction))

ggplot(feature_counts, aes(x='m6A peaks', y=fraction, fill=feature)) +
    geom_col(width=0.5) +
    scale_y_continuous(labels=scales::percent_format()) +
    labs(x=NULL, y='Fraction of peaks', title='m6A peak distribution across transcript features') +
    theme_minimal()

Per-Method Failure Modes

Metagene without stop-codon enrichment

Trigger: Guitar GuitarPlot of called peaks does NOT show enrichment at and around the stop codon.

Mechanism: Canonical m6A topology (Dominissini 2012 / Meyer 2012) shows stop-codon-proximal enrichment. Absence indicates (1) IP failure, (2) wrong antibody, (3) wrong protocol, (4) sample-RNA degradation, OR (5) the assay captured a different modification (m1A is TSS-centred; m5C distribution differs).

Symptom: Metagene is flat OR peaks at TSS (m1A signature) OR peaks in introns (unusual).

Fix: Do NOT proceed to downstream analysis. Diagnose at the merip-preprocessing layer: plotFingerprint, per-transcript IP/input distribution, antibody-lot QC. Re-do the IP if necessary. The metagene plot is the biological QC anchor; without it, all downstream interpretation is suspect.

DRACH logo not enriched

Trigger: ggseqlogo of peak-centre 5-mers shows no consensus, OR shows a non-DRACH-like motif.

Mechanism: Antibody specificity failure OR wrong protocol. Anti-m6A antibodies have ~70% DRACH-context enrichment on real m6A peaks; a failed IP captures random sequences with no consensus.

Fix: Re-inspect IP enrichment in merip-preprocessing. If IP is clean but DRACH logo is absent, the assay may have captured a different modification — investigate before claiming m6A.

Guitar txdb= vs txTxdb= argument confusion

Trigger: GuitarPlot(stBedFiles=..., txdb=txdb) rejected with "unused argument" error.

Mechanism: Guitar changed the argument name between Bioconductor releases — txdb= (older) vs txTxdb= (newer).

Fix: Try alternative; consult ?GuitarPlot for installed version. Pin Guitar version in reproducible analyses.

deepTools genome-coordinate metagene used where transcript-feature is needed

Trigger: computeMatrix scale-regions over a BED of genes used to show "5'UTR / CDS / 3'UTR enrichment".

Mechanism: deepTools scales by genomic length, NOT by transcript-feature length. A gene with long 5'UTR and short CDS will scale 5'UTR more than CDS; the metagene loses 5'UTR / CDS / 3'UTR semantics.

Fix: Use Guitar (transcript-feature-aware) for 5'UTR / CDS / 3'UTR semantics. Use deepTools for genome-coordinate metagene over arbitrary BED.

IGV-only browser figure in published paper

Trigger: Figure 4 of paper shows an IGV screenshot of one locus; not reproducible from code.

Mechanism: IGV is interactive; the figure cannot be re-generated from a config file. Reviewers cannot reproduce the figure if track files change.

Fix: Use pyGenomeTracks (INI config) or ggcoverage (ggplot2 script) for figures intended for publication. IGV is for ad-hoc inspection only.

bamCompare --ratio log2 deprecation

Trigger: Older deepTools syntax --ratio log2 used; newer requires --operation log2.

Fix: Switch to --operation log2. Both currently work but --ratio is being phased out.

ggseqlogo "sequences must be equal length"

Trigger: Mixed-length peak sequences passed to ggseqlogo.

Mechanism: ggseqlogo requires equal-length input strings.

Fix: Resize peak ranges to fixed width before extraction: resize(peaks, width=5, fix='center').

pyGenomeTracks INI typo

Trigger: Track section header missing brackets, OR file = instead of file= (whitespace inconsistency).

Fix: Use the documented INI syntax precisely; bracketed section headers; consistent whitespace around =. Validate with pyGenomeTracks --tracks tracks.ini --region 'chr:start-end' --outFileName out.pdf and iterate on errors.

Reconciliation: When Plots Disagree

| Pattern | Likely cause | Action | |---------|--------------|--------| | Metagene shows stop-codon enrichment but stacked bar has many 5'UTR peaks | 5'UTR peaks are present but density is concentrated at stop codon | Both plots are correct; report together | | Guitar metagene and deepTools metagene look very different | Guitar transcript-feature-scaled vs deepTools genome-scaled | Both correct; Guitar for 5'UTR / CDS / 3'UTR semantics; deepTools for genome coordinates | | Peak-centred heatmap shows two clusters; condition annotation crosses cluster boundary | Biological signal not condition-aligned; OR clustering driven by per-peak coverage variance | Inspect per-cluster fold-change; consider removing low-coverage peaks before re-clustering | | pyGenomeTracks shows IP track higher than Input but bamCompare bigWig shows log2 near zero | Track signal magnitudes are CPM-normalised; absolute counts and log2 ratios are different summaries | Report log2 ratio as the primary; per-track CPM as supplement | | DRACH logo enriched but stacked bar shows mostly intronic peaks | Intronic m6A (Louloupi 2018 nascent transcripts) | Genuine biology; report intronic vs exonic separately; consider library prep (poly-A vs ribo-depleted) | | Volcano plot symmetric but most differential peaks in 3'UTR | Differential is feature-restricted | Cross-check with per-feature differential testing; biological interpretation |

Quantitative Thresholds

| Quantity | Threshold | Source / rationale | |----------|-----------|--------------------| | Guitar metagene -- expected pattern | Stop-codon-proximal enrichment, 3'UTR > CDS > 5'UTR density | Dominissini 2012 Nature 485:201; Meyer 2012 Cell 149:1635 | | deepTools metagene scaled-region length | 2000 bp body + 500 bp flanks | Convention; covers typical mammalian gene span | | Peak-centred heatmap window | +/-500 bp around peak centre | Standard convention; covers MeRIP fragment width | | Peak-centred heatmap k-means clusters | 3-5 typical | Cluster count informed by condition count + signal heterogeneity | | ggseqlogo expected DRACH pattern | A dominant at position 3 (the methylated A); C dominant at position 4 | DRACH consensus | | pyGenomeTracks figure width | 10-14 inches | Standard publication width | | Browser-track region width | 5-50 kb | Locus-context dependent | | 5'UTR / CDS / 3'UTR / intron+other expected distribution | ~10% / ~30% / ~50% / ~10% for canonical m6A | Per published m6A atlases | | DRACH logo "method" parameter | 'probability' for visual; 'bits' for information-theoretic | ggseqlogo convention | | Per-feature stacked bar minimum peaks | >=100 | Below this, fractions are noisy | | Cross-replicate metagene divergence | Should be near-identical within condition | If replicates' metagenes diverge, failed-IP suspect in merip-preprocessing |

Common Errors

| Error / symptom | Cause | Solution | |-----------------|-------|----------| | Guitar txTxdb rejected | Older version uses txdb | Switch argument name; consult ?GuitarPlot | | Guitar PDF blank | BED file empty OR chromosome mismatch with TxDb | Verify peak BED has peaks; reconcile chromosome naming | | deepTools computeMatrix errors with "no regions" | BED file empty OR file path wrong | Verify BED is non-empty and path correct | | pyGenomeTracks INI parse error | Bracket / whitespace inconsistency | Match documented INI syntax exactly | | ggcoverage region not displayed | Region beyond bigWig coverage; OR chromosome naming mismatch | Verify bigWig contains region; reconcile chr1 vs 1 | | ggseqlogo throws "equal length" error | Mixed-length sequences | resize(peaks, width=5, fix='center') before extracting | | ComplexHeatmap clustering hangs | Very large peak set (>100k) | Subset to top N peaks; or use deepTools plotHeatmap k-means | | bamCompare --ratio log2 deprecation warning | Newer syntax | Switch to --operation log2 | | IGV screenshot not reproducible | Interactive tool | Switch to pyGenomeTracks / ggcoverage | | ggseqlogo logo blank | Empty seqs input OR all sequences are gaps / Ns | Verify peak BED resolves to valid genomic sequences via getSeq() | | Stacked bar shows >100% | Peak annotation overlap counted multiple times | Use annotatePeak with explicit hierarchy | | ComplexHeatmap colour scale wrong | colorRamp2 breaks at outliers | Set scale based on robust quantiles (quantile(x, 0.05), 0, quantile(x, 0.95)) |

Anticipated Reviewer Pushback

| Pushback | Response | |----------|----------| | "Does the MeRIP show the canonical stop-codon enrichment?" | Yes — Guitar metagene plot shows expected stop-codon-proximal enrichment; cited Dominissini 2012 / Meyer 2012 | | "Why Guitar and not deepTools?" | Guitar is transcript-feature-scaled (5'UTR / CDS / 3'UTR semantics); deepTools is genome-coordinate; both reported when needed | | "Is the DRACH motif enriched?" | ggseqlogo of peak-centre 5-mers; OR HOMER findMotifsGenome.pl E-value reported | | "Is the browser figure reproducible?" | Yes — pyGenomeTracks INI config OR ggcoverage R script; not IGV screenshot | | "How were peaks annotated to features?" | ChIPseeker annotatePeak with matched TxDb; hierarchy explicit | | "Why these specific clusters in the heatmap?" | k-means with k=3 chosen via elbow / silhouette; clusters reflect signal heterogeneity | | "Does the metagene differ between conditions?" | Per-condition metagenes plotted alongside; differences quantified at the feature level | | "Why is the colour scheme red-blue?" | Standard convention for log2 ratios (red = up, blue = down); colour-blind-safe palette via viridis available | | "Was a cross-check with published m6A-Atlas peaks done?" | Common-core overlap reported; cited m6A-Atlas v2 | | "Are the browser track signal magnitudes comparable across samples?" | bigWig CPM-normalised in merip-preprocessing; documented |

References

  • Dominissini D, Moshitch-Moshkovitz S, Schwartz S et al (2012) Topology of the human and mouse m6A RNA methylomes revealed by m6A-seq. Nature 485(7397):201-206. doi:10.1038/nature11112
  • Meyer KD, Saletore Y, Zumbo P, Elemento O, Mason CE, Jaffrey SR (2012) Comprehensive analysis of mRNA methylation reveals enrichment in 3' UTRs and near stop codons. Cell 149(7):1635-1646. doi:10.1016/j.cell.2012.05.003
  • Cui X, Wei Z, Zhang L et al (2016) Guitar: an R/Bioconductor package for gene annotation guided transcriptomic analysis of RNA-related genomic features. Biomed Res Int 2016:8367534. doi:10.1155/2016/8367534
  • Olarerin-George AO, Jaffrey SR (2017) MetaPlotR: a Perl/R pipeline for plotting metagenes of nucleotide modifications and other transcriptomic sites. Bioinformatics 33(10):1563-1564. doi:10.1093/bioinformatics/btx002
  • Ramírez F, Ryan DP, Grüning B et al (2016) deepTools2: a next generation web server for deep-sequencing data analysis. Nucleic Acids Res 44(W1):W160-W165. doi:10.1093/nar/gkw257
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Related Skills

  • merip-preprocessing - Generates the bigWig tracks (bamCompare log2 IP/input) used here
  • m6a-peak-calling - Generates the peak BED used for metagene + stacked bar + heatmap
  • m6a-differential - Differential results visualised via volcano + MA (those plots live in m6a-differential, not duplicated here)
  • m6anet-analysis - Per-site DRS modification calls; visualisation analogous via metagene
  • data-visualization/ggplot2-fundamentals - General ggplot2 grammar
  • data-visualization/multipanel-figures - Combining metagene + heatmap + volcano into figures
  • data-visualization/heatmaps-clustering - General heatmap clustering patterns
  • data-visualization/volcano-and-ma-plots - General volcano / MA recipes (modification-specific volcano lives in m6a-differential)
  • data-visualization/genome-tracks - General genome-track rendering (this skill adds the IP/input pairing specifics)
  • data-visualization/sequence-logos - General sequence-logo plotting (this skill adds DRACH-specific context)
  • chip-seq/chipseq-visualization - Closest sibling for browser-track + peak-centred heatmap patterns
  • pathway-analysis/enrichment-visualization - For visualising downstream pathway results