Cited by 867Gene expression and cancer classificationGenomics and Phylogenetic StudiesSingle-cell and spatial transcriptomics

The DOI matches its Crossref record; 37 of the 37 references it cites were found in a registry or an index.

GC-Content Normalization for RNA-Seq Data

Open access

Abstract

Background: Transcriptome sequencing (RNA-Seq) has become the assay of choice for high-throughput studies of gene expression. However, as is the case with microarrays, major technology-related artifacts and biases affect the resulting expression measures. Normalization is therefore essential to ensure accurate inference of expression levels and subsequent analyses thereof. Results: We focus on biases related to GC-content and demonstrate the existence of strong sample-specific GC-content effects on RNA-Seq read counts, which can substantially bias differential expression analysis. We propose three simple within-lane gene-level GC-content normalization approaches and assess their performance on two different RNA-Seq datasets, involving different species and experimental designs. Our methods are compared to state-of-the-art normalization procedures in terms of bias and mean squared error for expression fold-change estimation and in terms of Type I error and p-value distributions for tests of differential expression. The exploratory data analysis and normalization methods proposed in this article are implemented in the open-source Bioconductor R package EDASeq. Conclusions: Our within-lane normalization procedures, followed by between-lane normalization, reduce GC-content bias and lead to more accurate estimates of expression fold-changes and tests of differential expression. Such results are crucial for the biological interpretation of RNA-Seq experiments, where downstream analyses can be sensitive to the supplied lists of genes.

Overview

The claims and statistics of this paper haven’t been checked yet.

Run the check — free, no account needed. It reads the open-access text and checks the sources it cites.

A few free checks a day · papers already verified open instantly · results are public

Integrity signals

Registry

Crossref · 10.1186/1471-2105-12-480

Cites

37 of 37 references verified0 citation errors · 0 not checkable

Statistics

Figures

Figure 1 Yeast dataset: Read count vs. GC-content. Lowess fits of gene-level log(count + 1) vs. GC-content for the eight YPD lanes from the Yeast dataset, after FQ between-lane normalization. Curves are colored according to culture/library preparation. The GC-content effect is the same for lanes assaying the same culture/library preparation, but can be different for lanes assaying different cultures/library preparations. Figure S4 displays the scatterplot and lowess fit for the first YPD lane (culture/library preparation Y1, flow-cell 428R1).
Figure 1 Yeast dataset: Read count vs. GC-content. Lowess fits of gene-level log(count + 1) vs. GC-content for the eight YPD lanes from the Yeast dataset, after FQ between-lane normalization. Curves are colored according to culture/library preparation. The GC-content effect is the same for lanes assaying the same culture/library preparation, but can be different for lanes assaying different cultures/library preparations. Figure S4 displays the scatterplot and lowess fit for the first YPD lane (culture/library preparation Y1, flow-cell 428R1).CC BY · PubMed Central
Figure 2 Yeast dataset: Log-fold-change vs. GC-content. Stratified boxplots of count log-ratio vs. GC-content, after FQ between-lane normalization. Panel (a): Same culture/library preparation, YPD Y1 lanes from flow-cells 428R1 vs. 4328B. Panel (b): Different cultures/library preparations, YPD Y1 lane vs. Y2 lane from flow-cell 428R1. The GC-content effect is the same for the two lanes assaying the same culture/library preparation, so that fold-change estimates do not vary with GC-content. By contrast, the GC-content effect differs between cultures/library preparations and confounds fold-change estimation.
Figure 2 Yeast dataset: Log-fold-change vs. GC-content. Stratified boxplots of count log-ratio vs. GC-content, after FQ between-lane normalization. Panel (a): Same culture/library preparation, YPD Y1 lanes from flow-cells 428R1 vs. 4328B. Panel (b): Different cultures/library preparations, YPD Y1 lane vs. Y2 lane from flow-cell 428R1. The GC-content effect is the same for the two lanes assaying the same culture/library preparation, so that fold-change estimates do not vary with GC-content. By contrast, the GC-content effect differs between cultures/library preparations and confounds fold-change estimation.CC BY · PubMed Central
Figure 3 Yeast dataset: GC-normalized log-fold-change vs. GC-content. Stratified boxplots of count log-ratio vs. GC-content, for the two YPD cultures/library preparations of Figure 2, Panel (b), for four within-lane GC-content normalization procedures. Panel (a): Regression normalization using loess. Panel (b): Global-scaling normalization using the median. Panel (c): Full-quantile (FQ) normalization. Panel (d): Conditional quantile normalization (CQN). The first three within-lane procedures were followed by FQ between-lane normalization; CQN includes its own between-lane normalization. All methods seem to effectively reduce the dependence of fold-change on GC-content (compared to Figure 2, Panel (b)).
Figure 3 Yeast dataset: GC-normalized log-fold-change vs. GC-content. Stratified boxplots of count log-ratio vs. GC-content, for the two YPD cultures/library preparations of Figure 2, Panel (b), for four within-lane GC-content normalization procedures. Panel (a): Regression normalization using loess. Panel (b): Global-scaling normalization using the median. Panel (c): Full-quantile (FQ) normalization. Panel (d): Conditional quantile normalization (CQN). The first three within-lane procedures were followed by FQ between-lane normalization; CQN includes its own between-lane normalization. All methods seem to effectively reduce the dependence of fold-change on GC-content (compared to Figure 2, Panel (b)).CC BY · PubMed Central
Figure 4 MAQC-2 dataset: Bias in fold-change estimation. Bias in UHR/Brain expression log-fold-change estimation for different RNA-Seq normalization procedures, where bias is defined as the difference between the estimates from RNA-Seq and qRT-PCR for 638 genes assayed by both technologies. Panel (a): Boxplots of bias in log-fold-change estimates. Our three proposed normalization procedures reduce bias, while CQN tends to overestimate the UHR/Brain fold-change. Panel (b): Dependence of bias on GC-content. The points correspond to bias after only FQ between-lane normalization, the curves are lowess fits of bias vs. GC-content for different normalization procedures. There is still substantial dependence of bias on GC-content after CQN.
Figure 4 MAQC-2 dataset: Bias in fold-change estimation. Bias in UHR/Brain expression log-fold-change estimation for different RNA-Seq normalization procedures, where bias is defined as the difference between the estimates from RNA-Seq and qRT-PCR for 638 genes assayed by both technologies. Panel (a): Boxplots of bias in log-fold-change estimates. Our three proposed normalization procedures reduce bias, while CQN tends to overestimate the UHR/Brain fold-change. Panel (b): Dependence of bias on GC-content. The points correspond to bias after only FQ between-lane normalization, the curves are lowess fits of bias vs. GC-content for different normalization procedures. There is still substantial dependence of bias on GC-content after CQN.CC BY · PubMed Central
Figure 5 Yeast YPD pseudo-datasets: Type I error. Difference between actual and nominal Type I error rates vs. nominal Type I error rate, for different normalization procedures. The colored areas correspond to the most conservative and most anti-conservative curves obtained from the 35 YPD pseudo-datasets. The dashed line corresponds to a nominal unadjusted p-value of 0.05. The full-quantile GC-content normalization procedure yields the smallest area, meaning that the actual Type I error rate is closer to the nominal Type I error rate than with the other two procedures.
Figure 5 Yeast YPD pseudo-datasets: Type I error. Difference between actual and nominal Type I error rates vs. nominal Type I error rate, for different normalization procedures. The colored areas correspond to the most conservative and most anti-conservative curves obtained from the 35 YPD pseudo-datasets. The dashed line corresponds to a nominal unadjusted p-value of 0.05. The full-quantile GC-content normalization procedure yields the smallest area, meaning that the actual Type I error rate is closer to the nominal Type I error rate than with the other two procedures.CC BY · PubMed Central
Figure 6 Yeast dataset: Proportion of DE genes vs. GC-content. Here, a gene is declared DE between the three growth conditions if its nominal unadjusted p-value from the negative binomial LRT is below the threshold of 10-5 (corresponding to a nominal Bonferroni family wise error rate of 0.057 and Benjamini & Hochberg [37] false discovery rate of 4.22 × 10-5). There is a clear trend towards more detected differential expression at higher GC-content with all within-lane normalization procedures but the full-quantile.
Figure 6 Yeast dataset: Proportion of DE genes vs. GC-content. Here, a gene is declared DE between the three growth conditions if its nominal unadjusted p-value from the negative binomial LRT is below the threshold of 10-5 (corresponding to a nominal Bonferroni family wise error rate of 0.057 and Benjamini & Hochberg [37] false discovery rate of 4.22 × 10-5). There is a clear trend towards more detected differential expression at higher GC-content with all within-lane normalization procedures but the full-quantile.CC BY · PubMed Central
Figure 7 MAQC-2 dataset: p-value vs. GC-content. Median unadjusted p-value (log10) for each GC-content stratum, for microarray and RNA-Seq UHR vs. Brain DE analysis (11,081 genes detected by RNA-Seq and present on the Affymetrix chip). The figure shows that the GC-content bias is technology-related and that full-quantile within-lane normalization reduces the dependence of RNA-Seq p-values on GC-content.
Figure 7 MAQC-2 dataset: p-value vs. GC-content. Median unadjusted p-value (log10) for each GC-content stratum, for microarray and RNA-Seq UHR vs. Brain DE analysis (11,081 genes detected by RNA-Seq and present on the Affymetrix chip). The figure shows that the GC-content bias is technology-related and that full-quantile within-lane normalization reduces the dependence of RNA-Seq p-values on GC-content.CC BY · PubMed Central

Verification

Claims the paper makes

The claims and statistics of this paper haven’t been checked yet.

Run the check — free, no account needed. It reads the open-access text and checks the sources it cites.

A few free checks a day · papers already verified open instantly · results are public

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

The self-check needs the paper’s full text.

Citations

Cites

Show all 35 references

Cited by

Sorted by citations

Items 401–500 of 865

Metadata

Authors
Risso, D., Schwartz, K., Sherlock, G., & Dudoit, S.
Affiliations
  • University of Padua (IT)
  • Stanford University (US)
  • University of California, Berkeley (US)
Corresponding author
Dudoit, Sandrine
Venue
BMC Bioinformatics
Published
2011-12
Volume
12
Issue
1
Pages
480-480
ISSN
1471-2105 (ISSN-L)
OpenAlex
W2168342464
Cited by
867
References
35
Citations by year
2026: 29 · 2025: 58 · 2024: 83 · 2023: 80 · 2022: 89 · 2021: 97 · 2020: 74 · 2019: 55 · 2018: 60 · 2017: 49 · 2016: 59 · 2015: 38 · 2014: 48 · 2013: 30 · 2012: 18
FWCI
12.48
Type
journal article
Language
en
Open access
Licence
cc-by
Locations
  • BMC Bioinformatics (publishedVersion, cc-by)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Collection of Biostatistics Research Archive (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
  • eScholarship (California Digital Library) (submittedVersion)
  • Padua Research Archive (University of Padova) (submittedVersion, cc-by)
Funders
  • Università degli Studi di Padova
  • National Institutes of Health
  • National Human Genome Research Institute (R01 HG03468, R01HG003468)
  • National Institute of Allergy and Infectious Diseases (R01AI077737)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Gene expression and cancer classification
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Genomics and Phylogenetic Studies
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Single-cell and spatial transcriptomics
Keywords
RNA-seq, differential gene expression, gene expression bias, transcriptome sequencing
MeSH terms
Base Composition, Saccharomyces cerevisiae, Sequence Analysis, RNA, Gene Expression Profiling, Transcriptome

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

What counts as a claim ›How we measure confidence ›How we check this ›

Are you an author, or do you see a problem with this page? Request a review