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Effect of read-mapping biases on detecting allele-specific expression from RNA-sequencing data.

ABSTRACT: Next-generation sequencing has become an important tool for genome-wide quantification of DNA and RNA. However, a major technical hurdle lies in the need to map short sequence reads back to their correct locations in a reference genome. Here we investigate the impact of SNP variation on the reliability of read-mapping in the context of detecting allele-specific expression (ASE).We generated sixteen million 35 bp reads from mRNA of each of two HapMap Yoruba individuals. When we mapped these reads to the human genome we found that, at heterozygous SNPs, there was a significant bias towards higher mapping rates of the allele in the reference sequence, compared to the alternative allele. Masking known SNP positions in the genome sequence eliminated the reference bias but, surprisingly, did not lead to more reliable results overall. We find that even after masking, $\sim$5-10\% of SNPs still have an inherent bias towards more effective mapping of one allele. Filtering out inherently biased SNPs removes 40\% of the top signals of ASE. The remaining SNPs showing ASE are enriched in genes previously known to harbor cis-regulatory variation or known to show uniparental imprinting. Our results have implications for a variety of applications involving detection of alternate alleles from short-read sequence data. Scripts, written in Perl and R, for simulating short reads, masking SNP variation in a reference genome, and analyzing the simulation output are available upon request from JFD.

ORGANISM(S): Homo sapiens

PROVIDER: GSE18156 | GEO | 2009/10/22

SECONDARY ACCESSION(S): PRJNA119495

REPOSITORIES: GEO

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Effect of read-mapping biases on detecting allele-specific expression from RNA-sequencing data.

Project description:Next-generation sequencing has become an important tool for genome-wide quantification of DNA and RNA. However, a major technical hurdle lies in the need to map short sequence reads back to their correct locations in a reference genome. Here we investigate the impact of SNP variation on the reliability of read-mapping in the context of detecting allele-specific expression (ASE).We generated sixteen million 35 bp reads from mRNA of each of two HapMap Yoruba individuals. When we mapped these reads to the human genome we found that, at heterozygous SNPs, there was a significant bias towards higher mapping rates of the allele in the reference sequence, compared to the alternative allele. Masking known SNP positions in the genome sequence eliminated the reference bias but, surprisingly, did not lead to more reliable results overall. We find that even after masking, $\sim$5-10\% of SNPs still have an inherent bias towards more effective mapping of one allele. Filtering out inherently biased SNPs removes 40\% of the top signals of ASE. The remaining SNPs showing ASE are enriched in genes previously known to harbor cis-regulatory variation or known to show uniparental imprinting. Our results have implications for a variety of applications involving detection of alternate alleles from short-read sequence data. Scripts, written in Perl and R, for simulating short reads, masking SNP variation in a reference genome, and analyzing the simulation output are available upon request from JFD. RNA-Seq on two YRI Hapmap cell lines. Each individual sequenced on two lanes of the Illumina Genome Analyzer

2009-10-22 | E-GEOD-18156 | biostudies-arrayexpress

Allele-specific expression and eQTL analysis in mouse adipose tissue

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Allele-specific expression and eQTL analysis in mouse adipose tissue

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Analysis of Allelic bias in gDNA, cDNA and ChIP with H3K27me3 and H3K36me3 antibody with multiplexed padlock probe approach

Project description:In this experiment, we asked how the allelic distribution of the active and repressive chromatin marks in clonal cell lines relates to the transcriptional allelic bias. A multiplexed padlock probe approach (Zhang et al., 2009) enabled us to assess allelic bias in heterozygous exonic SNPs in two clones with GM12878 genotype, and four clones from GM13130 cells. We used this approach to assess allelic bias in H3K27me3 and H3K36me3 ChIP samples simultaneously with cDNA from the same cells, as well as ChIP input and genomic DNA controls. In order to pool data from two individuals, one of which (GM13130) lacked complete genotypes for parents, we assessed SNP bias as reference and alternative alleles (rather than maternal or paternal bias). SNPs in cDNA were assigned to one of three bins: reference allele bias; no bias; and alternative allele bias. For these groups, allelic bias in H3K27me3 (Fig.4B) and H3K36me3 (Fig.4C) was determined. In unbiased loci, both H3K27me3 and H3K36me3 were equally represented. In contrast, preferential expression of an allele was associated with elevated levels of H3K36me3 and decreased levels of H3K27me3 on that allele. Both effects were highly significant (p<2x10e-9). Genes predicted to have MAE were about four-fold over-represented among genes where SNPs showed significant bias (Fig.4D). SNPs with skewed H3K27me3 and H3K36me3 distribution were highly enriched in the genes predicted as MAE (p<10e-6 and p=0.01, respectively; two-tailed Fisher's exact test). This suggests that the asymmetric distribution of the histone modifications is to a large extent due to the genes that have the chromatin signature of monoallelic expression.

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Extensive and coordinated control of allele-specific expression by both transcription and translation in Candida albicans

Project description:Though sequence differences between alleles are often limited to a few polymorphisms, these differences can cause large and widespread allelic variation at the expression level. Such allele-specific expression (ASE) has been extensively explored at the level of transcription but not translation. Here we measured ASE in the diploid yeast Candida albicans at both the transcriptional and translational levels using RNA-seq and ribosome profiling, respectively. Since C. albicans is an obligate diploid, our analysis isolates ASE arising from cis elements in a natural, non-hybrid organism, where allelic effects reflect evolutionary forces. Importantly, we find that ASE arising from translation is of a similar magnitude as transcriptional ASE, both in terms of the number of genes affected and the magnitude of the bias. We further observe coordination between ASE at the levels of transcription and translation for single genes. Specifically, reinforcing relationships—where transcription and translation favor the same allele—are more frequent than expected by chance, consistent with selective pressure tuning ASE at multiple regulatory steps. Finally, we parameterize alleles based on a range of properties and find that SNP location and predicted mRNA-structure stability are associated with translational ASE in cis. Since this analysis probes more than 4,000 allelic pairs spanning a broad range of variations, our data provide a genome-wide view into the relative impacts of cis elements that regulate translation.

2014-03-14 | GSE52236 | GEO

Analysis of Allelic bias in gDNA, cDNA and ChIP with H3K27me3 and H3K36me3 antibody with multiplexed padlock probe approach

2014-02-07 | E-GEOD-53628 | biostudies-arrayexpress

Extensive and coordinated control of allele-specific expression by both transcription and translation in Candida albicans

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Powerful Identification of Cis-regulatory SNPs in Human Primary Monocytes Using Allele-Specific Gene Expression

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