Unknown,Transcriptomics,Genomics,Proteomics

Dataset Information

Tiling path analysis of yeast

ABSTRACT: There is abundant transcription from eukaryotic genomes unaccounted for by protein coding genes. A high-resolution genome-wide survey of transcription in a well annotated genome will help relate transcriptional complexity to function. By quantifying RNA expression on both strands of the complete genome of Saccharomyces cerevisiae using a high-density oligonucleotide tiling array, this study identifies the boundary, structure, and level of coding and noncoding transcripts. A total of 85% of the genome is expressed in rich media. Apart from expected transcripts, we found operon-like transcripts, transcripts from neighboring genes not separated by intergenic regions, and genes with complex transcriptional architecture where different parts of the same gene are expressed at different levels. We mapped the positions of 3' and 5' UTRs of coding genes and identified hundreds of RNA transcripts distinct from annotated genes. These nonannotated transcripts, on average, have lower sequence conservation and lower rates of deletion phenotype than protein coding genes. Many other transcripts overlap known genes in antisense orientation, and for these pairs global correlations were discovered: UTR lengths correlated with gene function, localization, and requirements for regulation; antisense transcripts overlapped 3' UTRs more than 5' UTRs; UTRs with overlapping antisense tended to be longer; and the presence of antisense associated with gene function. These findings may suggest a regulatory role of antisense transcription in S. cerevisiae. Moreover, the data show that even this well studied genome has transcriptional complexity far beyond current annotation.

ORGANISM(S): Saccharomyces cerevisiae

SUBMITTER: Wolfgang Huber

PROVIDER: E-TABM-14 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Publications

Transcript mapping with high-density oligonucleotide tiling arrays.

Huber Wolfgang W Toedling Joern J Steinmetz Lars M LM

Bioinformatics (Oxford, England) 20060620 16

<h4>Motivation</h4>High-density DNA tiling microarrays are a powerful tool for the characterization of complete transcriptomes. The two major analytical challenges are the segmentation of the hybridization signal along genomic coordinates to accurately determine transcript boundaries and the adjustment of the sequence-dependent response of the oligonucleotide probes to achieve quantitative comparability of the signal between different probes.<h4>Results</h4>We describe a dynamic programming algo ...[more]

PMID: 16787969

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Project description:Recent data from several organisms indicate that the transcribed portions of genomes are larger and more complex than expected, and many functional properties of transcripts are not based on coding sequences but on regulatory sequences in untranslated regions or non-coding RNAs. Alternative start and polyadenylation sites and regulation of intron splicing add additional dimensions to the rich transcriptional output. This transcriptional complexity has been sampled mainly using hybridization-based methods under one or a few conditions. We applied direct high-throughput sequencing of cDNAs, complemented with different expression data from high-density tiling arrays, to globally sample transcripts of the fission yeast Schizosaccharomyces pombe, independently from available gene annotations. We interrogated transcriptomes under multiple conditions, including exponential proliferation, meiotic differentiation and environmental stress, and in RNA processing mutants, to reveal the dynamic plasticity of the transcriptional landscape as a function of environmental, developmental, and genetic factors. High-throughput sequencing proved to be a powerful and quantitative method to deeply sample transcriptomes at unprecedented resolution. Unlike hybridization, sequencing showed little, if any, background noise and was sensitive enough to detect widespread transcription in >90% of the genome, including traces of RNAs that were not actively transcribed or rapidly degraded. The combined sequencing and strand-specific array data provided rich information on novel, mostly non-coding transcripts, untranslated regions and gene structures, thus refining the existing genome annotation. Sequence trans-reads spanning exon-exon or exon-intron junctions gave unique insight into a surprising variability in splicing efficiency across introns and genes. Splicing efficiency was largely coordinated with transcriptional efficiency, and hundreds of introns showed regulated splicing as a function of cellular proliferation or differentiation.

Project description:Background: Epigenetic modifications of histones and regulation of chromatin structure have been implicated in regulation of virulence gene families in P. falciparum. To better understand chromatin-mediated gene regulation, we used a high-density oligonucleotide microarray to map the position and enrichment of nucleosomes across the entire genome of P. falciparum at three time points of the intra-erythrocytic developmental cycle (IDC) in vitro. We used an unmodified histone H4 antibody for chromatin immunoprecipitation of nucleosome-bound DNA. Results: We observed generally low nucleosomal occupancy of intergenic regions and higher occupancy of protein coding regions. In contract to the overall small fluctuation of nucleosomal occupancy in most coding regions throughout the IDC, subtelomeric genes encoding surface proteins such as var and rif, as well as some core chromosomal genes such as transcription factors, showed large changes in chromatin structure. Telomeres harbored a region with the highest nucleosomal occupancy of the genome and also exhibited large changes with higher nucleosomal occupancy at schizont stages. While many of these subtelomeric genes were previously shown to be modified by H3K9 trimethylation, we also identified some housekeeping genes in core chromosome regions that showed extensive changes in chromatin structure but do not contain this modification. tRNA and basal transcription factor genes showed low nucleosomal occupancy at all times, suggesting of an open chromatin structure that might be permissive for constitutively high levels of expression. Generally, nucleosomal occupancy was not correlated with the steady-state mRNA levels. Several var genes were exceptions: the var gene with the highest expression level showed the lowest nucleosomal occupancy, and selection of parasites for var2CSA expression resulted in lower nucleosomal occupancy at the var2CSA locus. We identified nucleosome-free regions in intergenic regions that may serve as transcription start sites or transcription factor binding sites. Using the nucleosomal occupancy data as the baseline, we further mapped the genome-wide enrichment of H3K9 acetylation and detected general enrichment of this mark in intergenic regions. Conclusions: These data on nucleosome enrichment changes add to our understanding of the influence of chromatin structure on the regulation of gene expression. Histones are generally enriched in coding regions, and relatively poor in intergenic regions. Histone enrichment patterns allow for identification of new putative gene-coding regions. Most genes do not show correlation between chromatin structure and steady-state mRNA levels, indicating the dominant roles of other regulatory mechanisms. We present a genome-wide nucleosomal occupancy map, which can be used as a reference for future experiments of histone modification mapping. Three ChIP with unmodified histone H4 antibodies were performed on ring, trophozoite and schizont stage synchronized parasites. Only one experiment was performed per time point. H3K9ac antibody ChIP was performed on trophozoite stage cells. All samples were normalized to 3D7 strain genomic DNA hybridizations.

Dataset Information

Tiling path analysis of yeast

Publications

Transcript mapping with high-density oligonucleotide tiling arrays.

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