A system of cluster analysis for genome-wide expression data from DNA microarray hybridization is de- scribed that uses standard statistical algorithms to arrange genes according to similarity in pattern of gene expression. The output is displayed graphically, conveying the clustering and the underlying expression data simultaneously in a form intuitive for biologists. We have found in the budding yeast Saccharomyces cerevisiae that clustering gene expression data groups together efficiently genes of known similar function, and we find a similar tendency in human data. Thus patterns seen in genome-wide expression experiments can be inter- preted as indications of the status of cellular processes. Also, coexpression of genes of known function with poorly charac- terized or novel genes may provide a simple means of gaining leads to the functions of many genes for which information is not available currently.

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Cluster analysis and display of genome-wide expression patterns

We have mapped and quantified mouse transcriptomes by deeply sequencing them and recording how frequently each gene is represented in the sequence sample (RNA-Seq). This provides a digital measure of the presence and prevalence of transcripts from known and previously unknown genes. We report reference measurements composed of 41–52 million mapped 25-base-pair reads for poly(A)-selected RNA from adult mouse brain, liver and skeletal muscle tissues. We used RNA standards to quantify transcript prevalence and to test the linear range of transcript detection, which spanned five orders of magnitude. Although >90% of uniquely mapped reads fell within known exons, the remaining data suggest new and revised gene models, including changed or additional promoters, exons and 3′ untranscribed regions, as well as new candidate microRNA precursors. RNA splice events, which are not readily measured by standard gene expression microarray or serial analysis of gene expression methods, were detected directly by mapping splice-crossing sequence reads. We observed 1.45 × 10 5 distinct splices, and alternative splices were prominent, with 3,500 different genes expressing one or more alternate internal splices. The mRNA population specifies a cell’s identity and helps to govern its present and future activities. This has made transcriptome analysis a general phenotyping method, with expression microarrays of many kinds in routine use. Here we explore the possibility that transcriptome analysis, transcript discovery and transcript refinement can be done effectively in large and complex mammalian genomes by ultra-high-throughput sequencing. Expression microarrays are currently the most widely used methodology for transcriptome analysis, although some limitations persist. These include hybridization and cross-hybridization artifacts 1–3 , dye-based detection issues and design constraints that preclude or seriously limit the detection of RNA splice patterns and previously unmapped genes. These issues have made it difficult for standard array designs to provide full sequence comprehensiveness (coverage of all possible genes, including unknown ones, in large genomes) or transcriptome comprehensiveness (reliable detection of all RNAs of all prevalence classes, including the least abundant ones that are physiologically relevant). Other

/pdf/mapping-and-quantifying-mammalian-transcriptomes-by-rna-seq-1egh5oivst.pdf

Mapping and quantifying mammalian transcriptomes by RNA-Seq.

RNA-Seq is a recently developed approach to transcriptome profiling that uses deep-sequencing technologies. Studies using this method have already altered our view of the extent and complexity of eukaryotic transcriptomes. RNA-Seq also provides a far more precise measurement of levels of transcripts and their isoforms than other methods. This article describes the RNA-Seq approach, the challenges associated with its application, and the advances made so far in characterizing several eukaryote transcriptomes.

/pdf/rna-seq-a-revolutionary-tool-for-transcriptomics-bj1lajhogb.pdf

RNA-Seq: a revolutionary tool for transcriptomics

The Gene Expression Omnibus (GEO) project was initiated in response to the growing demand for a public repository for high-throughput gene expression data. GEO provides a flexible and open design that facilitates submission, storage and retrieval of heterogeneous data sets from high-throughput gene expression and genomic hybridization experiments. GEO is not intended to replace in house gene expression databases that benefit from coherent data sets, and which are constructed to facilitate a particular analytic method, but rather complement these by acting as a tertiary, central data distribution hub. The three central data entities of GEO are platforms, samples and series, and were designed with gene expression and genomic hybridization experiments in mind. A platform is, essentially, a list of probes that define what set of molecules may be detected. A sample describes the set of molecules that are being probed and references a single platform used to generate its molecular abundance data. A series organizes samples into the meaningful data sets which make up an experiment. The GEO repository is publicly accessible through the World Wide Web at http://www.ncbi.nlm.nih.gov/geo.

Gene Expression Omnibus: NCBI gene expression and hybridization array data repository

Glioblastoma multiforme (GBM) is the most common and lethal type of brain cancer. To identify the genetic alterations in GBMs, we sequenced 20,661 protein coding genes, determined the presence of amplifications and deletions using high-density oligonucleotide arrays, and performed gene expression analyses using next-generation sequencing technologies in 22 human tumor samples. This comprehensive analysis led to the discovery of a variety of genes that were not known to be altered in GBMs. Most notably, we found recurrent mutations in the active site of isocitrate dehydrogenase 1 (IDH1) in 12% of GBM patients. Mutations in IDH1 occurred in a large fraction of young patients and in most patients with secondary GBMs and were associated with an increase in overall survival. These studies demonstrate the value of unbiased genomic analyses in the characterization of human brain cancer and identify a potentially useful genetic alteration for the classification and targeted therapy of GBMs.

http://science.sciencemag.org/content/sci/321/5897/1807.full.pdf

An Integrated Genomic Analysis of Human Glioblastoma Multiforme

PROBLEM TO BE SOLVED: To provide a method for preparing a short nucleotide sequence (tag) which is useful to identify a cDNA oligonucleotide and is derived from a restricted position in a mRNA or a cDNA. SOLUTION: This is the method of preparing a tag for identifying the cDNA oligonucleotide. The above method comprises preparing the cDNA oligonucleotide bearing 5' and 3' terminals, collecting cDNA fragments by cutting the cDNA oligonucleotide with a restriction enzyme at the first restriction endonuclease site, separating a cDNA oligonucleotide bearing 5' or 3' terminal and connecting an oligonucleotide linker to the isolated cDNA fragment bearing the cDNA oligonucleotide 5' or 3' terminal. Here, the oligonucleotide linker contains the recognition site of the second restriction endonuclease enzyme and the isolated cDNA fragment is cut with the second restriction endonuclease enzyme which cuts the cDNA fragment in a section separated from the recognition site to obtain the tag for identifying the cDNA oligonucleotide.

http://science.sciencemag.org/content/sci/270/5235/484.full.pdf

Serial analysis of gene expression

Phosphatidylinositol 3-kinases (PI3Ks) are known to be important regulators of signaling pathways. To determine whether PI3Ks are genetically altered in cancers, we analyzed the sequences of the P13K gene family and discovered that one family member, PIK3CA, is frequently mutated in cancers of the colon and other organs. The majority of mutations clustered near two positions within the P13K helical or kinase domains. PIK3CA represents one of the most highly mutated oncogenes yet identified in human cancers and is useful as a diagnostic and therapeutic target.

Mutations of the pik3ca gene in human cancers

Serial analysis of gene expression, SAGE, a method for the rapid quantitative and qualitative analysis of transcripts, has been improved to provide more genetic information about each analyzed transcript. In SAGE, defined sequence tags corresponding to expressed genes are isolated and analyzed. Sequencing of over, 1,000 defined tags in a short period of time (e.g. hours) reveals a gene expression pattern characteristic of the function of a cell or tissue. Moreover, SAGE is useful as a gene discovery tool for the identification and isolation of novel squence tags corresponding to novel transcripts and genes.

Serial analysis of transcript expression using long tags

Serial analysis of gene expression, SAGE, a method for the rapid quantitative and qualitative analysis of transcripts, has been improved to provide more genetic information about each analyzed transcript by use of MmeI restriction endonuclease. In SAGE, defined sequence tags corresponding to expressed genes are isolated and analyzed. Sequencing of over 1,000 defined tags in a short period of time (e.g., hours) reveals a gene expression pattern characteristic of the function of a cell or tissue. Moreover, SAGE is useful as a gene discovery tool for the identification and isolation of novel sequence tags corresponding to novel transcripts and genes.

Victor Velculescu

Papers

Serial analysis of gene expression

Mutations of the pik3ca gene in human cancers

Serial analysis of transcript expression using long tags

Serial analysis of transcript expression using MmeI and long tags

Oligonucleotide, tagged with nucleotide sequences, for the serial analysis of gene expression (SAGE)