1 Institute for Systems Biology Enabling new genomics technologies in the ISB Microarray Facility B. Marzolf 1, P. Troisch 1 Multiple platforms support varying needs Institute for Systems Biology 7 th Annual International Symposium, Systems Biology and Engineering We gratefully acknowledge support from NIGMS P50GMO76547 The Microarray Facility at ISB supports multiple platforms to accommodate varying research needs. The platforms differ in probe density, cost and flexibility, giving each unique advantages for varying applications: Affymetrix – Highest probe density, lowest flexibility Agilent – Medium probe density, high flexibility Spotted – Low probe density, high flexibility, lowest cost for low density arrays Probe density Relative Cost 10K Affymetrix Mouse/Human Exon Affymetrix Tiling 10M 100K 1M Spotted Halobacterium expression Affymetrix Mouse/Human Gene ST Agilent Mouse/Human 4X Agilent Mouse/Human microRNA Agilent Tiling Increasing density and vendor competition reduce per-array costs for expression studies Early improvements in microarray probe density were focused on increasing the number of transcripts that could be interrogated per array. Eventually, densities increased to the point where roughly every gene in a mammalian genome could be probed on a single array. Now that densities well exceed whole-genome coverage (for per-gene expression arrays), commercial microarray manufacturers are producing lower-cost, smaller surface area arrays. Agilent Affymetrix NimbleGen Agilent synthesizes up to 8 separately hybridizable arrays of up to 15,000 probes each on a single microarray slide. New, lower-priced whole- genome mammalian arrays are available in 4 array slides, with 44,000 probes per array. Having multiple arrays on one slide allows the parallel processing multiple samples, increasing throughput. Affymetrix synthesizes probes onto a quartz wafer that has a standard size. The wafer can then be sliced into anywhere from 49 to 400 arrays, depending upon the size of each individual array. Each array is packaged in a separate cartridge. NimbleGen arrays, as with Agilent, have multiple arrays per each slide, with up to 4 (and soon 12) separately hybridizable arrays. The 4-array slides allow up to 72,000 probes per array. Collaboration with the Informatics Core New technologies require new tools for data management and analysis. Infrastructure development is done in close collaboration with the Informatics Core, making internally and externally developed analysis tools more accessible to a varied set of microarray users. GenePattern, a framework created by Broad Institute, is utilized in several of the analysis pipelines. Affymetrix raw CEL files Affymetrix Exon Array Normalization Bioconductor background subtraction, normalization, summarization Annotation with Synonym Web Service Annotated expression data Agilent Multiple Scan Normalization Raw intensity multi-scan intensity measurements Choice of Bioconductor normalization methods Combine scans to extend linear range with Masliner Normalized data Tiling microarrays increase in density and range of applications Tiling microarrays typically utilize the maximum probe densities available on each platform to provide the highest resolution of probe tiling. Initially usage of tiling microarrays focused on chromatin IP on chip (chIP- chip) experiments, but has expanded to include transcriptome structure profiling and more specific assays such as nucleosome mapping. Transcriptome Nucleosome Mapping RNA purification and labeling roughly follow conventional methods, except that specific subpopulations may be selected for: polyadenylated RNA negative selection for ribosomal RNA preservation of small RNAs that may be lost by conventional methods ÷ = Raw intensities must be corrected for probe-specific effects RNA genomic Signal is plotted against the chromosome and segmented into regions of differing expression Cross-link nucleosomes to DNA Digest linker DNA between nucleosomes Purify out nucleosome-bound DNA Label and hybridize Lee et al., Nature Genetics, September 2007 David et al., PNAS, March 2006 Aligning transcription start sites across all verified transcripts and plotting the average nucleosome occupancy reveals a pattern: Plotting nucleosome positions and tiling data long chromosomes provides additional evidence for non- annotated transcripts Targeting miRNA in Total RNA Samples on Agilent Microarrays Existence of miRNA in Samples Check for presence of miRNAs in the total RNA sample using a small RNA Bioanalyzer chip. The miRNAs will produce a shallow peak in the 10nt to 40nt region, followed by a larger tRNA peak and rRNAs. Labeling of miRNA Agilent uses a direct labeling method without amplification or size fractionation. A total RNA sample of 100ng is treated with calf intestinal alkaline phosphatase (CIP) to dephosphorylate the RNA in preparation for labeling. The sample is heat and DMSO denatured prior to the addition of a Cy3 fluorophore. A single Cy3 fluorophore is attached to the 3’ phosphate of a 3’, 5’-cytidine bisphosphate (pCp-Cy3). The pCp-Cy3 molecule is joined to the 3’ end of a miRNA by T4 RNA ligase. A mini chromatography column is used to desalt and remove any unincorporated pCp-Cy3 molecules. Total RNA  Dephosphorylate  Denature  Label with pCp-Cy3  Purify  Hybridize Probe Design To increase probe-miRNA specific binding Agilent has – *Added a G residue (shown in black) to the 5’ end of each probe complimentary to the 3’ C residue (green) attached during labeling (diagram A and B) *Devised a 5’ hairpin structure (shown in blue) added to the end of each probe to eliminate the binding of large non-specific pieces of RNA (diagram A and B) *Reduced probe length from the 5’ end of the complimentary miRNA in order to destabilize certain probes