Gene expression level ratios derived from spotted-glass microarrays provide valuable data on the molecular underpinnings of cellular states and behavior. However, it is difficult to relate ratio data to absolute expression levels and to compare experimental conditions assayed with different cDNA reference samples. Using a combination of experimental and computational tools, we have developed a system that (1) maintains the flexible, cost-effective, and high-throughput nature of the spotted-glass microarray platform, (2) avoids the loss of transcript abundance information in ratio data, (3) facilitates the direct comparison of data across multiple conditions, experiments, and laboratories, and (4) increases the range of gene expression detectable by correcting saturated values. Future application of this system should permit the measurement of RNA expression on the absolute scale of transcripts/cell from any organism for which oligo-based spotted-glass microarrays are available. For more information see:  

• General Introduction: an overview of the benefits of absolute abundance measurements and spotted glass microarrays
• Calibrated Oligo Reference: details of our calibrated oligo reference system for measuring RNA expression levels on an absolute scale using spotted glass microarrays
• Masliner: information about our masliner software for extending the signal intensity range by combining data from multiple scans of a single array
• Protocols: a collection of useful microarray-related protocols