Serial analysis of gene expression: Probing transcriptomes for molecular targets

Serial analysis of gene expression (SAGE) is a method to rapidly count expressed RNA transcripts in a population of cells. The basic approach is to isolate a small transcript tag, clone multiple tags into a sequencing vector and efficiently count the tags by automated sequencing. The result is the fractional representation of nearly every transcript (the transcriptome), in a digital format. These tag counts can be compared to other SAGE libraries yielding differentially expressed genes. Analysis of the differentially expressed genes has been used to determine which genes are involved in a disease process. The promise of this technology is that by understanding when genes are pathologically altered in expression, therapies can be formulated to target the appropriate gene or pathway.