Large-scale tag/PCR-based gene expression profiling.

An intriguing enigma in molecular biology is how genes within a single genome are differentially expressed in different cell types of a multicellular organism, or in response to different developmental or environmental queues in a single cell type. Quantification of transcript levels on a genome-wide scale, often termed transcript profiling, provides a powerful approach to identifying protein-coding and non-coding RNAs functionally relevant to a given biological process. Indeed, transcriptome analysis has been a key area of biological inquiry for decades and successfully produced discoveries in a multitude of processes and disease states, and in an increasingly large number of organisms. The evolution of technologies with increasing levels of informational content, ranging from hybridization-based technologies such as Northern blot analysis and microarrays to tag/polymerase chain reaction (PCR)- and sequence-based technologies including differential display and SAGE, along with the next-generation sequencing, has provided hope for revealing the molecular details of biological systems as they respond to change. This review is an overview of selected high throughput tag/PCR-based methods for genome-wide expression profiling amenable to high-throughput automated operation in any standard laboratory.