Expression Profiling as a Tool for Diagnosis and Pathway Discovery: Experimental Design and Technical Considerations

Expression profiling using microarrays is a widely used technique to scan for differences or changes in the steady-state levels of messenger ribonucleic acids (mRNAs) in cells or tissues. The majority of the genes of a number of organisms can be assayed for mRNA transcripts using 25 mer oligonucleotide probe sets (f10-40 oligonucleotides per gene) [human, mouse, rat, plant (Arabidopsis), Drosophila, worm (C. elegans), yeast, bacteria (E. coli, P. aeruginosa)]. In addition, 60-75 mer oligonucleotide microarrays (1 oligo/ gene) are becoming commercially available. The major technical advance in microarrays has been the ability to conduct highly parallel data generation (f1 million oligonucleotide hybridizations assayed per human sample).