Hunting for differentially expressed genes

Differentially expressed genes are usually identified by comparing steady-s tate mRNA concentrations. Several methods have been used for this purpose, including differential hybridization, cDNA subtraction, differential displa y and, more recently, DMA chips. Subtractive hybridization has significantl y improved after the polymerase chain reaction was incorporated into the or iginal method and many new protocols have been established. Recently, the a vailability of the well-known coding sequences for some organisms has great ly facilitated gene expression analysis using high-density microarrays. Her e, we describe some of these modifications and discuss the benefits and dra wbacks of the various methods corresponding to the main advances in this fi eld.