Expressed sequence tags for genes: A review

Abstract

Expressed sequence tags (ESTs) are partial sequences from the extremities of complementary DNA (cDNA) resulting from a single pass sequencing of clones from cDNA libraries, and different ESTs can be obtained from one gene. Sequence information from ESTs can be used for deciphering the function and the organisation of the genome. From a functional viewpoint, they allow the determination of the expression profiles of genes in any particular tissue, in different conditions or status, and thus the identification of regulated genes. In order to identify genes involved in particular processes one can select a specific group of mRNAs. For such a selection, classical techniques include subtraction or differential screening and new techniques, using polymerase chain reaction (PCR) amplification, are now available. For studies on the organisation of the genome the main use of ESTs is the determination of chromosomal localisation of the corresponding genes using a somatic hybrid cell panel. This chromosomal localisation information is needed to identify genes or quantitative trait loci, according to the 'positional candidate' approach. ESTs also contribute to comparative genetics and they can help to decipher gene function by comparison between species, even genetically distant ones. Thus, combining sequence, functional and localisation data, ESTs contribute to an integrated approach to the genome.