Expressed sequence tags for genes: a review

Expressed sequence tags (ESTs) are partial sequences from the extremities o f complementary DNA (cDNA) resulting from a single pass sequencing of clone s from cDNA libraries, and different ESTs can be obtained from one gene. Se quence information from ESTs can be used for deciphering the function and t he 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 regulate d genes. In order to identify genes involved in particular processes one ca n select a specific group of mRNAs. For such a selection, classical techniq ues include subtraction or differential screening and new techniques, using polymerase chain reaction (PCR) amplification, are now available. For stud ies on the organisation of the genome the main use of ESTs is the determina tion 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 can didate' approach. ESTs also contribute to comparative genetics and they can help to decipher gene function by comparison between species, even genetic ally distant ones. Thus, combining sequence, functional and localisation da ta, ESTs contribute to an integrated approach to the genome. (C) Inra/Elsev ier, Paris.