Specificity in JAK-STAT signalling

Abstract Since the original identification of Janus kinases by Wilks et al. (l, 2) and the isolation of STATl and STAT2 by the Darnell laboratory, an entire new field of discovery has emerged and come to dominate research in cytokine signalling during the last decade. This wealth of information now provides us with some clues as to the function of these novel tyrosine kinases and transcription factors. To date, four Janus kinases (Fig. 1) and seven STAT (Fig. 2) transcription factors have been identified in mammalian species. With the exception of TYK2 and STAT2, gene-targeting experiments have been reported for all members of the JAK-STAT family. Drosophila expresses a Janus kinase homologue, called hopscotch, indicating that the JAK-STAT pathway is conserved throughout evolution. The STAT transcription factors are more widespread, having been isolated in Caenorhabditis elegans, Drosophila spp., and Dictyostelium spp.