MARELLE ACTS DOWNSTREAM OF THE DROSOPHILA HOP/JAK KINASE AND ENCODES A PROTEIN SIMILAR TO THE MAMMALIAN STATS

Abstract We have identified a putative Drosophila STAT protein named Marelle that exhibits mutant phenotypes identical to mutations in the Hopscotch/JAK kinase. We show that a reduction in the amount of marelle gene activity suppresses the phenotype associated with a gain-of-function mutation in hopscotch and enhances the phenotype associated with a weak hopscotch mutation. We propose that Hopscotch activates Marelle to regulate transcription of target genes such as the pair rule gene even-skipped . Our results demonstrate the existence of an invertebrate JAK/STAT system.