JUN IN DROSOPHILA DEVELOPMENT - REDUNDANT AND NONREDUNDANT FUNCTIONS AND REGULATION BY 2 MAPK-SIGNAL-TRANSDUCTION PATHWAYS

Drosophila Jun is shown to be involved in different signal transductio n pathways and developmental decisions. Dorsal closure, a morphogeneti c process occurring during Drosophila embryogenesis, is regulated by H emipterous (Hep) and Basket (Bsk), homologs of JNKK and JNK, respectiv ely. Embryos lacking Jun activity exhibit a dorsal closure phenotype, very similar to that of bsk and hep mutants, indicating that Jun is a target of Hep/Bsk signaling. In eye and wing development Jun participa tes in a separate signaling pathway that is comprised of Ras, Raf, and the ERK-type kinase Rolled. In contrast to the strict requirement for Jun in dorsal closure, its role in the eye is redundant but can be un covered by mutations in other signaling components. The redundant func tion of Jun in eye development may contribute to the precision of phot oreceptor differentiation and ommatidial assembly.