PHOSPHORYLATION OF DROSOPHILA JUN BY THE MAP KINASE ROLLED REGULATES PHOTORECEPTOR DIFFERENTIATION

Drosophila Jun (D-Jun) is a nuclear component of the receptor tyrosine kinase/Ras signal transduction pathway which triggers photoreceptor d ifferentiation during eye development. Here we show that D-Jun is a su bstrate for the ERK-related Drosophila MAP kinase Rolled, which has pr eviously been shown to be a part of this pathway A D-Jun mutant that c arries alanines in place of the Rolled phosphorylation sites acts as a dominant suppressor of photoreceptor cell fate if expressed in the ey e imaginal disc. In contrast, a mutant in which the phosphorylation si tes are replaced by phosphate-mimetic Asp residues, as well as a VP16- D-Jun fusion protein, can promote photoreceptor differentiation. These data implicate Jun phosphorylation in the choice between neuronal and non-neuronal fate during Drosophila eye development.