JUN COOPERATES WITH THE ETS DOMAIN PROTEIN POINTED TO INDUCE PHOTORECEPTOR R7 FATE IN THE DROSOPHILA EYE

R7 photoreceptor fate in the Drosophila eye is induced by the activati on of the Sevenless receptor tyrosine kinase and the RAS/MAP kinase si gnal transduction pathway. We show that expression of a constitutively activated JUN isoform in ommatidial precursor cells is sufficient to induce R7 fate independent of upstream signals normally required for p hotoreceptor determination. We present evidence that JUN interacts wit h the ETS domain protein Pointed to promote R7 formation. This interac tion is cooperative when both proteins are targeted to the same promot er and is antagonized by another ETS domain protein, YAN, a negative r egulator of R7 development, furthermore, phyllopod, a putative transcr iptional target of RAS pathway activation during R7 induction, behaves as a suppressor of activated JUN. Taken together, these data suggest that JUN and Pointed act on common target genes to promote neuronal di fferentiation in the Drosophila eye, and that phyllopod might be such a common target.