JUN cooperates with the ETS domain protein pointed to induce photoreceptor R7 fate in the Drosophila eye

R7 photoreceptor fate in the Drosophila eye induced by the activation of the Sevenless receptor tyrosine kinase and the RAS/MAP kinase signal 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 photoreceptor determination. We present evidence that JUN interacts with the ETS domain protein Pointed to promote R7 formation. This interaction is cooperative when both proteins are targeted to the same promoter and is antagonized by another ETS domain protein, YAN, a negative regulator of R7 development. Furthermore, phyllopod, a putative transcriptional 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 differentiation in the Drosophila eye, and that phyllopod might be such a common target.