A SUBSET OF NOTCH FUNCTIONS DURING DROSOPHILA EYE DEVELOPMENT REQUIRESU(H) AND THE E(SPL) GENE-COMPLEX

The Notch signalling pathway is involved in many processes where cell fate is decided. Previous work showed that Notch is required at succes sive steps during R8 specification in the Drosophila eye. Initially, N otch enhances atonal expression and promotes atonal function. After at onal autoregulation has been established, Notch signalling represses a tonal expression during lateral specification. In this paper we invest igate which known components of the Notch pathway are involved in each signalling process. Using clonal analysis we show that a ligand of No tch, Delta, is required along with Notch for both proneural enhancemen t and lateral specification, while the downstream components Suppresso r-of-Hairless and Enhancer-of-Split are involved only in lateral speci fication. Our data point to a distinct signal transduction pathway dur ing proneural enhancement by Notch. Using misexpression experiments we also show that particular Enhancer-of-split bHLH genes can differ gre atly in their contribution to lateral specification.