THE NOTCH SIGNALING PATHWAY IS REQUIRED FOR ENHANCER OF SPLIT BHLH PROTEIN EXPRESSION DURING NEUROGENESIS IN THE DROSOPHILA EMBRYO

The Enhancer of split locus is required during many cell-fate decision s in Drosophila, including the segregation of neural precursors in the embryo. We have generated monoclonal antibodies that recognise some o f the basic helix-loop-helix proteins encoded by the Enhancer of split locus and have used them to examine expression of Enhancer of split p roteins during neurogenesis. The proteins are expressed in a dynamic p attern in the ventral neurogenic region and are confined to those ecto dermal cells that surround a neuroblast in the process of delaminating . There is no staining in the neuroblasts themselves. We have also exa mined the relationship between Enhancer of split protein accumulation and the Notch signalling pathway. Protein expression is abolished in a number of neurogenic mutant backgrounds, including Notch, but is incr eased as a result of expressing a constitutively active Notch product. We conclude that Notch signalling activity is directly responsible fo r the accumulation of basic helix-loop-helix proteins encoded by the E nhancer of split locus.