ROLE OF NOTCH AND ACHAETE-SCUTE COMPLEX IN THE EXPRESSION OF ENHANCEROF SPLIT BHLH PROTEINS

The proteins encoded by Notch and the Enhancer of split complex are co mponents of a cell-cell interaction mechanism which is important in ma ny cell fate decisions throughout development. One such decision is th e formation of the sensory organ precursor cell during the development of the peripheral nervous system in Drosophila. Cells acquire the pot ential to be neural through the expression of the proneural genes, and the Notch pathway is required to limit neural fate to a single cell f rom a proneural cluster. However, despite extensive analysis, the prec ise pathways linking the proneural with Notch and Enhancer of split ge ne functions remain obscure. For example, it has been suggested that a chaete-scute complex proteins directly activate Enhancer of split gene s leaving the action of Notch in the pathway unclear. Using monoclonal antibodies that recognise products of the Enhancer of split complex, we show that these proteins accumulate in the cells surrounding the de veloping sensory organ precursor cell and that their expression is dep endent on the activity of Notch and does not directly correlate with e xpression of Achaete. We further clarify the pathway by showing that u biquitous expression of an activated Notch receptor leads to widesprea d accumulation of Enhancer of split proteins even in the absence of ac haete-scute complex proteins. Thus Enhancer of split protein expressio n in response to Notch activity does not require achaete-scute complex proteins.