TRANSCRIPTIONAL REGULATION OF NOTCH AND DELTA - REQUIREMENT FOR NEUROBLAST SEGREGATION IN DROSOPHILA

Segregation of a single neural precursor from each proneural cluster i n Drosophila relies on Notch-mediated lateral signalling, Studies conc erning the spacing of precursors for the microchaetes of the periphera l nervous system suggested the existence of a regulatory loop between Notch and its ligand Delta within each cell that is under transcriptio nal control. Activation of Notch leads to repression of the achaete-sc ute genes,which themselves regulate transcription of Delta, perhaps di rectly, Here we have tested a requirement for transcriptional regulati on of Notch and/or Delta during neuroblast segregation in embryos, by providing Notch and Delta ubiquitously at uniform levels, Neuroblast s egregation occurs normally under conditions of uniform Notch expressio n, Under conditions of uniform Delta expression, a single neuroblast s egregates from each proneural group in 80% of the cases, more than one in the remaining 20%, Thus transcriptional regulation of Delta is lar gely dispensable, We discuss the possibility that segregation of singl e precursors in the central nervous system may rely on a heterogeneous distribution of neural potential between different cells of the prone ural group, Notch signalling would enable all cells to mutually repres s each other and only a cell with an elevated neural potential could o vercome this repression.