Fig. 6.

L'sc downregulates Notch and is sufficient to induce neuroblasts. (A,A′) The proneural factor L'sc is transiently expressed in the most medial neuroepithelial cells (arrow) that are about to transform into neuroblasts. Cells are outlined by Dlg (green). (B,B′) A single mCD8-GFP labelled clone misexpressing l'sc that has been induced within the neuroepithelium. Cells within the clone ectopically express the neuroblast-specific transcription factor Dpn (larger arrow). The ectopic neuroblasts generate smaller progeny cells (small arrows), indicating a switch to an asymmetric division mode. There is a second larger clone to the right of the white arrow, which also shows upregulated Dpn levels. (C,C′) In clonal cells expressing l'sc (green, arrows), the levels of intracellular Notch (red) are markedly reduced and similar to those observed in the neuroblast zone (to the left of the arrowhead). No change in expression of DE-Cad (blue) was detected. Arrowhead indicates neuroepithelial to neuroblast transition zone. (D,D′) Delta is expressed at low levels throughout the epithelium but expression is highest in the L'sc-positive transition zone (arrows). Delta expression is reduced in the neuroblasts (left from arrowhead). Scale bars: 10 μm.