• notch activity;
  • delta-like;
  • Dll1;
  • Dll4;
  • Dll3;
  • Ascl1;
  • Neurog2;
  • Hes1;
  • Hes5;
  • Hes6;
  • retinal development;
  • mutual and lateral inhibition;
  • molecular circuit


Delta gene expression in Drosophila is regulated by proneural basic helix–loop–helix (bHLH) transcription factors, such as acheate-scute. In vertebrates, multiple Delta-like and proneural bHLH genes are expressed during neurogenesis, especially in the retina. We recently uncovered a relationship between Acheate-scute like 1 (Ascl1), Delta-like genes, and Notch in chick retinal progenitors. Here, we report that mammalian retinal progenitors are also the primary source of Delta-like genes, likely signaling through Notch among themselves, while differentiating neurons expressed Jagged2. Ascl1 is coexpressed in Delta-like and Notch active progenitors, and required for normal Delta-like gene expression and Notch signaling. We also reveal a role for Ascl1 in the regulation of Hes6, a proneurogenic factor that inhibits Notch signaling to promote neural rather than glial differentiation. Thus, these results suggest a molecular mechanism whereby attenuated Notch levels coupled with reduced proneurogenic activity in progenitors leads to increased gliogenesis and decreased neurogenesis in the Ascl1-deficient retina. Developmental Dynamics 238:2163–2178, 2009. © 2009 Wiley-Liss, Inc.