Fig. 4.

Neural stem cells. (A) The structure of the embryonic neural stem cell niche. The neuroepithelium is composed of individual neurons arising in the ventrolateral region of the embryo. Neuroblasts are positioned adjacent to the neuroepithelium and express Delta (Dl), which represses neural fate in the neighboring epithelium by interacting with Notch (N). (B) A second wave of neurogenesis occurs in the first instar larva. The neuroblasts receive a Dilp signal from neighboring glial cells that causes them to enter the cell cycle. The inset shows the asymmetric division of a type 1 neuroblast giving rise to ganglion mother cells, which will further produce larval neurons. NE, neuroepithelium; AC, apical complex; BC, basal complex.