Neuroblast self-renewal vs. differentiation and tumorigenesis. (A) A wild type neuroblast divides to form two daughter cells, one of which becomes a self-renewing neuroblast (gray) and one of which becomes a ganglion mother cell (GMC) (red). The GMC divides terminally to become differentiated neurons. There is a balance between self-renewing neuroblasts and neurons. (B) A mutant neuroblast (such as Miranda knockouts or Pins, Lgl double knockouts) fail to divide asymmetrically and create only self-renewing neuroblasts. This results in an unrestricted growth of neural precursors at the expense of differentiated neurons, thus leading to neoplastic growth and tumor formation.