Fig. 4. Asymmetric division of Drosophila neuroblasts is regulated by intrinsic cell fate determinants. A Drosophila neuroblast divides asymmetrically, generating another neuroblast and a smaller ganglion mother cell (GMC) that will produce mature neurons. Cell fate determinants such as Numb and Prospero (blue crescent) are segregated only into the GMC. Spindle orientation is determined by the apical complex (red crescent), containing proteins such as Bazooka (Baz)/Par-3 and Inscuteable (Insc). Spindle orientation in the neuroblast is established by the programmed rotation of the spindle during mitosis so that it becomes perpendicular to the neuroepithelium, from which the neuroblast is derived. Pins, partner of Inscuteable; aPKC, a typical protein kinase C; Pon, partner of Numb.