Fig. 4. Notch-mediated asymmetric cell divisions are influenced by localized determinants. (A) An asymmetric cell division in which one cell divides to give two daughters that adopt different fates; Notch signaling is `on' in the green cell and `off' in the red cell. Although both cells express Notch and Delta, signaling is directional because the red cell inherits determinants [such as Numb (red crescent in the mother cell)] that inhibit Notch signaling in that cell. (B) Crescents are centered on one end of the mitotic spindle and segregated into only one daughter cell. Here, a crescent of Partner of Numb-GFP is visualized along with the spindle, which is labeled with tau-GFP (image courtesy of Fabrice Roegiers). (C) The two exterior cells of a Drosophila mechanosensory bristle are produced by the lineage shown in A. The shaft cell (sh) activates Notch signaling in its sister, the socket cell (so); the shaft cell does not have activated Notch because it inherits Numb. Activation of Notch in both cells results in two sockets (D), whereas a failure to activate Notch in either cell results in two shafts (E) (images courtesy of Scott Barolo).