Sanpodo notches up asymmetric divisions Available to Purchase

The generation of cell-type diversity in multicellular organisms involves asymmetric cell division. During such divisions in Drosophila, Notch signalling in one daughter cell induces its acquisition of the ‘A’ fate; antagonism of Notch signalling by the cell-fate determinant Numb in the other daughter cell induces the ‘B’ fate. Although Numb is expressed in other cells in which Notch regulates developmental decisions, Numb inhibits Notch signalling only during asymmetric divisions, but why? On p. 4089, James Skeath and colleagues answer this long-standing question by showing that the transmembrane protein Sanpodo (Spdo), which is only expressed in asymmetrically dividing cells, plays a dual role in regulating Notch signalling during asymmetric divisions. Their loss-of-function and misexpression studies demonstrate that Numb converts Spdo from an activator to an inhibitor of Notch signalling. Thus, in ‘B’ daughter cells, which express spdo, numb and Notch, Spdo inhibits Notch signalling, whereas it amplifies Notch...