Heterotrimeric G proteins direct two modes of asymmetric cell division in the Drosophila nervous system

In Drosophila, distinct mechanisms orient asymmetric cell division along the apical-basal axis in neuroblasts and along the anterior-posterior axis in sensory organ precursor (SOP) cells. Here, we show that heterotrimeric G proteins are essential for asymmetric cell division in both cell types. The G protein subunit G alphai localizes apically in neuroblasts and anteriorly in SOP cells before and during mitosis. Interfering with G protein function by G alphai overexpression or depletion of heterotrimeric G protein complexes causes defects in spindle orientation and asymmetric localization of determinants. G alphai is colocalized and associated with Pins, a protein that induces the release of the beta gamma subunit and might act as a receptor-independent G protein activator. Thus, asymmetric activation of heterotrimeric G proteins by a receptor-independent mechanism may orient asymmetric cell divisions in different cell types.