Bazooka is required for localization of determinants and controlling proliferation in the sensory organ precursor cell lineage in Drosophila

Asymmetric divisions with two different division orientations follow differ ent polarity cues for the asymmetric segregation of determinants in the sen sory organ precursor (SOP) lineage. The first asymmetric division depends o n frizzled function and has the mitotic spindle of the pI cell in the epith elium oriented along the anterior-posterior axis, giving rise to pIIa and p IIb, which divide in different orientations. Only the pIIb division resembl es neuroblast division in daughter-size asymmetry, spindle orientation alon g the apical-basal axis, basal Numb localization, and requirement for inscu teable function. Because the PDZ domain protein Bazooka is required for spi ndle orientation and basal localization of Numb in neuroblasts, we wondered whether Bazooka plays a similar role in the pIIb in the SOP lineage. Surpr isingly, Bazooka controls asymmetric localization of the Numb-anchoring pro tein Pon, but not spindle orientation, in pI and all subsequent divisions. Bazooka also regulates cell proliferation in the SOP lineage; loss of bazoo ka function results in supernumerary cell divisions and apoptotic cell deat h.