PARTNER OF NUMB COLOCALIZES WITH NUMB DURING MITOSIS AND DIRECTS NUMBASYMMETRIC LOCALIZATION IN DROSOPHILA NEURAL AND MUSCLE PROGENITORS

During mitosis of multiple types of precursor cells in Drosophila, Num b is asymmetrically distributed between the two daughter cells and con fers distinct daughter cell fates. Here we report the identification o f a novel gene product, Partner of Numb (PON), based on its physical i nteraction with Numb. PON is asymmetrically localized during mitosis a nd colocalizes with Numb. Loss of pon function disrupts Numb localizat ion in muscle progenitors and delays Numb crescent formation in neural precursors. Moreover, ectopically expressed PON responds to the apica l-basal polarity of epithelial cells and is sufficient to localize Num b basally. We propose that PON is one component of a multimolecular ma chinery that localizes Numb by responding to polarity cues conserved i n neural precursors and epithelial cells.