ASYMMETRIC LOCALIZATION OF NUMB AUTONOMOUSLY DETERMINES SIBLING NEURON IDENTITY IN THE DROSOPHILA CNS

The central nervous system (CNS) represents an excellent model system for examining how a multitude of unique cell fates are specified. We f ind that asymmetric localization of the numb protein autonomously cont rols a binary cell fate decision in the Drosophila CNS. The simplest l ineage in the Drosophila CNS is that of the MP2 precursor: it divides unequally to generate the dMP2 and vMP2 neurons. Both are interneurons but project in different directions: dMP2 projects its axon posterior ly while vMP2 projects anteriorly. During MP2 mitosis, numb is localiz ed into dMP2 and excluded from vMP2. Loss of numb transforms dMP2 into vMP2, whereas ectopic numb produces the opposite transformation of vM P2 into dMP2. Thus, numb is asymmetrically localized in the dividing M P2 and is necessary and sufficient to autonomously specify dMP2 neuron al identity.