Establishment of cell polarity by Par-1 kinase during Drosophila oogenesis: assessment of biochemically identified Par-1 substrates as targets in vivo

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The gene par-1 encodes an evolutionarily conserved Ser/Thr kinase. Genetic data show that par-1 is required for the establishment of polarity in organisms as divergent as worms and flies. Although biochemical data suggest a function of the mammalian Par-1 homologue, MARK, in regulating cytoskeletal organisation by phosphorylating microtubule-associated proteins (MAPs), this property of the kinase is not sufficient to explain the polarity defects observed in the par-1 mutants. We use Drosophila oogenesis as a model to understand the mechanisms of cell polarization. par-1 is required several times for establishment and maintenance of cell polarity during oogenesis, but the mechanism by which Par-1 regulates cell polarity is not understood, as neither in C. elegans nor in Drosophila are Par-1 target proteins known. We will use "in vitro expression cloning" to identify cDNAs encoding proteins that are phosphorylated by Par-1. Pools of cDNAs will be transcribed and translated in vitro to be tested as substrates of the kinase. We will systematically screen the Drosophila genome for Par-1 targets.