PAR for the course

In the January 23 Nature Sophie Martin and Daniel St Johnston from the University of Cambridge, UK, show that the Drosophila LKB1 protein, a homolog of the PAR kinases identified for their role in C. elegans embryonic polarity, is required for early anterior-posterior polarity in the fly oocyte (Nature 2003, 421:379-384). They performed a genetic screen for mutants that disrupt the localization of the posterior-polarized protein Stauffen. Genome mapping led them to the lkb1 gene, which encodes a serine/threonine kinase homologous to the human tumor suppressor LKB1 and the C. elegans PAR-4 kinase that is involved in embryonic polarity. LKB1 is phosphorylated by the related PAR-1 kinase and by protein kinase A. DrosophilaLKB1 is essential for cell polarity in the germ line and the follicle cells