In the January 23 Nature, Sophie Martin and Daniel St Johnston at the University of Cambridge, UK, show that the Drosophila LKB1 protein — a homolog of PAR kinases — is required for early anterior-posterior polarity in the fly oocyte (Nature, 421:379-384, January 23, 2003).

Martin and St Johnston performed a genetic screen for mutants that disrupt the localization of the posterior polarized protein Stauffen. Genome mapping lead them to the lkb1 gene, that encodes a serine/threonine kinase homologous to the human tumor suppressor LKB1 and the C. elegansPAR-4 kinase that is involved in embryonic polarity. LKB1 is phosphorylated by the related PAR-1 kinase and by protein kinase A. Drosophila LKB1 is essential for cell polarity in the germ line and the follicle cells.