Competition between kinesin-1 and myosin-V defineDrosophilaposterior determination

Abstract

AbstractLocal accumulation ofoskar (osk) mRNA in theDrosophilaoocyte determines the posterior pole of the future embryo. Two major cytoskeletal components, microtubules and actin filaments, together with a microtubule motor, kinesin-1, and an actin motor, myosin-V, are essential foroskmRNA posterior localization. In this study, we use Staufen, an RNA-binding protein that colocalizes withoskmRNA, as a proxy for posterior determination. We demonstrate that posterior localization ofosk/Staufen is determined by competition between kinesin-1 and myosin-V. While kinesin-1 removesosk/Staufen from the cortex along microtubules, myosin-V anchorsosk/Staufen at the cortex. Myosin-V wins over kinesin-1 at the posterior pole due to low microtubule density at this site, while kinesin-1 wins it at anterior and lateral positions because they have high density of cortically-anchored microtubules. As a result, posterior determinants are removed from the anterior and lateral cortex but retained at the posterior pole. Thus, posterior determination ofDrosophilaoocyte is defined by kinesin-myosin competition, whose outcome is primarily determined by cortical microtubule density.