Kinesin I-dependent cortical exclusion restricts pole plasm to the oocyte posterior

Abstract

Microtubules and the plus-end-directed microtubule motor Kinesin I are required for the selective accumulation of oskar mRNA at the posterior cortex of the Drosophila melanogaster oocyte, which is essential to posterior patterning and pole plasm assembly. We present evidence that microtubule minus ends associate with the entire cortex, and that Kinesin and microtubules are not required for oskar mRNA association with the posterior pole, but prevent ectopic localization of this transcript and the pole plasm proteins Oskar and Vasa to other cortical regions. Cortical binding of oskar mRNA seems to be dependent on the actin cytoskeleton. We conclude that most of the actin-rich oocyte cortex can support pole plasm assembly, and propose that Kinesin restricts pole plasm formation to the posterior by moving oskar mRNA away from microtubule-rich lateral and anterior cortical regions.

Microtubule–microtubule sliding by kinesin-1 is essential for normal cytoplasmic streaming in Drosophila oocytes

“…6). Consistent with this model, osk mRNA cortical localization is dependent on actin, but not on microtubules or KHC (58). Therefore, when ooplasmic streaming is decreased in Khc mutA flies, posterior determinants become more diffusely spread along the cortex (Fig.…”

“…Oocytes contain many different populations of microtubules that reorganize and change throughout different developmental stages. The microtubule network is initially polarized during early stages, with the majority of plus-ends at the posterior pole and minus-ends at the anterior pole (55,56), but later becomes less organized, with minus-ends associating with the cortex (31,(57)(58)(59)(60)(61). Microtubules are also concentrated at the posterior pole during early stages, and these microtubules reorganize and relocate to the anterior pole during stages 8-10A, forming a gradient of microtubules from anterior to posterior.…”

“…First, the microtubule network must be reorganized in preparation for fast ooplasmic streaming. Stable, cortically anchored microtubules must form at the cortex, and subcortical microtubules involved in cargo transport must be released from the cortex (58,59). Next, kinesin-1 slides free microtubules using the stable cortical microtubules as anchor points, whereas long kinesin-1-based cargo transport events occur along the dynamic subcortical microtubules.…”

Sending RNAs into the Future: RNA Localization and Germ Cell Fate

“…Thus, anchoring of osk RNA to the subcortex requires assembly of a protein complex that can interact with the subcortical microfilament system as well as osk RNA. Importantly, anchoring does not seem to depend on a specialized posterior cortex, but rather the polarized microtubule based transport of osk RNA to the posterior (59). Actin cytoskeleton is also required for the anchoring of the germ plasm to the subcortex and its disruption results in intact germ plasm being lost from the subcortical region (48).…”

Spindle assembly in the oocytes of mouse and Drosophila – similar solutions to a problem

“…These nucleating centers could be numerous. Microtubule growth is nucleated from many organizing centers along the cortex of Drosophila oocytes prior to nuclear envelop breakdown as part of the axis specification during oogenesis (Theurkauf et al 1992, Cha et al 2002, Steinhauer & Kalderon 2006. Assembling the spindle, therefore, could be primarily done by the bundling and sliding of microtubule fibers, the result of which would be a structure composed of an overlapping array of many short fibers.…”