Mechanism and function of poleward flux in Xenopus extract meiotic spindles

In Xenopus extract meiotic spindles, microtubules slide continuously towards their minus ends, a process called poleward flux. This article discusses recent progress in determining the mechanism of poleward flux, and its functions in spindle organization and generating force on chromosomes. Bipolar organization is required for flux and inhibition of the mitotic kinesin Eg5 inhibits flux, suggesting the sliding force for flux is generated by Eg5 pushing anti-parallel microtubules apart. An important function of flux in spindle organization may be to transport minus ends nucleated at chromatin towards the pole. By pulling microtubules through attachment sites at kinetochores, flux may generate poleward force on metaphase chromosomes.