Vers une description du mécanisme d'assemblage du fuseau mitotique à l'échelle moléculaire

Abstract

Morphogenesis of the mitotic spindle raises original questions because it is a transient, highly dynamic structure. The reorganization of microtubules from a radial array in interphase into a bipolar spindle during mitosis, results from phosphorylation events induced by the cyclin B-cdc2 kinase. These phosphorylations control microtubule dynamics and probably the activity of motor proteins essential in spindle assembly. At the onset of mitosis, microtubules become extremely dynamic and shorten dramatically. Their preferential orientation towards the chromosomes seems to result from a local effect of chromatin on the surrounding cytoplasm that stabilizes microtubules. Spindle bipolarity is established and maintained by interactions between anti-parallel microtubules in the equatorial area of the spindle. These interactions seem to involve motor proteins belonging to the kinesin superfamily. During their positioning on the metaphase plate, chromosomes move along microtubules. These movements are also due to motor proteins (probably belonging to both the kinesin and dynein families of proteins) localized in the kinetochores. Their directionality of movement along the microtubule lattice is regulated by phosphorylation suggesting a mechanism by which the chromosomes are positioned on the metaphase plate.