In a recent article in Current Biology, Métivier et al. show that tubulin co-chaperone (dTBCE) is required for mitotic spindle assembly in neural stem cells. They propose that dTBCE invades the nuclear space during early mitosis to generate a medium capable of enriching tubulin and thus promote optimal nucleation of microtubules around chromosomes.
The proper assembly of the mitotic spindle requires the nucleation of microtubules not only at the centrosomes but also around the chromatin. In this study, it was discovered that the tubulin-specific dTBCE chaperone is necessary for the enrichment of tubulin in the nuclear space and for the subsequent promotion of nucleation of the microtubules of the mitotic spindle. These events are dependent on the CAP-Gly motif found in dTBCE, and are regulated by the Ran protein and the laminae. The data suggest that during early mitosis, dTBCE and nuclear pore proteins enrich in the nucleus, where they interact with Ran GTPase to promote dynamic tubulin enrichment. The authors propose that this novel mechanism improves the nucleation of microtubules around the chromatin, thereby facilitating the assembly of the mitotic spindle.