Drosophila Tubulin-Specific Chaperone E Recruits Tubulin around Chromatin to Promote Mitotic Spindle Assembly

Proper assembly of mitotic spindles requires microtubule nucleation not only at the centrosomes but also around chromatin. In this study, we found that the Drosophila tubulin-specific chaperone dTBCE is required for the enrichment of tubulin in the nuclear space after nuclear envelope breakdown and for subsequent promotion of spindle microtubule nucleation. These events depend on the CAP-Gly motif found in dTBCE and are regulated by Ran and lamin proteins. Our data suggest that during early mitosis, dTBCE and nuclear pore proteins become enriched in the nucleus, where they interact with the Ran GTPase to promote dynamic tubulin enrichment. We propose that this novel mechanism enhances microtubule nucleation around chromatin, thereby facilitating mitotic spindle assembly. [Display omitted] •During early mitosis, dTBCE promotes tubulin enrichment in the nascent spindle region•dTBCE interacts with nuclear pore proteins and Ran•dTBCE is required for microtubule assembly around chromosomes•dTBCE localization and function require its conserved CAP-Gly motif. Métivier et al. show that the Drosophila tubulin-binding chaperone E (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 milieu able to enrich tubulin and for subsequent microtubule nucleation around chromosomes.