Zonka, J. C. | bioRxiv Science

bioRxiv2018

A two-step mechanism for the inactivation of microtubule organizing center function at the centrosome

SummaryDuring mitosis, the centrosome acts as a microtubule organizing center (MTOC), orchestrating microtubules into the mitotic spindle through its pericentriolar material (PCM). This activity is biphasic, cycling through assembly and disassembly during the cell cycle. Although hyperactive centrosomal MTOC activity is a hallmark of some cancers, little is known about how the centrosome is inactivated as an MTOC. Analysis of endogenous PCM proteins in C. elegans revealed that the PCM is composed of distinct protein territories that are removed from the centrosome at different rates and using different behaviors. Inhibition of PP2A phosphatases stabilized the PCM and perturbation of cortical pulling forces altered the timing and behavior by which proteins were removed from the centrosome. These data indicate that PCM disassembly is a two-step process, beginning with a phosphatase-dependent dissolution of PCM proteins followed by the ejection of ruptured PCM by cortical forces, ultimately inactivating MTOC function at the centrosome.

cell biology↗

bioRxiv2018

Tissue-specific degradation of essential centrosome components reveals distinct microtubule populations at microtubule organizing centers

Non-centrosomal microtubule organizing centers (ncMTOCs) are found in most differentiated cells, but how these structures regulate microtubule organization and dynamics is largely unknown. We optimized a tissue-specific degradation system to test the role of the essential centrosomal microtubule nucleators {gamma}-tubulin ring complex ({gamma}-TURC) and AIR-1/Aurora A at the apical ncMTOC, where they both localize in C. elegans embryonic intestinal epithelial cells. As at the centrosome, the core {gamma}-TURC component GIP-1/GCP3 is required to recruit other {gamma}-TuRC components to the apical ncMTOC including MZT-1/MZT1, characterized here for the first time in animal development. In contrast, AIR-1 and MZT-1 were specifically required to recruit {gamma}-TuRC to the centrosome, but not to centrioles or to the apical ncMTOC. Surprisingly, microtubules remain robustly organized at the apical ncMTOC upon {gamma}-TuRC and AIR-1 co-depletion, and upon depletion of other known microtubule regulators including TPXL-1/TPX2, ZYG-9/chTOG, PTRN-1/CAMSAP, and NOCA-1/Ninein. However, loss of GIP-1 removed a subset of dynamic EBP-2/EB1-marked microtubules, and the remaining dynamic microtubules grew faster. Together, these results suggest that different MTOCs use discrete proteins for their function, and that the apical ncMTOC is composed of distinct populations of {gamma}-TuRC-dependent and independent microtubules that compete for a limited pool of resources.

cell biology↗