Proximity Labeling at Non-Centrosomal Microtubule-Organizing Centers Reveals VAB-10B and WDR-62 as Distinct Microtubule Regulators

Microtubules are polarized intracellular polymers that play key roles in the cell including in transport, polarity, and cell division. Across eukaryotic cell types, microtubules adopt diverse intracellular organization to accommodate these distinct functions coordinated by specific cellular sites called microtubule organizing centers (MTOCs). Over 50 years of research on MTOC biology has focused mainly on the centrosome, however most differentiated cells employ non-centrosomal MTOCs (ncMTOCs) to organize their microtubules into diverse arrays which are critical to cell function. To identify essential ncMTOC components, we developed the biotin ligase-based proximity labeling approach TurboID for use in C. elegans. We identified proteins proximal to the microtubule minus end protein PTRN-1/Patronin at the apical ncMTOC of intestinal epithelial cells, focusing on two conserved proteins: spectraplakin protein VAB-10B and WDR-62, a protein we identify as homologous to vertebrate primary microcephaly disease gene WDR62. We found that WDR-62 and VAB-10B independently regulate the growth and localization of non-centrosomal microtubules and the apical targeting of microtubule minus end proteins. Depletion of VAB-10B resulted in disorganized microtubules and delayed localization of a microtubule nucleation complex γ-TuRC while loss of WDR-62 decreased the number of dynamic microtubules and abolished γ-TuRC localization. This regulation occurs downstream of cell polarity and in conjunction with actin. As this is the first report for non-centrosomal roles of WDR62 family proteins, our study expands the basic cell biological roles of this important disease protein. Together, our data suggest a division of labor where microtubule growth and anchoring are regulated by distinct complexes.