Abstract

Patronin/Shot cortical foci assemble the noncentrosomal microtubule array that specifies the Drosophila anterior-posterior axis A polarised microtubule (MT) cytoskeleton plays an important role in establishing and maintaining cell polarity. Even though centrosomes are commonly considered to be the main MT organising centers (MTOCs), in many polarised cells (e.g. epithelia, neurons, oocytes) centrosomes are inactivated and most microtubules are of noncentrosomal origin. How such microtubules are formed, organised and regulated is still poorly understood. So far several noncentrosomal g-tubulin based pathways for MT generation have been described: Augmin/TPX2-dependent, nuclear membrane-dependent and Golgi-dependent. However, their contribution to cell polarity is unclear. Here, we describe how the spectraplakin Shot and the MT minus end-binding protein Patronin form a new type of cortical noncentrosomal MTO Cs (ncMTOCs) that work in a g-tubulin independent way to assemble a polarised MT network in the Drosophila oocyte. Similar ncMTOCs accumulate apically in epithelial cells, where they are required for the formation of apical-basal microtubule arrays. Thus, Shot/Patronin ncMTOCs may provide a general mechanism for organising noncentrosomal microtubules in differentiated cells.