Microtubule organization : from the centrosome to the Golgi apparatus

Similar to the skeleton of a human body, every cell possesses the so-called cytoskeleton, a system of filaments that support cell shape and enable cells to divide and move. One of the major types of cytoskeletal fibers are microtubules, microscopic tubes that cells use as rails to transport their components. Studying microtubule organization is important from a fundamental perspective, and is also medically relevant because microtubules represent one of the major targets for cancer therapy. Microtubules can be organized by several cellular organelles that are generally termed microtubule-organizing centers (MTOC). The best known MTOC is the centrosome, which can generate a symmetric radial microtubule array. Recently, the Golgi apparatus has emerged as another important MTOC, which can promote asymmetric microtubule organization. In this thesis, we provide a comprehensive analysis of the interactions between microtubules and Golgi membranes. By using CRISPR/Cas9-based genome editing, biochemical and cell biological experiments, as well as light and electron microscopy, we systematically dissected the pathway of microtubule organization at the Golgi. We demonstrated that microtubule nucleation and anchoring at the Golgi are distinct processes, which require cooperation between proteins that associate with microtubule plus and minus ends and the factors that recruit them to Golgi membranes. We found that Golgi membranes and the centrosome can act redundantly in microtubule organization and can compete with each other for microtubule-nucleating factors. Furthermore, we showed that the Golgi-dependent microtubules are important for cell polarity and migration of cancer cells as well as endothelial cells during vessel development. To summarize, in this thesis we show a complex interplay between the centrosome, the Golgi apparatus and microtubules in controlling cell architecture.