Q&A: Who needs a centrosome?

What is the function of the centrosome?The centrosome has several functions.The central one is as the major microtubule organizing center (MTOC) in proliferating animal cells: thus, it helps to organize the microtubules that form the mitotic spindle in dividing cells, and orchestrate a wide variety of cellular processes, including cell motility, signaling, adhesion, coordination of protein trafficking by the microtubule cytoskeleton and the acquisition of polarity.The centrosome has crucial links to the nucleus, the Golgi, cell to cell junctions and acto-myosin cytoskeleton that are very important in positioning it and thus shaping the microtubule cytoskeleton in relation to the cell and the organism (reviewed in [1]).The role of the centrosome in organizing cellular microtubules can differ from cell to cell and be regulated differently in different phases of the life of a cell. How does the centrosome perform its 'organizing' function?By stimulating the formation of microtubules and anchoring them.Microtubules are dynamic structures formed by polymerization of tubulin.In dividing cells, for example, the microtubule cytoskeleton is continuously reshaped, changing dramatically from interphase to mitosis.The dynamic behavior of microtubules is regulated by associated proteins that can stabilize microtubules as required to form the mitotic spindle and other structures (reviewed in [2,3]).Although microtubules can form spontaneously from high concentrations of tubulin in vitro, in cells they are nucleated by specialized microtubule-nucleating proteins, some of which are associated with the centrosome.The centrosome is composed of two barrel-shaped microtubule-based organelles, the centrioles, surrounded by proteins collectively called the pericentriolar material (PCM).Proteins of both the centriole and the PCM can nucleate and anchor microtubules (reviewed in [2,3]).The role of the centrosome in directing cellular protein traffic depends upon the intrinsic polarity of microtubules, and microtubule-associated motor proteins that move differentially towards one microtubule end or the other.By nucleating microtubules, the centrosome thus determines the tracks along which different cellular components can be transported to different parts of the cell.It can also help to define the speed at which components move along those tracks, and act as a signaling center to modify some components before they are transported to their destinations.