Microtubules serve numerous functions in a cell—they provide the main structure of the mitotic spindle and serve as tracks for transport within a cell. Microtubules are assembled by subunits of tubulin in a polarized fashion so there is a plus and minus end. This polarity is significant—plus ends are very dynamic and are the sites of the majority of action and dynamics, while minus ends are stabilized and anchored at the microtubule organizing center in most cells. A recent paper describes the identification of a protein called Patronin that stabilizes the minus ends of microtubules. In cells without Patronin, microtubules are not anchored and are found freely moving throughout the cytoplasm, as seen in the images above. In normal interphase cells (left), microtubules are anchored at nucleating sites, but in cells without Patronin (right), entire microtubules can be seen in the cytoplasm (arrows, inset).
Reference: Sarah S. Goodwin and Ronald D. Vale. Cell 143 (2), 263-274. ©2010 Elsevier Ltd. All rights reserved. Paper (and many cool movies!) can be found here.
BONUS!! Cool movie of above image can be found below!