The ends of growing and fully assembled ciliary and flagellar microtubules are bound to the membrane by capping structures. Similar structures may be associated with the kinetrochores that bind microtubules to chromosomes. In cilia and flagella, these structures are specific for individual microtubules within a single cilium and, in organisms that contain two or more populations of cilia that differ in their function, length, or time of assembly, each population may have morphologically distinguishable capping structures. The structures that cap the tips of mammalian epithelial cilia, in the trachea and oviduct, link the ends of each of the 11 microtubules to the membrane via a common cap. The cap intrancheal and oviduct cilia appears to be essential for the transport of mucus over the epithelial surface and clearance of mucus from the lung. Since our studies have shown that the capping structures are tightly bound to the assembly sites of the microtubules, they appear to be important for the regulation of microtubule assembly. Our overall goal is to understand exactly how the capping structures function during microtubule assembly in vivo. The current studies are dedicated to isolating the capping structures to identify the proteins (or other material) that compose the caps and to study the manner by which they are associated with growing and fully grown microtubules. A major portion of this project is devoted to isolating monoclonal and polyclonal antibodies to the capping structure polypeptides and to using these antibodies to isolate capping structures and to study the function of the caps during ciliogenesis. Successful completion of these studies may lead to the discovery of new mechanisms by which cells regulate the assembly and disassembly of individual microtubules durng interphase as well as during cell division.
