Deciphering the role of a microtubule severing protein and a protein kinase in cell cycle and ciliogenesis in Chlamydomonas Reinhardtii

Many types of eukaryotic cells are ciliated – they project a microtubule-based structure extending from the cell surface called a cilium, which plays roles in cellular motility and sensing the environment. Cilia are anchored at the cell surface by microtubule-based structures called basal bodies or centrioles. In addition to nucleating cilia, centrioles act as spindle organizing centres during cell division. We are beginning to understand that several proteins are involved in simultaneously regulating cilia and centrioles with cell division. My research focused on the function of two proteins in the ciliated alga, Chlamydomonas. The first protein, katanin, severs microtubules and we predicted that it is required during the disassembly of cilia prior to mitosis. I used a genetic approach to repress expression of the gene encoding katanin in Chlamydomonas , and thereby demonstrated that katanin in fact severs microtubules at a distinct location between basal bodies and the cilium. The other gene that I studied encodes a cyclic GMP-dependent kinase type 2 (PKG2). Mutant cells deficient in PKG2 had either no cilia, or cilia of unequal length. I discovered that PKG2 is expressed in the cytoplasm as well as the flagella and may interact with other proteins to regulate ciliary length and structure. Taken together, this research identified novel mechanisms that help explain the coordinated regulation of cilia during the cell cycle, and a novel gene with roles in ciliary assembly was also identified.