Determinants of cytoplasmic microtubule depolymerization during ciliogenesis inChlamydomonas reinhardtii

Abstract

At the core of cilia are microtubules which are important for establishing length and assisting ciliary assembly and disassembly; however, another role for microtubule regulation on ciliogenesis lies outside of the cilium. The microtubule cytoskeleton is a highly dynamic structure which reorganizes rapidly to assist in cellular processes. Cytoplasmic microtubule dynamics have previously been thought to be necessary to free up tubulin and proteins in the ciliary precursor pool for ciliogenesis. However, we previously found that low concentrations of taxol can stabilize cytoplasmic microtubules during deciliation while allowing normal cilium regrowth. Here we look at the relationship between ciliogenesis and cytoplasmic microtubule dynamics inChlamydomonas reinhardtiiusing chemical and mechanical perturbations. We find that not only can stabilized cytoplasmic microtubules allow for normal ciliary assembly, but high calcium concentrations and low pH-induced deciliation cause microtubules to depolymerize separately from ciliary shedding. In addition, we find that through mechanical shearing, cilia regenerate more quickly despite intact cytoplasmic microtubules. Our data suggests that cytoplasmic microtubules are not a sink for a limiting pool of cytoplasmic tubulin, reorganization that occurs following deciliation is a consequence rather than a requirement for ciliogenesis, and intact microtubules in the cytoplasm and the proximal cilium support more efficient ciliary assembly.