Primary cilia cycle in PtK1 cells: Effects of colcemid and taxol on cilia formation and resorption

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Abstract
The effects of colcemid (0.16–1.0 μM) and taxol (10 μM) on the primary cilia cycle in PtK1 cells were studied by antitubulin immunofluorescence microscopy and by high‐voltage electron microscopy of serial 0.25‐μm sections. Although these dings induce a fully characteristic rearrangement (taxol) or disassembly (colcemid) of cytoplasmic microtubulcs, neither affects the structure of primary cilia formed prior to the treatment or the resorption of primary cilia during the initial stages of mitosis. Cells arrested in mitosis by taxol or colcemid remain in mitosis for 5–7 h at 37°C and then form 4N “micronucleated” restitution nuclei. Formation of primary cilia in these micronucleated cells is blocked by colcemid in a concentration‐dependent fashion: normal cilia with expanded (ie, bulbed) distal ends form at the lower (0.16–0.25 μM) concentrations, while both cilia formation and centriole replication are inhibited at the higher (≥ 1.0 μM) concentrations. However, even in the presence of 1.0 μM colcemid, existing centrioles acquire the appendages characteristically associated with ciliating centrioles and attach to the dorsal cell surface. Continuous treatment with colcemid thus produces a population of cells enriched for the early stages of primary cilia formation. Micronucleated cells formed from a continuous taxol treatment contain two normal centriole pairs, and one or both parenting centrioles possess a primary cilium. Taxol, which has been reported to stabilize microtubules in vitro, does not inhibit the cell‐cycle–dependent assembly and disassembly of axonemal microtubules in vivo.