Reversible effects of antimitotic agents on cortical morphogenesis in the marine ciliate Condylostoma magnum

Effects of antimitotic agents on morphogenesis in the marine ciliate Condylostoma were tested. Surgically transected cells or early predividers were placed in solutions of Colcemid, colchicine, vinblastine, griseofulvin, or chloral hydrate in varying concentrations and for varying periods of time. Although early dividers proceeded to complete cytokinesis and, in at least some instances, macronuclear fission while in the drug solutions, development of normal form and oral organelles in daughter cells and regeneration and remodeling in operated fragments were completely blocked by appropriate drug concentrations. Inhibition was in almost all cases reversible: blocked cells, when washed and returned to sea water, underwent normal morphogenesis. Like other ciliates, Condylostoma has in its ectoplasm highly organized systems of microtubules associated with kinetosomes of the body ciliature and the oral apparatus. Electron micrographs of Colcemid‐treated cells show that preexisting cortical microtubules are not destroyed by treatments that prevent morphogenesis. They thus resemble ciliary and kinetosomal microtubules of other cells in being resistant to agents that cause the disappearance of most cytoplasmic and spindle microtubules. Most of the recognizable events of morphogenesis involve the growth and migration of microtubular organelles, and these events did not occur in the presence of the inhibiting agents. It is concluded that microtubule growth is necessary for the development of structure and pattern in Condylostoma.