The Effect of Colchicine on Regenerating Membranellar Cilia in Stentor coeruleus

SYNOPSIS. Stentors treated with toxic substances can be induced to shed their oral bands (19, Fig. 1), complex structures composed of many cilia organized into membranelles. Regenerating membranellar bands were observed in control stentors removed from toxic (urea-containing) medium at about 3.5 hours. At 8 hours regenerated control organisms were indistinguishable from normal unshed stentors. Experimental animals replaced into colchicine medium were inhibited from regeneration at low, nontoxic concentrations of this mitotic spindle inhibitor. Upon removal of the colchicine and replacement of the shed animals into normal medium or normal medium to which GTP had been added, complete and normal regeneration of the membranellar band ensued. Our observations are consistent with many suggesting that colchicine acts by reversibly binding with a protein during processes involving microtubule formation. Colchicine inhibition of membranellar band formation further indicates that oral membranelles are specialized evolutionary homologs to other centriole (= basal body, = kinetosome) derivatives such as mitotic spindle fibers, cilia and flagella, axopods, etc. (structures containing the ubiquitous microtubules of eukaryotic cells)