THE DCC MUTATION AFFECTS CILIARY LENGTH IN TETRAHYMENA-THERMOPHILA

We have characterized ciliogenesis in a mutant Tetrahymena thermophila that both fails to regain motility following deciliation and that fai ls to complete cytokinesis. Scanning electron microscopic (SEM) observ ations revealed that starved deciliated cells regenerated fewer, short er cilia at the restrictive temperature than similarly treated cells i ncubated at the permissive temperature. Transmission electron microsco pic evaluation of isolated, regenerated cilia revealed no structural a bnormalities. Incorporation of S-35 methionine was similar during cili ary regeneration at both the restrictive and permissive temperatures, indicating the mutant phenotype was not due to a simple failure in tra nslation or transcription. Mutant cells incubated in growth medium at the restrictive temperature arrested in cytokinesis and assembled a la rge number of abnormally short cilia. These cells also developed irreg ular surface Projections that were not visible on wild-type cells. The se observations suggest that ciliogenesis can be initiated in growing cells as well as in starved deciliated cells but that elongation is in hibited before cilia reach full length. The mutation was named dcc for defective in ciliogenesis and cytokinesis.