Defective Micronuclei and Genomic Exclusion in Selected C* Subclones of Tetrahymena 1

Abstract

C* is a structurally heterogeneous clone containing normal and crinkled cells which are amicronucleate. Selection for structurally normal subclones did not result in the genesis of a diploid cell line. The stem cell of C* appears to be aneuploid with about 4 chromosomes instead of the usual 10, and from this line cells with fewer chromosomes or without micronuclei are generated. Only cells containing a portion of the micronucleus are viable. Amicronucleate cells die. They also mate very poorly. Consequently, little difference is observed between subclones having different proportions of amicronucleate cells in their ability to generate viable offspring by genomic exclusion. Our observations are discussed in terms of the separate functions of micronucleus and macronucleus and ways in which the nuclei seem to interact.