Date of Award

Summer 2005

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)




Tetrahymena thermophila has two nuclei, a small germline micronucleus and a large somatic macronucleus. Genes in the macronucleus are transcriptionally active during vegetative growth, while genes in the micronucleus are silent. During the conjugation, the old macronucleus is degraded and a new somatic macronucleus (the macronuclear anlagen) develops from a mitotic product of the zygotic micronucleus. An anlagen stage induced gene, ASIJ, was found to be required during the conjugation of Tetrahymena cells. Transcription of AS/J is induced at 6 hr after mixing and peaks at 9- 12 hrs during anlagen development. In order to determine the function of AS/ 1, the gene was knocked out in the somatic macronucleus and replaced by a drug resistance gene neo. The vegetative cell growth curve showed that AS/J somatic knockout cells grew at the same rate as wild type cells. Thus, ASIJ was not required for the vegetative growth of Tetrahymena. But both genetic and cytological analysis showed that, without somatic AS! 1 alleles, cells cannot finish the mating process and most mating pairs abort the mating before they enter the anlagen stage. Mating of a wild type strain with a somatic AS! 1 knockout strain partially rescued this phenotype. Genetic experiments showed that somatic AS! 1 knockout cells exchanged germline micronuclei and completed fertilization before they aborted the mating.