Author's School

Graduate School of Arts & Sciences

Author's Department/Program

Biology and Biomedical Sciences: Developmental, Regenerative and Stem Cell Biology


English (en)

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Douglas L. Chalker


During its somatic nuclear differentiation, the single cell eukaryote Tetrahymena thermophila undergoes genome-wide programmed DNA rearrangement to eliminate transposon-like elements from its future soma. This process involves small RNA-directed heterochromatin formation followed by extensive nuclear reorganization to form subnuclear domains. While more has been known about small RNAs and heterochromatin, the mechanisms and players involved in the process of nuclear reorganization and the subsequent removal of transposon-like elements from the somatic genome are just starting to unravel. My thesis work centers on the study of two novel nuclear proteins Die5p: Chapter 2) and Lia5p: Chapter 3) and their roles in DNA rearrangement. These essential proteins function downstream of small RNA targeted heterochromatin establishment. While Lia5p is essential for nuclear reorganization to form distinct subnuclear structures, Die5p is a protein conserved across ciliate species and appears to be important for the integrity of the differentiating genome. Maintaining genome integrity during somatic nuclear differentiation has proven to be an active process. Similar to V(D)J recombination during mammalian B and T cell maturation, programmed DNA rearrangement in Tetrahymena induces global DNA damage that requires proper response and repair. Through the study of LIA5 and DIE5, we show that nuclear reorganization during Tetrahymena DNA rearrangement is intimately associated with the response to DNA damage. Furthermore, we implicate a chromodomain protein Pdd1 as a component of the DNA damage response system, thus providing evidence to support the link between heterochromatin and DNA repair during the reprogramming of Tetrahymena somatic genome.


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