Telomere Protection and Length Regulation in Schizosaccharomyces Pombe.

Abstract

Eukaryotic genomes are almost exclusively contained within linear chromosomes, the structure of which poses a problem to the cellular machinery that must copy these chromosomes during each round of cell division—wherein DNA at each end of every chromosome is unable to be copied. Failure to prevent the loss of terminal DNA from linear chromosomes during DNA replication leads to cell cycle arrest—termed replicative senescence. Replicative senescence can lead to organ failure, and has been linked to the development of aplastic anemia, pulmonary fibrosis, and liver cirrhosis in humans. The near universal solution to this problem is the creation of the telomere by telomerase. Linear chromosomes terminate in an array of tandem DNA repeats that are bound by the highly conserved shelterin and CST protein complexes, which regulate cell cycle checkpoint activation and recruit the reverse transcriptase telomerase to chromosome ends. Telomerase synthesizes repetitive DNA sequence onto the ends of chromosomes in order to prevent replicative senescence. The Nakamura lab studies telomere regulation by the shelterin complex in Schizosaccharomyces Pombe, which is an attractive model for understanding regulation of the human telomere. S.pombe is highly tractable to genetic and biochemical studies, and the proteins of the shelterin complex are well conserved with human. Furthermore, S.pombe cells can survive severe telomere dysfunction through chromosome circularization which allows experiments to be carried out that would normally be impossible due to cell lethality. This thesis presents two major projects: 1) identification of a novel protein component of telomerase in S.pombe, and 2) identification of a novel motif in shelterin component Tpz1 regulating telomerase activation as well as DNA lagging strand replication at the telomere.