CHROMATIN ORGANIZATION DURING YEAST MEIOSIS

Open Access
Author:
Zhang, Liye
Graduate Program:
Cell and Developmental Biology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 09, 2012
Committee Members:
  • Benjamin Franklin Pugh, Dissertation Advisor
  • Joseph C. Reese, Committee Member
  • Yu Zhang, Committee Member
  • Hong Ma, Dissertation Advisor
Keywords:
  • nucleosome
  • meiosis
  • histone modification
  • linker histone
  • tetrasome
  • transcription
Abstract:
All eukaryote genomes are packaged with DNA-binding proteins into a structure called chromatin. Chromatin plays crucial roles in regulating gene expression and recombination. There are multiple levels of chromatin folding, and current studies focus on primary chromatin structure—positioning and occupancy of nucleosome across a genome. It has been shown that there is a general theme of nucleosome organization on the genes, and such patterns are conserved among several model organisms from yeast to human. Most of the current studies on primary chromatin structure have utilized unsynchronized cells during vegetative growth, meaning there is a gap in our knowledge regarding the changes of primary chromatin structure and histone modifications during meiotic cell cycle. To study primary chromatin structure during the meiotic cell cycle, we performed chromatin immunoprecipitation (ChIP) on samples from several stages of yeast meiosis to study nucleosome, modified histones, linker histone (Hho1p), and a partial nucleosome called tetrasome. These results revealed a few general principles regarding meiosis and transcription regulation, which may also apply to plant and metazoan. 1) Nucleosome positioning and occupancy is largely maintained during the meiotic cell cycle; 2) Repositioning of the +1 nucleosome correlates with transcription regulation in subsets of stress response genes; 3) The histone modification data suggest that antisense transcripts repress meiotic specific genes during vegetative growth; 4) linker histone Hho1p is enriched at linker DNA and promoter regions; 5) Globally elevated incorporation of Hho1p into chromatin may contribute to chromatin compaction in mature yeast spores; 6) The majority of tetrasome dyads are shifted approximately 25-50 bp away from nucleosome dyads and may be mainly positioned by DNA sequence. Taken together, the work presented in this thesis shows multiple aspects of primary chromatin architecture during stages of meiosis, and such a dynamic and comprehensive picture of primary chromatin structure will be able to provide a framework to integrate results from other chromatin associated factors, thus revealing the interplay between cellular events and chromatin structure.