Date of Award
Spring 2019
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Biological Sciences
First Advisor
Petrella, Lisa N.
Second Advisor
Abbott, Allison
Third Advisor
Blumenthal, Edward
Abstract
Tissue-specific establishment of repressive chromatin through creation of compact chromatin domains during development is necessary to ensure proper gene expression and cell fate. C. elegans synMuv B proteins are important for the soma/germline fate decision and mutants demonstrate ectopic germline gene expression in somatic tissue, especially at high temperature. To study chromatin compaction during development we visualized chromatin using both nuclear-spot assays and FISH of native synMuv B regulated loci. We showed that C. elegans synMuv B proteins regulate developmental chromatin compaction and that timing of chromatin compaction was temperature sensitive in both wild-type and synMuv B mutants. Chromatin compaction in mutants was delayed into developmental time-periods when zygotic gene expression is upregulated and demonstrates an anterior-to-posterior pattern. Loss of this patterned compaction coincided with the developmental time-period of ectopic germline gene expression that leads to a developmental arrest in synMuv B mutants. Thus, chromatin organization throughout development is regulated both spatially and temporally by synMuv B proteins to establish repressive chromatin in a tissue-specific manner to ensure proper gene expression. Furthermore, we showed that global loss of H3K9me2, but not H3K9me3 results in phenotypes similar to synMuv B mutants. This suggests that repression of germline genes in somatic tissue is at least in part due to establishment of H3K9me2 at synMuv B regulated promoters. Specific loss of H3K9me2 at synMuv B regulated promoters in lin-15B mutants suggests that LIN-15B establishes or maintains H3K9me2 for germline gene pression at promoters. Finally, we analyzed the genetic interactions of lin-15B with genes involved in methylation of H3 lysine 9. We found that there is no enhancement of any phenotypes when the DREAM complex or H3K9me2 are disrupted in a lin-15B background. This suggests that H3K9me2, the DREAM complex, and LIN-15B work in series to repress germline gene expression at in the soma. From this work we propose that LIN-15B driven enrichment of H3K9me2 on promoters of germline genes contributes to repression of those genes in somatic tissues.