Date of Award
Doctor of Philosophy (PhD)
Petrella, Lisa N.
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.
Available for download on Thursday, May 28, 2020