Date of Award
Summer 2020
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Biological Sciences
First Advisor
Petrella, Lisa
Second Advisor
Schlappi, Michael
Third Advisor
Maki, James
Abstract
It is important for organisms to establish and maintain proper gene expression for normal growth and development. In C. elegans, the DREAM repressor complex helps maintain proper gene expression in somatic cells by repressing germline genes. DREAM complex mutants show close to normal gene expression at 20°C; however, at 26°C, DREAM complex mutants display increased misexpression of germline genes ectopically in the soma and display a distinct High Temperature larval Arrest (HTA) phenotype. It is unclear what gene regulatory mechanisms lead to misexpression of germline genes in somatic cells of DREAM complex mutants. My dissertation research investigated three aspects of gene regulation in DREAM complex mutants: chromatin compartmentalization, transcription factors, and cell signaling pathways that function upstream of transcription factors. To study nuclear compartmentalization, we utilized nuclear spot assay to determine the localization of DREAM complex target promoter in three dimensional nuclear space. We found that DREAM complex target promoter loci are localized to nuclear periphery in both wild type and DREAM complex mutants. We also observed that multiple nuclear pore complex genes when knocked down in lin-54 mutant background allowed suppression of HTA phenotype, indicating a genetic interaction between DREAM complex and nuclear pore complex. In order to identify transcription factors required for the misexpression of germline genes in DREAM complex mutants at 26°C, we conducted a limited RNA interference knockdown screen for suppression of the HTA phenotype in lin-54 mutants. We found that 15 embryonically expressed transcription factors suppress the HTA phenotype in lin-54 mutants. Enrichment analysis of the HTA transcription factor suppressors showed significant enrichment of Wnt signaling pathway. A subsequent RNAi suppression screen of Wnt signaling factors showed that knock-down of the non-canonical Wnt/PCP pathway factors vang-1, prkl-1 and fmi-1 in the lin-54 mutant background resulted in strong suppression of the HTA phenotype. In fact, a lin-54; vang-1 double mutant showed almost complete suppression of both the HTA phenotype and germline gene pgl-1 misexpression. We propose that a set of embryonically expressed transcription factors, and the Wnt/PCP pathway, activate DREAM complex target genes potentially at the nuclear pore complex region in DREAM complex mutants at 26°C.