Wnt Signaling Drives Ectopic Gene Expression and Larval Arrest in the Absence of the Caenorhabditis elegans DREAM Repressor Complex

Establishment and maintenance of proper gene expression is a requirement for normal growth and development. The DREAM complex in Caenorhabditis elegans functions as a transcriptional repressor of germline genes in somatic cells. At 26°, DREAM complex mutants show increased misexpression of germline genes in somatic cells and High Temperature Arrest (HTA) of worms at the first larval stage. To identify transcription factors required for the ectopic expression of germline genes in DREAM complex mutants, we conducted an RNA interference screen against 123 transcription factors capable of binding DREAM target promoter loci for suppression of the HTA phenotype in lin-54 mutants. We found that knock-down of 15 embryonically expressed transcription factors suppress the HTA phenotype in lin-54 mutants. Five of the transcription factors found in the initial screen have associations with Wnt signaling pathways. In a subsequent RNAi suppression screen of Wnt signaling factors we found that knock-down of the non-canonical Wnt/PCP pathway factors vang-1, prkl-1 and fmi-1 in a lin-54 mutant background resulted in strong suppression of the HTA phenotype. Animals mutant for both lin-54 and vang-1 showed almost complete suppression of the HTA phenotype, pgl-1 misexpression, and fertility defects associated with lin-54 single mutants at 26°. We propose a model whereby a set of embryonically expressed transcription factors, and the Wnt/PCP pathway, act opportunistically to activate DREAM complex target genes in somatic cells of DREAM complex mutants at 26°.