The relationship between Mll1 and Notch signaling in epithelial stem cell homeostasis

• Applicant: Professor Dr. Adrian Francis Stewart
• Subject Area: Cell Biology
• Term: from 2011 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 202210441

Mixed lineage leukemia (Mll1) is the founding member of the mammalian family of six H3K4 methyltransferases. It was discovered as the main gene mutated in early onset leukemia and subsequently found to be required for the establishment and maintenance of hematopoietic stem cells. However, although ubiquitously expressed, the roles of Mll1 in non-hematopoietic tissues remain largely unexplored. In our previous DFG project, we found that loss of Mll1 in adult mice results in rapid failure of small intestinal function. Remarkably, the observed intestinal defect - an expansion of secretory cells together with a depletion of the stem cell compartment - recapitulated Notch signaling blockage in intestinal crypt stem cells. Consequently, we aim to decipher the role of Mll1 in the intestinal system and its relationship to Notch signaling. We propose that either Mll1 is required for expression of a component(s) of the Notch signaling pathway or is physically required at Notch target genes for Notch transcriptional responses. Using conditional mutagenesis in mice and organoids, we will identify Mll1 target genes by transcriptome profiling and chromatin immunoprecipitation studies. We will also investigate the embryonic role of Mll1 in the establishment of intestinal stem cells and determine whether Mll1 can re-establish functional crypts in adults upon re-expression after removal. In addition to tamoxifen-induced Cre/loxP conditional mutagenesis, we will explore the application of a new ligand-inducible loss-of-function strategy in mice based on the auxin-inducible degron. Our primary discovery connecting Mll1 to Notch signaling in intestinal stem cells has implications for other epithelial stem cell compartments where Notch signaling is also implicated. The link between Mll1 and Notch signaling in different epithelial compartments could be fundamental to all epithelial stem cells and central to mechanisms of epithelial tumorigenesis.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Andrea Kranz