MTGs in Intestinal Biology and Injury Responses - 1 This research proposal investigates the role of Myeloid Translocation Gene on chromosome 16 2 (MTG16) in regulating colon cell identity during homeostasis, regeneration, and dysplasia. 3 MTG16, a transcriptional co-repressor, plays a crucial part in stem cell function and lineage 4 determination in the hematopoietic system. Interestingly, we found that in the colon, MTG16 is 5 highly expressed in secretory precursors and goblet cells, implicating it in colonic goblet- 6 enteroendocrine (EE) cell allocation. Correspondingly, secretory lineages in the Mtg16-/- colon are 7 skewed toward goblet cells at the expense of enteroendocrine cells, positioning MTG16 at the 8 regulatory locus for goblet:EE allocation in the colon. This occurs through MTG16-mediated 9 repression of E protein transcription factors, key players in regenerative processes in numerous 10 tissues. Mtg16-/- mice also have increased sensitivity to colitis and colitis-associated dysplasia, 11 implicating MTG16 as an effector of colonic regeneration processes. However, just how MTG16 12 regulates these processes (i.e. genomic targets and repression complex composition) is largely 13 unknown, offering the potential for new therapeutic targets and interventions in IBD. Using yeast- 14 two-hybrid screens, we identified novel MTG16 interactors, including elongation-associated 15 factors, indicating transcriptional pausing as a new mechanism of MTG16-mediated gene 16 repression. Because MTG16 is expressed in both myeloid and epithelial cells, the observed gut 17 phenotypes could be caused by MTG16 loss in either population. We have observed that wild- 18 type bone marrow transplantation does not rescue Mtg16-/- colon phenotypes, and that these 19 phenotypes also persist in pure epithelial organoids. We hypothesize that MTG16 modulates 20 colonocyte identity during homeostasis, regeneration, and dysplasia by coordinating the 21 restructuring of epithelial transcriptional networks, thus promoting both stability and context- 22 dependent plasticity. Specifically, we predict that MTG16 enables the assembly of multi-protein 23 repression complexes to repress stem and enteroendocrine cell genes, and transcriptional 24 circuits, by modifying chromatin or pausing transcription, thus affecting colonic homeostasis, 25 regeneration, and dysplasia. We will test these hypotheses with three mechanistic, focused aims: 26 1) Define epithelial and/or myeloid MTG16’s contributions to homeostasis, regeneration, and 27 dysplasia; 2) identify context-dependent, colonic cell type-specific MTG16-mediated repression 28 targets; and 3) define colon-relevant MTG16 repression complexes. By unraveling MTG16's 29 molecular function and regulatory networks in colon biology, this project will provide pivotal 30 insights into the pathogenesis of IBD and colon cancer, offering potential therapeutic strategies.
