Regulation of stem cell development during tissue remodeling

Eunice Kennedy Shriver National Institute Of Child Health & Human Development

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Abstract

TR IS ESSENTIAL FOR LARVAL EPITHELIAL CELL DEATH AND ADULT EPITHELIAL STEM CELL DEVELOPMENT/PROLIFERATION DURING XENOPUS TROPICALIS METAMORPHOSIS. We have shown that knockout of either TRα or TRβ, the only two TR genes, in Xenopus tropicalis, delays but does not prevent intestinal remodeling, including stem cell formation and/or proliferation. On the other hand, TR double knockout (TRDKO) Xenopus tropicalis tadpoles fail to undergo either larval epithelial cell death or adult epithelial stem cell development and proliferation by stage 61, the climax stage when TRDKO animals die. Interestingly, adult epithelial morphogenesis occurs prematurely in TRDKO tadpoles. To investigate how TR regulates cell fate and tissue morphogenesis, we are now using scRNA-seq and snRNA-seq to determine TH-regulation of the changes within different types of cells in the intestine during metamorphosis. TH-REGULATION OF CELL TRANSFORMATIONS DURING LIVER METAMORPHOSIS IN XENOPUS TROPICALIS. Many mammalian organs and tissues including erythrocytes mature into their adult forms during postembryonic development when plasma TH level peaks, resembling amphibian metamorphosis. TR mutations/deletions can cause hematopoietic dysfunction, suggesting that TH plays a role in erythropoiesis during development. Our analyses of TR double knockout (TRDKO) Xenopus tropicalis revealed that TRDKO tadpoles exhibited characteristics similar to human iron deficiency anemia. As the liver is the hematopoietic organ, our finding suggests a defect in liver development in TRDKO tadpoles. Indeed, we found that TRDKO tadpoles had liver developmental defects during metamorphosis, including reduced cell proliferation and failure to undergo hepatocyte hypertrophy or activate the expression of urea cycle genes. To investigate how TR regulates the transformations of different cell types in the liver during metamorphosis, we are carrying scRNA-Seq and snRNA-Seq analyses of liver during natural and T3-induced metamorphosis of wild type and TRDKO tadpoles. PROTEIN ARGININE METHYLTRANSFERASE 1 REGULATES MOUSE INTESTINAL EPITHELIAL HOMEOSTASIS IN MOUSE. Earlier studies suggest that the formation of adult mouse intestinal stem cells takes place during the first few weeks after birth, the postembryonic period when plasma TH levels are high. Furthermore, deficiency in TH signaling leads to defects in adult mouse intestine, including reduced cell proliferation in the intestinal crypts, where stem cells reside. Thus, mouse intestinal maturation resembles intestinal remodeling during frog metamorphosis both in morphological development and in the likely role of TH in the process. Our previous studies have shown that protein arginine methyltransferase 1 (PRMT1), a TR coactivator, is important for adult intestinal stem cell development and/or proliferation during Xenopus metamorphosis. We have further shown that PRMT1 is also highly expressed during intestinal maturation in mouse, resembling its upregulation during intestinal metamorphosis. Importantly, we analyzed the expression of PRMT1 by immunohistochemistry and studied the effect of tissue-specific knockout of PRMT1 in the intestinal epithelium. We showed that PRMT1 was expressed highly in the proliferating transit amplifying cells and crypt base stem cells. The specific knockout of PRMT1 in the intestinal epithelium resulted in, surprisingly, more elongated adult intestinal crypts with increased cell proliferation in the adult mice. In addition, there were increased Goblet cells and reduced Paneth cells in the crypt. Furthermore, using a tamoxifen-inducible intestinal epithelium-specific PRMT1 knockout mouse model, we showed that the epigenetic enzyme PRMT1 is important for the maintenance of intestinal epithelial architecture and homeostasis. We are currently investigating if PRMT1 may also influence intestinal development, particularly via T3 signaling, by using morphological, molecular, and snRNA-seq analyses.