| Summary: | Reports have suggested that the two Notch ligands, Dll1 and Dll4, are indispensable to maintain the homeostasis of the intestinal epithelium. However, within the intestinal epithelium, the precise distribution of the cells that express those ligands at the protein level remains largely unknown. Here, we show a series of immunohistochemical analysis through which we successfully identified mice intestinal epithelial cells (IECs) that endogenously express Dll1 or Dll4. Results showed that Dll1-positive (Dll1+ve) IECs reside exclusively within the crypt, whereas Dll4-positive (Dll4+ve) IECs can locate both in the crypt and in the villus of the small intestine. Also in the colon, Dll1+ve IECs resided at the lower part of the crypt, whereas Dll4+ve IECs resided at both upper and lower part of the crypt, including the surface epithelium. Both Dll1+ve and Dll4+ve IECs were ATOH1-positive, but Hes1-negative cells, and located adjacent to Hes1-positive cells within the crypts. A sub-population of both Dll1+ve and Dll4+ve IECs appeared to co-express Muc2, but rarely co-expressed other secretory lineage markers. However, as compared to Dll1+ve IECs, Dll4+ve IECs included larger number of Muc2-postive IECs, suggesting that Dll4 is more preferentially expressed by goblet cells. Also, we identified that Dll4 is expressed in the Paneth cells of the small intestine, whereas Dll1 and Dll4 is expressed in the c-kit-positive IECs of the colon, indicating that Dll1+ve and Dll4+ve IECs may contribute to constitute the intestinal stem cell niche. Compared to the normal colon, analysis of DSS-colitis showed that number of Dll1+ve IECs significantly decrease in the elongated crypts of the inflamed colonic mucosa. In sharp contrast, number of Dll4+ve IECs showed a significant increase in those crypts, which was accompanied by the increase in number of Hes1-positive IECs. Those Dll4+ve IECs were mostly found adjacent to the Hes1-positive IECs, suggesting that Dll4 may act as a major Notch ligand in the crypts of the inflamed colonic mucosa. Our results illustrate distinct expression patterns of Dll1 and Dll4 within the intestinal epithelium, and suggest that these two ligands may have different roles in normal and inflamed mucosa.
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