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. Author manuscript; available in PMC: 2018 Dec 28.
Published in final edited form as: Int J Dev Biol. 2018;62(1-2-3):109–119. doi: 10.1387/ijdb.170325ct

Figure 3. Villification and intestinal stem cell localization.

Figure 3.

Cross-sectional illustrations of the small intestine demonstrating sequential transformation of the intestinal epithelium from a flat surface (E4–7), to longitudinal ridges (E8–12), to zigzags (E13–15), and finally to villi (E16-adult) as it coincides with progressive layers of aligned smooth muscle that differentiate within the mesoderm. Panels on right show close up views of the folds at each time point demonstrating how Shh, which is expressed by the epithelium, becomes focally localized within the mesenchyme at the tips of the folds to drive the high expression of villus cluster genes such as Bmp4, which in turn signals back to the epithelium to inhibit proliferation/stem cell identity.