Fig. 11.

Model for formation of intestinal epithelial secretory cells and requirement for motility. (A) We find that ascl1a expression is a critical step in specification of secretory cells. Loss of secretory cells results in loss of distal but not proximal intestinal motility. We find Notch signaling is active at two points in specification of intestinal epithelial cells as either secretory or enterocytes. (B) In this model, we propose that Notch signaling between 30 and 34 hpf is involved in the potentiation of intestinal epithelial cells to become either secretory cells or enterocytes via lateral induction. (C) Later, ascl1a is expressed in cells with secretory potential, inducing deltaD to activate Notch signaling in surrounding cells. We propose that this stage involves classical lateral inhibition to restrict the number of secretory cells.