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Fig. 5. Pancreatic and intestinal differentiation in explants treated with activin A. (A) Immunostaining for SMA (red), laminin (green) and nuclei (blue) on day 7 in culture in control explants (left panel) or in explants treated with activin A (right panel). In control explants, thin basement membranes, revealed by laminin staining, surround all the epithelial structures. SMA is not detected. In activin A-treated explants, a thick basal lamina separates the cylindrical epithelial cells layer from the smooth muscle layer, which is stained for SMA. This organization is typical of the intestinal wall structure. Scale bars, 100 µm. (B) Expression of FABP mRNAs, with TBP mRNA as a reference, as detected by RT-PCR in untreated explants (upper panel) and in explants treated with activin A (middle panel) or with a mixture of activin A and follistatin (lower panel) for the times indicated starting on day 1 (0 hours). Activin A induces i-Fabp and l-Fabp, two intestinal markers, and triggers the appearance of an intestinal structure (seen here on day 4 of culture). These effects, which do not occur spontaneously with time in culture, are blocked by follistatin. (C) Immunostaining for E-cad (red) and CPA (green) (left panel) or for glucagon (red), insulin (green) and nuclei (blue) (right panel) on day 7 of culture in activin A-treated explants. Exocrine (E-cad and CPA positive), ductal (E-cad positive and CPA negative) and endocrine (glucagon or insulin positive) cells are found, organized as in control explants (see Fig. 3). Note that the epithelium surrounding the lumen is positive for E-cad, but not for CPA. Scale bars, 100 µm.
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