Figure 3

Reporter gene activity in developing organs. A – D. In the developing gut, reporter gene activity is seen throughout the gut epithelium at both E12.5 (A) and E17.5 (C). Nuclear pSMAD1/5/8 staining is seen in a subset of epithelial cells at E12.5 (B, arrows), and all epithelial cells at E17.5 (D). Scattered cells in the mesenchyme show reporter gene activation (A, open arrowheads), similar to the pattern of nuclear pSMAD1/5/8 staining (B, arrows). In the villus of the small intestine, the majority of mesenchyme cells show neither reporter gene activation (C) nor nuclear pSMAD1/5/8 (D, inset). Likewise, the gut wall is largely devoid of reporter gene activation and nuclear pSMAD1/5/8 (C, D, inset) with the exception of some blood vessels. E – H. In the developing liver, reporter activation is seen in endothelial cells of vessels (asterisk), and in individual cells distributed through the liver parenchyme (open arrowheads). G. A similar distribution of nuclear pSMAD1/5/8 staining is seen (arrows, inset). H. Expression is maintained in the liver through development to E17.5. I – L. In the lung, the reporter is active in large airway epithelium from E10.5 (I) to E17.5 (L). A mixture of activated and non-activated cells can be seen in bronchiolar epithelium (J, L), similar to the pattern of nuclear pSMAD1/5/8 staining (K, arrows, inset). In the E12.5 mesenchyme, sporadic reporter gene activation and nuclear pSMAD1/5/8 can be seen (J, K, arrows). In the E17.5 lung, no reporter gene activation is seen in alveolar epithelium, whereas widespread activation can be seen in the mesenchyme between alveoli (L, inset). M – P. In the heart, the reporter is active in myocardium from E10.5 (M) to E17.5 (N), overlapping with widespread nuclear pSMAD1/5/8 (O, arrows). In endocardial cushions (M) and developing semilunar valves (N), reporter activation is limited to endocardial cells (P, open arrowheads), overlapping with nuclear pSMAD1/5/8 (P', arrows). Q – R. In blood vessels, overlapping reporter activation and nuclear pSMAD1/5/8 are seen in endothelial cells (Q, arrowheads, R, arrows). S – T. In skin, the basal layer is devoid of both reporter gene activation and nuclear pSMAD1/5/8, whereas the suprabasal layer stains strongly for both (T, inset). The reporter is weakly active in the subbasal layer. Single cells within the base of each dermal papilla display both reporter activation and nuclear pSMAD1/5/8 (S, T, insets). U – X. In the developing forelimb, reporter activation is seen in the interdigital region of the E12.5 limb (U). Reporter activation and nuclear pSMAD1/5/8 overlap in cartilage of the developing humerus (V, W). In cultures of E17.5 metatarsals, reporter activation is seen in cartilage, but is excluded from the calcified center, despite treatment with 50 ng/ml BMP4 (X). X'. An X-gal stained wild type metatarsal demonstrates absence of background staining. Abbreviations: Al: alveolus, Br: bronchiole, BL: basal layer, Ca: cartilage, CC: calcified center, Cush: endocardial cushion, DP: dermal papilla, E: epithelium, IR: interdigital region, M: mesenchyme, Myo: myocardium, Sub: subbasal layer, Supra: suprabasal layer, Va: valve.