Fig. 4. GFP expression under the control of the cdx2 promoter in long-term cultured mouse esophageal epithelioid cells maintained at pH 3.5. (A) Pluristratified `Malpighien-like' cells exposed for 18 days at pH 3.5 stained with propidium iodide (nuclear staining) showing GFP-positive cells (B) Western blot analysis of GFP expression on cell lysates of cells exposed for 18 days at pH 3.5, revealed a 27 kDa band corresponding to the GFP protein that is absent in cells grown at pH 7.4. (C) Same field as in (A) stained for CK14 antibody (red). Note that GFP-positive cells remained green indicating that they were CK14 negative. Scale bar, 20 µm. (D) The same field as in (A) stained for CK4; the dotted line deliniates the GFP-positive cells that also stain for CK4.