Fig. 4.
Vessel extension in the mesenchyme is in response to basilar epithelial cell VEGF (Cy3). Fetal mouse lungs from timed pregnant mothers indicate VEGF expression (Cy3) at the basilar region of the day E12.5 epithelial cells (yellow arrows and B, inset) as well as the epithelium of day E14.5 (E and F) and day E16.5 (H and I). VEGF-activated endothelial cells, identified by VEGF receptor-2 (VEGFR2) phosphorylation (FITC) surrounding DAPI-positive nuclei (A, white arrows), were found only in the mesenchyme at day E12.5 (A–C) and not at the epithelial/mesenchymal interface (“*” in A). Phosphorylated (P) VEGFR2 colocalized with basilar epithelial VEGF expression at day E14.5 (D, red arrows; D–F) and day E16.5 (G, red arrows; G–I). DAPI denotes nuclear staining. Magnification, ×600.