Fig. 5. Collagen I is associated with normal and ectopic vasculature in limb muscles. Transverse and consecutive sections of wings from E6.5/HH29 chick embryos were hybridized with the VE-cadherin (A) and collagen I (B) probes followed by immunohistochemistry with the MF20 antibody. collagen I transcripts are detected with endothelial cells in the recently cleaved sites of the ventral muscle masses. (C-H) VEGF/RCAS-expressing cells were grafted to the dorsal aspect of E4/HH22 wings and the embryos were fixed at E8/HH32. Consecutive sections of VEGF-infected right limbs (C-E) and control left wings (F-H) were hybridized with the Vegf (C,F), Hif2 (D,G) and collagen I (E,H) probes (blue) then incubated with the MF20 antibody (brown). High magnifications are shown of the same dorsal muscle in experimental wings (C-E) and in control wings (F-H) at the same level. Ectopic hypervascularization (C,D) leads to an obvious increase in collagen I expression in muscles (E) compared with control muscles (H).