Fig. 3. Endothelial Cx37 immunostaining is markedly reduced in Cx40^–/– aorta. Sections of thoracic aortas from E18.5 embryos (A-H) or 7-week-old mice (I-P) were immunostained for Cx37 or Cx40. Differential interference contrast images are shown to the right of each panel. In sections of aorta from E18.5 Cx40^–/– embryos (C,D), endothelial Cx37 immunostaining was virtually absent, whereas endothelial Cx37 staining was readily detected in wild-type sections (A,B). Cx40 immunostaining in sections of E18.5 Cx37^–/– aorta (G, H) was similar to that observed with sections of E18.5 wild-type aorta (E,F). Sections of aorta from a 7-week-old Cx40^–/– animal showed a substantial reduction in endothelial Cx37 immunostaining (K,L) compared with wild-type (I,J). Only rarely were punctate signals observed in the endothelium. Cx40 immunostaining in sections of 7-week-old Cx37^–/– aorta was slightly reduced (O,P) compared with wild-type signals (M,N). En face immunostaining of segments of 7-week-old aorta confirmed that endothelial Cx37 immunostaining was greatly reduced in Cx40^–/– aortic segments (R) compared with wild-type (Q). For the inset in panel R, the exposure level was adjusted to bring out faint Cx37 immunostaining in the Cx40^–/– endothelium. En face Cx40 staining was slightly reduced in Cx37^–/– aortic segments (T) compared with wild-type (S). Bars, 20 µm.