Fig. 4. Cx37 immunostaining is detectable in the medial layer of mouse aorta as well as in endothelium. Sections of thoracic aortas from 6-7-week-old wild-type (A), Cx37^–/– (B) and Cx40^–/– (C,D) mice were immunostained with anti-Cx37 antibody (A,B,C) or with secondary antibody only (D) and photographed at high magnification. The lumen of the aorta is on the right in each panel. (A) In wild-type aorta, very weak punctate staining was observed in the medial layer, as well as strong endothelial staining. (B) The specificity of the medial layer signal was confirmed by the absence of medial layer staining in Cx37^–/– aortic sections. (C) Medial layer Cx37 staining was elevated in Cx40^–/– sections. (D) Secondary antibody-only control showed no signal in the medial layer of Cx40^–/– aorta. (E,F) Sections of wild-type and Cx40^–/– aorta from 4-month-old mice were immunostained for Cx37. In addition to endothelial signal, faint punctate Cx37 staining was observed in the medial layer of wild-type sections. Medial layer Cx37 staining was particularly evident in aortas from 4-month-old Cx40^–/– mice. Bar, 20 µm.