β3 integrin protein expression in the mouse heart. Immunostaining serial sections for PECAM-1 and β3 integrin confirms the hamster antimouse antibody can detect β3 protein expression in wild-type (but not β3-null) mouse hearts (A). During the first few postnatal weeks, β3 protein expression decreases and is only faintly detected on smooth muscle cells on small arteries in the adult heart (B). In late-stage embryo hearts, β3 integrin is found near areas of vascular remodeling (C, arrows indicate clusters of vessels) or associated with vascular structures (D, left), interstitial cells (D, middle), and myocytes (D, right). Bar = 100 μm (A-B) or 200 μm (C-D).