The mvWF LacZ transgene is expressed in a vascular bed-specific pattern. LacZ staining of 10-μm tissue sections from mvWFlacZ line no. 47 shows reporter gene activity in endothelial cells of the heart (A), skeletal muscle (B), and brain (D). An en face preparation of the thoracic aorta shows diffuseLacZ staining of endothelial cells (C). A bone marrow aspirate shows the X-Gal reaction product in megakaryocytes (F). There is no detectable β-galactosidase activity in other tissues (E shows lung). The blue staining in the lung represents backgound.