Transmission electron microscopy analysis reveals distorted and defective endothelium in tumor vessels in Cryab^−/− mice. (A) A representative micrograph of a small tumor vessel in a wild-type (wt) mouse shows a fenestrated endothelial cell (arrow) resting on a basal lamina (*) and sealed to the neighboring endothelial cell with tight junctions (TJ). A pericyte (PC) with its own basal lamina (**) is located in close contact with the endothelium. A red blood cell (RBC) is seen in the lumen (L). (B-D) Representative micrographs of tumor vessels in Cryab^−/− mice. (B) A blood vessel partially lined with fenestrated endothelium (arrow). (C) Defective endothelial lining (arrowheads) and remnants of an endothelial cell with fenestration (arrow). A red blood cell and 2 thrombocytes (Tr) are present in the lumen. (D) A vessel lacking endothelial lining with fibrous deposits (F) located directly on the surface of one of the surrounding tumor cells (TC). Original magnification for A,B, ×25 000; C,D, ×15 000. Bar equals 500 nm.