Punctate Vwf staining and presence of WPBs in hagfish endothelial cells. Representative electron microscopy image of hagfish endothelium from aorta (A) and skeletal muscle arteriole (B) showing the presence of cigar-shaped organelles containing electron-dense tubules, consistent with WPBs. (C) Confocal laser scanning microscopy image of en face hagfish aorta processed for immunofluorescence staining of Vwf using polyclonal anti-human VWF antibody (see supplemental Figure 3 for images using hagfish monoclonal Vwf antibody). Nuclei are stained with DAPI. Note the presence of punctate staining in the endothelial cells. All stain and magnification information for photomicrographs is provided in the supplemental Material.