Probable serine protease. In the embryo, localizes to paraxial regions at the neurula stage and anterior ventral regions at the tailbud stage. From the late tailbud to tadpole stage, expressed along the forming blood vessels including the anterior cardinal veins, posterior cardinal veins, intersomitic veins, dorsal longitudinal anastomosing vessel, dorsal aorta, pronephric sinus and most prominently around the vascular vitelline network, where expression shows left-right asymmetry in the stage 42 embryo. Localizes to endothelial cells. In adults, shows highest expression in liver with moderate levels of expression in the fat body, lung, gut and vessels. Weakly expressed in adult heart, muscle, testis and ovary. First expressed at the mid-neurula stage (stage 16) and remains at a constant level until the tadpole stage. Was named 'ami' because of its expression pattern; 'ami' means 'mesh' or 'net' in Japanese. Belongs to the peptidase S1 family.