Aminopeptidase N during the ontogeny of the chick

Little is known about the production and function of metallopeptidases in embryonic development. One such enzyme, aminopeptidase N (APN), is present in several epithelia, the brain and angiogenic vessels in adults. APN promotes vascular growth and endothelial cell proliferation in physiological and pathological models of angiogenesis. However, its possible role in embryonic angiogenesis or other developmental processes is unknown. Its expression profile in the early phase of embryonic development has not been reported. We report here the expression of this enzyme during the early development of the chick embryo, using complementary techniques for monitoring APN mRNA, protein, and enzymatic activity. We detected APN in the embryo as early as gastrulation. In addition to the known sites of APN production identified in both adults and rat fetuses toward the end of gestation, APN was found in unexpected sites, such as the primitive streak, the dorsal folds of the neural tube, the somites, and the primordia of several organs. APN was present mostly in the cardiovascular compartment during the first 13 days of incubation, and in the hematopoietic compartment (yolk sac and aorta–gonad–mesonephros region) early in development. This study provides clues as to the possible role of APN in embryonic development.