Lymphatic development in mouse small intestine.

Lymphatic vessels in the small intestine serve as essential conduits for the absorption and transport of lipids from the intestine to the thoracic duct. Although the morphology and function of the intestinal lymphatic vasculature are well known, little is known about the embryonic development of these vessels. In this study, we examined development of lymphatic and blood vasculatures in the intestinal tube during mouse embryonic development by immunostaining with recently discovered molecular markers for lymphatic endothelial cells: LYVE-1, VEGFR3, Prox-1, and podoplanin. Immature lymphatics became detectable in mesentery, but not in intestinal tube, around E13.5-E14.5, while organized lymphatic vessel plexuses and capillaries were observed in intestinal tube and villi around E17.5. These lymphatic plexuses and capillaries in the intestinal tube appeared to be formed through an active branching process associated with activation of VEGFR3 and involvement of LYVE-1+ macrophages. Our data also reveal that the lymphatic vessels in the intestinal tube, unlike the blood vessels, have not originated from the mesoderm of intestine. All lymphatic vessels in the intestinal tube originated by extension of mesenteric lymphatic vessels through an active branching process. Although the formation of lymphatic vessels follows the formation of blood vessels in the intestine, a mature lymphatic vasculature is formed before birth. Together, our study reveals the temporal and spatial windows of intestinal lymphatic development during embryonic development in mouse. Copyright 2007 Wiley-Liss, Inc.