The vitelline artery (VA) undergoes extensive remodeling during embryonic development. (A) The VE-cadherin Cre mouse line, crossed to a R26R Cre reporter (lacZ in blue), exhibits vascular and hematopoietic labeling in the AGM at E11.0 (left) and in the VA at E10.5 (right, arrows). (B) The VA at E10.25 connects to the dorsal aorta via multiple smaller vessels that run along the midgut loop (mgl). The vitelline vein (VV) runs directly to the fetal liver (Lv). Orthogonal planes of section demonstrate hematopoietic clusters in the main arterial segment (top right) and in the tributaries associated with the midgut (mg, bottom right). (C) The remodeling of the VA (also called the omphalomesenteric artery [OA]) can be followed in embryo dissections from E9.0 to E11.0. The VA is initially connected to the umbilical arteries (UA) at E9.0. The UA connection is later eliminated on the establishment of a new connection to the dorsal aorta (DA). Subsequent to the dissolution of the UA connection, large clusters of cells are noted (arrows). (D) The remodeling events are shown in this schema. On vascular remodeling of the VA, large clusters of cells are collected in the regressing vessel within close proximity to the midgut loop. (E) Optical projection tomography scans of an embryo at E10.5 demonstrate the VA remodeling events in 3 dimensions, where the VA and yolk sac are highlighted in red, the heart and umbilical vessels are in yellow, and the regressing part of the VA and clusters noted by arrowheads. (A-C) Scale bars as labeled per row.