Prox1-expressing LECs migrate as an interconnected group of cells. (A) Sagittal sections along the anterior region of the embryo showing that Prox1-expressing LEC progenitors that bud off from the CV (white dashed line) and ISVs migrate dorsally and longitudinally (arrowheads) into the surrounding mesenchymal tissue starting at approximately E10.0. (B) Prox1-expressing LECs remain interconnected during migration into the surrounding mesenchyme (arrowheads), and Prox1-expressing LECs from the CV and the ISVs eventually merge together at E10.5. (C) Migrating LECs that have been merging together at earlier stages form a capillary-like structure (arrowheads) at approximately E11.0 in the anterior region. (D) Prox1-expressing LECs organize into a lymph sac-like structure (white dashed line) at approximately E11.5 after further sprouting and migration. LS, lymph sac (n = 4 embryos of each stage). Scale bars: 100 μm (A-D).