LEC differentiation occurs outside the CV and ISVs. (A) In the anterior region of the embryo, the lymphatic marker podoplanin starts to be expressed in the migrating front of Prox1-expressing LECs (arrowheads) outside the CV at approximately E10.5. The Prox1⁺podoplanin⁻ cells seen outside the CV are located in the ISVs. (B) Extensive podoplanin expression is only detected after Prox1-expressing LEC progenitors fully exit the CV at around E11.5 (arrowheads). (C) Similarly, Prox1-expressing cells on the ISV are negative for podoplanin (arrow), which is expressed as soon as those cells bud off (arrowhead; n = 5 embryos of each stage). Scale bars: 100 μm (A), 20 μm (B-C).