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Figure 2. Extension of the cardiac lymphatic system along arteries in adult zebrafish. Whole-mount confocal imaging of adult transgenic zebrafish hearts expressing the pan-endothelial fli1a:GFP (green: A-E, G), venous/lymphatic endothelial marker flt4:mCitrine (blue: A-D, red: F), arterial endothelial cell marker flt1enh:tdTomato (red: A-D, G), lymphatic endothelial marker prox1:Gal4-UAS:RFP (red: E), arterially enriched blood endothelial marker kdrl:mTurquoise (blue: E) and arterial marker dll4:GFP (F). (A-C) flt4:mCitrine-positive sprouts migrate along flt1enh:tdTomato expressing arteries not flt1enh:tdTomato-negative veins (white arrowheads). The extension appears somewhat dynamic and fluid, with gaps or dissociations observed during extension and formation (blue arrowheads). This association continues as the cardiac lymphatic vessel forms on the ventricle (D). The formed vessel endothelium is kdrl:mTurquoise-negative and is in close proximity to high-kdrl:mTurquoise (E), dll4:GFP (F) expressing arteries. flt1enh:tdTomato expressing arteries also express high levels of cxcr4a:mCitrene in young adult zebrafish (G). Scale bars 200 μm (A-G) and 50 μm (insets A, C, E, F and G), n ≥ 3 (A-G).