Fig. S1

Fmnl3 regulates endothelial filopodia formation but not ISV formation. Related to Figure 1. (A – C) Mosaic endothelial fmnl3-EGFP expression in the ISV and DLAV in 31hpf Tg(kdr-l:ras-Cherry)^s916 embryos. During the development of ISV and DLAV, fmnl3 localizes in vesicular structures in the cytoplasm and filopodia of ECs. (D) Fmnl3 localizes at cell junctions in lumenized ISV of a 48hpf embryo. (A – D) Arrows, filopodia. Arrowheads, cell junction. Scale bars, 10µm. (E - H) ISVs of 31 hpf Tg(kdr-l:ras-Cherry)^s916;Tg(fli:nEGFP)^y7 embryos injected with control or fmnl3 morpholino. Filopodia number per 100µm vessel length (G) and filopodia length (H) were quantified in 28 to 31 hpf Tg(kdr-l:ras-Cherry)^s916 embryos. Filopodia number: Control MO, N = 38 ISVs, N = 22 embryos; fmnl3 MO, N = 45 ISVs, N = 30 embryos. Filopodia length: Control MO, N = 168 filopodia, N = 11 embryos; fmnl3 MO, N = 181 filopodia, N = 11 embryos. Bars represent mean ± SD. Scale bars, 10µm. (I – K) ISV length of fmnl3 morphants is comparable to that of control morphants. The length of the most posterior 15 ISVs in Tg(fli:GFP)^y1 was measured at 50 hpf. Control MO, N = 10; fmnl3 MO, N = 12 embryos. Data represent mean ± SD. Scale bar, 500µm. (L – M) Vein plexi of 48hpf Tg(fli1ep:Lifeact-EGFP);Tg(kdrl: ras-Cherry)^s916 embryos. Control morphants developed dorsal aorta (DA), dorsal vein (DV) and ventral vein (VV) at the vein plexus while fmnl3 morphants fail to form the VV. Scale bars, 10µm. (N) ISV and DLAV of Tg(fli1ep:Lifeact-EGFP) embryo at 32hpf with fmnlΔC-mCherry expression. Arrowhead, cortical F-actin cables. Scale bar, 10µm.