First of all, we performed phenotyp

First of all, we performed phenotypic analysis on retinal vasculature (Fig. 2a–d), a system that has been well established for studying vascular morphogenesis35. Cds2iΔEC caused significant reduction in endothelium coverage and the number of branch points, compared to those of retinal vasculature in the control mice (Fig. 2b, d). Furthermore, there were significantly reduced endothelial sprouts, but increased Collagen 4 (COL4)-positive and isolectin B4 (IB4)-negative sleeves (an indication of regressed vessel) in the angiogenic front of retinal vasculature in Cds2iΔEC mice (Fig. 2c, d). Importantly, as observed in zebrafish cds2 mutants, this defective vascular morphogenesis in Cds2iΔEC mice could be further enhanced by injection of recombinant VEGFA at postnatal day (P) 4 and 5, which resulted in blunted angiogenic front with further reduced endothelial sprouts (Fig. 2a–d). We next assessed whether cell apoptosis and proliferation were altered in Cds2iΔEC mice. In line with zebrafish study, endothelial apoptosis was also observed in the retinal vasculature of Cds2iΔEC mice (Supplementary information, Fig. S2e, f), and a reduction of EC proliferation in Cds2iΔEC mice was revealed by EdU incorporation, which was further declined by VEGFA stimulation (Supplementary information, Fig. S2g, h).