Adam10 deficiency in endothelial cells causes increased vascular density at the front of the developing retinal vasculature. (A,B) Lac-Z staining of retinas from A10ΔEC-R26R or A10flox/flox-R26R control mice. (C) Immunoblot of Adam10 and Adam17 in primary endothelial cells isolated from lungs of A10flox/flox control or A10ΔEC mice (p: pro-form, m: mature form). (D-G) Isolectin-B4 staining of retinas from 5-day-old A10ΔEC or control mice. Panels F and G correspond to the area marked by insets in panels D and E, respectively. (H-J) Quantitative analysis of tip cell density (H, A10ΔEC: 6.9 ± 1.8 per 100 μm of vascular front, n = 15; controls: 4.9 ± 1.4, n = 15), endothelial cell coverage at the front of the retinal vascular tree (I, A10ΔEC: 54.8% ± 4.42, n = 17; controls: 35.3% ± 3.8, n = 21), and vascular loops per field (J, A10ΔEC: 980 loops per mm² ± 65, n = 17, controls 628 ± 68 per mm², n = 21). (K,L) Micrographs of tip cells at the leading edge of the developing retinal vascular tree in A10ΔEC and control mice, and quantitative analysis of filopodia density (M, A10ΔEC: 26.4 ± 6.8 per 100 μm vessel length, n = 15, controls: 18.6 ± 5.6, n = 15). Please see “Evaluation of developmental retinal angiogenesis” and supplemental Figure 1 for details. Error bars represent mean ± SEM. ** indicates P < .01, and *** indicates P < .001 in a 2-tailed Student t test. Scale bars in panels A-B: 300 μm; D-E: 400 μm; F-G: 100 μm, K-L: 20 μm.