Addition of recombinant MDK in three-dimensional (3D) HUVEC monocultures. (A): Effect of RhMDK on HUVEC network formation in 3D HUVEC monocultures as per confocal microscopy over a 4-day timeline. Quantification of the effect of RhMDK on total network area in HUVEC monocultures on day 2 (B); total cord length on day 2 (C); and number of branch points on day 2 (D) (∗∗, p < .01; ∗∗∗, p < .001; n = 3 independent biological replicates; scale bars = 100 μm). Abbreviations: D, day; HUVEC, human umbilical vein endothelial cell; MDK, midkine; RhMDK, recombinant human midkine.