PI3Kβ loss alters expression of tip cell markers. Primary human ECs were cultured on beads in fibrin gels as in Figure 5 for 18 hours, stimulated with SingleQuot growth factors or not, then imaged to evaluate tip cell morphology (A). Total RNA was extracted, then expression of characteristic tip cell transcripts was quantified (B). (C) Quantification of gene expression after growth factor stimulation of nontransfected (NT), nonspecific siRNA (NS)-transfected, or p110β (Siβ)-transfected cells at 18 hours of culture in fibrin gels. (D) NS or Siβ ECs were isolated from the fibrin gels by digestion with collagenase type 1 for 1 hour, lysed with RIPA buffer, and proteins were resolved using SDS polyacrylamide gel electrophoresis and quantified (E). The bars represent the mean ± SEM of ≥4 independent experiments; *P < .05, Siβ vs NS.