Role of HoxA9 and HoxD3 for MLL-dependent endothelial-cell sprouting. (A) HUVECs were transfected with scrambled or MLL siRNA oligonucleotides and empty vector or HoxA9 wild-type plasmid. Endothelial sprouting was assessed using the spheroid assay. Data are shown as percent scrambled + mock and mean ± SEM. (B-C) HUVECs were transfected with scrambled, HoxA9, or MLL siRNA oligonucleotides. (B) A spheroid assay was performed to investigate endothelial sprouting. Data are shown as percent scrambled and mean ± SEM. *P < .05 versus scrambled; #P < .05 versus scrambled and HoxA9 siRNA, n = 3. (C) RT-PCR analysis of HoxA9 and MLL expression. A representative gel is shown. GAPDH serves as loading control. (D) HUVECs were transfected with scrambled or MLL siRNA oligonucleotides and empty vector or HoxD3 wild-type plasmid. Endothelial sprouting was assessed using the spheroid assay. Data are shown as percent scrambled + mock and mean ± SEM, n = 4. (E-F) HUVECs were transfected with scrambled or MLL siRNA oligonucleotides and empty vector or HoxA9 wild-type + HoxD3 wild-type plasmids. (E) RT-PCR analysis of MLL and Hox expression. GAPDH serves as loading control. (F) A spheroid assay was performed to analyze the effect of simultaneous HoxA9 and HoxD3 overexpression on sprouting capacity. Data are shown as percent scrambled + mock and mean ± SEM. *P < .05 versus scrambled + mock, n = 4.