Transfection of siRNAs in primary endothelial cells

siRNA transfection was performed using lipofectamine RNAiMAX Reagent (Invitrogen) according to the manufacturer’s recommended protocol. Briefly, cells were firstly seeded at the density of 0.2–0.3 × 10⁶ cells/well/2mL in 6-well plate in full medium for 24 h. Two rounds of transfection (24 and 48 h after plating) were then performed before cells were plated in basal medium with/without FGF-2 and spliceosome inhibitors for xCELLigence analysis or sprouting assays. The siRNAs used in this study were from Eurogentec (Seraing, Belgium): mismatch: 5′-UCG-GCU-CUU-ACG-CAU-UCA-A-3′ (forward) and 5′-UUG-AAU-GCG-UAA-GAG-CCG-A-3′ (reverse); SRSF1-a: 5′-GAA-AGA-AGA-UAU-GAC-CUA-U-3′ (forward) and 5′-AUA-GGU-CAU-AUC-UUC-UUU-C-3′ (reverse); SRSF1-b: 5′-UAA-CUU-ACC-UCC-AGA-CAU-C-3′ (forward) and 5′-GAU-GUC-UGG-AGG-UAA-GUU-A-3′ (reverse); SRSF3-a: 5′-CGA-GAG-CUA-GAU-GGA-AGA-ACA-3′ (forward) and 5′-UGU-UCU-UCC-AUC-UAG-CUC-UCG-3′ (reverse); SRSF3-b: 5′-GAC-GGA-AUU-GGA-ACG-GGC-UUU-3′ (forward) and 5′-AAA-GCC-CGU-UCC-AAU-UCC-GUC-3′ (reverse); SRPK1-a: 5′-GCU-AAU-GAC-UGU-GAU-GUC-CAA-AA-3′ (forward) and 5′-UUU-UGG-ACA-UCA-CAG-UCA-UUA-GC-3′ (reverse); SRPK1-b: 5′-CCA-UGU-GAU-CCG-AAA-GUU-AGG-3′ (forward); 5′-UAA-CUU-UCG-GAU-CAC-AUG-GUA-3′ (reverse); sVEGFR1-i13-a: 5′-UAA-CAG-UUG-UCU-CAU-AUC-A-3′ (forward) and 5′-UGA-UAU-GAG-ACA-ACU-GUU-A-3′ (reverse); sVEGFR1-i13-b: 5′-UCU-CGG-AUC-UCC-AAA-UUU-A-3′ (forward) and 5′-UAA-AUU-UGG-AGA-UCC-GAG-A-3′ (reverse); sVEGFR1-ex12-a: 5′-CAA-GCU-UCU-CUU-CCA-ACU-ACU-3′ (forward) and 5′-UAG-UUG-GAA-GAG-AAG-CUU-GUA-3′ (reverse); sVEGFR1-ex12-b: 5′-CCA-GCU-AAC-AGU-UCU-UUC-AUG-3′ (forward) and 5′-UGA-AAG-AAC-UGU-UAG-CUG-GUG-3′ (reverse).