Fig. 5. Suppressed TGFβ signaling in Lkb1-deficient ECs. (A) Quantitative RT-PCR analysis of LKB1, TGFβ1 and PAI1 mRNA levels in immortalized HUVECs, or wild-type and Lkb1^lox/-, Tie1-Cre yolk sacs, as indicated. HUVECs were transfected with a control-siRNA or two independent siRNAs targeting LKB1 (LKB1-si1 and LKB1-si2). Measurements were normalized according to GAPDH mRNA levels and are presented relative to control samples (control-siRNA transfected HUVECs or wild-type yolk sac). Bars represent the mean (±s.d.) of two samples (siRNA treated), four samples (control-siRNA) or three samples (yolk sacs; ^*P<0.05, ^**P<0.01). (B,C) pSMAD2 (red) and PECAM1 (brown) staining of E12 wild-type (B) and Lkb1^lox/-, Tie1-Cre (C) yolk sac sections. (D,E) Higher magnifications of boxed areas in B and C. (F) Percentage of pSMAD2-positive ECs and mesenchymal cells in wild-type and Lkb1^lox/-, Tie1-Cre yolk sacs, with means (±s.d.) of three embryos indicated (^*P<0.05). e, endoderm; EC, endothelial cell; mes, mesenchymal cell.