Nr2f1b modulates vein cell number and marker expression. a-c At 30 hpf, loss of nr2f1b function in Tg(fli1a:negfp) y7 embryos results in reduced vein cell number (b, blue bracket) as compared to uninjected wild type controls (a). The artery is marked by a red bracket. c Quantitative analysis shows a significant reduction in vein cell number in nr2f1b morphants. Compared to wild type controls. e, g, i, k, expression of the venous markers flt4 (f) and mrc1 (g) is reduced in the trunk of nr2f1b morphants at 24 hpf while there is no obvious change in the expression of arterial markers notch3 (i) and ephrinb2 (k). e′-l′ are cross sections of embryos in (e-l). d Quantification by qPCR shows a 60 % reduction in flt4 expression but no change in ephrinb2 expression in nr2f1b morphants (***refers to p < 0.0001 and **refers to p < 0.001 by an unpaired student′s t-test. Scale bars represent 50 µm in a, b, e-l and scare bar in cross-sections e′-l′ is 30 µm). Abbreviations: posterior cardinal vein (pcv), dorsal aorta (da), neural tube (nt) and pronephric ducts (pd).