Fig. 4. EC detachment and absence of neural tube invasion upon Tie1-Cre-mediated deletion of β1 integrins at e10.5. (A-B') Control (A) and Tie1-Cre mutant (B) mouse embryos were whole-mount stained with anti-VE-cadherin (red), embedded in paraffin, sectioned and counterstained with DAPI (blue). The dashed white line indicates the boundary between the neural tube (nt) and the mesenchyme. The arrow indicates an area of discontinuous endothelium in the cardinal vein (cv) and the arrowhead indicates an EC apparently undergoing detachment. Asterisks indicate dilated blood vessels. da, dorsal aortae. The cardinal veins in the boxed regions (green dashed lines) in A and B are shown at high magnification in A' and B', respectively. (C,D,F,G) Control (C,F) and Tie1-Cre mutant (D,G) mouse embryo cryosections stained with anti-CD31 (red), DAPI (blue), and anti-fibronectin (green, C,D) or anti-laminin (green, F,G). Arrowheads in D indicate discontinuous endothelium along the vascular basement membrane, and the dashed line encircles an EC within the lumen that has apparently detached. In F and G, the laminin-rich basement membrane (green) indicated by the dashed lines separates the neural tube from the mesenchyme. Note the absence of ECs in the neural tubes in mutants, and that significant laminin surrounds ECs within the control neural tubes. (E,H) Quantification of EC discontinuity in major blood vessels (E) and of EC failure to invade the neural tubes (H). Bars are the mean values + s.e.m. of four control/mutant pairs at e10.5. ^*P<0.001 by Student's t-test. Scale bars: 20 µm.