Figure 4. EC detachment and absence of neural tube invasion upon Tie1-Cre-mediated deletion of β1 integrins at e10.5.

(A,B) Embryos were whole mount stained with anti-VE-cadherin (red), embedded in paraffin, sectioned, and counterstained with DAPI (blue). The dashed 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 endothelial cell apparently undergoing detachment. Asterisks indicate dilated blood vessels. Dorsal aortae (da) are labeled. The cardinal veins in the dashed boxes are shown at high magnification in A′ and B′. (C,D,F,G) 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 endothelial cell within the lumen that has apparently detached. In F and G, the laminin-rich basement membrane (green) indicated by the dashed lines separates the nt 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) Bars are the mean values + SEM of 4 control/mutant pairs at e10.5. *p < 0.001 by Student’s T-test. Bars, 20 μm.