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Figure 4


Fig. 4. The yolk sac vasculature of the Tak1{Delta}/{Delta} embryos fails to undergo angiogenesis. (A,B) E9.5 yolk sacs of Tak1+/{Delta} and Tak1{Delta}/{Delta} embryos, respectively. The yolk sac vascular plexus in A has undergone angiogenesis to create a branched network of mature vitelline vessels (arrowhead). The yolk sac vascular plexus in B has not remodeled but has retained its honeycomb-like structure of blood islands (arrowhead). The vessels in B are also prone to rupture, causing pooling of blood in the yolk sac (arrow). (C,D) Cross-sections of Tak1+/{Delta} and Tak1{Delta}/{Delta} yolk sacs, respectively, that are immunostained for vSMCs with an antibody to SMA (brown). The Tak1+/{Delta} yolk sac in C contains a mature vitelline vessel surrounded by a layer of smooth muscle (arrowhead). The Tak1{Delta}/{Delta} yolk sac in D has no mature vitelline vessels, the existing vessels are extremely dilated and have little SMA expression.