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Fig. 1. Vascular plexus formation and remodeling. Embryos and yolk sacs were
dissected at E8.25-8.5 (three- to six-somite stage). Morphological examination
revealed that a vascular plexus had formed in both wild-type (A) and
Raldh2-/- (B) yolk sac tissues. Hematoxylin and Eosin
(H/E) staining of 5 µm paraffin wax-embedded sections of yolk sacs revealed
dilated vessels within the Raldh2-/- plexi (D) compared
with wild type (C). Embryos and yolk sacs were also dissected at E9.5.
Morphological examination of wild-type yolk sacs (E) revealed a well-defined,
branched network that circulated blood throughout the embryo. Yolk sacs of
Raldh2-/- mutants (F) exhibited no remodeling and lacked
large vitelline vessels. In wild-type yolk sac (G), SM-
-actin
expression was evident around large vessels. In Raldh2-/-
yolk sacs (H), investment of endothelial tubes by SM-
-actin-positive
cells was not evident.