Fig. 6. Histological and immunocytochemical analysis of 11.5 dpc Ihh+/– and Ihh –/– yolk sacs. (A) Hematoxylin and Eosin stained sections illustrate the small diameter of blood vessels, as well as the flattened morphology, in mutant yolk sacs compared with heterozygotes (arrows). (B) PECAM stains endothelial cells more robustly in Ihh +/– yolk sacs than in Ihh mutants (first panel). 
-SMA stains vascular smooth muscle cells encircling the blood vessels in Ihh+/– yolk sacs, whereas it fails to do so in the mutants (second panel, note arrow on right side). Additional endothelial cell markers, CD34 and Flk1, also exhibit reduced expression levels in the Ihh mutant yolk sacs compared with Ihh+/– yolk sacs (third and fourth panels). Scale bars: 100 µm.
