Fig. 8. Smo mutant yolk sacs exhibit severe vascular defects. (A) Whole-mount immunocytochemistry for PECAM demonstrates the arrest in the primary vascular plexus stage and total absence of large vitelline vessels in the mutant yolk sacs (note proximal staining in upper right panel and enlargements below). Scale bars: 1mm. (B) Hematoxylin and Eosin stained sections show the vessels packed with hematopoietic cells in the mutant yolk sacs compared with the heterozygotes. In situ hybridization for Bh1 (C) identifies the clustered cells as erythrocytes. (D) PECAM staining is reduced in the Smo mutant yolk sacs compared with Smo^+/– yolk sacs. Scale bars: 100 µm in B-D.