FIG. 4.
Intact vessel integrity and pericyte coverage in Tie2F1100/F1100 embryos. (A to I) No hemorrhages were seen in wild-type (WT) (A) or Tie2F1100/F1100 (C) embryos, whereas Tie2-null embryos displayed hemorrhages in the head (B) at E9.5. A cross-section of Tie2-null embryos with toluidine blue staining shows hemorrhaging (arrowhead) through a gap in the blood vessel wall (inset in B). Ultrastructural analysis depicts gaps in the vascular endothelial cells of the perineural plexus in the head region of Tie2-null embryos (arrow in E), whereas no gaps were observed in wild-type (D) or Tie2F1100/F1100 (F) embryos. Furthermore, endothelial cells were surrounded by pericytes in wild-type (19 of 21 samples) (G) and Tie2F1100/F1100 (20 of 24 samples) (I) embryos, whereas no pericyte coverage along endothelial cells was observed in Tie2-null embryos (0 of 20 samples) (H). (J) Sections of blood vessels were scored for pericytes closely attached to endothelial cells. end, endothelium; per, pericytes; lu, lumen; HC, hematopoietic cells; EC, endothelial cells.