title: Integration of repulsive guidance cues generates avascular zones that shape mammalian blood vessels.
abstract: BACKGROUND
  Positive signals, such as vascular endothelial growth factor, direct endothelial cells (ECs) to specific locations during blood vessel formation. Less is known about repulsive signal contribution to shaping vessels. Recently, "neuronal guidance cues" have been shown to influence EC behavior, particularly in directing sprouting angiogenesis by repelling ECs. However, their role during de novo blood vessel formation remains unexplored.
  
  
  OBJECTIVE
  To identify signals that guide and pattern the first mammalian blood vessels.
  
  
  RESULTS
  Using genetic mouse models, we show that blood vessels are sculpted through the generation of stereotyped avascular zones by EC-repulsive cues. We demonstrate that Semaphorin3E (Sema3E) is a key factor that shapes the paired dorsal aortae in mouse, as sema3E(-/-) embryos develop an abnormally branched aortic plexus with a markedly narrowed avascular midline. In vitro cultures and avian grafting experiments show strong repulsion of ECs by Sema3E-expressing cells. We further identify the mouse notochord as a rich source of multiple redundant neuronal guidance cues. Mouse embryos that lack notochords fail to form cohesive aortic vessels because of loss of the avascular midline, yet maintain lateral avascular zones. We demonstrate that lateral avascular zones are directly generated by the lateral plate mesoderm, a critical source of Sema3E.
  
  
  CONCLUSIONS
  These findings demonstrate that Sema3E-generated avascular zones are critical regulators of mammalian cardiovascular patterning and are the first to identify a repulsive role for the lateral plate mesoderm. Integration of multiple, and in some cases redundant, repulsive cues from various tissues is critical to patterning the first embryonic blood vessels.
authors.affiliation: Department of Molecular Biology, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd, NA8.300, Dallas, TX 75390-9148, USA.
authors.forename: Stryder M
authors.initials: SM
authors.lastname: Meadows
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Fletcher
authors.forename: Carlos
authors.initials: C
authors.lastname: Moran
authors.forename: Ke
authors.initials: K
authors.lastname: Xu
authors.forename: Gera
authors.initials: G
authors.lastname: Neufeld
authors.forename: Sophie
authors.initials: S
authors.lastname: Chauvet
authors.forename: Fanny
authors.initials: F
authors.lastname: Mann
authors.forename: Paul A
authors.initials: PA
authors.lastname: Krieg
authors.forename: Ondine
authors.initials: O
authors.lastname: Cleaver
mesh_terms: D000818:Animals; D001011:Aorta / Q000166:cytology / Q000196:embryology; D001808:Blood Vessels / Q000166:cytology / Q000196:embryology*; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins; D004622:Embryo, Mammalian / Q000098:blood supply*; D004730:Endothelium, Vascular / Q000166:cytology / Q000196:embryology*; D051858:Forkhead Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D006023:Glycoproteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D051542:Hepatocyte Nuclear Factor 3-beta / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D066298:In Vitro Techniques; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D008648:Mesoderm / Q000166:cytology / Q000196:embryology; D051379:Mice; D018345:Mice, Knockout; D023421:Models, Animal; D018919:Neovascularization, Physiologic / Q000502:physiology*; D009672:Notochord / Q000166:cytology / Q000196:embryology; D039961:Semaphorins; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D003598:Cytoskeletal Proteins; D051858:Forkhead Transcription Factors; C496503:Foxa2 protein, mouse; C491117:Foxh1 protein, mouse; D006023:Glycoproteins; D008565:Membrane Proteins; C111150:Sema3e protein, mouse; D039961:Semaphorins; D051542:Hepatocyte Nuclear Factor 3-beta
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