title: Activated N-Ras signaling regulates arterial-venous specification in zebrafish.
abstract: BACKGROUND
  The aberrant activation of Ras signaling is associated with human diseases including hematological malignancies and vascular disorders. So far the pathological roles of activated Ras signaling in hematopoiesis and vasculogenesis are largely unknown.
  
  
  METHODS
  A conditional Cre/loxP transgenic strategy was used to mediate the specific expression of a constitutively active form of human N-Ras in zebrafish endothelial and hematopoietic cells driven by the zebrafish lmo2 promoter. The expression of hematopoietic and endothelial marker genes was analyzed both via whole mount in situ hybridization (WISH) assay and real-time quantitative PCR (qPCR). The embryonic vascular morphogenesis was characterized both by living imaging and immunofluorescence on the sections with a confocal microscopy, and the number of endothelial cells in the embryos was quantified by flow cytometry. The functional analyses of the blood circulation were carried out by fluorescence microangiography assay and morpholino injection.
  
  
  RESULTS
  In the activated N-Ras transgenic embryos, the primitive hematopoiesis appeared normal, however, the definitive hematopoiesis of these embryos was completely absent. Further analysis of endothelial cell markers confirmed that transcription of arterial marker ephrinB2 was significantly decreased and expression of venous marker flt4 excessively increased, indicating the activated N-Ras signaling promotes the venous development at the expense of arteriogenesis during zebrafish embryogenesis. The activated N-Ras-expressing embryos showed atrophic axial arteries and expansive axial veins, leading to no definitive hematopoietic stem cell formation, the blood circulation failure and subsequently embryonic lethality.
  
  
  CONCLUSIONS
  Our studies revealed for the first time that activated N-Ras signaling during the endothelial differentiation in vertebrates can disrupt the balance of arterial-venous specification, thus providing new insights into the pathogenesis of the congenital human vascular disease and tumorigenic angiogenesis.
authors.affiliation: Key Laboratory of Stem Cell Biology, Institute of Health Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences & Shanghai Jiao Tong University School of Medicine, Shanghai, China. ren_chunguang@163.com
authors.forename: Chun-Guang
authors.initials: CG
authors.lastname: Ren
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.forename: Xiao-E
authors.initials: XE
authors.lastname: Jia
authors.forename: Yi-Jie
authors.initials: YJ
authors.lastname: Liu
authors.forename: Zhi-Wei
authors.initials: ZW
authors.lastname: Dong
authors.forename: Yi
authors.initials: Y
authors.lastname: Jin
authors.forename: Yi
authors.initials: Y
authors.lastname: Chen
authors.forename: Min
authors.initials: M
authors.lastname: Deng
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhou
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhou
authors.forename: Rui-Bao
authors.initials: RB
authors.lastname: Ren
authors.forename: Wei-Jun
authors.initials: WJ
authors.lastname: Pan
authors.forename: Ting-Xi
authors.initials: TX
authors.lastname: Liu
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001158:Arteries / Q000502:physiology; D002454:Cell Differentiation / Q000235:genetics; D011905:Genes, ras; D006410:Hematopoiesis / Q000235:genetics / Q000502:physiology; D006801:Humans; D015398:Signal Transduction; D014680:Veins / Q000502:physiology; D015027:Zebrafish / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D029961:Zebrafish Proteins; D018631:ras Proteins