title: Etsrp/Etv2 is directly regulated by Foxc1a/b in the zebrafish angioblast.
abstract: BACKGROUND
  Endothelial cells are developmentally derived from angioblasts specified in the mesodermal germ cell layer. The transcription factor etsrp/etv2 is at the top of the known genetic hierarchy for angioblast development. The transcriptional events that induce etsrp expression and angioblast specification are not well understood.
  
  
  OBJECTIVE
  We generated etsrp:gfp transgenic zebrafish and used them to identify regulatory regions and transcription factors critical for etsrp expression and angioblast specification from mesoderm.
  
  
  RESULTS
  To investigate the mechanisms that initiate angioblast cell transcription during embryogenesis, we have performed promoter analysis of the etsrp locus in zebrafish. We describe three enhancer elements sufficient for endothelial gene expression when place in front of a heterologous promoter. The deletion of all 3 regulatory regions led to a near complete loss of endothelial expression from the etsrp promoter. One of the enhancers, located 2.3 kb upstream of etsrp contains a consensus FOX binding site that binds Foxc1a and Foxc1b in vitro by EMSA and in vivo using ChIP. Combined knockdown of foxc1a/b, using morpholinos, led to a significant decrease in etsrp expression at early developmental stages as measured by quantitative reverse transcriptase-polymerase chain reaction and in situ hybridization. Decreased expression of primitive erythrocyte genes scl and gata1 was also observed, whereas pronephric gene pax2a was relatively normal in expression level and pattern.
  
  
  CONCLUSIONS
  These findings identify mesodermal foxc1a/b as a direct upstream regulator of etsrp in angioblasts. This establishes a new molecular link in the process of mesoderm specification into angioblast.
authors.affiliation: Department of Molecular, Cell, and Developmental Biology, University of California, Los Angeles, 621 Charles E Young Dr South, Los Angeles, CA 90095-1606, USA.
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Veldman
authors.forename: Shuo
authors.initials: S
authors.lastname: Lin
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D001665:Binding Sites; D019070:Cell Lineage / Q000235:genetics; D047369:Chromatin Immunoprecipitation; D024202:Electrophoretic Mobility Shift Assay; D004625:Embryo, Nonmammalian / Q000378:metabolism; D053595:Embryonic Stem Cells / Q000378:metabolism*; D042783:Endothelial Cells / Q000378:metabolism*; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D055785:Gene Knockdown Techniques; D017403:In Situ Hybridization; D008648:Mesoderm / Q000166:cytology / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic; D015027:Zebrafish / Q000196:embryology / Q000235:genetics / Q000378:metabolism*; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C509408:Etv2 protein, zebrafish; D051858:Forkhead Transcription Factors; C426857:Foxc1a protein, zebrafish; C426858:Foxc1b protein, zebrafish; D011993:Recombinant Fusion Proteins; D029961:Zebrafish Proteins