ABSTRACT
Arteries and veins are morphologically, functionally and molecularly very different, but how this distinction is established during vasculogenesis is unknown. Here we show, by lineage tracking in zebrafish embryos, that angioblast precursors for the trunk artery and vein are spatially mixed in the lateral posterior mesoderm. Progeny of each angioblast, however, are restricted to one of the vessels. This arterial-venous decision is guided by gridlock (grl), an artery-restricted gene that is expressed in the lateral posterior mesoderm. Graded reduction of grl expression, by mutation or morpholino antisense, progressively ablates regions of the artery, and expands contiguous regions of the vein, preceded by an increase in expression of the venous marker EphB4 receptor (ephb4) and diminution of expression of the arterial marker ephrin-B2 (efnb2). grl is downstream of notch, and interference with notch signalling, by blocking Su(H), similarly reduces the artery and increases the vein. Thus, a notch-grl pathway controls assembly of the first embryonic artery, apparently by adjudicating an arterial versus venous cell fate decision.
Subject(s)
Arteries/embryology , Drosophila Proteins , Proteins/physiology , Signal Transduction , Zebrafish Proteins , Animals , Aorta/embryology , Aorta/metabolism , Arteries/metabolism , Basic Helix-Loop-Helix Transcription Factors , Cell Differentiation/genetics , Cell Lineage , Embryo, Nonmammalian/blood supply , Ephrin-B2 , Membrane Proteins/metabolism , Neovascularization, Physiologic/drug effects , Neovascularization, Physiologic/physiology , Oligonucleotides, Antisense/pharmacology , Proteins/genetics , Receptor Protein-Tyrosine Kinases/metabolism , Receptor, EphB4 , Receptors, Eph Family , Receptors, Notch , Repressor Proteins/physiology , Stem Cells , Veins/embryology , Veins/metabolism , ZebrafishABSTRACT
Following hepatic injury or stress, gluconeogenic and acute-phase response genes are rapidly upregulated to restore metabolic homeostasis and limit tissue damage. Regulation of the liver-restricted insulin-like growth factor binding protein 1 (IGFBP-1) gene is dramatically altered by changes in the metabolic state and hepatectomy, and thus it provided an appropriate reporter to assess the transcriptional milieu in the liver during repair and regeneration. The cytokine interleukin-6 (IL-6) is required for liver regeneration and repair, and it transcriptionally upregulates a vast array of genes during liver growth by unknown mechanisms. Evidence for a biologic role of IL-6 in IGFBP-1 upregulation was demonstrated by increased expression of hepatic IGFBP-1 in IL-6 transgenic and following injection of IL-6 into nonfasting animals and its reduced expression in IL-6(-/-) livers posthepatectomy. In both hepatic and nonhepatic cells, IL-6 -mediated IGFBP-1 promoter activation was via an intact hepatocyte nuclear factor 1 (HNF-1) site and was dependent on the presence of endogenous liver factor HNF-1 and induced factors STAT3 and AP-1 (c-Fos/c-Jun). IL-6 acted through the STAT3 pathway, as dominant negative STAT3 completely blocked IL-6-mediated stimulation of the IGFBP-1 promoter via the HNF-1 site. HNF-1/c-Fos and HNF-1/STAT3 protein complexes were detected in mouse livers and in hepatic and nonhepatic cell lines overexpressing STAT3/c-Fos/HNF-1. Similar regulation was demonstrated using glucose-6-phosphatase and alpha-fibrinogen promoters, indicating that HNF-1/IL-6/STAT3/AP-1-mediated transactivation of hepatic gene expression is a general phenomenon after liver injury. These results demonstrate that the two classes of transcription factors, growth induced (STAT3 and AP-1) and tissue specific (HNF-1), can interact as an adaptive response to liver injury to amplify expression of hepatic genes important for the homeostatic response during organ repair.
