Analysis of a zebrafish VEGF receptor mutant reveals specific disruption of angiogenesis.
Blood vessels form either by the assembly and differentiation of mesodermal precursor cells (vasculogenesis) or by sprouting from preexisting vessels (angiogenesis). Endothelial-specific receptor tyrosine kinases and their ligands are known to be essential for these processes. Targeted disruption of vascular endothelial growth factor (VEGF) or its receptor kdr (flk1, VEGFR2) in mouse embryos results in a severe reduction of all blood vessels, while the complete loss of flt1 (VEGFR1) leads to an increased number of hemangioblasts and a disorganized vasculature. In a large-scale forward genetic screen, we identified two allelic zebrafish mutants in which the sprouting of blood vessels is specifically disrupted without affecting the assembly and differentiation of angioblasts. Molecular cloning revealed nonsense mutations in flk1. Analysis of mRNA expression in flk1 mutant embryos showed that flk1 expression was severely downregulated, while the expression of other genes (scl, gata1, and fli1) involved in vasculogenesis or hematopoiesis was unchanged. Overexpression of vegf(121+165) led to the formation of additional vessels only in sibling larvae, not in flk1 mutants. We demonstrate that flk1 is not required for proper vasculogenesis and hematopoiesis in zebrafish embryos. However, the disruption of flk1 impairs the formation or function of vessels generated by sprouting angiogenesis.
Habeck
Hinrich
H
Artemis Pharmaceuticals/Exelixis Deutschland GmbH, 72076, Tübingen, Germany.
Odenthal
Jörg
J
Walderich
Brigitte
B
Maischein
Hans
H
Schulte-Merker
Stefan
S
D000483:Alleles; D000818:Animals; D001808:Blood Vessels / Q000502:physiology; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000502:physiology; D016228:Endothelial Growth Factors / Q000235:genetics / Q000378:metabolism; D017403:In Situ Hybridization; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D007814:Larva / Q000033:anatomy & histology / Q000502:physiology; D008222:Lymphokines / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D018919:Neovascularization, Physiologic / Q000235:genetics* / Q000502:physiology; D010641:Phenotype; D051789:Proto-Oncogene Protein c-fli-1; D011518:Proto-Oncogene Proteins; D040262:Receptors, Vascular Endothelial Growth Factor / Q000235:genetics* / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000235:genetics* / Q000378:metabolism; D042442:Vascular Endothelial Growth Factors; D015027:Zebrafish / Q000196:embryology / Q000235:genetics / Q000502:physiology*
D004268:DNA-Binding Proteins; D016228:Endothelial Growth Factors; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines; D051789:Proto-Oncogene Protein c-fli-1; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D040262:Receptors, Vascular Endothelial Growth Factor; D040301:Vascular Endothelial Growth Factor Receptor-2