title: Flt1 acts as a negative regulator of tip cell formation and branching morphogenesis in the zebrafish embryo.
abstract: Endothelial tip cells guide angiogenic sprouts by exploring the local environment for guidance cues such as vascular endothelial growth factor (VegfA). Here we present Flt1 (Vegf receptor 1) loss- and gain-of-function data in zebrafish showing that Flt1 regulates tip cell formation and arterial branching morphogenesis. Zebrafish embryos expressed soluble Flt1 (sFlt1) and membrane-bound Flt1 (mFlt1). In Tg(flt1(BAC):yfp) × Tg(kdrl:ras-cherry)(s916) embryos, flt1:yfp was expressed in tip, stalk and base cells of segmental artery sprouts and overlapped with kdrl:cherry expression in these domains. flt1 morphants showed increased tip cell numbers, enhanced angiogenic behavior and hyperbranching of segmental artery sprouts. The additional arterial branches developed into functional vessels carrying blood flow. In support of a functional role for the extracellular VEGF-binding domain of Flt1, overexpression of sflt1 or mflt1 rescued aberrant branching in flt1 morphants, and overexpression of sflt1 or mflt1 in controls resulted in short arterial sprouts with reduced numbers of filopodia. flt1 morphants showed reduced expression of Notch receptors and of the Notch downstream target efnb2a, and ectopic expression of flt4 in arteries, consistent with loss of Notch signaling. Conditional overexpression of the notch1a intracellular cleaved domain in flt1 morphants restored segmental artery patterning. The developing nervous system of the trunk contributed to the distribution of Flt1, and the loss of flt1 affected neurons. Thus, Flt1 acts in a Notch-dependent manner as a negative regulator of tip cell differentiation and branching. Flt1 distribution may be fine-tuned, involving interactions with the developing nervous system.
authors.affiliation: Department of Angiogenesis and Cardiovascular Pathology, Max-Delbrueck Center for Molecular Medicine, D13125 Berlin, Germany.
authors.forename: Janna
authors.initials: J
authors.lastname: Krueger
authors.forename: Dong
authors.initials: D
authors.lastname: Liu
authors.forename: Katja
authors.initials: K
authors.lastname: Scholz
authors.forename: Anja
authors.initials: A
authors.lastname: Zimmer
authors.forename: Yu
authors.initials: Y
authors.lastname: Shi
authors.forename: Christian
authors.initials: C
authors.lastname: Klein
authors.forename: Arndt
authors.initials: A
authors.lastname: Siekmann
authors.forename: Stefan
authors.initials: S
authors.lastname: Schulte-Merker
authors.forename: Melissa
authors.initials: M
authors.lastname: Cudmore
authors.forename: Asif
authors.initials: A
authors.lastname: Ahmed
authors.forename: Ferdinand
authors.initials: F
authors.lastname: le Noble
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D001808:Blood Vessels / Q000196:embryology / Q000378:metabolism; D002454:Cell Differentiation; D018507:Gene Expression Regulation, Developmental; D008264:Macrophages / Q000378:metabolism; D018919:Neovascularization, Physiologic; D009420:Nervous System / Q000196:embryology / Q000378:metabolism; D020319:Oligodeoxyribonucleotides, Antisense / Q000235:genetics; D051880:Receptors, Notch / Q000378:metabolism; D015398:Signal Transduction; D012995:Solubility; D014018:Tissue Distribution; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics / Q000378:metabolism*; D029961:Zebrafish Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D020319:Oligodeoxyribonucleotides, Antisense; D051880:Receptors, Notch; D029961:Zebrafish Proteins; D040281:Vascular Endothelial Growth Factor Receptor-1