Department of Angiogenesis and Cardiovascular Pathology, Max-Delbrueck Center for Molecular Medicine, D13125 Berlin, Germany.
Development. 2011 May;138(10):2111-20. doi: 10.1242/dev.063933.
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.
血管内皮细胞通过探测血管内皮生长因子（VegfA）等导向线索，引导血管生成芽。本文呈现了斑马鱼中 Flt1（Vegf 受体 1）的缺失和功能获得数据，表明 Flt1 调节尖端细胞的形成和动脉分支形态发生。斑马鱼胚胎表达可溶性 Flt1（sFlt1）和膜结合 Flt1（mFlt1）。在 Tg(flt1(BAC):yfp) × Tg(kdrl:ras-cherry)(s916) 胚胎中，flt1:yfp 在节段性动脉芽的尖端、柄部和基部细胞中表达，与这些区域中 kdrl:cherry 的表达重叠。flt1 突变体显示出尖端细胞数量增加、血管生成行为增强和节段性动脉芽过度分支。额外的动脉分支发育成携带血流的功能性血管。为支持 Flt1 的细胞外 VEGF 结合域的功能作用，sflt1 或 mflt1 的过表达挽救了 flt1 突变体中的异常分支，而 sflt1 或 mflt1 在对照中的过表达导致动脉芽变短，丝状伪足数量减少。flt1 突变体显示 Notch 受体和 Notch 下游靶标 efnb2a 的表达减少，以及血管中 flt4 的异位表达，这与 Notch 信号的缺失一致。flt1 突变体中 notch1a 细胞内裂解域的条件过表达恢复了节段性动脉模式。发育中的中轴神经系统对 Flt1 的分布有贡献，而 Flt1 的缺失影响神经元。因此，Flt1 以 Notch 依赖性方式作为尖端细胞分化和分支的负调节剂起作用。Flt1 的分布可能经过精细调节，涉及与发育中的神经系统的相互作用。
