Fox genes in arterial-venous endothelial cell identity

描述（由申请人提供）：在成人循环系统中，动脉和静脉在解剖学上是不同的，以前认为动脉和静脉内皮细胞的不同身份是对血液动力学力（如血压和血流方向）的反应。然而，最近的证据表明，在循环活跃开始之前，动脉和静脉的规范/分化是由遗传机制控制的。这一事件发生在血管重塑之前，动脉和静脉的规范/分化受损导致血管重塑失败。虽然已有研究表明VEGF、Notch和ephrin信号通路等多种信号系统参与了这一过程，但转录因子如何调节这些基因表达的分子机制仍有待阐明。我们之前已经表明，两个基因编码密切相关的Fox转录因子Foxc1和Foxc2，在重叠的细胞群中表达，这些细胞有助于血管内皮细胞和间充质细胞的形成。缺少Foxc1或Foxc2的胚胎，以及大多数复合杂合子，在产前或围产期死亡时都有类似的异常表型，包括心血管系统缺陷。复合Foxc1;Foxc2纯合子比单独的纯合子死得早，缺陷也严重得多。最重要的是，复合纯合子具有动静脉畸形和血管重塑失败，并且在复合纯合子的内皮细胞中Notch信号基因和ephrinB2下调。这些数据导致了Foxc1和Foxc2在动-静脉细胞命运决定/分化过程中发挥剂量依赖、相互作用的中心假设。该基金的目标之一是测试Foxc蛋白是否在VEGF信号的下游发挥作用以调节动静脉身份（Aim 1）。提出的假设将通过(a)分析与Tie2-Cre小鼠杂交的内皮细胞中Foxc1和Foxc2的条件复合突变体，以及(b)将Tie2-Foxc转基因小鼠与复合Foxcl杂交的拯救实验来验证。Foxc2突变体（Aims 2）。最后，将确定Foxc1和Foxc2在动脉和静脉的规范/分化过程中调控的直接靶基因（Aim 3）。阐明Foxcl/c2在血管发育过程中如何发挥作用的分子机制，将有助于我们了解基因如何合作控制哺乳动物心血管发育，并有助于更好地理解人类先天性缺陷。

DESCRIPTION (provided by applicant): Arteries and veins are anatomically distinct within the adult circulatory system, and it was previously thought that the differentiated identities of arterial and venous endothelial cells arose in response to hemodynamic forces such as blood pressure and the direction of blood flow. However, recent evidence suggests that the specification/differentiation of arteries and veins is governed by genetic mechanisms before the active onset of circulation. This event occurs before remodeling of blood vessels, and impaired specification/differentiation of arteries and veins leads to failure to remodel blood vessels. Although it has been shown that several signaling systems such as the VEGF, Notch, and ephrin signaling pathways are involved in this process, molecular mechanisms of how transcription factors function to regulate expression of such genes remain to be elucidated. We have previously shown that the two genes encoding closely related Fox transcription factors, Foxc1 and Foxc2, are expressed in overlapping populations of cells contributing to the endothelial and mesenchymal cells of the blood vessels. Embryos lacking either Foxc1 or Foxc2, and most compound heterozygotes, die pre or perinatally with similar abnormal phenotypes, including defects in the cardiovascular system. Compound Foxc1; Foxc2 homozygotes die earlier and with much more severe defects than single homozygotes alone. Most importantly, compound homozygotes have arteriovenous malformations and the failure of blood vessels to remodel, and in the endothelial cells of compound homozygotes Notch signaling genes and ephrinB2 are downregulated. These data lead to the central hypothesis that Foxc1 and Foxc2 play dose-dependent, interactive roles in the process of arterial-venous cell fate determination/differentiation. One of the goals of this grant is to test whether Foxc proteins act downstream of VEGF signaling to regulate arterial-venous identity (Aim 1). The proposed hypothesis will be tested by (a) analyzing conditional compound mutants of Foxc1 and Foxc2 in endothelial cells crossed with Tie2-Cre mice and (b) rescue experiments in which Tie2-Foxc transgenic mice are crossed with compound Foxcl; Foxc2 mutants (Aims 2). Finally, direct target gene(s) regulated by Foxc1 and Foxc2 in the process of specification/differentiation of arteries and veins will be identified (Aim 3). Elucidating the molecular mechanisms of how Foxcl/c2 function during vascular development will significantly contribute to our knowledge of how genes cooperate to control mammalian cardiovascular development and will lead to a better understanding of human congenital defects.