Hiratsuka S, Minowa O, Kuno J, Noda T, Shibuya M
Department of Genetics, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
Proc Natl Acad Sci U S A. 1998 Aug 4;95(16):9349-54. doi: 10.1073/pnas.95.16.9349.
Receptor tyrosine kinases Flt-1 and Flk-1/KDR, and their ligand, the vascular endothelial growth factor (VEGF), were shown to be essential for angiogenesis in the mouse embryo by gene targeting. Flk-1/KDR null mutant mice exhibited impaired endothelial and hematopoietic cell development. On the other hand, Flt-1 null mutation resulted in early embryonic death at embryonic day 8.5, showing disorganization of blood vessels, such as overgrowth of endothelial cells. Flt-1 differs from Flk-1 in that it displays a higher affinity for VEGF but lower kinase activity, suggesting the importance of its extracellular domain. To examine the biological role of Flt-1 in embryonic development and vascular formation, we deleted the kinase domain without affecting the ligand binding region. Flt-1 tyrosine kinase-deficient homozygous mice (flt-1(TK-/-)) developed normal vessels and survived. However, VEGF-induced macrophage migration was strongly suppressed in flt-1(TK-/-) mice. These results indicate that Flt-1 without tyrosine kinase domain is sufficient to allow embryonic development with normal angiogenesis, and that a receptor tyrosine kinase plays a main biological role as a ligand-binding molecule.
通过基因靶向技术已证明，受体酪氨酸激酶Flt-1和Flk-1/KDR及其配体血管内皮生长因子（VEGF）对小鼠胚胎血管生成至关重要。Flk-1/KDR基因敲除突变小鼠表现出内皮细胞和造血细胞发育受损。另一方面，Flt-1基因敲除突变导致胚胎在第8.5天早期死亡，出现血管紊乱，如内皮细胞过度生长。Flt-1与Flk-1的不同之处在于，它对VEGF具有更高的亲和力，但激酶活性较低，这表明其细胞外结构域的重要性。为了研究Flt-1在胚胎发育和血管形成中的生物学作用，我们删除了激酶结构域，同时不影响配体结合区域。Flt-1酪氨酸激酶缺陷型纯合小鼠（flt-1(TK-/-)）发育出正常血管并存活下来。然而，在flt-1(TK-/-)小鼠中，VEGF诱导的巨噬细胞迁移受到强烈抑制。这些结果表明，没有酪氨酸激酶结构域的Flt-1足以支持正常血管生成的胚胎发育，并且受体酪氨酸激酶作为配体结合分子发挥主要生物学作用。
