Angiogenesis is the main mechanism of vascular remodeling during late development and, after birth, in wound healing. Perturbations of angiogenesis occur in cancer, diabetes, ischemia, and inflammation. While much progress has been made in identifying factors that control angiogenesis, the understanding of the precise molecular mechanisms involved is incomplete. Here we identify a small GTPase, Rap1b, as a positive regulator of angiogenesis. Rap1b-deficient mice had a decreased level of Matrigel plug and neonatal retinal neovascularization, and aortas isolated from Rap1b-deficient animals had a reduced microvessel sprouting response to 2 major physiological regulators of angiogenesis: vascular endothelial growth factor (VEGF) and basic fibroblasts growth factor (bFGF) , IntroductionAngiogenesis, sprouting of new capillaries from existing vascular beds, and vasculogenesis, de novo vessel formation via differentiation of endothelial precursor cells, angioblasts, provide 2 mechanisms through which blood vessels form. While vasculogenesis involves differentiation of embryonic progenitor cells and predominates in the early embryonic development, most vascular remodeling in late development and during physiological processes of organ growth and repair occurs via angiogenesis. This complex process is regulated by a controlled balance of proangiogenic and antiangiogenic factors and, when deregulated, contributes to multiple metastatic, ischemic, inflammatory, and immune disorders. 1 Vascular endothelial growth factors (VEGFs), in particular VEGF-A, are involved in the regulation of the processes required for angiogenesis: endothelial cell activation, proliferation, migration, and tubule formation. 2 The tyrosine kinase receptor VEGFR2 (flk-1/KDR) is the major receptor responsible for the biochemical effects of VEGF-A on cells and is indispensable for normal vascular development. 3 Activation of VEGFR2 leads to recruitment and activation of multiple signaling molecules. Among those are 2 MAP kinases: p42/44 ERK1/2 involved in regulation of endothelial proliferation and p38 MAPK, one of the critical modulators of actin cytoskeleton remodeling required for migration. 4 Targeted genetic deletion of either p38␣ or ERK2 is embryonic lethal, as each has been shown to be required for placental development and angiogenesis. [5][6][7] Signaling from VEGFR2 is bidirectionally regulated by integrins. 8,9 Rap1 is a small GTPase that becomes activated downstream from multiple surface receptors via guanine nucleotide exchange factors (GEFs) and regulates several basic cellular functions: adhesion, migration, polarity, differentiation, and growth. 10,11 Rap1 has been shown to regulate integrin activation, and specific molecular links between activation of Rap1 and activation of integrins have been proposed. 12 Rap1 has also been shown to activate MAP kinase pathway in several cell types. 13 Much of the research on Rap1 in endothelial cells has focused on its role in regulation of cadherin-based cell-cell junctions and vascular permeabi...

Mammalian endothelial cells (ECs) display marked phenotypic heterogeneity. Little is known about the evolutionary mechanisms underlying EC heterogeneity. The last common ancestor of hagfish and gnathostomes was also the last common ancestor of all extant vertebrates, which lived some time more than 500 million years ago. Features of ECs that are shared between hagfish and gnathostomes can be inferred to have already been present in this ancestral vertebrate. The goal of this study was to determine whether the hagfish endothelium displays phenotypic heterogeneity. Electron microscopy of the aorta, dermis, heart, and liver revealed ultrastructural heterogeneity of the endothelium. Immunofluorescent studies demonstrated marked differences in lectin binding between vascular beds. Intravital microscopy of the dermis revealed IntroductionEndothelial cells (ECs) participate in many physiologic processes, including the regulation of vasomotor tone, hemostasis, leukocyte trafficking, angiogenesis, and permeability. These functions are differentially regulated in space and time (reviewed in Aird 1 ). Although there have been remarkable advances in our understanding of proximate mechanisms of endothelial structure and function in health and disease, far fewer studies have addressed the evolutionary history of this cell lineage.ECs are absent in invertebrates, cephalocordates, and tunicates, but are present in the 3 major groups of extant vertebrates: hagfish (myxinoids), lampreys, and jawed vertebrates (gnathostomes) ( Figure S1, available on the Blood website; see the Supplemental Figure link at the top of the online article). The fact that the endothelium is shared by jawless and jawed vertebrates is evidence that the endothelium was present in the ancestor of these animals. The absence of an endothelium in cephalochordates and tunicates suggests that this structure evolved after the divergence of these groups from the vertebrate lineage, between 540 and 510 million years ago.The last common ancestor of hagfish and gnathostomes was also the last common ancestor of all extant vertebrates, which lived some time more than 500 million years ago. Features of ECs that are shared between hagfish and gnathostomes can be inferred to have already been present in this ancestral vertebrate. Here, we show that hagfish endothelium displays structural, molecular, and functional heterogeneity, suggesting that phenotypic heterogeneity is an ancestral rather than a derived feature of this cell lineage. Materials and methodsAtlantic hagfish, Myxine glutinosa, were purchased from a commercial supplier (Huntsman Marine Science Center, St Andrews, NB, Canada) who caught the specimens in the Bay of Fundy, Canada. Hagfish were maintained in the dark in circular tanks with running seawater at 10 Ϯ 2°C. The animals were anesthetized in seawater containing tricaine methanesulfonate (MS 222; Sigma-Aldrich, St Louis, MO). For lectin staining, 5-m cryosections were fixed with acetone at Ϫ20°C for 2 minutes and 80% methanol at 4°C for 5 minutes, foll...

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Next-generation sequencing has been invaluable in the elucidation of the genetic etiology of many subtypes of intellectual disability in recent years. Here, using exome sequencing and whole-genome sequencing, we identified three de novo truncating mutations in WAS protein family member 1 (WASF1) in five unrelated individuals with moderate to profound intellectual disability with autistic features and seizures. WASF1, also known as WAVE1, is part of the WAVE complex and acts as a mediator between Rac-GTPase and actin to induce actin polymerization. The three mutations connected by Matchmaker Exchange were c.1516C>T (p.Arg506Ter), which occurs in three unrelated individuals, c.1558C>T (p.Gln520Ter), and c.1482delinsGCCAGG (p.Ile494MetfsTer23). All three variants are predicted to partially or fully disrupt the C-terminal actin-binding WCA domain. Functional studies using fibroblast cells from two affected individuals with the c.1516C>T mutation showed a truncated WASF1 and a defect in actin remodeling. This study provides evidence that de novo heterozygous mutations in WASF1 cause a rare form of intellectual disability.