Vascular remodeling of the mouse yolk sac requires hemodynamic force

The embryonic heart and vessels are dynamic and form and remodel while functional. Much has been learned about the genetic mechanisms underlying the development of the cardiovascular system, but we are just beginning to understand how changes in heart and vessel structure are influenced by hemodynamic forces such as shear stress. Recent work has shown that vessel remodeling in the mouse yolk sac is secondarily effected when cardiac function is reduced or absent. These findings indicate that proper circulation is required for vessel remodeling, but have not defined whether the role of circulation is to provide mechanical cues, to deliver oxygen or to circulate signaling molecules. Here, we used time-lapse confocal microscopy to determine the role of fluid-derived forces in vessel remodeling in the developing murine yolk sac. Novel methods were used to characterize flows in normal embryos and in embryos with impaired contractility (Mlc2a^(–/–)). We found abnormal plasma and erythroblast circulation in these embryos, which led us to hypothesize that the entry of erythroblasts into circulation is a key event in triggering vessel remodeling. We tested this by sequestering erythroblasts in the blood islands, thereby lowering the hematocrit and reducing shear stress, and found that vessel remodeling and the expression of eNOS (Nos3) depends on erythroblast flow. Further, we rescued remodeling defects and eNOS expression in low-hematocrit embryos by restoring the viscosity of the blood. These data show that hemodynamic force is necessary and sufficient to induce vessel remodeling in the mammalian yolk sa

Variants of Rab GTPase–Effector Binding Protein-2 Cause Variation in the Collateral Circulation and Severity of Stroke

The extent (number and diameter) of collateral vessels varies widely and is a major determinant, along with arteriogenesis (collateral remodeling), of variation in severity of tissue injury following large artery occlusion. Differences in genetic background underlie the majority of the variation in collateral extent in mice, through alterations in collaterogenesis (embryonic collateral formation). In brain and other tissues, ~80% of the variation in collateral extent among different mouse strains has been linked to a region on chromosome 7. We recently used congenic (CNG) fine-mapping of C57BL/6 (B6, high extent) and BALB/cBy (BC, low extent) mice to narrow the region to a 737 Kb locus, Dce1. Herein, we report the causal gene

Congenic Fine-Mapping Identifies a Major Causal Locus for Variation in the Native Collateral Circulation and Ischemic Injury in Brain and Lower Extremity

Severity of tissue injury in occlusive disease is dependent on the extent (number and diameter) of collateral vessels, which varies widely among healthy mice and humans. However, the causative genetic elements are unknown. Recently, much of the variation among different mouse strains, including C57Bl/6J (B6, high extent) and BALB/cByJ (Bc, low), was linked to a QTL on chromosome 7 (Candq1)

Printed in U.S.A. REVIEW ARTICLES Moving Toward the Light: Using New Technology to Answer Old

ABSTRACT: Fluorescence microscopy has become a principle methodology in the field of developmental biology. Recent technological advances have led to the design of high-speed and highresolution confocal and multiphoton microscopes that enable researchers to obtain three- and four-dimensional information in living cells and whole embryos. Paralleling this progress, the development of stable and bright vital fluorescent probes has revolutionized the ability to track individual cells in vitro and in vivo and to visualize intercellular and subcellular molecular interactions in real time. Combining imaging modalities and labeling techniques that are increasingly unobtrusive to cell and whole animal function, our understanding of how proteins interact, tissues take form, and organs synchronize to create a functioning animal is reaching a whole new level. (Pediatr Res 60: 1–5, 2006) Microscopy has been an essential tool in the investigatio

Vascular remodeling of the mouse yolk sac requires hemodynamic force

The embryonic heart and vessels are dynamic and form and remodel while functional. Much has been learned about the genetic mechanisms underlying the development of the cardiovascular system, but we are just beginning to understand how changes in heart and vessel structure are influenced by hemodynamic forces such as shear stress. Recent work has shown that vessel remodeling in the mouse yolk sac is secondarily effected when cardiac function is reduced or absent. These findings indicate that proper circulation is required for vessel remodeling, but have not defined whether the role of circulation is to provide mechanical cues, to deliver oxygen or to circulate signaling molecules. Here, we used time-lapse confocal microscopy to determine the role of fluid-derived forces in vessel remodeling in the developing murine yolk sac. Novel methods were used to characterize flows in normal embryos and in embryos with impaired contractility (Mlc2a(-/-)). We found abnormal plasma and erythroblast circulation in these embryos, which led us to hypothesize that the entry of erythroblasts into circulation is a key event in triggering vessel remodeling. We tested this by sequestering erythroblasts in the blood islands, thereby lowering the hematocrit and reducing shear stress, and found that vessel remodeling and the expression of eNOS (Nos3) depends on erythroblast flow. Further, we rescued remodeling defects and eNOS expression in low-hematocrit embryos by restoring the viscosity of the blood. These data show that hemodynamic force is necessary and sufficient to induce vessel remodeling in the mammalian yolk sac.status: publishe

Formation of the collateral circulation is regulated by vascular endothelial growth factor-A and a disintegrin and metalloprotease family members 10 and 17

Rationale: The density of native (preexisting) collaterals varies widely and is a significant determinant of variation in severity of stroke, myocardial infarction, and peripheral artery disease. However, little is known about mechanisms responsible for formation of the collateral circulation in healthy tissues. Objective: We previously found that variation in vascular endothelial growth factor (VEGF) expression causes differences in collateral density of newborn and adult mice. Herein, we sought to determine mechanisms of collaterogenesis in the embryo and the role of VEGF in this process. Methods and Results: Pial collaterals begin forming between embryonic day 13.5 and 14.5 as sprout-like extensions from arterioles of existing cerebral artery trees. Global VEGF-A overexpressing mice (Vegf(hi/+)) formed more, and Vegf(lo/+) formed fewer, collaterals during embryogenesis, in association with differences in vascular patterning. Conditional global reduction of Vegf or Flk1 only during collaterogenesis significantly reduced collateral formation, but now without affecting vascular patterning, and the effects remained in adulthood. Endothelial-specific Vegf reduction had no effect on collaterogenesis. Endothelial-specific reduction of a disintegrin-and-metalloprotease-domain-10 (Adam10) and inhibition of gamma-secretase increased collateral formation, consistent with their roles in VEGF-induced Notch1 activation and suppression of prosprouting signals. Endothelial-specific knockdown of Adam17 reduced collateral formation, consistent with its roles in endothelial cell migration and embryonic vascular stabilization, but not in activation of ligand-bound Notch1. These effects also remained in adulthood. Conclusions: Formation of pial collaterals occurs during a narrow developmental window via a sprouting angiogenesis-like mechanism, requires paracrine VEGF stimulation of fetal liver kinase 1-Notch signaling, and adult collateral number is dependent on embryonic collaterogenesis

Cell signaling directing the formation and function of hemogenic endothelium during murine embryogenesis

During developmental hematopoiesis, multilineage hematopoietic progenitors are thought to derive from a subset of vascular endothelium. Herein, we define the phenotype of such hemogenic endothelial cells and demonstrate, on a clonal level, that they exhibit multilineage hematopoietic potential. Furthermore, we have begun to define the molecular signals that regulate their development. We found that the formation of yolk sac hemogenic endothelium and its hematopoietic potential were significantly impaired in the absence of retinoic acid (RA) signaling, and could be restored in RA-deficient (Raldh2−/−) embryos by provision of exogenous RA in utero. Thus, we identify a novel, critical role for RA signaling in the development of hemogenic endothelium that contributes to definitive hematopoiesis