As seen in many other developmental interactions, it appears likely that endothelium provides inductive signals that are part of a step-wise series of sequential inductive events required during organogenesis. Many components important for vascular development have been discovered. A bona fide vasculature is associated with vertebrates, although many 3. Thus, it appears that the mouse diVers from the zebrafish in the requirement for the notochord for dorsal aorta assembly. Expression of the platelet-derived growth factor beta receptor during organogenesis and tissue diVerentiation in the mouse embryo.
A conserved role for H15-related T-box transcription factors in zebrafish and Drosophila heart formation. The importance of this conservation is highlighted by the fact that the vascular system does not simply supply metabolic sustenance, but also provides critical inductive signals required for the diVerentiation and development of organs such as the pancreas and liver Cleaver and Melton, 2003; Lammert et al. Endothelial cell diversity revealed by global expression profiling. Transgenic overexpression of Shh in the dorsal neural tube of mice results in hypervascularization of the tissue Rowitch et al. Somite and presomitic mesoderm grafts produced vascular cells that migrated cranially, caudally, and laterally, but never crossed the axial midline Pardanaud et al. Murine gene-targeting has enabled the elucidation of many of the molecular events that are essential for mammalian vascular development and helped to define whether these processes were critical for either vasculogenesis or angiogenesis Carmeliet, 2003a; Jain, 2003. In these experiments, wild-type cells are transplanted into both wild-type and cloche mutant tissues.
Thrombopoietin rescues in vitro erythroid colony formation from mouse embryos lacking the erythropoietin receptor. These early studies were built on by the Clarks, who elegantly described vessel formation and remodeling in frog tails by examining living specimens Clark and Clark, 1939. Normally, intersegmental vessels migrate dorsally from the aorta and traverse between the somites. For instance, mouse embryos that lack vascular endothelium die very early due to a lack of nutrition—gas exchange in their tissues Shalaby et al. Understanding blood vessel communication with surrounding cells will also certainly impact cancer research.
Hypoxia occurs in a number of physiological settings, and the mechanisms mediating hypoxic responses are similar during embryogenesis, postnatal life, and pathological states. In addition, it is rather certain that regionally specific vascular cross-talk exists across organs and tissues in both embryonic and adult tissues. Cell-autonomous shift from axial to paraxial mesodermal development in zebrafish floating head mutants. Copyright ß 2004, Elsevier Inc. Isolation and expression analysis of three Zebrafish angiopoietin genes. Caveolin regulation of endothelial function.
Dense capillary beds can be found in both the inner medulla, which consists of catecholamine-secreting chromaYn cells, and the outer cortex, which consists of steroidogenic zona glomerulosa cells Dobbie and Symington, 1966. The existence of vascular guidance mechanisms is directly supported by the identification or generation of mutations that manifest in the disruption of normal vessel trajectories. Podocyte diVerentiation in the absence of endothelial cells as revealed in the zebrafish avascular mutant, cloche. Three steps are required for the formation of a mature vascular network. The true challenge for future studies is, therefore, to develop better experimental methods to study the issue of endothelial signaling and to uncouple tissue metabolic requirements for vascular blood circulation from actual developmental signals from blood vessels themselves. Current Topics in Developmental Biology, Vol. In the second experiment, the converse approach is taken to increase contact of endothelium and pancreatic endoderm.
In fact, there is data to support a role for the notochord as a source of both positive and negative vascular patterning signals. Vascular Endothelial Growth Factor and Its Receptors in Embryonic Zebrafish Blood Vessel Development by Katsutoshi Goishi and Michael Klagsbrun of Harvard rightly promotes the zebrafish as an emerging model for the study of the regulation of vessel formation, and reviews the work done to date. While the clinical implications of endothelial cell signaling and cell diVerentiation are tremendous, ultimately — the author concludes — the answers to these questions will not be achieved without the development of superior models which can isolate endothelial signaling and cell development from confounding issues of tissue metabolism. Possible role in the hematopoietic microenvironment. We do not discuss in detail interesting mutations, such as out-of-bounds, that have not yet been cloned. Midline Vessel Patterning 71 et al. The Notochord as the Source of Positive Vascular Patterning Signal s One area of recent focus has been the role of notochord in assembly of the dorsal aorta, which comes to lie ventral to the notochord.
Neuropilin-1 was originally recognized as a neuronal cell-surface protein, the ligands for which are a family of secreted glycoproteins, the semaphorins, that function as chemorepellents for a subset of embryonic nerves He and Tessier-Lavigne, 1997; Kolodkin et al. Third, there are juxtacrine inhibitory cues that constrain axon sprouting along specific paths. Although little is known about the initial segregation of angioblasts into arterial and venous subpopulations in mammals, key insights from zebrafish studies suggest that the formation of separate arterial and venous vessels relies on Notch 4. Blood Vessel Signals 31 Franck-Lissbrant, I. A more complete knowledge of vascular patterning is likely to come from Current Topics in Developmental Biology, Vol. Posterior to the heart, the aortae lie in immediate contact with the underlying endoderm, the overlying paraxial mesoderm, and the lateral plate mesoderm. The dorsal domain of Pdx-1 expression is initiated in the endoderm adjacent to the fusing dorsal aortate Fig.
Development of the biliary tract. Mecham 153 , Washington University School of Medicine, Department of Cell Biology and Physiology, St. Similarly, lung endothelium is continuous; however, it is characterized by active trnascytosis and the presence of abundant vesicles called caveolae Fig. The role of ephrins and their receptors 66 Hogan and Bautch in vascular development is likely to be complex, as other family members such as EphB3 and ephrin-B1 are also expressed in the vasculature. Results indicate that transplanted cells are less likely to express blood markers, such as gata-1, when transplanted into cloche mutant tissues than in wild-type tissues. Both also have a major axial artery s called the dorsal aorta, and a major axial vein s called the cardinal vein.
The molecular basis for leukocyte behavior during infection has been the focus of much investigation Fig. Investigations into the nature of these interactions reveal the critical importance of cues within the endothelial microenvironment. Embryos lacking Notch activity fail to express artery-specific markers in the dorsal aorta, and mutation of a downstream target of Notch signaling, gridlock, results in defective dorsal aorta patterning Lawson et al. However, as chondrocytes begin to proliferate and diVerentiate, they also begin to secrete angiogenic molecules that stimulate the invasion of subchondral blood vessels into the growth plate. The avascular zone surrounding the notochord has been observed but not experimentally manipulated. A Endocrine cells of pancreatic islets secrete hormones into the blood via permeable fenestrae in the islet capillary endothelium. This striking discrepancy awaits satisfactory explanation.