DESIGN AND PHYSIOLOGY OF ARTERIES AND VEINS | Anatomical Pathways and Patterns

M.R. Olson , in Encyclopedia of Fish Physiology, 2011

Arteries to the trunk

The dorsal aorta traverses the longitudinal centrality of the body catastrophe in the caudal peduncle anterior to the caudal (tail) fin. While this unabridged vessel is frequently referred to as the dorsal aorta, posterior to the peritoneal cavity, it is technically the caudal artery (CA). The dorsal aorta travels but beneath the vertebra and above the dorsal surface of the kidney. As the dorsal aorta diminishes in diameter (there is progressive loss of blood to segmental arteries) and leaves the peritoneal region to get the caudal avenue, ventral processes of the spine go fused forming the hemal arch and the caudal artery travels within this arch (the hemal canal), along with the caudal vein and several secondary veins. Longitudinally, both the dorsal aorta and caudal artery take on a characteristic undulating grade due to their close clan with the vertebrae. In some fish, including rainbow trout, the dorsal wall of the dorsal aorta and caudal avenue tightly adhere to the vertebrae and the vessel cannot be dissected free. In other fish, such as eels ( Anguilla), the vessel is more readily isolated from surrounding tissue. In improver, in some fish such as the rainbow trout, at that place is a longitudinal elastic ligament in the lumen of the dorsal aorta. This ligament is attached to the dorsal wall of the vessel via the basioccipital os and forms a dorso-ventral vertical septum that nearly completely divides the long axis of the vessel for upwardly to a quarter of its length. Although its exact function is unclear, it most probable helps propel blood down the dorsal aorta when the trunk undulates during active pond.

A pair of segmental arteries arise from the dorsal aorta shortly later on the union of the lateral aortas and anterior to the anastomosis of the epibranchial arteries with the dorsal aorta (not shown in Figure 1 ). Paired subclavian arteries (SC) arise from the lateral wall of the dorsal aorta simply posterior to the anastomoses of the epibranchial arteries. The subclavian arteries run ventrally and supply the pectoral girdle, pectoral fins, and adjacent musculature. Branches of the subclavian arteries may connect directly to the epigastric arteries (EG) or may communicate with them via the coracoid artery (CC). The subclavian arteries often anastomose anteriorly, with the hypobranchial circulation (see below). As the dorsal aorta travels posteriorly from the origin of the subclavian arteries, it gives rise to numerous segmental arteries. The celiac and mesenteric arteries supply the anterior (tummy) and posterior (intestines) viscera, respectively. In some fish, such equally rainbow trout, these vessels may ascend every bit a single vessel, the celiacomesenteric artery (CM), but even in the aforementioned strain of trout, some individuals may take separate vessels. Small renal arteries (RA) perfuse the kidney and one or two small posterior intestinal arteries (PI) supply the posterior gut (see likewise DESIGN AND PHYSIOLOGY OF ARTERIES AND VEINS | The Gastrointestinal Circulation).

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Heart, Blood Vessels and Lymphatics

Ruth Bellairs , Marker Osmond , in Atlas of Chick Evolution (Third Edition), 2014

The Aortic Arches (Arterial Arches)

The aortic arches ( Plates 45, 46, 108–110, 119 Plate 45 Plate 46 Plate 108 Plate 109 Plate 110 Plate 119 ) are the blood vessels that supply the pharyngeal arches (Chapter 8), and they serve as a communication between the ventral and dorsal aortae. They are formed mainly from neural crest cells (Brockman et al., 1990). A splanchnic plexus forms around the foregut and gives ascension to the pharyngeal arch arteries besides as the pulmonary and bronchial vessels (DeRuiter et al., 1993). The ventral aorta is the main artery into which the truncus arteriosus leads ( Text-Figure 39 ; Plates 45, 46 Plate 45 Plate 46 ). It bifurcates into left and right vessels which extend forward as the paired external carotids, whilst the paired dorsal aortae extend forward as the internal carotids. The aortic arches do not all develop at once, and some are of a transitory nature, disappearing earlier others have fifty-fifty begun to class. They are paired, serving the left and right pharyngeal regions. A morphological written report of their formation was published by Hiruma and Hirakow (1995) using corrosion casts analysed past scanning electron microscopy ( Plates 45, 46 Plate 45 Plate 46 ). The first pair forms at about phase 9 (Coffin and Poole, 1988) and passes through the left and right first pharyngeal (mandibular) arches, respectively. The remaining arterial arches course sequentially over the next 3 days of incubation ( Table 3 , p. 81). The basic pattern is characteristic of all amniotes and is indicated diagrammatically in Text-Figure 39 . The aortic arches are formed, like the dorsal and ventral aortae, from solid angioblastic cords which develop in situ from mesoderm and subsequently become canalized. Equally the pharyngeal arches differentiate into other structures, the private arterial arches either disappear or become converted. The cranial extensions of the dorsal aortae become the internal carotids in all young amniote embryos, whilst the cranial extensions of the ventral aortae become the external carotids. They are retained equally such in mammals, but in birds the internal carotids in the head anastomose with the external carotids at about vi.5 days (Hughes, 1934), and the remnants of the internal carotids in the neck region disappear. The paired external carotids come to prevarication in close proximity to one another, fusing into a unmarried vessel in some species (e.grand. herons), though not in the fowl. The carotids branch to supply all the arteries of the head; the main branches accept formed by vii.v days and are illustrated in Text-Figure forty . A number of other anastomoses occur between the arteries of the head, forming structures that are sometimes compared to the circle of Willis of mammals. Some anastomoses have place too between arteries and veins. There is evidence that sonic hedgehog plays an important role in the germination and modelling of the aortic arches (Kolesova et al., 2008).

Text-Figure twoscore. Arteries of the head and cervix at 7.5 days.

 (After Hughes, 1934.)

Another of import manner in which birds differ from mammals is that in birds ( Text-Figure 39 ), the communication of the fourth arterial arch with the dorsal aorta is retained on the correct and lost on the left (well-nigh days vi–seven), whereas in mammals the the left is retained and the right lost. In amphibians and reptiles both sides are retained, resulting in a double 'systemic' arch.

In the chick it has been possible to induce experimentally the mammalian design by ligaturing the 4th curvation on the right side (Stéphan, 1949), so that the blood is then diverted through the left aortic arch, which therefore fails to get obliterated. Experiments of this sort (e.chiliad. ligation experiments by Wang et al. (2009)) provide further evidence of the importance of the blood flow in modifying the vascular design, but have piddling to tell usa near the factors that provoke the normal closure and disappearance of blood vessels during embryogenesis. Hughes (1937) suggested that the 'posteriorward shift' in the position of the chick center and aortic arches every bit the centre 'descends', together with the torsion and elongation of the truncus arteriosus, pb to mechanical tension which obliterates the lumina of the aortic arches (but come across p. 57).

The fifth arch is transitory and disappears on both sides soon after germination. Although information technology is traditionally considered that the pulmonary arteries in amniotes are derived from branches of the sixth aortic arches (as in Text-Figure 40 ), there is now evidence that they develop as branches of the fourth aortic curvation which connect with the endothelial vesicles in the pulmonary mesenchyme (Noden, 1990), and that only later does a advice arise with the sixth aortic curvation.

On the right side the connection with the aorta remains equally the ductus arteriosus. The distal part of the ductus is very muscular, whereas the proximal region is more elastic, and it is the lumen of the proximal role that becomes occluded at the fourth dimension of hatching, though information technology may remain patent for several days (Belanger et al., 2008).

The two dorsal aortae unite posterior to the heart ( Plate 90 ) to class a single median vessel which gives rise to:

•

The arteries supplying the limbs.

•

The segmental (intersegmental) arteries ( Text-Figure 40 ; Plates 43, 155 Plate 43 Plate 155 ), which are branches of the dorsal aorta and extend out betwixt the somites. They contribute to the formation of the vertebral and subclavian arteries, and by stage xi have formed between all existing somites.

•

The omphalo-mesenteric (vitelline) arteries ( Plates 154, 174 Plate 154 Plate 174 ).

•

The primary mesonephric arteries ( Plate 48 ) from which the secondary and tertiary mesonephric arteries are formed, the latter becoming the afferent glomerular arteries (Carretero et al., 1995).

•

The allantoic (umbilical) arteries.

•

The caudal artery, which is the near posterior end of the dorsal aorta.

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Development of the Vascular Organisation

Bruce Thousand. Carlson , in Reference Module in Biomedical Sciences, 2014

Aorta, Aortic Arches, and Their Derivatives

The dorsal aorta forms from the direct aggregation of endothelial precursor cells derived from the lateral plate mesoderm. These cells course a vessel straight by a vasculogenesis mechanism. Vasculogenesis is stimulated by VEGF and other factors produced by the endoderm and BMP (bone morphogenetic poly peptide) in the lateral mesoderm. When first formed, the cranial part of the dorsal aorta is a paired, with each member located lateral to the midline. The reason is that in the midline, the notochord secretes the BMP antagonists noggin and chordin, which inhibit the activity of BMP and also inactivate the vasculogenic influences from the endoderm. Late in the 4th calendar week, hematopoietic stalk cells form in the lining of the ventral office of the aorta.

The organisation of aortic arches in early on human embryos is organized along the aforementioned principles as the organization of arteries supplying claret to the gills of many aquatic lower vertebrates. Blood exits from a mutual ventricle in the eye into a ventral aortic root, from which it is distributed through the branchial arches past pairs of aortic arches ( Figure three(a) ). In gilled vertebrates, the aortic arch arteries branch into capillary beds, where the blood becomes reoxygenated equally it passes through the gills. In mammalian embryos, the aortic arches remain continuous vessels because gas substitution occurs in the placenta and not in the pharyngeal arches. The aortic arches empty into paired dorsal aortas where the claret enters the regular systemic circulation. In homo embryos, all aortic arches are never nowadays at the aforementioned time. Their formation and remodeling evidence a pronounced craniocaudal gradient. Claret from the outflow tract of the center (the truncoconal region) flows into an aortic sac, which differs from the truncoconal region in the construction of its wall. The aortic arches branch off from the aortic sac.

Effigy 3. (a) Schematic representation of the embryonic aortic arch system. (b and c) Later steps in the transformation of the aortic curvation system in a man. Disposition of the recurrent laryngeal nervus in relation to the right fourth and left sixth arch is also shown in (c).

The developmental beefcake of the aortic arch organization illustrates well the principle of morphological adaptation of the vascular bed during different stages of embryogenesis ( Table 1 ). Continued development of the cranial and cervical regions causes components of the commencement three arches and associated aortic roots to be remodeled into the carotid artery system (see Figure 3 ). With the remodeling of the center tube and the internal division of the outflow tract into aortic and pulmonary components, the 4th arches undergo an asymmetrical adaptation to the early asymmetry of the heart. The left fourth aortic arch is retained every bit a major channel (curvation of the aorta), which carries the entire output from the left ventricle of the centre. The right 4th arch is incorporated into the right subclavian avenue.

Table 1. Adult derivatives of the aortic arch system

Right side Left side
Aortic arches
1 Disappearance of most of structure Disappearance of most of structure
Part of the maxillary avenue Part of the maxillary artery
2 Disappearance of nigh of construction Disappearance of most of structure
Hyoid and stapedial arteries Hyoid and stapedial arteries
3 Ventral part – the mutual carotid artery Ventral part – the mutual carotid artery
Dorsal function – the internal carotid artery Dorsal part – the internal carotid artery
iv Proximal office of the right subclavian artery Role of arch of the aorta
5 Rarely recognizable, even in early on embryo Rarely recognizable, even in early embryo
half-dozen (pulmonary) Part of the right pulmonary avenue Ductus arteriosus
Part of the left pulmonary avenue
Ventral aortic roots
Cranial to third arch External carotid avenue External carotid artery
Between third and fourth arches Common carotid avenue Common carotid artery
Between 4th and sixth arches Right brachiocephalic artery Ascending part of the aorta
Dorsal aortic roots
Cranial to third arch Internal carotid artery Internal carotid artery
Between third and quaternary arches Disappearance of structure Disappearance of construction
Betwixt quaternary and pulmonary arches Central part of the right subclavian artery Descending aorta
Caudal to pulmonary arch Disappearance of structure Descending aorta

The 5th aortic curvation, if it exists at all, is represented by no more a few capillary loops. The sixth (pulmonary arch) arises equally a capillary plexus associated with the early trachea and lung buds. The capillary plexus is supplied by ventral segmental arteries arising from the paired dorsal aortas in that region ( Figure four ). The equivalent of the sixth curvation is represented by a discrete distal segment (the ventral segmental artery) connected to the dorsal aorta and a plexus-like proximal segment that establishes a connection between the aortic sac at the base of the fourth arch and the distal segmental component. As the respiratory diverticulum and early on lung buds elongate, parts of the pulmonary capillary network consolidate to grade a pair of discrete pulmonary arteries that connect to the putative sixth curvation.

Figure 4. (a and b) Development of the pulmonary arch, showing the early pulmonary plexus in relation to several ventral segmental arteries associated with the early respiratory diverticulum (a) and their consolidation into detached vessels that establish a connection with the bases of the 4th aortic arches (b).

 Based on DeRuiter, M. C., et al. (1989). Beefcake and Embryology 179, 309–325.

Similar to the fourth aortic curvation, the pulmonary arch develops asymmetrically. On the left side, it becomes a big channel. Its distal segment, which was derived from a ventral segmental avenue, persists equally a major channel (ductus arteriosus) that shunts claret from the left pulmonary avenue to the aorta (see Figure 3(c) ). The lungs are protected past this shunt from a flow of claret that is greater than what their vasculature can handle during most of the intrauterine menstruation. On the right side, the distal segment of the pulmonary arch regresses, and the proximal segment (the base of the right pulmonary artery) branches off from the pulmonary trunk.

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Development, Differentiation and Disease of the Para-Alimentary Tract

Andrew D. Rhim , Ben Z. Stanger , in Progress in Molecular Biology and Translational Science, 2010

C Early on Signals from the Aortic Endothelium

Midline fusion of the dorsal aorta occurs at E8.five, leading to the interposition of the aorta between the notochord and the endoderm. Work by Melton and colleagues showed that endothelial cells from the aorta are required for dorsal budding every bit well equally subsequently endocrine differentiation. 23 In fact, removal of the dorsal aortae in Xenopus embryos before fusion led to the lack of dorsal pancreas bud formation, presumably by preventing the induction of Pdx-1-expressing cells in the dorsal anlage. 23,24 This observation led to the implication of vascular endothelial growth factor A (VEGF-A) every bit a factor involved in the specification of the developing pancreas. FGF10 is besides released by the merged aortic endothelium and acts on the endoderm to promote the expression of Ptf1a, a key transcription cistron necessary for normal pancreas evolution. 25–27

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Angiogenesis

1000. Luisa Iruela-Arispe , Ann Zovein , in Fetal and Neonatal Physiology (Fifth Edition), 2017

Endothelial Specification: Arteries, Veins, and Lymphatics

Before fusion of the paired dorsal aorta, the angioblasts com­prising the ii aortic vessels achieve arterial identity through the expression of arterial cistron programs. Somite-derived VEGF signals actuate the Notch pathway within the nearby angioblastic chords. 16 The Notch pathway, initially described in Drosophila equally Notch mutant flies exhibiting "notched" wings, 17,xviii is critical for multiple developmental cell fate decisions. In the vasculature, the Notch pathway is responsible for defining arterial and venous identity. xix The signaling pathway in mammals is composed of Notch receptors (Notch1-four) that bind membrane-bound ligands: Delta-like (DLL1, 3, 4) and Jagged (Jag1-two) through either heterotypic or homotypic cell-prison cell interactions. Upon ligand binding, the Notch receptor undergoes multiple proteolytic cleavage steps resulting in the release of the intracellular domain that in turn binds DNA, regulating gene expression. VEGF signaling in the somites results in Notch1 expression by nearby angiogenic cords, relegating the ensuing vessel equally an avenue. 16 The accompanying cardinal veins form next to the paired aortae as angioblasts coalesce in a second vessel. Endothelial cells from both the aorta and cardinal vein can interchange for some fourth dimension earlier the establishment of permanent arterial and venous identity. xx-22 Every bit office of the institution of arterial and venous identity, respective repulsive cues are caused to maintain boundaries between the arterial and venous systems.

An important repulsive signaling cascade in the vasculature involves the ephrin ligands and Eph receptors. 23 Eph receptors consist of a tyrosine kinase receptor family capable of both forward and reverse signaling in a multitude of cellular contexts. 24 Within the vasculature, EphB4 and ephrinB2 predominate. Designated venous cells limited high levels of EphB4 receptor, and alternatively, arterial cells express high levels of ephrinB2. 25,26 Repulsion between EphB4 and ephrinB2 is thought to help maintain borders between the arterial and venous circulation to avoid arteriovenous malformations (AVMs). 27 These signals likewise play a role in determining avenue and vein size. 28 Abnormal connections between arteries and veins in the form of AVMs are thought to occur when arteries and veins lose their identity markers. Loss of ephrins results in a loss of repulsive cues between the two endothelial prison cell types and subsequent mixing of circulations. Aberrant Notch signaling tin misidentify arterial and venous endothelial cells, resulting in misexpression of ephrins and subsequent AVM formation. 27,29 However, many man diseases of AVM germination and arterial mispatterning, including hereditary hemorrhagic telangiectasia (HHT), have mutations associated with the transforming growth factor (TGF)-β/BMP family of signaling molecules, including its receptors, endoglin (ENG) 30 and Alk1 (ACVRL1), 31 as well equally downstream transcriptional mediators of the pathway including SMAD4. 32 The mechanism leading to abnormal vascular patterning has been linked to changes in angiogenic mediators. Very recently, a connection to the Notch pathway has been suggested, unifying the similar phenotypes of AVM seen in both Notch pathway mutants and TGF-β pathway mutations. 33 Although the complete flick of interacting signaling pathways and cellular changes leading to AVM and HHT emergence is unfinished, the cumulative contribution of these signals during normal vascular morphogenesis is necessary to ensure that remodeling of arteries and veins occurs, while separated by interconnecting capillaries.

In addition to arterial and venous circulation, a third circulatory system of lymph vessels develops through the associates of lymphatic endothelial cells. 34 The beginning lymphatic endothelial cells originate from the key vein, where a subset of endothelial cells bud off and express Prox1, an early transcriptional regulator of lymphatic fate. 35 These cells and so proliferate and drift to form the lymphatic arrangement with lymphatic identity defined past Prox1 and LYVE-i expression. 35,36 Abnormalities in lymphatic identity that are due to Prox1 levels take been associated with chylous-filled lymphatics and adult obesity. 37 Lymphatic dysplasia syndromes in humans take been linked to mutations in CCBE1, 38 a gene implicated in lymphatic cell emergence and migration. 39 The connection of the lymphatic system to the circulatory system occurs at the lymphatic duct, the formation of which relies on platelet aggregation and thrombosis to separate the vascular and lymphatic systems. 40 Thus astringent thrombocytopenia or platelet disorders during development can lead to claret-filled lymphatics. 40,41

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Design AND PHYSIOLOGY OF CAPILLARIES AND SECONDARY CIRCULATION | Secondary Apportionment and Lymphatic Anatomy

K.R. Olson , A.P. Farrell , in Encyclopedia of Fish Physiology, 2011

Arterio-arterial Anastomoses

Secondary vessels usually originate from the dorsal aorta and segmental arteries. Tunas are notable exceptions as the secondary vessels originate from rete arterioles in the heat exchanger. Secondary arterio-arterial anastomoses typically emerge perpendicularly from a relatively large primary artery and they follow a long (200–300  μm) and surprisingly tortuous, twisting path before joining with numerous other secondary vessels to form progressively larger arterioles and arteries. Some other unique feature of secondary arterioles is the dilated lumen at their origin, forming a funnel-like archway ( Effigy 3 (a)). Microvilli have been reported on the surface of endothelial cells on the parent avenue near the origin of the arterio-arterial anastomoses in some fish. These grade long microvillous ribbons parallel to the axis of the parent vessel and announced to be guarding the archway to the secondary arteriole ( Figure 3 (c)). This may physically restrict access of red claret cells into the secondary vessels and contribute to the low hematocrit in the secondary circulation. Leukocytes may also adhere to the microvilli. It has also been suggested that the microvilli provide chemo- or mechanosensory information, only this is notwithstanding to exist demonstrated experimentally. The tortuous part of the secondary circulation tin can exist embedded within the muscle wall of the primary artery. Thus, it is possible that constriction or dilation of the primary vessel may exert a straight mechanical effect on the arterio-arterial anastomoses besides, perchance decision-making the flow of claret entering the secondary circulation from the chief circulation.

Effigy three. Vascular corrosion replicas from the gill of the climbing perch, Anabas testudineus, showing the origin of the secondary arterio-arterial anastomoses. These micrographs of anastomoses are from the gill, but the full general beefcake is too typical of systemic secondary arterio-arterial anastomoses. (a) Numerous tortuous vessels arise from the wall of the principal (efferent filamental) artery (pointer) and rejoin to class progressively larger nutrient arteries (North). (b) A big nutrient artery (North) in the gill arch is formed from the anastomosis of numerous tortuous arterioles that arise from both the efferent branchial artery (EBA) and efferent filamental arteries (EFA). (c) Drawing showing the microvillous endothelial cells (VE) lining the efferent filamental avenue and preventing a red blood jail cell (RBC) from entering the narrow-bore vessels that supply the interlamellar organization. SM, polish muscle cells; AE, normal arterial endothelium of the efferent filamental artery; BM, basement membrane.

 (a, b) Reproduced from Olson KR, Munshi JSD, and Ojha J (1986) Gill microcirculation of the air-breathing climbing perch, Anabas testudineus (Bloch): Relationships with the accompaniment respiratory organs and systemic apportionment. American Journal of Anatomy 176: 305–320.

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Developmental Biology of Stem Cells

Momoko Yoshimoto , Mervin C. Yoder , in Fetal and Neonatal Physiology (Fifth Edition), 2017

Blood Cells are Derived From Endothelial Cells

Claret cells "bud" from endothelial cells in the dorsal aorta of developing mouse embryos (like to avian, frog, zebrafish, and many mammalian embryos). 34-36 The endothelial cells that directly produce the blood cells are called hemogenic endo­thelial cells. Various experiments have demonstrated that endothelial cells generate or differentiate into claret cells. For example, endothelial cells labeled with DiI-labeled acetylated depression-density lipoprotein were traced to differentiate into CD45+ blood cells in vivo. 34 VE-cadherin+ endothelial cells were isolated from mouse YS and paraaortic splanchnopleura at a pre-HSC stage and plated onto stromal cells to reveal that VE-cadherin+CD45–CD41– endothelial cells produced definitive erythroid, myeloid, and B lymphoid cells. 37-39 The hematopoietic clusters budding from the endothelial cells in murine dorsal aorta express runt-related transcription gene 1 (Runx1), a critical transcription factor for hematopoiesis. 35 Deletion of the Runx1 gene induces embryonic lethality at embryonic 24-hour interval 12.5, and there are no identifiable erythromyeloid progenitors (EMPs) in the YS or HSCs in the fetal liver. 40 In addition, the intravascular hematopoietic clusters were completely absent in the dorsal aorta and YS vessels. Similarly, GATA2- and RBPj-knockout embryos brandish lack of hematopoietic clusters and HSCs in the dorsal aorta. 41,42 The observation that hematopoietic clusters in the dorsal aorta are linked to the presence of HSCs suggests that HSCs emerge from the hemogenic endothelial cells in the dorsal aorta. When VE-cadherin-expressing cells were labeled with yellow fluorescent protein to trace their progeny past a transgenic approach, nigh of the blood cells in the developed bone marrow were yellow fluorescent protein positive, suggesting that all the bone marrow claret cells are derivatives of the vascular endothelium. 43,44 When the Runx1 cistron product is deleted in VE-cadherin-expressing endothelial cells, embryos display a phenotype similar to that of full Runx1-knockout embryos: no EMPs and HSCs and embryonic death. 44 Thus, Runx1 is indispensable for the 2nd and third waves of hematopoiesis derived from hemogenic endothelial cells.

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Skeletal Muscle Regeneration

Denis C. Guttridge , in Muscle, 2012

Mesoangioblasts/Pericytes

Mesoangioblasts were first identified in the wall of embryonic dorsal aortas in mice (17,104). These blood vessel-associated stem cells share characteristics with endothelial and pericyte cells, and in civilization showroom a robust proliferative potential capable of differentiating into multiple prison cell types of mesenchymal origin. In postnatal skeletal muscle, mesoangioblasts closely resemble pericytes and their in vitro activities, with respect to proliferation, are similar to their embryonic counterpart. An advantage of using mesoangioblasts for cell-based therapies is their ability to be delivered intra-arterially and to successfully engraft in skeletal musculus. This technique was used to rescue mice with a primary defect in α-sarcoglycan that underlies limb-girdle muscular dystrophy (105), and whose engraftment could be significantly improved by stimulating mesoangioblast migration with assistants of selective cytokine and adhesion factors (106). A highly favorable response was also observed with respect to dystrophin expression and improved skeletal muscle function when wild-blazon mesoangioblasts were systemically administered in a golden retriever model of Duchenne muscular dystrophy (107). These findings are highly promising and have far-reaching therapeutic implications.

Related pericytes are located on the periphery of blood vessels and therefore can also be isolated from the vascular organization, and like mesoangioblasts, are efficiently expanded in culture and display a high propensity to differentiate into myotubes (108). Human tissue pericytes can exist isolated by their cellular surface markings NG2, CD146, and alkali metal phosphatase. In uninjured skeletal muscle, pericytes are negative for Pax7, simply prefer a myogenic fate when prompted by injury factors in vivo or under differentiation conditions in vitro (108). Furthermore, expression of a human mini-dystrophin transgene in pericytes isolated from patients with Duchenne muscular dystrophy was successfully expanded in culture and subsequently transplanted in immunocompromised mdx mice to produce a pregnant degree of dystrophin positive myofibers.

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Evolution and Phylogeny of the Allowed System

Aldo Ciau-Uitz , ... Alexander Medvinsky , in Encyclopedia of Immunobiology, 2016

From Mesoderm to Hematogenic Endothelium

The mechanism past which nascent HSCs are created in the dorsal aorta niche is under intense enquiry and a number of factors have been identified to influence the EHT. Still, this process represents the last step in the programming of HSCs and is preceded by formation of the dorsal aorta and HE.

Lineage labeling has demonstrated that the embryonic dorsal aorta also as nigh all claret cells in the developed mouse originate from lateral plate mesoderm (LPM), indicating that HE and HSCs originate from this tissue (Wasteson et al., 2008; Zovein et al., 2008). Indeed, LPM gives rise to a archaic vascular plexus which later segregates into the precursors of the posterior cardinal vein and the dorsal aorta (Chong et al., 2011). Driven by footling known mechanisms, the primal vein progenitors stay in the lateral plate to mature, whereas the dorsal aorta progenitors migrate to the midline where they form a lumenized vessel. Due to the technical difficulties of studying embryos in utero, the understanding of the early stages of HSC development has greatly benefited from model organisms that provide large numbers of experimentally accessible embryos, that is, zebrafish and Xenopus.

In Xenopus, hemangioblasts giving rise to the posterior cardinal veins and the dorsal aorta localize to the lateral plate, adjacent to the somites (Figure 4; Ciau-Uitz et al., 2013). The key steps in the specification of these adult hemangioblasts are shown in Effigy 4. Transcription factors (TFs) define cell identity and office, and the influence of exogenous signaling pathways ultimately converges on these transcriptional regulators. A number of TFs are critical for hematopoiesis (Tabular array 1) and a subset of them drive mesodermal programing toward the HSC fate. These primary regulators are recurrently used throughout HSC ontogeny and control key fate decisions taken by HSC precursors. Members of four families of TFs are particularly prominent in HSC programming: ETS, GATA, bHLH, and Runx (Table 1). Interaction between these TFs is highly conserved throughout evolution and their combinatorial activities regulate multiple aspects of hematopoiesis, from YS hematopoiesis, HSC ontogenesis to steady country hematopoiesis in the bone marrow and terminal blood differentiation.

Figure four. Development of the definitive HSC lineage before their emergence in the dorsal aorta. (a) The general anatomy of the embryo using Xenopus as an instance at the time when the first precursors of the HSC lineage are specified. due north, notochord; NT, neural tube; PLPM, posterior lateral plate mesoderm. Dorsal is to the top. (b) HSC precursors are specified from the PLPM. (c) The hematopoietic program is initiated in PLPM next to the somites and is indicated past ETS TF expression. (d) ETS TFs together with Gata2 induce Flk1 expression, which is required for VEGFA signalling. (due east) VEGFA secreted from the somites triggers the specification of adult hemangioblasts which culminates with the expression of Scl/Tal1. (f) Subsequent VEGFA signaling from midline structures stimulates hemangioblast migration toward the midline. (grand) Typically, hematopoietic expression is absent in migrating cells and during their migration physical contact with somite cells primes them to get hematogenic endothelium (HE) when they reach the midline. Priming is controlled past VEGFA and Notch-Jam1-Jam2 signaling. (h) Once at the midline, before lumen formation and the onset of blood flow, the dorsal aorta becomes an artery. (i) VEGFA and Notch signaling also drive lumen formation. (j) Dorsal–ventral signaling gradients polarize the lumenized dorsal aorta to establish HE in the ventral wall whereas the dorsal wall, becomes structural endothelium. (yard) hematogenic endothelium maturation culminates with the formation of intra-aortic clusters containing MMPs and HSCs.

Table 1. Genetic mutations affecting HSC evolution

Gene Genetic defect – species Phenotype References
Transcription factors (TFs)
Fli1 KO – mouse Embryonic lethal, claret vessels defects Hart et al. (2000), Liu et al. (2008), and Ciau-Uitz et al. (2013)
MO KD – Xenopus Absence of developed hemangioblast and lack of blood vessels
Gata2 KO – mouse Lethal earlier hematopoietic stem cell (HSC) emergence, blood vessel defects Tsai et al. (1994), Lim et al. (2012), de Pater et al. (2013), Butko et al. (2015), Liu et al. (2008), and Ciau-Uitz et al. (2013)
Endothelial KO – mouse Absence of HSCs
MO KD – zebrafish Absence of HSC emergence in Gata2b morphants
MO KD – Xenopus Absence of adult hemangioblast
Etv2 KO – mouse Lack of blood and blood vessels Lee et al. (2008), Sumanas and Lin (2006), Ciau-Uitz et al. (2013), and Salanga et al. (2010)
MO KD – zebrafish Lack of blood vessels
MO KD – Xenopus Absence of developed hemangioblast and lack of claret vessels
Scl/Tal1 KO – mouse Lethal earlier HSC emergence Porcher et al. (1996), Robb et al. (1995), Patterson et al. (2005), Dooley et al. (2005), Zhen et al. (2013), and Ciau-Uitz et al. (2013)
Lack of embryonic and definitive claret
MO KD – zebrafish Absence of hemangioblast and dorsal aorta
MO KD – zebrafish Specific impairment or HSC emergence in Sclβ morphants
MO KD – Xenopus Absence of adult hemangioblast and dorsal aorta
Lmo2 KO – mouse Lethal before HSC emergence, blood vessel defects Warren et al. (1994), Yamada et al. (2000), and Patterson et al. (2007)
MO KD – zebrafish Absence of hemangioblast
Etv6 KO – mouse Lethal earlier HSC emergence, no definitive blood, blood vessel defects Wang et al. (1997) and Ciau-Uitz et al. (2010)
MO KD – Xenopus Absence of adult hemangioblast
Eto2 MO KD – Xenopus Absence of hematogenic endothelium (HE) in the dorsal aorta (DA), lack of HSCs Leung et al. (2013)
Notch1 KO – mouse Lack of HSCs emergence Kumano et al. (2003), Hadland et al. (2004), and Kim et al. (2014)
MO KD – zebrafish Lack of HE and HSCs
Rbpjκ KO – mouse Embryonic lethal Oka et al. (1995), Souilhol et al. (2006), and Krebs et al. (2004)
All-encompassing vascular defects
Endothelial KO – mouse Extensive vascular defects, no arterial specification Krebs et al. (2004) and Robert-Moreno et al. (2005)
KO – mouse Lack of HE and HSCs
β-catenin Endothelial KO – mouse Lack of HSCs Ruiz-Herguido et al. (2012)
Runx1 KO – mouse Lack of HSCs emergence Okuda et al. (1996), Li et al. (2006), Chen et al. (2009), Gering and Patient (2005), and Kissa and Herbomel (2010)
Endothelial KO – mouse Hematogenic endothelium impairment, lack of HSCs
MO KD – zebrafish Lack of HSCs emergence
CBFβ KO – mouse Lack of definitive blood Wang et al. (1996), Sasaki et al. (1996), and Bresciani et al. (2014)
KO – zebrafish Blockage of HSC migration from the dorsal aorta
Ikbaa MO KD – zebrafish Increased expression of Runx1 and cMyb in the dorsal aorta, and Rag1 in the thymus He et al. (2015)
Signaling
VegfA KO – mouse Lethal before HSC emergence, lack of blood, and endothelial cells Carmeliet et al. (1996), Ferrara et al. (1996), Ciau-Uitz et al. (2013), and Leung et al. (2013)
MO KD – Xenopus Absence of adult hemangioblast and lack of blood vessels
Isoform-specific KD – Xenopus Impairment of HE specification in medium/long VegfA isoform depleted embryos without arterial defects
Flk1 KO – mouse Lethal before HSC emergence, lack of blood, and endothelial cells Shalaby et al. (1995, 1997) and Ciau-Uitz et al. (2013)
MO KD – Xenopus Absence of developed hemangioblast and lack of claret vessels
Flt1 KO – mouse Hemangioblast overproliferation, abnormal vascular assembly Fong et al. (1995)
Jagged1 KO – mouse Lethal before HSC emergence, blood vessel defects Xue et al. (1999), Robert-Moreno et al. (2008), and Espin-Palazon et al. (2014)
Lack of HE and HSCs
MO KD – zebrafish Reduced numbers of Runx1-expressing cells in the dorsal aorta
Mind bomb KO – zebrafish Lack of HSC emergence Gering and Patient (2005) and Burns et al. (2005)
Dll4 KO – mouse Lack of arterial specification and damage of DA morphogenesis Duarte et al. (2004)
Jam1a, Jam2a MO KD – zebrafish Damage of HE specification and lack of HSC emergence Kobayashi et al. (2014)
Ifng KO – mouse Decreased numbers of functional HSC Li et al. (2014) and Sawamiphak et al. (2014)
MO KD – zebrafish Lack of HE and HSCs in Ifng1-2 morphants
Ifngr1 KO – mouse Decreased numbers of functional HSC Li et al. (2014) and Sawamiphak et al. (2014)
MO KD – zebrafish Lack of HE and HSCs
Tnfa MO KD – zebrafish Decreased number of Runx1, cMyb, and CD41+ cells in the dorsal aorta Espin-Palazon et al. (2014)
Tnfr2 MO KD – zebrafish Decreased number of Runx1, cMyb, and CD41+ cells in the DA Espin-Palazon et al. (2014) and He et al. (2015)
Tlr4 KO – mouse Reduced expression of Runx1 and cMyb in the AGM, reduced numbers of functional HSCs He et al. (2015)
MO KO – zebrafish Decreased number of Runx1- and cMyb-expressing cells in the dorsal aorta He et al. (2015)
Plcg1 KO – zebrafish Lack of arterial specification and HSC emergence Gering and Patient (2005)
Cxcl8 MO KD – zebrafish Reduced numbers of Runx1/cMyb-expressing cells in the dorsal aorta Jing et al. (2015)
IL-3 KO – mouse Reduced numbers of transplantable HSCs in the AGM, damage of HSC survival and proliferation Robin et al. (2006)
Thursday KO – mouse Reduction of functional HSCs in the AGM Fitch et al. (2012)
Cxcl12 MO KD – zebrafish Reduced numbers of cMyb-expressing cells in the DA Nguyen et al. (2014)
Metabolism
Raldh2 Endothelial KO – mouse Lack of HSC emergence Chanda et al. (2013)
A2b MO KD – zebrafish Cell outburst when undergoing EHT, decreased numbers of Runx1 and cMyc cells in the DA and Rag1 cells in the thymus Jing et al. (2015)

KO, knock out; KD, knock downwards; MO, morpholino antisense oligonucleotide.

In the LPM, ETS TFs (Fli1 and Etv2) initiate programming toward the hemangioblast programme (Figure 4(c)) by activating and maintaining Gata2 expression (Ciau-Uitz et al., 2013). ETS and Gata2 together activate the expression of Flk1 (Effigy 4(d)), a receptor tyrosine kinase which makes them responsive to VEGFA, a pivotal signaling molecule in HSC programing. The adjacent somites function equally a signaling center throughout HSC development. VEGFA produced nether the control of the ETS TF Etv6 (Ciau-Uitz et al., 2010, 2013), is secreted past the somites to stimulate the lateral plate Flk1+ cells to become hemangioblasts (Figure 4(d)), a cellular state defined by the bHLH TF Scl/Tal1 (Effigy iv(eastward)).

In all vertebrates, the dorsal aorta forms in the midline. In amniotes, such every bit the chick, mouse, and human, before migration, the dorsal aorta precursors coalesce and lumenize in the lateral plate to class the paired dorsal aortae, which migrate to the midline where they fuse in an anterior to posterior fashion, a procedure which requires the repression of BMP antagonists in the midline (Garriock et al., 2010; Reese et al., 2004). In contrast, in anamniotes (fish and amphibians), dorsal aorta precursors migrate as single cells to coalesce in the midline (Figure 4(g)). Although its significance is non understood, blood TFs (Gata2 and Scl/Tal1) are switched off during migration (Ciau-Uitz et al., 2000). Migration is driven past VEGFA released from the midline (Effigy 4(f)) and cell-to-cell contact with the somites is critical for farther programing toward the HE fate (Figure 4(one thousand)). At this fourth dimension, the TF Eto2 is expressed in the somites and controls the expression of nondiffusible extracellular matrix–leap VEGFA isoforms which are required for priming the migrating cells to express Notch1 after they reach the midline (Figure iv(g); Leung et al., 2013). Notch signaling mediated past intercellular junctional adhesion molecules Jam1 and Jam2 is also critical during migration (Figure four(g); Kobayashi et al., 2014). Migrating cells limited Jam1 and Notch1, whereas somite cells express Jam2 and Notch ligands, the interaction between Jam1 and Jam2 is necessary for Notch signaling activation in the migrating cells. In this context, Notch ligand expression past somite cells requires Wnt16 signaling (Clements et al., 2011).

HSC emergence only occurs from arterial and non venous endothelium (de Bruijn et al., 2002; Gordon-Keylock et al., 2013). In the midline, the dorsal aorta precursors coagulate into an endothelial cord, which almost immediately expresses arterial genes. Arterial specification is dependent on VEGFA signaling from the somites, which activates the Notch pathway in dorsal aorta endothelium (Lawson et al., 2001; Gering and Patient, 2005); this VEGFA function is Eto2-independent as arterial specification is unaffected in Eto2-deficient embryos (Leung et al., 2013). In zebrafish, although not in mice and Xenopus, expression of VEGFA in the somites requires HH signaling (Coultas et al., 2010; Gering and Patient, 2005; Lawson et al., 2001; Leung et al., 2013). Activation of the arterial programme in the dorsal aorta requires not only VEGFA signaling which is mediated by TFs FoxC1 and FoxC2 (Seo et al., 2006), but also Wnt signaling mediated by SoxF TF and Sox17 (Morini and Dejana, 2014). Arterial specification, as indicated by Dll4 expression, takes place earlier lumenization (Figure 4(h); Chong et al., 2011) and therefore is non triggered by claret flow shear stress. Accordingly, deficiency in Nrp1, a VEGFA coreceptor specifically expressed in arterial endothelial cells in the mouse, impairs arterial differentiation independent of blood flow (Jones et al., 2008). Yet, after on, shear stress plays a cardinal role in the maintenance of arterial identity (Eichmann et al., 2005; Jahnsen et al., 2015; le Noble et al., 2004). Repression of arterial Sox17 is required later to actuate the hematopoietic program (Lizama et al., 2015).

Lumenization of the dorsal aorta is poorly understood and the mechanism might be different between species (Xu et al., 2011). Nevertheless, VEGFA and Notch signaling, mediated by Dll4, have been implicated (Figure iv(i); Benedito et al., 2008; Scehnet et al., 2007). VEGFA could as well act independently of Dll4 by activating Egfl7, a key factor in endothelial lumenization (Charpentier et al., 2015). The endothelial-restricted Ras-interacting protein, Rasip1, is essential for vessel lumenization by suppressing RhoA-Rock signaling (Xu et al., 2011). Whether Rasip1 activeness is controlled by VEGFA or Notch is not known.

Hematogenic endothelium giving rise to HSCs is localized in the ventral wall of the dorsal aorta. How dorsal–ventral polarization of the dorsal aorta is not yet fully understood. It has been suggested that a number of signaling gradients operate in the dorsal aorta niche and regulate endothelium polarization. Strong support for this view is the genetic prove indicating that a cross-antagonistic interaction between ventral-derived BMP and dorsal-derived HH signaling is critical for setting the boundary betwixt structural endothelium and HE (Effigy iv(j); Wilkinson et al., 2009). Similarly, a cross-combative slope betwixt VEGFA and estrogen has been proposed to fix the boundary between structural endothelium and HE (Carroll et al., 2014). Finally, a VEGFD gradient from the somites might likewise be disquisitional for HE specification (Wei et al., 2014).

Defining when the endothelium becomes hematogenic has been controversial. What is known, however, is that Gata2, Scl/Tal1, and Runx1 are essential for the EHT and that these TFs are expressed in the dorsal aorta long before the generation of HSCs (Chen et al., 2009; de Pater et al., 2013; Gao et al., 2013; Lim et al., 2012; North et al., 1999; Swiers et al., 2013; Zhen et al., 2013). Ultimately, all signaling pathways converge on these TFs to modulate the creation of HSC together with other progenitor cells (HSPCs) created in the AGM (Figure 4(m)).

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ARTERIES AND VEINS

D.Eastward. deMello , in Encyclopedia of Respiratory Medicine, 2006

Bronchial Arteries

Early in gestation, primitive bronchial arteries arise from the dorsal aorta in the neck region well-nigh the celiac axis and are distributed with the early branches of the airways ( Table 1). When lobar or segmental airway branches are present at virtually the sixth calendar week of embryonic life, the cardinal bronchial artery branches disappear. Between the ninth and twelfth weeks, definitive bronchial arteries arise from the aorta, pass along the superior surface of the airways, and communicate with the pre-existing capillary bed in the distal airways. Sometimes the archaic bronchial arteries persist and migrate with their point of origin, to a site below the diaphragm, still most the celiac axis. A portion of the lung bud may remain attached and manifests later as a lung sequestration.

Table 1. The development of the bronchial arteries

Week of gestation Airway Blood vessels
quaternary Principal Archaic ventral aorta
Pulmonary vein links to eye
6th arch supplies lung
Paired systemic arteries from dorsal aorta
fifth Lobar Only blood from right ventricle to pulmonary artery
sixth Segmental Systemic arteries disappear
9th to 12th Bronchial arteries enter peribronchial plexus

The primitive paired bronchial arteries arise from the dorsal aorta most the celiac centrality in the cervix. These accept usually disappeared before the 5th week; if they persist, they then migrate with the celiac axis to below the diaphragm as seen in certain abnormal atmospheric condition (eastward.g., sequestered segment).

Reproduced from deMello DE and Reid LM (1997) Arteries and veins. In: Crystal RG, West JB, Barnes PJ, Cherniack NS, and Weibel ER (eds.) The Lung: Scientific Foundations, 2nd edn., pp. 1117–1127. Philadelphia: Lippincott-Raven Press, with permission from Lippincott Williams & Wilkins.

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