An ultrastructural study of developing extracellular matrix in vitelline blood vessels of the early chick embryo

This investigation was designed to describe the morphological events in embryonic development of peripheral blood vessels (vasculogenesis) and to relate this process to the appearance of extracellular matrix (ECM) during growth and maturation of these tissues. Extraembryonic vitelline vessels of the early chick embryo were chosen for this study and light, transmission, and scanning electron microscopy were carried out on vessels excised from chick embryos (Hamburger-Hamilton stages 8 through 23). Our data show that early (stage 10) vessels are composed of two distinct epithelial layers, an inner layer of presumptive endothelium surrounded by a layer of splanchnopleuric mesoderm. During development, the inner layer gives rise to mature vascular endothelium while splanchnopleuric mesoderm differentiates to form primitive vascular smooth muscle. Ultrastructural studies show the presence of collagen and basal lamina in the extracellular space between these two layers during initiation of endothelial and smooth muscle cytodifferentiation. Furthermore, ruthenium red-positive material is present on basal surfaces of developing vascular endothelium at this time, indicating possible glycosaminoglycans (GAG) or other polyanionic components of the ECM. These data suggest that the sequential production of basal lamina, collagen(s), and/or GAG's by developing peripheral vessel wall epithelia may be critical to their final differentiation.     

The fine structure of developing cartilage in the chick embryo

The fine structure of developing cartilage is described in the area of the future vertebral bodies in the cervical region of chick embryos. Incubation ages range from 36 hours, when the sclerotome of the somite begins to break up, to the thirteenth day. In the 36- to 72-hour interval cells of the sclerotome become free and assume stellate form. Polyribosomes nearly fill the largely undifferentiated cytoplasm. Microfibrils and amorphous material appear in the connective tissue space

1 The extent of the connective tissue space is determined by boundary (basement) membranes; externally by those of epithelium facing the geometric exterior of the organism and internally by those of endothelium, mesothelium, muscle, nerve and fat. The true contents of the connective tissue space are the connective tissues. As used in this paper “connective tissue space” refers to the extracellular portion, in which the fibrous and amorphous components exist.

by the end of the third day. From the fourth through the sixth day both cellular contours and contents suggest fibroblasts. Microfibrillar diameter increases from 50 to 150 Å. Periodicity does not occur. Matrix granules appear and establish contact with microfibrils. From the eighth through the eleventh day the predominating cell types are chondroblasts and chondrocytes whose fine structure is typical. Microfibrils become more numerous and matrix granules larger. During days 11 through 13, chondrocytes show degenerative changes including lucid areas of nucleoplasm and cytoplasm with fragmentation of endoplasmic reticulum. Microfibrils and matrix granules are heavily concentrated in the connective tissue space and lucent osteoid appears.     

The fine structure of blood vessels of the telencephalic germinal matrix in the human fetus

Blood vessels of the human telencephalic germinal matrix during the tenth through the twenty-second week of gestation have been examined by light and electron microscopy. In all fetuses studied the ependymal and sub-ependymal zones of the germinal matrix have a prominent vascular network. During the tenth and twelfth weeks of gestation, the endothelial cells are plump and display numerous organelles, junctional complexes, conspicuous luminal microvilli and stub-like abluminal projections. Coated and micropinocytotic vesicles were found both in the cytoplasm and on luminal and abluminal surfaces. In endothelial cells intracytoplasmic, membrane-limited, rod-shaped bodies were frequently observed. These bodies have been linked to endothelial thromboplastic and clotting activities and related to abnormal clotting status. Their role in the pathogenesis of subependymal germinal matrix hemorrhage in premature infants remains unknown. Pericytes apposing the endothelial cells were recognized in all gestational periods. The endothelial basal lamina and astrocytic end-feet are ill defined, and the extracellular space is pronounced. By the fifteenth and seventeenth weeks of gestation the endothelial cells are still large and now possess more numerous luminal microvilli and abluminal projections. At this stage the pericytes, basal lamina and astrocytic end-feet are all well developed, resulting in a decrease in the surrounding extracellular space. By the twenty-second week the endothelial cells possess few luminal and abluminal projections and the associated basal lamina, glia, pericytes and extracellular compartment appear mature. The relationship of the germinal matrix vasculature to the pathogenesis of subependymal hemorrhage is discussed.     

The dehydrogenase activity in the human vaginal anlage

Summary The authors have studied the activity of succinate dehydrogenase, malate dehydrogenase, lactate dehydrogenase and 6-phosphogluconate dehydrogenase in the vaginal plate (the anlage of the vaginal epithelium), the sinus epithelium, the müllerian epithelium and the wolffian epithelium from eight human female fetuses. The vaginal plate has a very low activity of succinate dehydrogenase compared with that in the other epithelia. The low activity in the vaginal plate might be explained by its origin from the differentiated epithelium (a wolffian derivate) covering the müllerian tubercle. In case of the other enzymes, no differences in activity could be found between the epithelia studied.     

Changes in the distribution and fine structure of the intralobular blood vessels of the submandibular gland in the postnatally developing mouse

Previous studies have shown that the blood vessels supplying the endocrine organs and the mucosa of the intestinal canals change in terms of not only their distribution but also their structure with the development and growth of each organ. We examined changes in the distribution and structure of intralobular blood vessels, including capillaries, throughout the postnatal development of the submandibular gland, an exocrine organ. The mouse submandibular gland from days 0 (birth) to 49 was investigated chronologically and ultrastructurally. The capillaries changed from continuous to fenestrated on day 10, coincident with an increase in the number of acini to more than the number of terminal tubules. The number of sections of intralobular blood vessels per unit area gradually decreased with increasing acinar size and was lowest on day 21 when pups were weaned; the same number was maintained from then on. In contrast with the reduction in the number of intralobular blood vessels, the number of capillary pores appeared to increase gradually. Acinar size increased further till day 28. Capillary pore number also increased further, till day 35, apparently in relation to the increasing acinar size. These findings suggest that the changes in distribution and structure of the intralobular blood vessels in the submandibular gland of the postnatally developing mouse are closely related to the development of the parenchymal cells in preparation for weaning and sexual maturity.     

The identification of pericyte-like cells in the subendothelium of human blood vessels]

We identified pericyte-like cells in various regions of human vascular bed using 3G5 monoclonal antibodies against brain capillary pericytes' surface antigen. Pericyte-like cells were revealed in the subendothelial layer of the arterioles, venules, brain microvascular bed and in vasa vasorum adventitia. In arteries and veins of small, medium and large caliber pericyte-like cells were found in intimal subendothelial space. Pericyte-like cells form subendothelial network and may play an important role in physiological processes of vascular wall function.     

The architecture of internal blood vessels in human fetal vertebral bodies

The internal vascular system of vertebral bodies was investigated in 17–24 wk human fetuses by acrylic dye injection and by corrosion casting/scanning electron microscopy. The regions of intervertebral spaces did not contain blood vessels. The radial metaphyseal vessels were at the stage of centripetal ingrowth into the vertebral body cartilage and their terminal, blindly ending segments had a form of cuff-like capillary plexuses. The anterolateral equatorial arteries communicating with the vessels of the ossification centre were only rarely found. The centre was usually supplied by 2 posterior (nutrient) arteries which branched into an arcade-like array of arterioles equipped with occasional sphincters and giving origin to a dense network of peripherally located capillaries. Numerous blind capillary buds formed the advancing border of the ossification centre. The veins usually accompanied the arteries. In the ossification centre the venous compartment consisted of sinuses drained by larger posterior veins. In the 17 wk fetus, an axial avascular area was observed in the place of notochord localisation, indicating the formation of a ring-shaped ossification centre around the notochord remnants at earlier stages of fetal development.     

Analysis of intrapulmonary vessels and epithelial-endothelial interactions in the human developing lung

The establishment of a sufficiently wide and functional blood-gas interface is of critical importance in lung development, but development of the intrapulmonary vascular system including alveolar capillary vessels still remains unclear. In this study, we first characterized the structural development of the vascular system in accordance with that of airways in human fetal lungs at the pseudoglandular phase (8, 13, and 16 weeks gestation) by examining the immunohistochemical distribution of CD34 and alpha-smooth muscle actin (SMA). Using double immunohistochemistry and 3-dimensional reconstruction techniques, endothelial cells in the developing lung could be classified into two different types according to the characteristics of their adjacent cells (presence or absence of SMA-positive cells) and their distribution (proximal or distal lung parenchyme). Endothelial cells without SMA-positive cells developed into a capillary network surrounding the budding components of distal airways during the mid-pseudoglandular phase before communicating with proximal vessels. We then examined the immunoreactivity of thrombomodulin and von Willebrand factor (vWF) in endothelial cells. Endothelial cells of the capillary network were mainly positive for vWF during the early gestational stages, but altered their phenotypes to those of mature lungs (vWF negative and thrombomodulin positive) during the terminal sac phase. We subsequently determined the immunohistochemical distribution of vascular endothelial growth factor (VEGF). Epithelial cells of the most distal airways were intensely positive for VEGF. These results suggest that VEGF present in airway epithelial cells is involved in the maturation as well as proliferation of capillary endothelial cells. Epithelial-endothelial interactions during lung development are considered very important in the establishment of the functional blood-gas interface.     

Cultivation of human tumors on the chorioallantoic membrane of the developing chick embryo

Summary Twenty-eight human tumors of various localization and structure were cultivated on chorioallantoic membrane of developing chick embryo. True growth of the tumors could not be obtained. Small parts of tumors survive for a short time and cause turbulent reaction in the chorioallantoic membrane. These pieces may be retransplanted, but later they are subjected to destruction and resolution. When normal human embryonic tissue was introduced — this only promoted a more prolonged preservation of the transplantate. However, it did not result in the true growth of transplanted tumors. Small pieces of papilloma of the urinary bladder appeared to be the most viable and withstood nine transplantations.Submitted by Active Member Acad. Med. Sci. USSR L.A. Zil'ber     

SEM characterization of a cellular layer separating blood vessels from endoderm in the quail embryo

The associations between the developing blood vessels and both endoderm and splanchnic mesoderm in quail embryos at stages 9-11 were examined by using scanning electron microscopy. Embryos were pinned ventral-side up on agar plates and the endoderm was surgically removed prior to fixation and dehydration. This procedure exposes a netlike layer of cells closely apposed to the ventral surface of paraxial mesoderm and all visible blood vessels; we are calling this the subvascular layer. Development of this layer proceeds rostral-to-caudal, and lateral-to-medial, with the earliest stages of formation being visible over the unsegmented paraxial mesoderm of the segmental plate. The subvascular layer increases markedly in density slightly medial to the innermost boundary of the intraembryonic vascular plexus. Cells of this layer eventually establish a continuous sheet beneath the lateral plate and paraxial mesoderm and the notochord. With maturation, the cells of the subvascular layer approach confluence. The spatial and temporal patterns of development of the embryonic vascular tissues and the subvascular layer are closely correlated, suggesting a possible role for the subvascular layer in normal embryonic vascular development.     

The lining of the gut in the developing rat embryo

Summary A light microscopical study of the morphogenesis of the gut in the rat embryo was undertaken to provide a careful map of temporal changes in the topographical relations of the (definitive) endoderm, the notochord and the hypoblast (primary endoderm). The borderline between the (definitive) endoderm and the hypoblast that appears upon gastrulation defines the lateral extension of the future gut epithelium. Within this initially semiglobular disk, the foregut and hindgut originate sequentially as blind, rapidly growing pouches. Upon the turning of the embryo, the hardly growing peripheral part of the disk becomes located in the vitelline duct. Within the head process, endodermal and notochordal cells could not be separately identified. However, slightly more posteriorly notochordal cells are seen to become embedded into the endoderm of the foregut during gastrulation. This process is not seen over the hindgut and may explain why the detachment of the notochord from the (fore) gut begins caudally.Abbreviations Arrow endoderm-hypoblast junction - bar 0.1 mm - ect ectoderm - end (definitive) endoderm - fg foregut - hg hindgut - hp head process - hyp hypoblast - mes mesoderm - not notochord - ps primitive streak - vd vitelline duct