The histogenesis of basement membranes

Developmental and mechanical roles of Reichert's membrane in mouse embryos

Embryonic development and growth in placental mammals proceeds in utero with the support of exchanges of gases, nutrients and waste products between maternal tissues and offspring. Murine embryos are surrounded by several extraembryonic membranes, parietal and visceral yolk sacs, and amnion in the uterus. Notably, the parietal yolk sac is the most outer membrane, consists of three layers, trophoblasts and parietal endoderm (PaE) cells, and is separated by a thick basal lamina termed Reichert's membrane (RM). RM is composed of extracellular matrix (ECM) initially formed as the basement membrane of the trophectoderm of pre-implanted embryos and followed by the heavy deposition of ECM mainly produced in PaE cells of post-implanted embryos. In addition to the physiological roles of RM, such as gas and nutrient exchange, it also plays a crucial role in cushioning and dispersing intrauterine pressures exerted on embryos for normal egg-cylinder morphogenesis. Mechanistically, such intrauterine pressures generated by uterine smooth muscle contractions appear to be involved in the elongation of the egg-cylinder shape, along with primary axis formation, as an important biomechanical element in utero. This review focuses on our current views of the roles of RM in properly buffering intrauterine mechanical forces for mouse egg-cylinder morphogenesis. This article is part of the theme issue 'Extraembryonic tissues: exploring concepts, definitions and functions across the animal kingdom'.

IMMUNO-ELECTRON MICROSCOPE ANALYSIS OF THE SURFACE LAYERS OF THE UNFERTILISED SEA URCHIN EGG. II. LOCALISATION OF SURFACE ANTIGENS

The immunological properties of the surface layers of Paracentrotus lividus eggs have been studied further by using ferritin-labelled antibody to localise specific antigenic sites. In order to detect a wider spectrum of antigenic determinants, several antisera against egg and jelly substance have been employed in combination with absorption procedures using lyophilised antigen. This use of absorbed antisera was made feasible by adding ferritin label in a second antiserum layer of ferritin-anti-γ-globulin. Eggs were treated with antibody for short periods to detect antigenic sites without incurring structural changes (shown in previous paper) resulting from long antibody treatment. Unspecific ferritin uptake, found in pinocytotic vesicles and yolk granules, is considered in relation to yolk formation. The jelly layer, found to be immunologically heterogeneous, included one component interacting with antijelly γ-globulin and one with antiegg γ-globulin. The vitelline membrane proved to be rich in egg antigens (heat-stable and heat-labile). The role of this layer in specificity of fertilisation, parthenogenetic activation, and the possibility of being analogous to a basement membrane are discussed. Few antigenic sites were found on the plasma membrane with antiegg γ-globulin. This γ-globulin resulted in some specific labelling of cortical granules and its action is considered in relation to the permeability properties of the egg.

Morphological changes of microvilli on different surfaces of epithelial cells in the rat bladder treated with N-butyl-N-(4-hydroxybutyl) nitrosamine

This study investigates morphological changes of microvilli occurring on different surfaces of epithelial cells, including luminal surfaces, intercellular surfaces, and basal cell surfaces adjacent to the basement membrane (BM), in the rat bladder treated with N-butyl-N(4-hydroxybutyl) nitrosamine (BBN) by transmission electron microscopy (TEM). The present results showed that the microvilli were observed not only on the luminal surfaces of epithelial cells but also on the intercellular surfaces and basal cell surfaces adjacent to the BM following administration of BBN. There were a variety of morphological changes of microvilli on the luminal surfaces, intercellular surfaces and basal cell surfaces adjacent to the BM, respectively. It is suggested that the microvilli occurring on the luminal surfaces may not represent characteristics of the microvilli occurring on the intercellular surfaces and on the basal cell surfaces adjacent to the BM, and that occurrence of the microvilli on the epithelial cell surfaces may reflect a higher metabolic activity of proliferative epithelial cells and may play an important role in the processes of tumor growth during bladder carcinogenesis.

A practical approach to the diagnosis of renal disease by biopsy

The pathologist has an important role in the diagnosis and monitoring of renal disease. However, for optimal useful information to be derived from renal biopsy specimens, certain guidelines must be adhered to and these are enunciated here. The 3 avenues of observation of renal biopsies viz. light microscopy, immunofluorescence and electron microscopy, all have important roles to play and give differing data which informs the diagnosis for the renal biopsy report. The relative emphasis on each of these modalities of investigation will vary depending upon the situation in which the renal biopsy is performed. The methods used here have been shown to be effective in practice over a period of 20 yrs. Although there may be variations in methodology from centre to centre, the general background aims and principles remain the same. The emphasis in this paper has been on common practical aspects of renal biopsies. Much of the practical information concerning renal biopsies, which is brought together here, is otherwise scattered and not readily available. The aim of this article is to allow the reader to understand the rationale for the steps that are involved in renal biopsy diagnosis.

Basement membrane and carcinogenesis: ultrastructural observations in the basement membrane of the bladder epithelium in rats treated with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN)

This study investigated the structural alterations in the basement membrane (BM) of the bladder epithelium in rats treated with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) using transmission electron microscopy. Following administration of BBN, thickening of the BM of the bladder epithelium was observed and remained almost constant from 4 to 20 weeks, although the pathological changes in the rat bladder epithelium induced by BBN altered over the same period of 20 weeks. The reason for this phenomenon can be explained by the increased interfacial area between the basal epithelial cells and the BM of the rat bladder epithelium due to an increase in the number and size of the microvilli on the basal cell surfaces adjacent to the BM. Our results also showed that the frequency of hemidesmosomes increased progressively during the period of carcinogenesis, especially in the lesions of noninvasive transitional cell carcinoma (TCC) in the rat bladder. It is suggested that the neosynthesis of BM components can be carried out both by benign hyperplastic cells and by noninvasive TCC cells of rat bladder. The alterations in the BM thickness may be affected by the changes in the number and size of the microvilli occurring on the basal cell surfaces adjacent to the BM. Both an increased frequency of hemidesmosomes and the neosynthesis of BM are closely related to cell proliferation during carcinogenesis.

Development of kidney tubular basement membranes

Although some progress has been made in recent years, there are truly large gaps in our basic knowledge on how the TBM is assembled during development. Some of the new evidence presented here indicates that both the tubular epithelium and interstitial fibroblasts participate in TBM protein biosynthesis during nephrogenesis. In addition, newly assembled segments of TBM are spliced or inserted into existing TBM during tubule expansion and elongation. A similar splicing mechanism has been described previously in the GBM, endocrine organs, and intestinal villi, and this mechanism therefore probably represents a fundamental process of basement membrane formation. A major unresolved question at present, however, is how this mechanism operates at the molecular level. Does the newly formed basement membrane contain identical components as that already present? Since an enzymatic process is likely occurring in the insertion of new matrix into old, which enzymes are involved? What is the cellular origin of these enzymes and which matrix component(s) is their substrate? Even more fundamental yet unanswered questions have to do with the mechanisms of epithelial induction, basement membrane gene activation, and tubular morphogenesis. Once the basement membrane is fully formed at the completion of nephrogenesis, what controls basement membrane turnover and how does this operate? Clearly, much additional research is necessary to address these questions. This work is needed, however, before we can fully understand the important roles basement membranes play in normal development as well as in disease.

Gross and cellular analysis of 6-mercaptopurine-induced cleft palate in hamster

The present study analyzes the morphological, histochemical, and ultrastructural aspects of the pathogenesis of 6-mercaptopurine (6MP)-induced cleft palate in hamster fetuses. Gross and light microscopic observations indicated that 6MP stunts the growth of vertical palatal shelves and thus induces cleft palate. Ultrastructural analysis showed that, in contrast to controls, 6MP-induced alterations were first seen in the mesenchymal cells 24 hr after drug administration. The initial alterations were characterized by swelling of the nuclear membrane. During the next 12 hr, lysosomes were seen first in the mesenchymal cells and then in the cells of the medial edge epithelium (MEE) of the developing palatal primordia. The appearance of lysosomes was temporally abnormal and was interpreted as a sublethal response to 6MP treatment. Subsequently, the nuclear alterations and the lysosomes diminished; and 48 hr after 6MP administration, they were absent from the palatal tissues. Ninety hours after 6MP administration, unlike the controls (in which the palatal shelves were already fused), changes were seen at the epithelial-mesenchymal interface in the developing cleft palatal shelves. These changes were characterized by breakdown of the basal lamina and epithelial-mesenchymal contacts. Eventually, at term, the MEE of the vertical shelf stratified. It was suggested that 6MP affected cytodifferentiation in the palatal tissues during the critical phase of early vertical shelf development and thereby induced cleft palate.

Distribution of basement membrane in squamous cell carcinoma of the head and neck

The immunohistologic distribution of the basement membrane components, type IV collagen and laminin, was evaluated in 57 alcohol-fixed, paraffin-embedded tissue sections which demonstrated immunostaining patterns with antigen preservation similar to that of frozen tissue sections. Normal and hyperplastic squamous mucosa, a spectrum of intraepithelial neoplasia, and invasive squamous cell carcinomas of the upper aerodigestive tract were evaluated by this technique. Prominent and continuous basement membrane staining characterized normal and reactive hyperplastic squamous mucosa. The basement membrane varied greatly with epithelial dysplasia and was usually prominent and continuous in mild to moderate dysplasias. In severe dysplasia/carcinoma in situ, the basement membrane was often thinned and occasionally discontinuous. The distribution of basement membrane in invasive carcinomas was also varied. Basement membrane was usually present in invasive tumors with well-defined tumor host borders and cohesive patterns of stromal invasion which were interpreted as foci of histologic differentiation. In contrast, invasive carcinomas with irregular cords or single tumor cells distributed through the host stroma invariably lacked basement membrane at the tumor-stromal interface; this was interpreted as a decreased expression of histologic differentiation. We conclude that 1) severe intraepithelial neoplasia is often associated with irregularities of basement membrane and that the absence of basement membrane does not necessarily define invasive cancer; 2) immunolocalization of basement membrane in invasive carcinomas is common in areas displaying histologic differentiation; and 3) the association of basement membrane distribution and histologic pattern of tumor invasion suggests that squamous cell carcinomas are capable of undergoing focal histologic differentiation after invasion has occurred.

Lesions of the renal papilla induced by paracetamol

The acute nephrotoxic effects of paracetamol in the uninephrectomized homozygous Gunn rat are different from those of aspirin. Both compounds induce renal papillary necrosis but paracetamol produces accumulation of non-cellular material in the interstitial space, less damage to interstitial cells, more damage to tubular epithelium, and more severe necrosis of proximal convoluted tubules. In both cortex and papilla only a small fraction of the cells at risk are affected. It is concluded that the findings are consistent with a synergistic nephrotoxic effect between the two compounds, but that the lesions are not sufficiently severe for the natural history of analgesic nephropathy to be wholly explicable by such synergism.

Epithelial inclusions and Tamm-Horsfall protein in paranephric lymph nodes. A light microscopy and immunocytochemical study

An unusual histological pattern made up of tubular structures and clusters of apparently epithelial cells floating within sinusoidal deposits of Tamm-Horsfall (TH) protein was observed in several lymph nodes removed with renal tumours (3 Wilms' tumours, 1 cystic nephroma) and pathological but non neoplastic kidneys (2 cases of reflux nephropathy). Masses of TH protein, often containing desquamated tubular epithelial cells, were also found in tubules, interstitium and perivascular lymphatic vessels of the resected kidneys, but never in the tumour tissue. Lymph nodes draining renal tumours, although moderately enlarged because of reactive hyperplasia and TH protein deposits, did not contain metastases. Our findings suggest that these inclusions originate from renal tubular epithelium and are transported to paranephric lymph nodes along with TH protein.

Ultrastructural and cytochemical observations on 5-fluorouracil-induced cleft-palate development in hamster

Sequential alterations in 5-fluorouracil-treated hamster fetal palate were studied by light and electron microscopy and by acid phosphatase cytochemistry. At an early stage in 5-fluorouracil-treated fetuses, when the palatal shelves were vertical, lysosomes first appeared in cells of the prospective fusion epithelium and then in the cells of subjacent mesenchyme. In contrast to controls, increasing numbers of both the epithelial and mesenchymal cells of the vertical palate showed lysosomal injury in 5-fluorouracil-treated fetuses as development progressed. Subsequently, the basal lamina in the vertical palate showed alterations, characterized initially by disturbances in lamina lucida, by fingerlike extensions of lamina densa, and ultimately by its complete breakdown. At a later stage, when shelves became horizontal, the lysosomes were absent in both the epithelial and mesenchymal cells, and the basal lamina continuity was restored. Unlike controls, however, 5-fluorouracil-treated horizontal shelves never contacted one another. Instead, the epithelia of the horizontal shelves underwent stratification. It appears that premature formation of lysosomes in palatal epithelial and mesenchymal cells following 5-fluorouracil treatment disrupts normal cytodifferentiation and affects the integrity of the basal lamina; both effects are associated with cleft-palate development.

Transformation of an AFP-positive yolk sac carcinoma into an AFP-negative neoplasm. Evidence for in vivo cloning of the human parietal yolk sac carcinoma

An alpha-fetoprotein (AFP)-positive ovarian yolk sac carcinoma of typical histologic appearance was surgically removed from a 19-year-old woman. The AFP-positive tumor recurred and was treated with x-rays and cytotoxic drugs to full remission, i.e., until no clinical or biochemical signs of tumor were evident. The second recurrence, which proved to be fatal, was noticed approximately 1 year after the initial diagnosis, but was not associated with elevated levels of serum AFP. At autopsy, the widespread tumor had the histologic appearance reminiscent of murine parietal yolk sac (PYS) carcinoma. The tumor cells did not form the characteristic histologic features of the classical human yolk sac carcinoma, did not secrete AFP, and were surrounded by extensive hyalinous extracellular matrix rich in laminin and collagen. It is thus shown that recurrent human yolk sac carcinomas could change their histologic morphology due to selective outgrowth and cloning of the parietal yolk sac component. Clinical recognition of this cloning is important because the PYS carcinoma cells do not secrete AFP, and the tumor growth cannot be biochemically monitored with this classical tumor marker.

Light microscopic immunolocalization of type IV collagen, laminin, heparan sulfate proteoglycan, and fibronectin in the basement membranes of a variety of rat organs

Immunohistochemical methods were used to determine whether type IV collagen, laminin, fibronectin, and heparan sulfate proteoglycan were present in diverse basement membranes. Antisera or antibodies against each substance were prepared, tested by enzyme-linked immunosorbent assay, and exposed to frozen sections of duodenum, trachea, kidney, spinal cord, cerebrum, and incisor tooth from rats aged 20 days to 34 months. Bound antibodies were then localized by indirect or direct peroxidase methods for examination in the light microscope. Immunostaining for type IV collagen, laminin, fibronectin, and heparan sulfate proteoglycan was observed in all of the basement membranes encountered. Fibronectin was also found in connective tissue. In general, the intensity of immunostaining was strong for type IV collagen and laminin, moderate for heparan sulfate proteoglycan, and weak for fibronectin. The pattern was similar in the age groups under study. Very recently the sulfated glycoprotein, entactin, was also detected in the basement membranes of the listed tissues in 20-day-old rats. It is accordingly proposed that, at least in the organs examined, type IV collagen, laminin, fibronectin, heparan sulfate proteoglycan, and entactin are present together in basement membranes.

Monoclonal antibody analysis of ocular basement membranes during development

As a first step in a study of the role(s) of basement membranes in ocular morphogenesis, we have produced a variety of monoclonal antibodies against native lens capsule from adult chicks, and have used these reagents to stain histological sections of ocular tissues from 4 1/2- to 18-day-old chicken embryos. Four different patterns of immunofluorescence were observed in sections of corneas of 18-day-old chicken embryos stained with these antibodies. The antibodies in group 1 stained the basement membranes of both the corneal epithelium and the endothelium (as well as Descemet's membrane). Those in groups 2 and 3 stained only the epithelial or endothelial basement membranes, respectively. The group 4 antibody stained the corneal stroma as well as Bowman's membrane and Descemet's membrane. The antibodies in group 1 could be further subdivided into groups 1a and 1b on the basis of temporal differences in the onset of staining in corneas from 4 1/2- to 7-day-old embryos. Thus, this series of monoclonal antibodies appears to recognize at least five different antigenic determinants. When these antibodies were used to stain sections of eyes at different stages of development, we found that the characteristic differential staining of some basement membranes was maintained throughout development, while the staining properties of others changed. This indicates that many of the ocular basement membranes may differ from one another in composition or conformation, and that at least some of them may undergo developmental changes. We also noticed a similarity in the pattern of fluorescence associated with the basement membranes of the limbal blood vessels and the corneal endothelium that is consistent with the hypothesis that the corneal endothelium is derived from the early periocular vascular endothelium. Our observations of developing corneas also revealed that the antigen recognized by the group 4 antibody may be produced by both the corneal epithelium and the stromal fibroblasts. The suitability of monoclonal antibodies for probing basement membrane heterogeneity is discussed.

Biosynthesis of basement membrane by parietal yolk sac cells

The biosynthesis of basement membrane (Reichert's membrane) by parietal yolk sac cells of the mouse embryo was studied using immunohistochemistry and autoradiography with the electron microscope. Fab' fragments of characterized antisera to either a mixture of type IV collagen and laminin, or to type IV collagen alone, were conjugated to horseradish peroxidase for the immunohistochemical study; radiolabeled proline, leucine, and glucosamine were utilized either in vivo or in isolated yolk sac membranes in vitro for autoradiography. Whereas neither of the two antisera employed localized in either the Golgi apparatus or in the cytosol, both localized in the rough endoplasmic reticulum (RER) and in the extracellular basement membrane. Furthermore, no evidence of passage of isotopically labeled precursors of basement membrane from the RER to the Golgi apparatus was observed. Consequently, it is concluded that the basement membrane precursors are synthesized in the RER of parietal yolk sac cells and neither traverse the Golgi apparatus nor diffuse across the cytosol of the cell in the process of secretion. By elimination, secretion must be via direct communications between RER and plasma membrane or via small vesicles observed in the cytosol between RER and plasma membrane. These data are not in accord with the concept of the universality of the Golgi apparatus in the biosynthesis of glycoprotein. Parietal yolk sac cells do not use the Golgi apparatus in the biosynthesis of basement membrane, but do use the Golgi apparatus for the biosynthesis of other proteins.

A quantitative study of lamina densa alterations in hamster cheek pouch carcinogenesis

Lesions produced by topical application of 0.5 per cent. DMBA to the hamster cheek pouch epithelium were classified as hyperplasia, dysplasia and carcinoma groups using strict histological criteria. Untreated epithelium served as a control. Tissue samples from five animals in each group were processed for electron microscopy and electron micrographs from the epithelial-connective tissue junction were obtained from 5 blocks per animal. The micrographs were subjected to stereological intersection counting to determine the relative surface (SSLD, BM) of lamina densa which was in normal relationship to the basal cell plasma membranes. Quantitative results indicated a progressive loss of lamina densa during carcinogenesis and this was accompanied by the extrusion of pseudopodia from the basal cells through the gaps. The pseudopodia were frequently related to peripheral cytoplasmic microfilaments. Quantitative data confirmed the progressive nature of this loss, with values for SSLD,BM being of the order of 98 per cent., 88 per cent., 76 per cent, and 42 per cent. for normal epithelium and for the hyperplastic, dysplastic and carcinomatous lesions respectively. The loss of lamina densa is discussed in relation to the specificity of the response and to the development of features indicative of motility in transforming cells.

Formation of basement membranes in the embryonic kidney: an immunohistological study

Specific antibodies to laminin, type IV collagen, basement-membrane proteoglycan, and fibronectin have been used in immunofluorescence microscopy to study the development of basement membranes of the embryonic kidney. Kidney tubules are known to form from the nephrogenic mesenchyme as a result of an inductive tissue interaction. This involves a change in the composition of the extracellular matrix. The undifferentiated mesenchyme expresses in the composition of the extracellular matrix. The undifferentiated mesenchyme expresses fibronectin but no detectable laminin, type IV collagen, or basement-membrane proteoglycan. During the inductive interaction, basement-membrane specific components (laminin, type IV collagen, basement membrane proteoglycan) become detectable in the induced area, whereas fibronectin is lost. While the differentiation to epithelial cells of the kidney requires an inductive interaction, the development of the vasculature seems to involve an ingrowth of cells which throughout development deposits basement-membrane specific components, as well as fibronectin. These cells form the endothelium and possibly also the mesangium of the glomerulus, and contribute to the formation of the glomerular basement membrane. An analysis of differentiation of the kidney mesenchyme in vitro in the absence of circulation supports these conclusions. Because a continuity with vasculature is required for glomerular endothelial cell differentiation, it is possible that these cells are derived from outside vasculature.

Immunolocalization of entactin, a sulfated basement membrane component, in rodent tissues, and comparison with GP-2 (laminin)

Entactin is a sulfated glycoprotein in the extracellular basement membrane like matrix produced by M1536-B3 cells, a mouse endodermal line derived from an embryonal carcinoma. It has a molecular weight of 158,000 and is chemically and immunologically distinguishable from GP-2 (laminin) and fibronectin. Antibodies produced against entactin and GP-2 react with subepithelial and vascular basement membranes in rat lung, liver, spleen, and kidney and mouse placenta and kidney when examined by light microscopy. Both antibodies yield staining around the marginal sinus of the white pulp of the spleen. Antientactin reacts with basement membrane and mesangium in rat glomeruli, and anti-GP2 does not. Ultrastructurally, staining in kidneys is strongest at epithelial or endothelial cell membranes bordering basement membranes, with only moderate staining of the basement membrane proper. Intracellular staining is not present. The location of entactin suggests that it has a role in the interaction of cells with extracellular matrix, possibly in adhesion. Lack of intracellular staining suggests that the tissues studied are not actively producing entactin or GP-2 and that these substances may be fairly stable in adult organisms.

Biosynthesis of the basal lamina as a result of interaction between thyroid and mesenchymal cells in culture

Porcine thyroid cells were cultured alone or in mixed cultures with mesenchymal cells. The formation of a basal lamina in vitro was investigated ultrastructurally. Follicular reassociation of thyroid cells occurred in both types of culture; however, it was followed by formation of the basal lamina only when mesenchymal cells were present. The present findings suggest an epithelial origin of the basal lamina resulting from an interaction with mesenchymal cells.

New findings of a lamina densa in relation to plasma cells

In an ultrastructural study of oral lesions in lichen planus, it was found that some plasma cells have an associated lamina densa. Subsequently, similar appearances have been found in pemphigus vulgaris, in the inflammatory cell infiltrates in dental granulomas and cysts and in a patient with Ehlers-Danlos syndrome. The lamina densa was mainly present adjacent to those parts of the membrane of the plasma cell that were invested with fibrillar connective tissue. The lamina was similar in thickness and electron density to that surrounding Schwann cells and endothelial cells. It is believed that lamina densa has not previously been reported in relation to plasma cells. It is of interest that in all other situations in which lamina densa has been described, the cells are considered to be part of the normal cell population of the tissue, whereas plasma cells are not regarded as part of the resident population of connective tissue.

Myoepithelial differentiation and basal lamina deposition in fibroadenoma and adenosis of the breast

Sixteen cases of breast fibroadenomas and 11 of adenosis were studied ultrastructurally; emphasis was placed on the patterns of myoepithelial differentiation and the number and appearance of the basal laminae. Ducts of both fibroadenomas and adenosis showed well differentiated, peripherally arranged myoepithelial elements with conspicuous cytoplasmic filaments and numerous hemidesmosomes; focal myoepithelial multilayering occurred. Myoepithelial cells exhibited complex, convoluted cytoplasmic processes extending into the stroma and resulting in the formation of pseudocysts containing stromal material. Basal lamina deposition was invariably found; basal lamina reduplication was extremely frequent. Basal lamina discontinuities with cytoplasmic processes extending directly into the stroma were seen in adenosis. Myoepithelial features and conspicuous basal lamina deposition indicate advanced differentiation and correlate well with the benign prognosis of these lesions. The focal basal lamina gaps in adenosis may be significant in the long-term evolution of this and similar dysplastic processes.

The basement membrane of the atrophic kidney tubule. An electron microscopic study of changes in rats

In a light and electron microscopic study of the rat's kidney after obstruction of the renal vein or after subtotal nephrectomy the tubular basement membrane changes occurring during the ensuing atrophy of the tubules have been examined. Characteristically, they consist of diffuse widening, focal thickening with vesicular and granular inclusions, circumscribed dissolution, or reduplication of this structure. These observations have led to the conclusion that the tubular basement membrane is formed by both interstitial and tubular cells, although the interstitial cells contribute the greater share to its formation, maintenance and renewal. The thickening of the basement membrane taking place in tubular atrophy must, however, be attributed entirely to the interstitial cells.

Ultrastructural basis of the vasculopathy in and around brain tuberculomas. Possible significance of altered basement membrane

The fine structure of small blood vessels in and around ten brain tuberculomas was examined. In the peripheral reactive zone of the tuberculomas, examination of 1-mu-thick survey sections established the chronic inflammatory process and the vasculitis characterized by infiltration of the vasomurium (vessel wall) by large and small mononuclear cells. This reaction was typical of chronic epithelioid cell granuloma. Electron microscopic examination of the reactive zone confirmed the vascular proliferation and vasculitis, the venule being the most frequently involved type of blood vessel. It showed the infiltrating cells to lie amidst osmiophilic, concentrically proliferated basement membrane laminae, which formed the greater part of the thickened vessel wall, generally surrounding the endothelial cells directly, the pericytes having disappeared. This appearance, together with the results of Gomori's reticulin stain on paraffin sections, suggested that the altered basement membrane material was reticulin. The possibility is discussed that the altered basement membrane material could be antigenic and that it might be responsible for perpetuating the necrotic vascular and perivascular reaction in tuberculous meningitis and tuberculomas. The above change in the basement membrane was not encountered in the blood vessels of the surrounding edematous brain. The endothelial cells and tight junctions were relatively well-preserved. Intact arterioles could be recognized even in severely edematous brain tissue. At both sites the fine structure of the blood vessels was typical of that expected in the central nervous system. Fenestrated vessels were not seen. The perivascular astrocytic end-feet were destroyed in the reactive zone and either distended or ruptured in the overtly edematous brain tissue also. In the central caseous part of the tuberculoma, there were few blood vessels, and they were in a state of advanced necrosis, but ghost outlines of proliferated basement membrane could be seen.

Studies on the fine structure of invertebrate blood vessels. II. The valves of the lateral sinus of the leech, Hirudo medicinalis L

The position, structure and function of the valves within the lateral sinus of the medical leech, Hirudo medicinalis, are described on the basis of vital, light- and electron microscopy. In this species the valvular apparatus consists of multiple elongated fir cone-shaped fibrous villi surrounding the orifices of the latero-lateral and latero-dorsal vessel like a tentacular crest. Each villus is covered by a thin sheet of a continuous endothelium. The valves prevent the backflow of hemolymph during systolic contraction of the lateral sinus. The endothelium contains many small mitochondria and polyribosomes in the perinuclear cytoplasm and it develops deep projections into the underlying connective tissue. Each of these consists of a multilayered system of closely interwoven thin endothelial membranes. The endothelium is anchored to its basement membrane by means of a great number of poorly defined hemidesmosomes. The fibrous tissue of the villi consists mainly of a homogeneous vitreous matrix in which few cellular components and very fine filaments are dispersed. Close to the endothelium this matrix appears to be condensed to form a multilayered framework made out of a basement membrane-like material. Though the valves themselves are devoid of muscle cells, those situated at their base and thus belonging to the vascular wall proper, display some specific morphological features: in particular the nuclei of these cells show a distinct fibrous lamina. Moreover, these muscle cells seem to be innervated only by one type of axon, containing both small, lucent synaptic vesicles as well as some of the dense-core variety. These findings are compared with data from earlier works and are discussed in relation to the hemodynamic functions of this valvular apparatus.

Squamous differentiation and basal lamina deposition in endometrial adenoacanthoma

Eleven endometrial adenoacenthomas were studied ultrastructurally. Special emphasis was placed on patterns of squamous metaplasia and the appearance of the basal laminae. Tonofibrils, irregular keratohyaline, abundant desmosomes, and foci of frank keratinization were observed. However, the granule population was small, with relatively scanty keratohyaline and no definite membrane coating granules. These features resemble squamous metaplasia observed in various epithelia; experimental models utilizing estrogens also resulted in similar changes. This observation appears pertinent in view of the possible etiologic role played by high estrogen levels in the development of human endometrial carcinoma. Most tumor cell clusters were surrounded by a well-defined basal lamina; focal basal lamina reduplication was also observed. These observations suggest a high level of differentiation in respect to synthetic capabilities and cell surface recognition. They correlate well with the relatively favorable prognosis generally observed in endometrial adenoacanthomas. However, these conclusions are tempered by the finding of occasionally absent or defective basal lamine, indicative of partial dedifferentiation of some neoplastic cells.

Comparative ultrastructure of tubular carcinoma and sclerosing adenosis of the breast

The innocuous histologic appearance of tubular carcinoma of the breast and its superficial histologic resemblance to sclerosing adenosis will occasionally present diagnostic problems. A comparative ultrastructural analysis of two tubular carcinomas and three cases of sclerosing adenosis was made that showed definite differences in the pattern of myoepithelial cell differentiation and basal lamina deposition in these two entities. Prominent myoepithelial cells and basal lamina reduplication were both conspicuous features of sclerosing adenosis that appeared to be absent in tubular carcinoma. Intracytoplasmic "pseudocysts" were frequently found in sclerosing adenosis, but not in tubular carcinoma. Conversely, intracytoplasmic lumina and incomplete tubular structures were present in tubular carcinoma and seemingly absent in sclerosing adenosis. Such basic ultrastructural differences may help to differentiate these two mammary lesions when diagnostic problems occur at the conventional light microscopic level.

Biosynthesis of glycosaminoglycans by mammalian corneal epithelium and fibroblasts in vitro. I. Isolation and fractionation-differences of GAG from the two cell types

Labeled glycosaminoglycans (GAG) were isolated and fractionated from cultured rabbit corneal epithelium, rabbit or bovine corneal fibroblasts and rabbit bone fibroblasts that had been previously incubated with either Na235SO4 or D-glucosamine-6-3H precursors. Thus it was demonstrated that the epithelium produces GAG. The fractionations indicated that the epithelial cells predominantly synthesize GAG with a lower degree of sulfation than those produced by corneal fibroblasts. The GAG-fractionation-patterns of the corneal epithelium and bone fibroblasts were similar.

Ultrastructure of anaplastic (spindle and giant cell) carcinoma of the thyroid

Three anaplastic (spindle and giant cell) carcinomas of the thyroid were studied by light and electron microscopy; two of the tumors also included foci of recognizable follicular carcinoma. The follicular carcinoma cells desplayed prominent mitochondria and rough endoplasmic reticulum, and showed evidence of secretory activity. Desmosomes and complex cellular interdigitations were evident. Basal laminae were present, with conspicuous reduplication in the well-differentiated foci. However, some epithelial clusters were surrounded by basal lamina, showing focal discontinuities through which epithelial cells protruded into the stroma. The pleomorphic spindle and giant cells showed cytoplasmic and nuclear characteristics similar to the better differentiated carcinomatous follicular elements, but showed rare desmosomes and no basal laminae. The basic ultrastructural similarity between follicular and anaplastic tumor cells confirms their common epithelial origin. However, while partially retaining their secretory capability, the anaplastic cells progressively lose their capacity to synthetize basal lamina and develop complex cellular attachments.

Intracellular localization of basement membrane antigen in parietal yolk sac cells

Basement membrane antigen was localized in murine parietal yolk sac cells using the peroxidase-labeled antibody technic. In these cells the antigen can be localized in the rough endoplasmic reticulum and perinuclear space. In spite of the proven ability of the antibody to permeate all cell compartments, the antigen was never localized within elements of the Golgi complex. These findings suggest that the rough endoplasmic reticulum of the parietal yolk sac cells is responsible for the synthesis of the antigenic portion of the basement membrane molecule. At the present time there is no evidence implicating the Golgi complex in the synthesis or intracellular transport of the antigenic portion of basement membrane.

Fine structure, origin and fate of extracellular materials in the interspace between the presumptive lens and presumptive retina of the chick embryo

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Vascular basement membrane changes in diabetic retinopathy. Montgomery lecture, 1973

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