Epithelial collagens and glycosaminoglycans in the embryonic cornea. Macromolecular order and morphogenesis in the basement membrane

Proteomic analysis of potential keratan sulfate, chondroitin sulfate A, and hyaluronic acid molecular interactions

PURPOSE

Corneal stroma extracellular matrix (ECM) glycosaminoglycans (GAGs) include keratan sulfate (KS), chondroitin sulfate A (CSA), and hyaluronic acid (HA). Embryonic corneal keratocytes and sensory nerve fibers grow and differentiate according to chemical cues they receive from the ECM. This study asked which of the proteins that may regulate keratocytes or corneal nerve growth cone immigration interact with corneal GAGs.

METHODS

Biotinylated KS (bKS), CSA (bCSA), and HA (bHA) were prepared and used in microarray protocols to assess their interactions with 8268 proteins and a custom microarray of 85 extracellular epitopes of nerve growth-related proteins. Surface plasmon resonance (SPR) was performed with bKS and SLIT2, and their ka, kd, and KD were determined.

RESULTS

Highly sulfated KS interacted with 217 microarray proteins, including 75 kinases, several membrane or secreted proteins, many cytoskeletal proteins, and many nerve function proteins. CSA interacted with 24 proteins, including 10 kinases and 2 cell surface proteins. HA interacted with 6 proteins, including several ECM-related structural proteins. Of 85 ECM nerve-related epitopes, KS bound 40 proteins, including SLIT, 2 ROBOs, 9 EPHs, 8 Ephrins (EFNs), 8 semaphorins (SEMAs), and 2 nerve growth factor receptors. CSA bound nine proteins, including ROBO2, 2 EPHs, 1 EFN, two SEMAs, and netrin 4. HA bound no ECM nerve-related epitopes. SPR confirmed that KS binds SLIT2 strongly. The KS core protein mimecan/osteoglycin bound 15 proteins.

CONCLUSIONS

Corneal stromal GAGs bind, and thus could alter the availability or conformation of, many proteins that may influence keratocyte and nerve growth cone behavior in the cornea.

Proteoglycans in basement membranes

Previous studies have shown that sulphated proteoglycans are integral components of basement membranes. We have used mouse parietal yolk sac cells as a model system for our studies. These cells produce several basement membrane components, including a heparan sulphate proteoglycan and a chondroitin sulphate proteoglycan. The structure of the heparan sulphate proteoglycan has been described previously. The chondroitin sulphate proteoglycan has an Mr of 200 000-300 000 and contains 10-20 chondroitin sulphate chains (Mr = 14 000-16 000), attached to a core protein that on polyacrylamide gel electrophoresis appears as a doublet (with Mr = 34 000 and 27 000). Further structural analysis suggests that the majority of the polysaccharide chains are clustered around one segment of the core protein. The polysaccharide chains carry sulphate residues predominantly attached to C-4 of the galactosamine unit. More than 60% of the uronic acid residues are of the glucuronic configuration, the rest being iduronic acid. The parietal yolk sac cells secrete about equal amounts of the two proteoglycans into the culture medium, whereas heparan sulphate proteoglycan is the predominant proteoglycan found in the extracellular matrix of these cells. This proteoglycan appears to be anchored in the matrix by interactions involving the core protein rather than the polysaccharide chains.

The epidermal basement membrane: structure, ontogeny and role in disease

Since many dermatological diseases affect the epidermal basement membrane zone (BMZ), there has been intense investigation into the role of epidermal BMZ constituents in various skin diseases, particularly subepidermal skin diseases. The epidermal BMZ consists of four major structural components--the basal cell plasma membrane, the lamina lucida, the lamina densa and the sublamina densa zone, which contains anchoring fibrils. The lamina lucida is composed of laminin, bullous pemphigoid antigen (a disease-specific glycoprotein identified by antibodies circulating in patients' sera), and other as yet poorly defined antigens which are identified by in vivo bound and circulating antibodies in the sera of patients with herpes gestationis, scarring pemphigoid and other conditions. The lamina densa consists of type IV collagen and KF-1 antigen (which is non-collagenous and is identified by a skin-specific monoclonal antibody). Knowledge of the structure and chemical composition of the BMZ is critical to an understanding of some of the genetic and immunologically mediated blistering skin diseases.

Biosynthesis and structure of the basement membrane proteoglycan containing heparan sulphate side-chains

Endothelial, epithelial and muscle cells produce a similar proteoglycan for deposition in basement membrane. This proteoglycan is initially synthesized as a low buoyant density proteoglycan containing 3-5 heparan sulphate side-chains (15,000-65,000 Mr each), along one half of a 400,000 Mr core protein. A portion of the population of these macromolecules is degraded to produce small high density proteoglycans containing a variable-sized core protein less than 100,000 in Mr. This biosynthetic and degradative process probably accounts for the variety of differently sized heparan sulphate proteoglycans that have been isolated from various basement membrane sources.

Cellular invasion of the chicken corneal stroma during development: regulation by multiple matrix metalloproteases and the lens

Avian corneal development requires cellular invasion into the acellular matrix of the primary stroma. Previous results show that this invasion is preceded by the removal of the fibril-associated type IX collagen, which possibly stabilizes matrices through interfibrillar cross-bridges secured by covalent crosslinks. In the present study, we provide evidence for the expression of three matrix metalloproteinases (MMPs) in early corneas, two of which act cooperatively to selectively remove type IX collagen in situ. In organ cultures, MMP inhibitors (either TIMP-2 or a synthetic inhibitor) resulted in arrested development, in which collagen IX persisted, and the stroma remained compact and acellular. We also show that blocking covalent crosslinking of collagen allows for cellular invasion to occur, even when the removal of type IX collagen is prevented. Thus, one factor regulating corneal invasion is the physical structure of the matrix, which can be modified by either selective proteolysis or reducing interfibrillar cross-bridges. We also detected another level of regulation of cellular invasion involving inhibition by the underlying lens. This block, which seems to influence invasive behavior independently of matrix modification, is a transient event that is released in ovo just before invasion proceeds.

The ultrastructure of periductal connective tissue and distinctive populations of collagen fibrils associated with ductal epithelia of exocrine glands

The ultrastructure of the connective tissue around the intraglandular ducts was observed in rat exocrine glands. Connective tissue with a dense population of collagen fibrils was found either around the ducts and blood vessels (perivasculoductal connective tissue; PVDCT) as in the lacrimal and salivary glands and liver, or solely surrounding the ducts (periductal connective tissue; PDCT) as in the exocrine pancreas, whereas the interlobular and intralobular interstitium of the glands-except for the liver-contained substantially fluid-filled spaces without collagen fibrils. The PVDCT and PDCT of these glands contained two populations of collagen fibrils-fibroblast-associated and epithelium-associated-although the development and density of these fibrils varied considerably in individual glands. Both populations of collagen fibrils were most developed in the lacrimal glands, in which the basal aspects of the ductal epithelium and the basement membrane showed considerable undulation associated with a distinctive peribasement membrane zone with amorphous matter and a small population of the fibrils. In the parotid and submandibular glands, both populations were distinct, though poorly developed. In the exocrine pancreas and hepatic Glisson's sheath, the two populations of collagen fibrils were moderately developed, and the basal aspects of the ductal epithelium were characterized by prominent invaginations in which the multilaminar basement membranes and the epithelium-associated collagen fibrils were frequently engulfed. These observations provide evidence that the two populations of collagen fibrils around the ducts are found universally in exocrine glands, and support the hypothesis of the collagen fibril-synthesizing and -secreting ability of ductal epithelial cells.

Repeated UVR exposures cause keratocyte resistance to apoptosis and hyaluronan accumulation in the rabbit cornea

PURPOSE

To evaluate hyaluronan (HA) production and level of apoptosis of corneal cells after repeated UVR exposures.

METHODS

Fifteen albino rabbit corneas were exposed to 310 nm UVR at a dose that causes biomicroscopically significant keratitis (0.47 J/cm2). Nine rabbits received a single dose of UVR. Six rabbits were irradiated 3 times at 7-day intervals. Rabbits exposed to the single dose of UVR, were sacrificed 24 hours, 7 and 14 days after irradiation. Rabbits exposed to the repeated doses of UVR, were sacrificed 24 hours and 14 days after the last irradiation. The corneal tissue specimens were processed for histological analysis using specific staining for HA, and the TdT-dUTP terminal nick-end labeling (TUNEL) assay.

RESULTS

Corneas exposed to a single UVR dose showed extensive positive TUNEL staining 24 hours after exposure. Almost all basal epithelial cells, keratocytes throughout the entire thickness of the stroma, and endothelial cells were TUNEL-positive. No HA was found 24 hours after exposure. Extracellular HA staining of high intensity was found at day 7 throughout the entire central stroma, except the anterior one-fourth. At day 14 only a faint HA staining was detected in the posterior stroma, close to Descemet's membrane. Corneas exposed to repeated UVR doses showed at 24 hours positive TUNEL staining only in epithelial cells and in very few stromal cells. The majority of stromal cells and endothelial cells were unaffected. At the same time HA staining of very high intensity was found both at 24 hours and day 14, and it was evenly distributed throughout the entire thickness of the stroma.

CONCLUSION

Repeated UVR exposures lead to increased production and accumulation of HA in the corneal stroma. The repopulated keratocytes are much more resistant to apoptosis than the native ones. HA accumulation may be a sign of long-term changes in the cornea.

Mutations in KERA, encoding keratocan, cause cornea plana

Specialized collagens and small leucine-rich proteoglycans (SLRPs) interact to produce the transparent corneal structure. In cornea plana, the forward convex curvature is flattened, leading to a decrease in refraction. A more severe, recessively inherited form (CNA2; MIM 217300) and a milder, dominantly inherited form (CNA1; MIM 121400) exist. CNA2 is a rare disorder with a worldwide distribution, but a high prevalence in the Finnish population. The gene mutated in CNA2 was assigned by linkage analysis to 12q (refs 4, 5), where there is a cluster of several SLRP genes. We cloned two additional SLRP genes highly expressed in cornea: KERA (encoding keratocan) in 12q and OGN (encoding osteoglycin) in 9q. Here we report mutations in KERA in 47 CNA2 patients: 46 Finnish patients are homozygous for a founder missense mutation, leading to the substitution of a highly conserved amino acid; and one American patient is homozygous for a mutation leading to a premature stop codon that truncates the KERA protein. Our data establish that mutations in KERA cause CNA2. CNA1 patients had no mutations in these proteoglycan genes.

Ultrastructural localisation and size distribution of collagen fibrils in Glisson's sheath of rat liver: implications for mechanical environment and possible producing cells

The ultrastructure and size distributions of collagen fibrils in Glisson's sheath were investigated in the rat liver to analyse the mechanical environment around the fibrils and their possible cells of origin. Glisson's sheath was found to contain 2 populations of collagen fibrils with different diameters and distinct localisations, namely fibroblast-associated and bile epithelium-associated. Fibroblast-associated collagen was composed of fibrils arranged in bundles and constituted the majority of the collagen in Glisson's sheath. Bile epithelium-associated collagen was represented by small dispersed groups of fibrils just beneath the basement membrane of the bile duct. The basement membrane of the bile duct was frequently reduplicated into a few or as many as 10 layers of laminae densae, with scattered collagen fibrils between these laminae. The diameters of the fibrils of both groups of collagen increased in relation to the calibre of the bile duct, whereas at any given place in Glisson's sheath bile epithelium-associated collagen fibrils had a smaller diameter compared with those of the fibroblast-associated fibrils. The increment in fibril diameter along the bile duct is considered to be correlated with the increase in mechanical stress acting on Glisson's sheath. The difference in diameter between the 2 populations as well as the incorporation of fibrils between the laminae densae of the basement membrane of the bile duct supports the view that the bile epithelium-associated collagen is produced by the epithelial cells of the bile duct, thus having a different origin from that of fibroblast-associated collagen. These findings provide the first evidence that the epithelial cells of the interlobular bile duct produce fibril-forming collagen. Furthermore, it is suggested that cholestasis stimulates the epithelial cells of interlobular bile duct to increased synthesis of fibril-forming collagen that is also produced by these cells under physiological conditions.

Collagen type IX and developmentally regulated swelling of the avian primary corneal stroma

A critical event in avian corneal development occurs when the acellular primary stroma swells and becomes populated by mesenchymal cells that migrate from the periphery. These cells then deposit the mature stromal matrix that exhibits the unique features necessary for corneal function. Our previous work correlated the disappearance of collagen type IX immunoreactivity at stage 27 (5 1/2-6 days) with matrix swelling and invasion. To investigate further the mechanism of this disappearance, we employed immunohistochemistry after tissue fixation with Histochoice, a non-crosslinking fixative, immunoblot analysis of protein extracts, and gel substrate chromatography (zymography) to detect endogenous proteolytic activity. We found that corneas fixed in Histochoice retain immunoreactivity for type IX collagen for 1-2 days after corneal swelling. This immunoreactivity, however, becomes extractable from tissue sections of unfixed corneas at the time of initiation of stromal swelling and mesenchymal cell invasion. Immunoblot analysis confirmed that, following swelling, immunoreactivity for collagen IX decreased substantially in corneas, but not in the vitreous body, which served as a comparison. Analysis of ammonium sulfate (AS) fractions of such extracts indicated that, at the time of swelling, much of the immunoreactivity for type IX collagen in cornea shifted from the AS precipitate (containing high molecular weight molecules) to the AS supernatant (containing smaller fragments). In contrast, collagen IX immunoreactivity from the vitreous was precipitated by ammonium sulfate throughout the period of study. Collagen type II, a major fibrillar collagen in both the corneal stroma and vitreous, remained in the high molecular weight fraction at all times examined. Zymography detected the presence of the latent (proenzyme) form of gelatinase A (MMP-2) before corneal swelling and invasion (4 days), and both the latent and active forms of the enzyme after corneal swelling. This suggests tissue-specific, developmentally regulated proteolysis of collagen IX as a trigger for corneal matrix swelling.

Hyaluronan in the exfoliation syndrome

PURPOSE

To histochemically analyze if the glycoseaminoglycan component of pseudoexfoliation material consists of hyaluronan.

METHODS

The hyaluronan binding region of cartilage proteoglycans was utilized in a staining specific for hyaluronan. The technique has been described and employed previously. Human donor eyes with and without the presence of visible pseudoexfoliations were analyzed.

RESULTS

Hyaluronan was found to coat the fibrillar exfoliation material on the lens, the zonules, the iris epithelium and the ciliary body. It was also found on a capsular bag following cataract surgery.

CONCLUSION

In the anterior chamber hyaluronan constitutes one part of the exfoliation material. Abnormal findings of hyaluronan could be found in the cornea.

Immunohistochemical localization of extracellular matrix components in human breast tumours with special reference to PG-M/versican

Immunohistochemical localization of the large proteoglycan, PG-M/versican, was studied in 36 breast tumours, including infiltrating ductal carcinomas, benign tumours and fibrocystic diseases. The relation between the proteoglycan and the other extracellular matrix components was also investigated. In the carcinoma tissues, the interstitial elements of the 'specific stroma', consisting of fibroblastic cells and fine fibrils, were reactive to antibody 2B1, which specifically recognizes the large proteoglycan, PG-M/versican. In the peripheral invasive areas of infiltrating ductal carcinoma, the most intense 2B1-positive reaction was visualized in mesenchymal tissues between carcinoma cells clumps and the surrounding tissues, where hyaluronic acid could be demonstrated histochemically. The 2B1-positive elements were not reactive to antibody 6B6, which specifically recognizes small proteoglycan. In the central sclerotic areas, where antibody 6B6 was reactive, a 2B1-positive reaction was detected only in elastosis masses, which also bound antibodies to type IV collagen and laminin, and to some extent antibody raised against chondroitin 6-sulphate proteoglycan. Elastic tissues of blood vessel walls and perivascular elements became reactive to antibody 2B1 when they were involved in carcinoma invasion. The present results have shown that PG-M/versican was localized in the proliferating interstitial tissues, in particular in hyaluronic acid-rich portions, in association with carcinoma cell growth, and also that PG-M/versican accumulated in vascular and perivascular elastic tissues involved in carcinoma invasion. The biological significance of PG-M/versican was briefly discussed.

The interstitial space of the thyroid gland of marmosets (Callithrix jacchus)

The interstitial space of the thyroid gland of adult marmosets contains, like the stroma of other organs, cells and intercellular substance (matrix), blood vessels (predominantly capillaries), lymph vessels and unmyelinated nerves. It is demarcated from the follicular epithelium, the capillaries and Schwann cells by a basal lamina (BL). The perifollicular BL shows thickenings of up to 3 microns over long distances or a multilayered arrangement. These thickened segments exhibit numerous epithelial processes and ridges; in other words, the contour of the basal cell membrane is very irregular in these areas. Indentations of capillaries into the epithelium are rarely observed. The endothelium is only slightly porous. Lymph capillaries occur in large numbers. They originate freely in the interstitial space, show gaps or unspecific contacts between the thin endothelial cells; a basal lamina is missing. Bundles of 10-nm thick filaments (anchor filaments) extend to the endothelial cells of the lymph capillaries. Thin and very long (up to 8 microns) plate-like processes surround the capillaries or run parallel to the outer contour of the follicles. They originate at the poles of oval, fibroblast-like cells. Since these cells are FXIII- and C3bi-positive, they can be considered as dendritic cells. They obviously play a role in the frequently-observed autoimmune diseases of this species. In addition, monocytes and all transitional forms including macrophages, fibrocytes and lymphocytes as well as numerous mast cells occur. In the region of the BL, integrins of the beta 1-group (alpha 6) can be demonstrated immunohistologically in addition to the usual components (collagen type IV, laminin and heparan sulfate-proteoglycan). Of the fibrillar collagens type I does not occur, type III occurs only in small amounts, whereas types V and VI are observed in large amounts. The presented findings may serve as basis for more extensive experiments on these primates.

Analysis of transcriptional isoforms of collagen types IX, II, and I in the developing avian cornea by competitive polymerase chain reaction

The genes for the alpha 1(IX), alpha 1(II), and alpha 2(I) collagen chains can give rise to different isoforms of mRNA, generated by alternative promotor usage [for alpha 1(IX) and alpha 2(I)] or alternative splicing [for alpha 1(II)]. In this study, we employed competitive reverse transcriptase PCR to quantitate the amounts of transcriptional isoforms for these genes in the embryonic avian cornea from its inception (about 3 1/2 days of development) to 11 days. In order to compare values at different time points, the results were normalized to those obtained for the "housekeeping" enzyme, glycerol-3-phosphate dehydrogenase (G3PDH). These values were compared to those obtained from other tissues (anterior optic cup and cartilage) that synthesize different combinations of the collagen isoforms. We found that, in the cornea, transcripts from the upstream promotor of alpha 1(IX) collagen (termed "long IX") were predominant at stage 18-20 (about 3 1/2 days), but then fell rapidly, and remained at a low level. By 5 days (just before stromal swelling) the major mRNA isoform of alpha 1(IX) was from the downstream promoter (termed "short IX"). The relative amount of transcript for the short form of type IX collagen rose to a peak at about 6 days of development, and then declined. Throughout this period, the predominant transcriptional isoform of the collagen type II gene was IIA (i.e., containing the alternatively spliced exon 2). This indicates that the molecules of type II collagen that are assembled into heterotypic fibrils with type I collagen possess, at least transiently, an amino-terminal globular domain similar to that found in collagen types I, III, and V. For type I, the "bone/tendon" mRNA isoform of the alpha 2(I) collagen gene was predominant; transcripts from the downstream promotor were at basal levels. In other tissues expressing collagen types IX and II, long IX was expressed predominantly with the IIA form in the anterior optic cup at stage 22/23; in 14 1/2 day cartilage, long IX was expressed predominantly along with the IIB form of alpha 1(II). The downstream transcript of the alpha 2(I) gene (Icart) was found at high levels only in cartilage.

Embryonic development of the cornea in the eye of the clearnose skate, Raja eglanteria: I. Stromal development in the absence of an endothelium

Embryos of the clearnose skate, Raja eglanteria, develop in sea water at 20-22 degrees C, hatching after 82 +/- 4 days (Luer and Gilbert, Environ. Biol. Fishes, 13:161-171, 1985). Eyes develop as steadily enlarging spheres whose corneas have the same radius of curvature as the sclera. The cornea begins development as a 2-cell thick epithelium beneath which by Day 12 there is only a basal lamina and a wispy matrix separating it from the underlying lens. This matrix, modified by Day 16, is displaced on Day 22 by a few orthogonal plies of fibrillar primary stroma. Ply number increases to at least 13 by Day 30, reaching the final number of 20 +/- 2 by Day 42. Stromal fibroblasts (keratocytes) appear at the corneal periphery by Day 22, and in increased numbers by Day 30, a time at which no keratocytes are seen in the central stroma. However, by Day 40, many fibroblasts are present at the corneal periphery, invading the primary stroma between plies, occasionally reaching even the central cornea. By Day 53, keratocytes are present between all plies, from corneal periphery to center. Thickness of each ply in this secondary stroma increases, but the number of plies remains the same as in the primary stroma. Bowman's layer, non-invaded matrix beneath the epithelial basal lamina, is not evident until Day 53. Sutural fibers, first seen on Day 22, originate in the corneal epithelial basal lamina, traversing perpendicularly the plies of the primary stroma. Sutural fibers persist throughout development of the secondary stroma and into adulthood. In contrast to chicks, skate corneas remain transparent throughout development, and never form an endothelium.

Morphology of the basement membrane

The aim of this contribution is to summarize our knowledge of the morphology of the basement membrane (BM). The first step in this direction is the attempt to define this term. The BM is composed of the Lamina lucida, densa, and fibroreticularis. Subsequently, the historical development of this term is discussed. Our main interest is, of course, focused on the description of the BM-structure up to the macromolecular level and the special forms of this structure. This is supplemented by discussing its chemical composition and establishing a relationship between morphology and biochemistry. The obtained findings yielded some indications as to the molecular composition of the BM which may serve for the construction of "models." The composition of the Lamina lucida (L.l.) and the Lamina or Pars fibroreticularis (L.f.) must be discussed separately, since, if present, they show a different and strongly varying structure (L.f.). An important aspect is the function of this extracellular layer which comprises mechanical tasks up to inductive effects. Finally, the concepts of the formation of the BM, especially of the Lamina densa (L.d.), are summarized. It obviously consists of a sequence of individual steps which starts with expression and secretion of the L.d.-components and is followed by an induction of integrin expression.

The basement membranes of cryofixed or aldehyde-fixed, freeze-substituted tissues are composed of a lamina densa and do not contain a lamina lucida

When tissues are processed for electron microscopy by conventional methods, such as glutaraldehyde fixation followed by rapid dehydration in acetone, basement membranes show two main layers: the electron-lucent "lamina lucida". (or rara) and the electron-dense "lamina densa". In an attempt to determine whether this subdivision is real or artefactual, two approaches have been used. Firstly, rat and mouse seminiferous tubules, mouse epididymis and associated tissues, and anterior parts of mouse eyes were subjected to cryofixation by instant freezing followed by freeze substitution in a -80 degrees C solution of osmium tetroxide in dry acetone, which was gradually warmed to room temperature over a 3-day period. The results indicate that, in areas devoid of ice crystals, basement membranes consist of a lamina densa in direct contact with the plasmalemma of the associated cells without an intervening lamina lucida. Secondly, a series of tissues from mice perfused with 3% glutaraldehyde were cryoprotected in 30% glycerol, frozen in Freon 22 and subjected to a 3-day freeze substitution in osmium tetroxide-acetone as above. Under these conditions, no lamina lucida accompanies the lamina densa in the basement membranes of the majority of tissues, including kidney, thyroid gland, smooth and skeletal muscle, ciliary body, seminiferous tubules, epididymis and capillary endothelium. Thus, even though these tissues have been fixed in glutaraldehyde, no lamina lucida appears when they are slowly dehydrated by freeze substitution. It is concluded that the occurrence of this lamina in conventionally processed tissues is not due to fixation but to the rapid dehydration. However, in this series of experiments, the basement membranes of trachea and plantar epidermis include a lamina lucida along their entire length, while those of esophagus and vas deferens may or may not include a lamina lucida. To find out if the lamina lucida appearing under these conditions is a real structure or an artefact, the trachea and epidermis were fixed in paraformaldehyde and slowly dehydrated by freeze substitution. Under these conditions, no lamina lucida was found. Since this result is the same as observed in other tissues by the previous approaches, it is proposed that the lamina lucida is an artefact in these as in the other investigated basement membranes. Thus, basement membranes are simply composed of a lamina densa that closely follows the plasmalemma of the associated cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytochemical localisation and characterisation of proteoglycans (glycosaminoglycans) in the epithelial-stromal interface of the seminal vesicle of the guinea pig

The proteoglycans (PGs) in the guinea pig seminal vesicle were demonstrated ultrastructurally by both cuprolinic blue (CB) and ruthenium red (RR) staining. The PGs appeared as electron-dense granules with RR, but were filamentous following CB staining using the critical electrolyte concentration method. Three major types of PGs (T1, T2, T3) have been described according to their different locations and sizes. T1 filaments were short and were found mostly on both sides of the lamina densa of the basal lamina of the glandular epithelium (40-60 nm long) and also on the basal laminae of smooth muscle cells and capillary endothelial cells (20-30 nm long). In the epithelial basal lamina they were regularly spaced at an interval of 40-60 nm. T1 filaments in the lamina densa were smaller and more randomly distributed. Cytochemical characterisation of these PGs by various GAG degrading enzymes showed that T1 PGs are rich in heparan sulphate. T2 filaments were 30-40 nm long and closely associated with the collagen fibrils. They were arranged perpendicular to the long axis of collagen fibrils, also at intervals of about 60 nm. T2 filaments were removed by chondroitinase (Ch)-ABC, Ch-ABC plus Streptomyces (S)-hyaluronidase and pronase, but resistant to nitrous acid, heparitinase, heparinase, neuraminidase and S-hyaluronidase. These show that T2 filaments are rich in dermatan sulphate. T3 filaments (60-100 nm) were widely distributed in the stroma at sites such as the interstitial spaces of the lamina propria, the reticular layer below the basal lamina, around individual collagen fibrils or bundles of such fibres, and on the cell surfaces of fibroblasts. The T3 filaments were removed by Ch-ABC, Ch-AC and pronase but were resistant to heparitinase, heparinase, S-hyaluronidase, neuraminidase and nitrous acid. They are therefore rich in chondroitin sulphate.

Age-dependent disruption of basal lamina and extracellular matrix formation in L-proline analog treated otic explants

L-azetidine-2-carboxylic acid, LACA, a naturally occurring vegetable imino acid, can be incorporated into mammal proteins instead of proline. This incorporation has an especially inhibitive effect on collagen secretion. Exposure of embryonic mouse inner ear explants to LACA causes dysmorphogenesis and retarded differentiation, reduces the number of collagen fibrils in the perilymphatic spaces and capsules, and gives rise to a dose-dependent derangement of the basal lamina. In control specimens, both in vivo and in vitro, the inner ear epithelia had a dense contiguous basal lamina overlying a well-developed network of collagen fibrils. When the inner ears were exposed to LACA at a concentration of 150 micrograms per ml of medium, there was a loss of the collagen network and gaps appeared in the basal lamina. At exposure to 300 micrograms LACA/ml, scarcely any collagen fibrils were present and the basal lamina was disrupted in many areas, especially beneath the sensory epithelia.

Immunohistochemical characterisation of extracellular matrix components of salivary gland tumours

Proteoglycans (PGs) were localised immunohistochemically in 52 salivary gland tumours including pleomorphic adenoma, adenoid cystic carcinoma, acinic cell carcinoma, oncocytoma, mucoepidermoid carcinoma, clear cell tumour and Warthin tumour, using antibodies raised against large PG, small PG, chondroitin 4-sulphate PG, chondroitin 6-sulphate PG, heparan sulphate PG and keratan sulphate PG. Large PGs were mainly observed in mucinous materials of extracellular matrix (ECM) and interstitial fibrous element of tumour tissues, while small PGs were located only in hyaline matrix and surrounding fibrous (capsular) connective tissues. Chondroitin 6-sulphate PG was detected in the ECM of pleomorphic adenomas and clear cell carcinomas and in pseudocystic spaces of adenoid cystic carcinomas, but only in vessel walls in non-neoplastic tissues. Keratan sulphate PG was observed to locate in mucinous material of pleomorphic adenomas, acinic cell carcinomas and clear cell carcinomas, but not in the adenoid cystic carcinomas examined, and it was also unobservable in non-neoplastic salivary gland tissues. Heparan sulphate PG was observed on the inner surfaces of true ductal spaces of adenoid cystic carcinomas and on cell surfaces of oncocytoma cells. By HPLC analysis, individual glycosaminoglycans contained in tumour tissues were compared. Chondroitin 6-sulphate PG was very rich in ECM of pleomorphic adenomas and adenoid cystic carcinomas. Pleomorphic adenomas contained relatively more low-sulphated chondroitin sulphate than adenoid cystic carcinomas and other tumours.

Effect of puromycin on metanephric differentiation: morphological, autoradiographic and biochemical studies

Effect of aminonucleoside of puromycin (PAN) on metanephric development and proteoglycans (PGs) was investigated. Murine metanephric tissues, obtained on the thirteenth day of gestation, were exposed to PAN in a culture medium for one to seven days and processed for morphological, histochemical and immunofluorescent studies. For tissue autoradiographic and biochemical studies, kidneys were labelled with a precursor product of PGs, that is, [35S]-sulfate. A generalized decrease in the glomerular population along with swelling and deformation in the ureteric bud branches was observed. These changes were accompanied with a diminution in the total incorporated radioactivity and a reduction in the autoradiographic grains, especially over the tips of ureteric bud branches. Sepharose CL-4B chromatography revealed a major high molecular weight PG (Mr greater than 2.5 x 10(6], and a relative increase in the chondroitinase-ABC sensitive PGs. The media PGs were of relatively smaller size. Immunoprecipitation experiments with [35S]-methionine-labeled tissues and immunofluorescent studies revealed a significant decrease of PGs in metanephric tissues, while type IV collagen and laminin were relatively unaffected. Significant glomerular changes included failure in differentiation of the visceral epithelial foot processes, formation of villi and in maturation of glomerular basement membrane. The latter was seen as fragments of extracellular matrices interspersed among undifferentiated podocytes and had reduced staining with ruthenium red--a dye marker for the PGs. This deficiency of PGs was confirmed by electron microscopic autoradiography, where a reduction in the number of silver grains was observed. The fact that the PAN-induced cellular and extracellular alterations were associated with perturbances in biosynthesis of PGs, suggests that the morphogenetic regulators, that is, PGs play a vital role in various differentiation processes involved during metanephric development.

Stromal assemblies containing collagen types IV and VI and fibronectin in the developing embryonic avian cornea

The morphogenesis of type IV collagen-containing structures in the stromal matrix of the developing avian cornea was investigated using immunofluorescence and immunoelectron microscopic histochemistry. Two forms of type IV collagen-containing structures were seen; these differed in their probable origin, structure, molecular composition, and developmental fate. The major form of stromal type IV collagen-containing material, termed "strings," was observed only after swelling of the primary stroma and the onset of mesenchymal invasion. These strings are presumed to be products of the stromal cells. In immunofluorescence histochemistry they appeared as linear segments of type IV collagen-specific immunoreactivity. In immunoelectron microscopy, they appeared initially as electron-dense sausages of variable length and orientation. They frequently were associated with cell surfaces and, in fortuitous sections, appeared to connect adjacent cells. The strings also contained type VI collagen and fibronectin, but very little, if any, of the basement membrane components laminin and heparin sulfate proteoglycan (HSPG). As the stroma continued to expand in thickness, more of these structures were observed in a radial orientation, becoming quite long and less tortuous. Later in development, as stromal condensation proceeded, they disappeared. We suggest that the strings function to stabilize the stromal matrix, and perhaps to limit the rate and/or extent of stromal expansion, during a phase of rapid swelling and matrix deposition. The other form of type IV collagen-containing stromal material appeared as irregularly shaped plaques of basement membrane-like material identical to those previously described in mature corneas. These are likely derived from the corneal endothelial cells. They contained other basement membrane-associated components (laminin, HSPG) and fibronectin, but not type VI collagen. This material persists in mature corneas as sparse irregular stromal plaques and as matrix in the interface between Descemet's membrane and the corneal stroma.

Histologic, morphometric, and immunocytochemical analysis of myometrial development in rats and mice: I. Normal development

Myometrial development from the prenatal to adult period was examined in rats and mice 1) by histologic and immunocytochemical methods with anti-actin, -vimentin, and -laminin to assess cytodifferentiation of smooth muscle and fibroblastic cells; and 2) by morphometric procedures to assess quantitatively the expression of cellular orientation in the emerging inner circular myometrial layer. Uterine mesenchymal cells initially were uniformly vimentin-positive, undifferentiated, and randomly oriented during the late fetal period. By the early neonatal period, three mesenchymal layers became recognizable histologically, the middle one of which (prospective circular myometrium) developed distinct circular orientation and differentiated into a layer composed of actin-positive smooth muscle cells. The cells of the inner mesenchymal layer initially exhibited radial orientation. By 10 days postpartum, the outer longitudinal mesenchymal layer differentiated into bundles of smooth muscle cells representing the longitudinal myometrium. The inner mesenchymal layer remained vimentin-positive and differentiated into the randomly ordered endometrial stroma. The cells of the middle and outer mesenchymal layers that were destined to form myometrium initially expressed vimentin throughout and then coexpressed vimentin and actin, but with time vimentin staining disappeared in the maturing smooth muscle cells as they expressed actin.

Stimulation of glycosaminoglycan synthesis in cultured human dermal fibroblasts by interleukin 1. Induction of hyaluronic acid synthesis by natural and recombinant interleukin 1s and synthetic interleukin 1 beta peptide 163-171

Hyaluronic acid (HA) is believed to play a critical role in wound healing and in morphogenesis. Factors controlling the production of HA by fibroblasts in normal and pathological states are not completely understood. In this report we have observed that natural human interleukin (IL-1)1 beta and human recombinant (hrIL)-1 alpha and beta are potent stimulators of HA production by fibroblasts in vitro. Hyaluronic acid is the major species of glycosaminoglycan (GAG) stimulated by IL-1 in fibroblasts. PGE2 does not appear to be involved directly in this IL-1 effect on fibroblasts, but stimulation of HA production by IL-1 is dependent on protein synthesis. The synthetic human IL-1 beta peptide 163-171 (Val-Gln-Gly-Glu-Glu-Ser-Asn-Asp-Lys), which has been previously shown to stimulate thymocyte proliferation but not fibroblast PGE2 production, is also able to stimulate fibroblast HA production. The synthesis and secretion of IL-1 by mononuclear phagocytes at sites of inflammation and immune reactions in vivo could potentially serve as a signal for fibroblasts to synthesize HA, which in turn could serve to facilitate and modulate reparative and immune processes by virtue of its ability to alter cell-cell, cell matrix, and cell-membrane receptor interactions.

Establishment of a cell line producing basement membrane components from an adenoid cystic carcinoma of the human salivary gland

A new cell line has been established from an adenoid cystic carcinoma arising in the submandibular gland of a 63-year-old woman. The cultured epithelial-like cells grew vigorously and adhered together to form a sheet. Immunohistochemical stainings for type IV collagen, laminin and fibronectin were clearly positive in the intercellular matrix and on the surface of the culture cells. Chondroitin 6-sulfate proteoglycan and heparan sulfate were also detected. Ultrastructural studies showed that the cells had abundant rough endoplasmic reticulum and a well-developed Golgi apparatus. Rough endoplasmic reticulum near the cell surface was markedly dilated, and contained material of low electron density. This cell line would be useful for biological and biochemical studies on the mechanisms by which the stromal component is formed.

beta-Xyloside effects on basal lamina structure and anionic site distribution the embryonic mouse submandibular salivary gland

beta-D-Xyloside is a proteoglycan biosynthesis inhibitor. Previous studies on embryonic salivary glands have demonstrated that 0.5 mM beta-xyloside (1) inhibits proteoglycan synthesis by 50%; (2) severely depresses sulphated glycosaminoglycan deposition at the basal epithelial surface, and (3) dramatically inhibits epithelial branching morphogenesis. Electron microscopy revealed a conventional three-layered basal lamina that is altered in the presence of beta-xyloside by a 35% reduction in the number of tannic acid-resolved particles in the lamina densa. Basal lamina anionic sites, resolved with ruthenium red (RR) and polyethyleneimine (PEI) cationic probes, were also reduced in the presence of beta-xyloside. PEI particles were reduced by 28%, and RR particles by 24%, per two-dimensional unit of basal lamina. These beta-xyloside effects on anionic sites are consistent with an hypothesis that sulphated glycosaminoglycans account for 50% of the basal lamina anionic sites and a predicted 25% decrease in anionic sites in the presence of beta-xyloside.

Collagen secretion granules in reactive stromal myofibroblasts, with preliminary observations on their occurrence in spindle cell tumours

Collagen secretion granules, representing stages in the intracellular packaging, transport and secretion of collagen-fibril precursor, have been studied by transmission electron microscopy in non-neoplastic human myofibroblasts and in neoplastic cells from a preliminary study of tumours exclusively or partly of spindle cell type. Vesicles, newly separated from Golgi saccules and containing finely fibrillar material, were identified as early presecretory granules, the most immature type of granule. Later stages exhibited longitudinally arranged, densely fibrillar bundles. Subsequently, secretory granules developed more homogeneously dense content. Fibril-containing cisternae near the plasma membrane were interpreted as either endocytotic or lysosomal structures, or as participants in the final stages of secretion. The features by which collagen secretion granules can be distinguished from other Golgi products, in particular melanosomes. Weibel-Palade bodies and lysosomes, are pointed out. The significance of these organelles for cell identification and tumour diagnosis is discussed.

Role of proteoglycans in renal development

The role of proteoglycans (PGs) in morphogenesis was investigated. Fetal kidneys were obtained from 13-day-old mouse embryos and maintained for 7 days in culture. The biosynthesis of PGs was perturbed by addition of p-nitrophenyl-beta-D-xylopyranoside in the culture medium. The kidneys were processed for morphological and biochemical studies. The morphological studies included staining of tissues with anti-basement membrane antibodies and ruthenium red. [35S]sulfate was used as the precursor product for biosynthetic and autoradiographic studies. The kidneys treated with xyloside had loose mesenchyme, inhibition of ureteric bud branching, diminution in the population of developing nephron elements, decreased immunofluorescence with anti-proteoglycan antibodies and staining with ruthenium red, and a reduced [35S]sulfate incorporation into poorly organized extracellular matrices. The biochemical studies included characterization of PGs/glycosaminoglycans (GAGs) by Sepharose CL-4B, -6B, and DEAE-Sephacel chromatographies and cellulose acetate electrophoresis. Under the influence of xyloside, the total radioactivities decreased 2 to 4-fold in tissues and increased 18 to 42-fold in media fractions. A reduction in the size of macromolecular form of PGs, i.e., from MW approximately 2.5 X 10(6) to approximately 2.5 X 10(4), was noted. The PGs/GAGs synthesized were mainly made up of heparan sulfate and small amounts of chondroitin sulfate. They eluted at a lower salt concentration as compared to the controls. A similar diminution in the size of media PGs, i.e., from MW approximately 1.8 X 10(5) to approximately 2.8 X 10(4), was observed. Additional studies with [3H]xyloside indicated that the chains initiated on xyloside residues were similar in size and composition to GAG-chains. These findings indicate that a perturbance in the biosynthesis of PGs/GAGs leads to abnormalities in renal organogenesis.

Sulfated glycosaminoglycans modify growth factor-induced neurite outgrowth in PC12 cells

Glycosaminoglycans (GAGs), localized on the surfaces of cells and in the basement membrane, modulate the growth and differentiation of many cell types. Recent studies have shown that heparin, a GAG found in mast cells, potentiates the ability of acidic fibroblast growth factor (aFGF) to induce neurite outgrowth in pheochromocytoma (PC12) cells. We examined the effect of a variety of GAGs on aFGF, basic fibroblast growth factor (bFGF), and nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells. The effects observed were dependent upon the specific GAG, the concentration of the GAG, and the growth factor. Heparin potentiated aFGF-induced neurite outgrowth in a concentration-dependent fashion; potentiation increased with increasing heparin concentrations of 0.01-100 micrograms/ml. At concentrations greater than 100 micrograms/ml, heparin potentiation decreased. The maximally active concentration of heparin (100 micrograms/ml) increased the potency of aFGF 102-fold. Increasing concentrations of heparan sulfate, dermatan sulfate, and chondroitin sulfate correlated with increasing aFGF potentiation. The maximally active concentrations of heparan sulfate (100 micrograms/ml), dermatan sulfate (10 mg/ml), and chondroitin sulfate (1 mg/ml) increased the activity of aFGF 11-, 110-, and 11-fold, respectively. Hyaluronic acid did not affect the neurite outgrowth-promoting activity of aFGF. Heparin also altered the activity of bFGF; increasing concentrations of heparin (0.01-1 micrograms/ml) correlated with increased potentiation. At concentrations greater than 1 microgram/ml, heparin concentration was inversely correlated with potentiation. Chondroitin sulfate only increased the percentage of neurite-bearing cells at concentrations greater than 10 micrograms/ml. Maximally active concentrations of heparin (1 microgram/ml) and chondroitin sulfate (1 mg/ml) increased the potency of bFGF 5-fold. The highest concentration of heparan sulfate studied (1 mg/ml) inhibited the activity of bFGF. Dermatan sulfate and hyaluronic acid (0.01-1000 micrograms/ml) had no effect on bFGF activity. Heparan sulfate and chondroitin sulfate showed concentration-dependent potentiation of NGF; maximally active concentrations of heparan sulfate (100 micrograms/ml) and chondroitin sulfate (1 mg/ml) increased the potency of NGF 3-fold, whereas heparin, dermatan sulfate and hyaluronic acid had no effect. None of the GAGs had any effect on PC12 neurite outgrowth when added alone. The specificity of the activity of the GAGs was verified by selective enzyme degradation.(ABSTRACT TRUNCATED AT 400 WORDS)

Visualization of the large heparan sulfate proteoglycan from basement membrane

Kleinschmidt spreading, negative staining, and rotary shadowing were used to examine the large form of (basement membrane) heparan sulfate proteoglycan in the electron microscope. Heparan sulfate proteoglycan was visualized as consisting of two parts: the core protein and, emerging from one end of the core protein, the glycosaminoglycan side chains. The core protein usually appeared as an S-shaped rod with about six globules along its length. Similar characteristics were observed in preparations of core protein in which the side chains had been removed by heparitinase treatment ("400-kDa core") as well as in a 200-kDa trypsin fragment ("P200") derived from one end of the core protein. The core protein was sensitive to lyophilization and apparently also to the method of examination, being condensed following Kleinschmidt spreading (length means = 52 nm) and extended following negative staining (length means = 83 nm) or rotary shadowing (length means = 87 nm; 400-kDa core length means = 80 nm; P200 length means = 44 nm). Two or three glycosaminoglycan side chains (length means = 146 +/- 53 nm) were attached to one end of the core protein. The side chains often appeared tangled or to merge together as one. Thus, the large heparan sulfate proteoglycan from basement membrane is an asymmetrical molecule with a core protein containing globular domains and terminally attached side chains. This structure is in keeping with that previously predicted by enzymatic digestions and with the proposed orientation in basement membranes, i.e., the core protein bound in the lamina densa and the heparan sulfate side chains in the lamina lucida arranged along the surface of the basement membranes.

Glomerular basement membrane proteoglycans are derived from a large precursor

The basement membrane heparan sulfate proteoglycan produced by the Englebreth-Holm-Swarm (EHS) tumor and by glomeruli were compared by immunological methods. Antibodies to the EHS proteoglycan immunoprecipitated a single precursor protein (Mr = 400,000) from [35S]methionine-pulsed glomeruli, the same size produced by EHS cells. These antibodies detected both heparan sulfate proteoglycans and glycoproteins in extracts of unlabeled glomeruli and glomerular basement membrane. The proteoglycans contained core proteins of varying size (Mr = 150,000 to 400,000) with a Mr = 250,000 species being predominant. The glycoproteins are fragments of the core protein which lack heparan sulfate side chains. Antibodies to glomerular basement membrane proteoglycan immunoprecipitated the precursor protein (Mr = 400,000) synthesized by EHS cells and also reacted with most of the proteolytic fragments of the EHS proteoglycan. This antibody did not, however, react with the P44 fragment, a peptide situated at one end of the EHS proteoglycan core protein. These data suggest that the glomerular basement membrane proteoglycan is synthesized from a large precursor protein which undergoes specific proteolytic processing.

Developmental changes in the extracellular matrix of the dental follicle during tooth eruption

Eruption of the third and fourth mandibular premolars in the dog begins at 15 weeks of age, is dependent upon the dental follicle, and is complete by 23 weeks. Our study covered the period from 12 to 20 weeks, and revealed several changes in extracellular matrix structure and organization of the follicle which correlate with specific physiological events in eruption. First, the average DNA content per follicle reached a maximum at 14 weeks. Two weeks later, follicle size had increased 1.3- to 2.4- times. Second, the collagen content of follicles increased 2.5-fold over the study period, with two-thirds of this increase over the last four weeks. Type I collagen was the major collagen at all stages of follicular development. The amount of proteoglycan rose 45% from 16 to 20 weeks of age. Third, the ultrastructure of the dental follicle prior to eruption (12 weeks) indicated a disorganized interstitial connective tissue matrix; during eruption, two size classes of fibrils were observed which clustered together in linearly aligned bundles. Fourth, gel electrophoretic analyses resolved more than twenty follicle proteins with the major species a Mr = 95k glycoprotein. Immunoblotting demonstrated only one minor component was derived from serum. Comparison of noncollagenous proteins from different aged follicles indicated that three small polypeptides (Mr = 20-25 k) were present primarily at 16 weeks, the same time at which root elongation begins. A different sequence of changes was exhibited by two other proteins of Mr = 13 and 15 k. These findings may serve as biochemical markers of stages of dental follicle development and facilitate a search for local control mechanisms.

The role of lysyl oxidase and collagen crosslinking during sea urchin development

Lysyl oxidase, the only enzyme involved in collagen crosslinking, is shown to be present in embryos of the sea urchin Strongylocentrotus purpuratus. The enzyme specific activity increases over six-fold during development, showing the greatest rise during gastrulation and prism larva formation. The enzyme is inhibited by the specific inhibitor, beta-aminoproprionitrile (BAPN). Continuous BAPN treatment of S. purpuratus and Lytechinus pictus embryos from late cleavage stages onward increases the amount of noncrosslinked collagen present in prism larvae. When BAPN is added at the 128- or 256-cell stage it causes developmental arrest at the mesenchyme blastula stage. Embryos can be maintained in the arrested state for at least 96 h and will resume normal development and morphogenesis following BAPN removal. If BAPN is added after the mesenchyme blastula stage, it has little adverse effect on development; consequently nonspecific toxic effects of the drug are unlikely. The results suggest that lysyl oxidase and collagen crosslinking play a vital role in primary mesenchyme migration, gastrulation, and morphogenesis during sea urchin development and indicate that BAPN may be very useful in studying the extracellular matrix-cell interactions at the cellular and molecular level.

Development of the electromotor system in Torpedo marmorata: cationic staining of the electric organ

The electric organs of embryonic Torpedo marmorata have been reacted with three cationic stains to evaluate the appearance and distribution of anionic sites. Ruthenium red, alcian blue and lysozyme were used at different pHs and found to react in a time-related manner to anionic components within the interelectrocyte space. The basal lamina covering the ventral electrocyte surface possesses the greatest number of anionic sites whereas growth cone, presynaptic terminal and glial membranes displayed almost no staining. Since this lamina serves as the exclusive substrate for ingrowing neurites during synaptogenesis, the results are consistent with the idea that charge distribution on the membrane surface may provide a necessary cue for neurite motility, extension and eventual synaptogenesis.

A new concept of basal cell epitheliomas based on the three-dimensional growth pattern of the superficial multicentric type

Little is known about the growth characteristics of basal cell epitheliomas (BCEs), largely because of the difficulty in studying these tumors, both in situ and in vitro. In this study, the authors report that a scanning electron microscopic examination of 2 cases of superficial BCEs reveals that the tumor proliferates centrifugally as a monolayer beneath the epidermis as well as over the surfaces of hair follicles, while eroding and replacing the original basal architecture. Behind the leading edge of this monolayer, the cells split away from the epidermis to form a round border resembling a carpet being rolled up. This border then develops into a mass lesion, which represents the tumor cell foci seen in routine paraffin sections. These findings have led the authors to propose a fundamentally different explanation for the pathogenesis of these tumors: BCEs are conditioned neoplasms that require contact with the epidermal or hair follicular epithelium in order to grow. This hypothesis could explain the behavior of BCEs as well as the clinical and pathologic varieties observed in clinical practice.

Potential study of basement membrane

The membrane potential of a basement membrane (bovine-anterior-lens-capsule) was studied by use of the Gibbs-Donnan systems. The T.M.S. (Teorell, Meyer, Sievers) theory was applied to these systems for the treatment of experimental data. The results show that, in the basement membrane, the density of fixed charges such as ionogenic groups encountered in heparan sulfate proteoglycan is low. The ratios of the mobilities from the chloride anion and the alkaline cation are different to those in water. In this type of membrane, the mobility of Cl- is higher than the mobilities of K+, Na+ and Ca2+. This result leads us to investigate further the diffusion problem of electrolytes through basement membrane.

Eye development in the normal and Pupoid foetus (pf/pf) mutant mouse

Embryonic development of the mammalian eye has not been studied in such great detail as that of the avian eye, and preliminary observations have suggested that the sequence of events may differ. It is therefore likely that the relative importance of the cell and tissue interactions involved also differs and it would be interesting to compare these two systems. The pupoid foetus mutation in the mouse shows disruption of eye development due to abnormal epidermal properties and so the relative importance of individual events in triggering subsequent development can be studied by seeing what happens when the situation is modified in the mutant. The behaviour of the pupoid foetus epidermal cells in the interactive system of the eye may also help to further characterise the phenotype of the mutation.

Cytochemistry of the gas-exchange area in vertebrate lungs

Considerable progress has been made in the localization of chemical substances within the gas-exchange zones of vertebrate lungs since cytochemical techniques suitable for use with the electron microscope have been developed. The light microscope, an instrument with an effective resolution limit of about 0.2 micron, is ill-suited for studying regions such as these where small tissue elements are arranged in a complex manner. A wide range of acid hydrolases have been detected in the vacuoles and dense bodies of alveolar macrophages by means of cytochemical techniques. The enzymes demonstrated in this way include acid phosphatase, aryl sulphatase, cathepsin D, beta-glucuronidase, acetyl glucosaminidase, nonspecific esterase, dipeptidyl peptidase II and dipeptidyl peptidase IV. Such enzymes are, of course, to be expected in the lysosomes of cells which have a primary phagocytic role. Nevertheless, it must be confessed that very little is yet known about the actual mechanism of phagocytosis or of the fate of the digested material. It is fortunate, however, that some of the tools which are likely to be of value in research on these aspects of macrophage function are currently being developed. Of particular interest in this connection are the immunocytochemical techniques which permit the localization of surface-associated antigens and intracellular contractile proteins. It must be emphasized that phagocytosis is not the only function of macrophages in the gas-exchange zone of the lung. These cells are thought to be involved in the presentation of exogenous antigenic material to the reactive cells of the lymphoid system. Recent research has also indicated that mammalian alveolar macrophages synthesize a diverse range of substances. Furthermore, the elastases associated with pulmonary macrophages are now thought to be involved in the pathogenesis of emphysema. All of the above-mentioned activities are of great biological and clinical significance and, consequently, merit the cytochemists' attention in future. The epithelial lining of the greater part of the pulmonary gas-exchange area is composed of type I pneumonocytes. In terms of ultrastructure, these are very specialized cells; their extensive and highly-attenuated cytoplasmic processes form the outer layer of the air-blood barrier. No special carrier systems have been identified within type I pneumonocytes and this is in keeping with the claims that oxygen is transferred across the alveolar tissue barrier by a process of simple diffusion. Type II pneumonocytes, in contrast, have considerable metabolic activity.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of secretory granules in the transport of basement membrane components: radioautographic studies of rat parietal yolk sac employing 3H-proline as a precursor of type IV collagen

Biosynthesis of type IV collagen in the parietal endodermal cells of 12 day gestant Sherman rats was examined following intraconceptal injection of 3H-proline. The concepti were removed at times varying from 2 minutes to 24 hours after the injection. The parietal wall of the yolk sac, including endodermal cells and the associated basement membrane known as Reichert's membrane were processed for electron microscopic radioautography. Silver grains were counted over the organelles of endodermal cells as well as over Reichert's membrane. Radioactivity was high in endodermal cells during the first 2 hr after 3H-proline injection and later dropped to some extent, while radioactivity rose in Reichert's membrane. Examination of endodermal cell organelles showed some early labeling over rER and Golgi apparatus without a clear-cut trend, except for a drop in Golgi label at late times after 3H-proline injection. The density of silver grains over secretory granules rose significantly by 40 min, reached a high peak by 4 hr and then declined at the time when radioactivity increased over Reichert's membrane. Furthermore, the radioactively-labeled secretory granules were localized mainly at the trans Golgi face soon after injection and near the cell surface adjacent to Reichert's membrane at later times. Biochemical reports indicate that a substantial amount of the proline taken up by the 12-14.5 day rat embryo endodermal cells is incorporated into type IV collagen. Since there is high labeling of the secretory granules from 40 min to 4 hr and the labeled granules are associated with the Golgi apparatus at early times, it is proposed that collagen precursors are processed through rER and Golgi apparatus, packaged into secretory granules and then transported to the cell surface where type IV collagen or its precursors are released and subsequently deposited into Reichert's membrane.

Distribution of hyaluronic acid and sulfated glycosaminoglycans during blood-vessel development in the chick chorioallantoic membrane

This study uses histochemical methods to determine the ultrastructural distribution of specific glycosaminoglycans (GAGs) during the development of blood vessels in the chick chorioallantoic membrane (CAM) and to correlate changes in GAG composition with the significant structural events in the development of these vessels. Tissues were stained with tannic acid, ruthenium red, and high iron diamine and digested in various GAG-degrading enzymes to identify specific GAGs. The results are consistent with a role for hyaluronic acid in the formation, alignment, or migration of the capillary plexus of the CAM and a role for sulfated GAGs (heparan sulfate, chondroitin sulfate, dermatan sulfate) in the differentiation and development of arterial and venous vessels of the chorioallantoic membrane.

Isolation and partial characterization of endothelial cell extracellular complexes

Human endothelial cells release components into the growth medium that stimulate cell-substratum adhesion. Several macromolecular components were isolated by ultracentrifugation of the endothelial cell conditioned medium. The components were heterogeneous, consisting of several sizes when examined by sedimentation velocity and gel filtration. When the extracellular components were evaluated by electron microscopy, structurally discrete particles were observed. The extracellular components and the complexes mediated cell-substratum adhesion to both human umbilical and arterial endothelial cells. The majority of the extracellular components that promote endothelial cell adhesion were pelleted by ultracentrifugation. Although the complexes contained fibronectin, antibodies to fibronectin did not inhibit cell adhesion to the complexes. Significant inhibition of endothelial cell adhesion was observed in the presence of heparin and heparan sulfate. The supernatant fraction following ultracentrifugation of the growth medium contained a component that suppressed endothelial cell adhesion to culture dishes coated with fibronectin, type I collagen, and endothelial cell complexes. SDS-polyacrylamide gel electrophoresis indicated that the complexes contained several components, and the majority of the large-molecular-weight components were pelleted by ultracentrifugation. The conditioned medium from human endothelial cells contains specific complexes that promote cell-substratum adhesion and components that suppress cell-substratum adhesion.

Development of extracellular matrix in chick paravertebral sympathetic ganglia

Alcian blue staining coupled with enzyme digestion or critical electrolyte staining revealed differences in the development of extracellular matrix (ECM) within sympathetic ganglia compared with the surrounding capsule. On day 5 of chick development (Hamburger-Hamilton stage 26) only hyaluronic acid (HA) could be detected in the ECM surrounding condensing primary ganglia. By day 7 (st 30) the ganglionic capsule contained HA, as well as sulfated glycosaminoglycans (GAGs), and this pattern continued into the adult stage. During the later stages of embryonic life (st 41-45) satellite cells appear, showing fine structural characteristics that point to their role in the secretion of intraganglionic ECM. Only during these stages could ECM be detected histochemically within ganglia, the same stages (days 15-19) when routine electron microscopic methods reveal collagen fibrils embedded in a granular ground substance. Thus, the intraganglionic environment appears as a separate compartment free of detectable amounts of GAG until late embryonic stages when ECM is secreted around satellite cells. This developmental pattern could represent a role of ECM in the histological stabilization of ganglia during the late stages of differentiation, since the appearance of intraganglionic ECM is correlated with the appearance of small dense-cored vesicles characteristic of adult neurons. The developmental pattern of ECM in differentiating sympathetic ganglia is compared with that of other tissues that undergo condensation and morphogenesis.

Histochemical demonstration of hyaluronic acid molecules by alcian blue

Specimens of vitreous humour (monkey eye), Wharton jelly (human umbilical cord) and commercial hyaluronates were immersed in buffered fixative solutions containing either aldehydes and Alcian Blue, or aldehydes and Alcian Blue with MgCl2 as electrolyte. Two MgCl2 concentrations were used, 0.025 M and 0.3 M. Immersion in both solutions induced formation of precipitates which were postfixed in OsO4, dehydrated and embedded for thin section electron microscopy. The use of the same fixative solution produced morphologically comparable precipitates from all three materials. The precipitates, especially after fixation in the presence of electrolyte, were composed of linear, unbranched filaments, frequently aggregated into bundles. The filaments were considered to be molecules of hyaluronic acid.