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PubMed1983

The zonules and the elastic microfibrillar system in the ciliary body.

It has been proposed that elastic fibers occur in some tissues as a three-part interconnecting system. The system includes two sizes of elastin-containing fibers surrounded by tubular microfibrils (elastic microfibrils), besides isolated bundles of tubular microfibrils without elastin (oxytalan fibers). This little-studied system was identified in the bovine ciliary body by light and electron microscopy. Its architecture varied regionally, suggesting different vectors of tractional force in the anterior and posterior ciliary body related to accommodation. Zonular fibers had the staining characteristics of oxytalan fibers, and their fibrils were ultrastructurally similar to the tubular microfibrils around elastic fibers and those composing oxytalan fibers. Antibodies to microfibrillar protein bound to zonules and to tubular microfibrils in all sites. This is the first evidence that tubular microfibrils both with and without elastin share antigenic determinants and confirms the close antigenic relationship of the zonules to this class of proteins.

Animals↗
PubMed2006

The morphology of adsorbed extracellular matrix assemblies is critically dependent on solution calcium concentration.

The adsorption of proteins to surfaces may alter their biological properties. Understanding and controlling these interactions is important in ultrastructural, biochemical and cellular studies. We have previously demonstrated that both the morphology and biological function of extracellular matrix assemblies such as fibrillin and type VI collagen microfibrils are influenced by surface chemistry. In this study we have employed atomic force microscopy to determine if the morphology of extracellular matrix microfibrils is influenced by solution chemistry. Microfibrils were adsorbed to mica or poly-L-lysine modified mica (mica-PLL) in the presence of 31 microM-1000 microM Ca(2+). Although both microfibrillar species adsorbed to mica and mica-PLL at all calcium concentrations, maximal adsorption was observed on mica at 125-250 microM. On mica surfaces fibrillin microfibril morphology varied continuously with calcium concentration from laterally diffuse assemblies at high concentrations to compact assemblies at low concentrations. In contrast, distinct type VI collagen microfibril morphologies were observed at high, intermediate and low calcium concentrations. Similar calcium dependent microfibrillar morphologies were evident on mica-PLL. Therefore physiologically relevant concentrations of solution calcium, independent of surface charge, profoundly influenced both the adsorbed amount and morphology of native extracellular assemblies. These studies highlight the importance not only of surface chemistry but also of solute composition and concentration in influencing the morphology and hence biological function of adsorbed proteins.

Adsorption↗
PubMed2004

Progress in understanding the role of microtubules in plant cells.

Microtubules have long been known to play a key role in plant cell morphogenesis, but just how they fulfill this function is unclear. Transverse microtubules have been thought to constrain the movement of cellulose synthase complexes in order to generate transverse microfibrils that are essential for elongation growth. Surprisingly, some recent studies demonstrate that organized cortical microtubules are not essential for maintaining or re-establishing transversely oriented cellulose microfibrils in expanding cells. At the same time, however, there is strong evidence that microtubules are intimately associated with cellulose synthesis activity, especially during secondary wall deposition. These apparently conflicting results provide important clues as to what microtubules do at the interface between the cell and its wall. I hypothesize that cellulose microfibril length is an important parameter of wall mechanics and suggest ways in which microtubule organization may influence microfibril length. This concept is in line with current evidence that links cellulose synthesis levels and microfibril orientation. Furthermore, in light of new evidence showing that a wide variety of proteins bind to microtubules, I raise the broader question of whether a major function of plant microtubules is in modulating signaling pathways as plants respond to sensory inputs from the environment.

Cell Division↗
PubMed2002

Expression of fibrillins and tropoelastin by human gingival and periodontal ligament fibroblasts in vitro.

The elastic system fibers consist of three different types, oxytalan, elaunin and elastic fibers, which differ in the relative content of microfibrils and elastin. In periodontal tissues, oxytalan fibers are known to be distributed in the periodontal ligament and gingiva, while elaunin and elastic fibers are present only in the gingiva. We examined the in vitro synthesis of microfibrils and elastin by human gingival fibroblasts (HGF) and periodontal ligament fibroblasts (HPLF). The two kinds of HGF and HPLF were cultured in MEM containing 10% newborn calf serum for 30 days. Since fibrillin-1 and fibrillin-2 are the major components of microfibrils involved in elastogenesis, we investigated the synthesis of fibrillins and tropoelastin in the conditioned medium of HGF and HPLF. Western blot analysis revealed fibrillin-1 and fibrillin-2 to occur in the HGF and HPLF culture medium, HGF exhibiting a higher level of synthesis than HPLF. Tropoelastin, on the other hand, was detected only in the medium of HGF after day 24. In addition, analysis of RNA extracted from HGF and HPLF on day 30 showed that only HGF expressed mRNA encoding tropoelastin. Immunohistochemically, accumulation of tropoelastin in the perinuclear area was found only in HGF. These results show that HGF expressed microfibrils and elastin, while HPLF expressed only microfibrils for the experimental period, and suggest a biochemical basis for the different distribution of elastic system fibers of the gingiva and periodontal ligament in vivo.

Blotting, Northern↗
PubMed2003

Raman microscopy and X-ray diffraction, a combined study of fibrillin-rich microfibrillar elasticity.

Fibrillin-rich microfibrils are essential elastic structures contained within the extracellular matrix of a wide variety of connective tissues. Microfibrils are characterized as beaded filamentous structures with a variable axial periodicity (average 56 nm in the untensioned state); however, the basis of their elasticity remains unknown. This study used a combination of small angle x-ray scattering and Raman microscopy to investigate further the packing of microfibrils within the intact tissue and to determine the role of molecular reorganization in the elasticity of these microfibrils. The application of relatively small strains produced no overall change in either molecular or macromolecular microfibrillar structure. In contrast, the application of larger tissue extensions (up to 150%) resulted in a markedly different structure, as observed by both Raman microscopy and small angle x-ray scattering. These changes occurred at different levels of architecture and are interpreted as ranging from alterations in peptide bond conformation to domain rearrangement. This study demonstrates the importance of molecular elasticity in the mechanical properties of fibrillin-rich microfibrils in the intact tissue.

Animals↗
PubMed1960

Multinet growth in the cell wall of Nitella.

Plant cell walls typically consist of crystalline microfibrils embedded in a non-crystalline matrix. The growing cylindrical Nitella cell wall contains microfibrils predominantly oriented in the transverse direction. The present study has shown that the transversely oriented microfibrils are primarily located toward the inner surface of the wall and that, proceeding outward from the inner surface, the wall contains microfibrils of ever poorer transverse orientation, the fibrils being randomly or axially arranged in the outermost regions of the wall. Because cell expansion is primarily in the axial direction, the texture of the fibrillar elements of the wall can be explained by assuming that new microfibrils of transverse orientation are added only at the inner surface of the wall and that they become passively reoriented to the axial direction during cell elongation. The described structure corresponds to that proposed by Roelofsen and Houwink for cells showing "multi-net growth." The demonstration of a continuous gradient of microfibrillar arrangement and its partial quantitative description was accomplished by the analysis, with the polarized light and interference microscopes, of wedge-like torn edges of developing cell walls which were 1 micron or less in optical thickness.

Cell Wall↗
PubMed1977

Arrangement of connective tissue components in the walls of seminiferous tubules of man and monkey.

In primates the membrane separating the seminiferous epithelium from the interstitial space is composed of one to three (monkey) or two to six layers (man) of myoid cells associated with one to two layers of fibrocyte-like adventitial cells. All these cells are separated from each other by irregular spaces filled with various connective tissue intercellular components. Subjacent to the elements of the seminiferous epithelium is a continuous, often redundant, basement membrane. A similar basement membrane-like material forms a layer next to and over small areas of the plasma membrane of myoid cells. Collagen fibrils grouped in bundles of various sizes are seen in all connective tissue layers but are particularly abundant in the space between the seminiferous epithelium and the innermost layer of myoid cells. Elastic fibrils demonstrated by the Verhoeff iron hematoxylin technique are also present. Composed of a homogeneous material, the elastic fibrils are short, irregular, branching entities with a diameter comparable to or smaller than that of collagen fibrils. In addition, an abundance of microfibrils with a diameter of 12-15 nm is present in the various connective tissue layers. These microfibrils have a densely stained cortex and a lightly stained core. When seen close to the myoid cells, bundles of micro fibrils appear to insert on well defined areas next to the plasma membrane. These areas commonly face the patches of electron-dense material observed on the inner aspect of the plasma membrane of the myoid cells and in which the actin filaments are inserted. Bundles of microfibrils often span the gap between myoid cells of the same layer as well as those of adjacent layers. Microfibrils are also closely related to the surface of elastic fibrils and are seen intertwining with collagen fibrils. Thus microfibrils appear to bridge and bind together adjacent myoid cells and anchor the surface of these cells to the bundles of elastic and collagen fibrils present in the intercellular spaces of the limiting membrane.

Animals↗
PubMed1977

High-voltage electron microscopy of extracellular fibrillogenesis.

High-voltage electron microscopy was employed to observe developing extracellular connective tissue elements in the cervical perinotochordal and perivertebral regions in the chick embryo from 2 through 15 days' incubation. During days 2 and 3, small (10 nm) and large (18-20 nm) microfibrils surrounded the notochord, becoming evident around fibroblast-like cells in day 4. Amorphous material, globular granules and microfibrillar bundles were present at this time. Microfibrillar length increased as did the total population of microfibrils. At four days microfibrils 3-5 nm in diameter arose in all directions from globular granules. During day 9 and thereafter to day 15, microfibrillar diameters increased. This growth formed unit collagenous fibrils 30 nm in diameter or greater. Axial periodicity became evident at day 14. Small microfibrils appear to be composed largely of glycoproteins and do not contain a significant amount of collagen. The globular granules and associated filaments are probably proteoglycans. The amorphous material is believed to provide molecular collagen to developing fibrils. Large microfibrils and unit collagenous fibrils contain significant amounts of molecular collagen.

Animals↗
PubMed1982

Ultrastructure of mucocartilage in the larval anadromous sea lamprey, Petromyzon marinus L.

The fine structure of mucocartilage, a tissue unique to larval lampreys, was examined in Petromyzon marinus L. This tissue is surrounded by a perichondrium of vascularized, dense connective tissue composed of fibroblasts, collagen fibrils, and elastic-like microfibrils, but it is avascular itself and consists of elastic-like microfibrils, ground substance, and a few diffusely scattered fibroblasts. Fibroblasts possess rough endoplasmic reticulum, may free ribosomes, a well-developed Golgi apparatus, a tubulo-vesicular network, and a number of secondary lysosomes containing crystalline material. The appearance of the organelles suggests the involvement of the cell in the synthesis and secretion of the ground substance and microfibrils. Tubular microfibrils, 11-13 nm in diameter, comprise the major portion of the matrix, and they are similar to those described in developing mammalian elastic tissue (Ross and Bornstein, 1969). The retention of the microfibrils may represent either a primitive form of elastic fiber in this "primitive" vertebrate or reflect the larval condition of the lampreys under examination. Scattered spherical to polyhedral-shaped mitrix granules and intergranular filaments make up the remainder of the matrix. It was concluded that mucocartilage in larval lampreys is not a conventional type of vertebrate connective tissue.

Animals↗
PubMed1990

Ultrastructural and cytochemical study of elastic fibers in the ventral aorta of a teleost, Anguilla japonica.

Previous studies have revealed that amorphous elastin and microfibrils are structural entities of mammalian elastic fibers. Elastin shows a wide phylogenetic distribution, but the presence of elastin-associated microfibrils has not been demonstrated in teleost aorta. Thus, we have ultrastructurally and cytochemically examined elastic fibers in the ventral aorta of eel, a teleost, by utilizing routine uranyl acetate and lead double staining, the tannic acid (pH 7.0)-uranyl acetate (TA-UA) method, elastase en bloc digestion, Thiéry's periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) method, and the horseradish-peroxidase-labeled concanavalin A (Con A) method. In the ventral aorta of eel, a little ultrastructural difference between elastic fibers in the intima and media and those in the adventitia was noticed, but in either tunic each elastic fiber was basically composed of a "fibrillar core" and surrounding microfibrils. The fibrillar core was a collection of fibrils which showed a tendency to coalesce with each other, and these constituent fibrils were TA-UA positive and elastase-sensitive, representing their nature of elastin. By contrast, microfibrils associated with the fibrillar core were TA-UA negative and elastase-resistant, and their glycoproteinaceous nature was demonstrated by PA-TCH-SP and Con A methods. Thus, this study provides evidence for the presence of elastin-associated microfibrils in teleost aorta. These results are discussed in relation to the topographical difference of elastic fibers in eel aortic wall.

Anguilla↗
PubMed1990

Elastin in human, baboon, and mouse liver: an immunohistochemical and immunoelectron microscopic study.

Light microscope histochemistry and immunohistochemistry, and routine electron microscopy techniques were performed to analyse elastin distribution and structure in the human liver compared with that in baboon and mouse. In man and baboon, elastic fibers stained by iron hematoxylin or orcinolnew fuchsin seemed to be solitary and were few in number; in the mouse they were thinner but abundant, both in the portal tract and in hepatic veins. Orcein or resorcin-fuchsin stains, employed after oxidation of tissue sections, revealed a network comprising elastic, elaunin, and oxytalan fibers, which was also demonstrated by immunofluorescence with anti-elastin antibody in man and baboon. At the ultrastructural level, the elastic fibers of the human portal tract corresponded to discontinuous patches of amorphous material intermingled with few microfibrils. These contrasted with the thinner elastic fibers of baboon and mouse liver which had a core of amorphous material. In man and baboon, these fibers meshed into slender bundles of microfibrils often exhibiting small spots of amorphous material (elaunin fibers) and terminated as isolated microfibrils (oxytalan fibers). Immunoelectron microscopy of elastin carried out on baboon liver tissue labelled the amorphous material and also its microfibrillar component. Immunoperoxidase deposits were also associated with isolated bundles of microfibrils in the baboon portal stroma. Immunolabelling and elastic stains disclosed an important elastin portal network located around vascular, biliary structures and interspaced with collagen bundles. The structural polymorphism of elastin, assembling different relative amounts of amorphous material and microfibrils, might have a relationship with the required elasticity in a given species.

Adult↗
PubMed1990

Distribution of hyaluronic acid and chondroitin sulfate proteoglycans in the presumptive aganglionic terminal bowel of ls/ls fetal mice: an ultrastructural analysis.

The terminal colon of the ls/ls mouse is aganglionic because an intrinsic defect prevents its colonization by cells migrating from the neural crest. Previous studies showed that laminin, type IV collagen, and glycosaminoglycans accumulate in the region of the presumptive aganglionic ls/ls bowel through which crest-derived cells would be expected to migrate. It was suggested that crest-derived cells might fail to enter the abnormal bowel because they receive inappropriate signals from a defective extracellular matrix. This hypothesis was evaluated by analyzing the ultrastructure of the extracellular matrix in mutant and control gut. Tissue was fixed in the presence of ruthenium red before or after selective enzymatic digestion. Heparan sulfate proteoglycan (diameter approximately equal to 15 nm) and chondroitin sulfate proteoglycan (diameter approximately equal to 20-50 nm) granules were found in both control and presumptive aganglionic gut. The heparan sulfate proteoglycan granules were primarily located within formed basal laminae, while chondroitin sulfate proteoglycan granules decorated plasma membranes and 5 nm hyaluronic acid microfibrils that formed a network in the extracellular matrix. At day E11.5, the mutant gut differed from the control in the following: 1) Hyaluronic acid microfibrils were longer and more numerous. 2) There were larger numbers of chondroitin sulfate proteoglycan granules associated with cell membranes and with hyaluronic acid microfibrils. By day E13 the spaces between mesenchymal cells of the outer wall of the control bowel contained a regular lattice of hyaluronic acid microfibrils studded with chondroitin sulfate proteoglycan granules. Instead of this lattice, tangles of excessively long hyaluronic acid microfibrils, coated more heavily than in the control with chondroitin sulfate proteoglycan granules, were found in the presumptive aganglionic gut. These results confirm that the extracellular matrix is abnormal in the presumptive aganglionic bowel of the ls/ls mouse; moreover, they also indicate that the defect involves not one, but several components of the extracellular matrix, as well as their distribution. The defective extracellular matrix is apparent at a time when crest-derived cells would be expected to be migrating in the terminal bowel and is located in their path. The observations thus support the idea that a localized abnormality of the extracellular matrix interferes with the colonization of the terminal bowel by crest-derived cells in the ls/ls mouse.

Animals↗
PubMed1996

Structural biology of the fibres of the collagenous and elastic systems.

The different types of fibres of the collagenous and elastic systems can be demonstrated specifically in tissue sections by comparing the typical ultrastructural picture of each of the fibre types with studies using selective staining techniques for light microscopy. A practical modus operandi, which includes the recommended staining procedures and interpretation of the results, is presented. Micrographs and tables are provided to summarize the differential procedures. Reticulin fibres display a distinct argyrophilia when studied by means of silver impregnation techniques, and show up as a thin meshwork of weakly birefringent, greenish fibres when examined with the aid of the Picrosirius-polarization method. In addition, electron-microscopic studies showed that reticulin fibres are composed of a small number of thin collagen fibrils, contrasting with the very many thicker fibrils that could be localized ultrastructurally to the sites where non-argyrophilic, coarse collagen fibres had been characterized by the histochemical methods used. The three different fibre types of the elastic system belong to a continuous series: oxytalan-elaunin-elastic (all of the fibre types comprising collections of microfibrils with, in the given sequence, increasing amounts of elastin). The three distinct types of elastic system fibres have different staining characteristics and ultrastructural patterns. Ultrastructurally, a characteristic elastic fibre consists of two morphologically different components: a centrally located solid cylinder of amorphous and homogeneous elastin surrounded by tubular microfibrils. An oxytalan fibre is composed of a bundle of microfibrils, identical to the elastic fibre microfibrils, without amorphous material. In elaunin fibres, dispersed amorphous material (elastin) is intermingled among the microfibrils.

Animals↗
PubMed1998

Molecular imaging of halocynthia papillosa cellulose

The molecular organization of cellulose Ibeta microfibrils in the tunic of Halocynthia papillosa was analyzed by high-resolution cryoelectron microscopy on ultrathin cross sections of artificially highly oriented microfibrils. The arrangement of cellulose chains intersected by the 0.6-, 0.53-, and 0.39-nm equatorial lattice planes was clearly imaged over the whole area of a parallelogram-shaped cross section of a microfibril. One, edge of the parallelogram was parallel to the 0.6-nm lattice plane, while the other did not correspond to a crystallographic plane. Such organization is distinct from previous findings on algal cellulose Ialpha-rich microfibrils, which have an almost square cross section bounded by both 0.6- and 0.53-nm crystallographic planes. A tentative model for microfibril formation is proposed by introducing a two-step biocrystallization mechanism: the formation of molecular sheets spaced by 0.53 nm between adjacent molecules, followed by self-deposition of these sheets by hydrogen bonding between them. Copyright 1998 Academic Press.

Journal Article↗
PubMed1993

Ultrastructural comparison of slack and stretched myotendinous junctions, based on a three-dimensional model of the connecting domain.

The vertebrate myotendinous junction contains junctional microfibrils, located in the lamina lucida of the basement membrane. The junctional microfibrils are thought to transmit muscular force across the junctional lamina lucida, also called the connecting domain. If true, deformation of the terminal muscle cell processes and connecting domain during force transmission would be detected as a change in spacing and/or orientation of the junctional microfibrils. This study compared connecting domain morphology in frog semitendinosus muscles fixed in two extremes of resting tension, to elucidate the mechanical properties of the myotendinous junction. An initial study of connecting domain ultrastructure revealed that junctional microfibrils are punctate or spinelike in shape, and that they are distributed in a linear, helically-oriented array on the muscle cell surface. The rows in the surface lattice are 10-15 nm in thickness, have a centre-to-centre distance between rows of approximately 24 nm, and are oriented at approximately 41 degrees with respect of the long axis of the muscle fibre. Comparison of slack and highly stretched myotendinous junctions shows no significant changes in spacing or orientation of either individual junctional microfibrils or rows in the helical surface lattice. Thus, both the connecting domain and terminal cell processes at the myotendinous junction are essentially inextensible under the loading conditions used in this study.

Animals↗
PubMed1990

A fibrillar elastic apparatus around human lymph capillaries.

A fibrillar elastic apparatus around the wall of human lymph capillaries is demonstrated by means of histochemical and ultrastructural techniques. This apparatus consists of three interlinked components listed here in order of increasing distance from the capillary wall: 1) oxytalan fibres connected to the abluminal surface of the endothelial cells, known also as "anchoring filaments" and consisting of bundles of microfibrils; 2) elaunin fibres consisting of microfibrils and a small amount of elastin; and 3) typical elastic fibres consisting of microfibrils and abundant elastin. The microfibrillar constituent has similar ultrastructural features in the three components of the elastic apparatus. Microfibrils have a diameter of 12-14 nm, an electron-transparent core and a wall with 3-5 electron-dense subunits and oblique cross striations with a period of 15-17 nm. Microfibrils are the common element of the three components of the elastic apparatus and they link them to one another and to the elastic network of the perivascular connective tissue. An elastic apparatus was not found around blood capillaries and it can thus provide a histological marker to identify lymph capillaries. The possible role of the lymphatic elastic apparatus in the physiological activity of the lymphatic absorbing network is discussed and it is proposed that its disconnection from the elastic network of the tissue may promote pathological conditions such as lymphoedema or diseases related to impaired immune responses.

Actin Cytoskeleton↗
PubMed1987

Ultrastructural cytochemistry of oxytalan fibres in monkey periodontal ligaments with the high iron diamine method.

Monkey periodontal ligaments have been examined at the ultrastructural level to demonstrate the nature of reactive sites in oxytalan fibres. The high iron diamine (HID) and HID-thiocarbohydrazide-silver proteinate methods specific for sulphate groups, with and without prior oxidation with monopersulphate, were used. Oxytalan fibres were composed of bundles of microfibrils with a diameter of 11.5 +/- 1.7 nm (mean +/- S.D., n = 50). In cross section the microfibrils were found to have a denser periphery, giving them a 'tubular' appearance. The oxytalan microfibrils of non-oxidized specimens showed little reactivity with either HID method, except that the extracellular matrix material in close association with collagen fibrils stained weakly; in oxidized specimens, both HID methods strongly stained oxytalan microfibrils and weakly stained the extracellular matrix material. Such reactivity of oxytalan microfibrils was not altered by digestion with testicular hyaluronidase or chondroitinase ABC, performed prior to or after persulphate oxidation. Further, the sequential thiosulphation and HID method for the demonstration of disulphide and sulphhydryl groups stained oxytalan fibres moderately. These results indicate that the oxidative generation of sulphate groups in oxytalan fibres may occur from either disulphide or sulphhydryl groups, or both, rather than the result of unmasking of sulphated glycosaminoglycans.

Animals↗
PubMed1999

The anchoring zone in the human placental amnion: bunches of oxytalan and collagen connect mesoderm and epithelium.

This study deals with the examination of the elastic fibre system as well as collagen fibrils and collagen type IV in the amnion of the human chorionic plate of uncomplicated pregnancies at term. In organs other than placenta, the elastic fibre system comprises elastic fibres, elaunin and oxytalan microfibrils. The investigation was performed by light and electron microscopy and immunocytochemistry. Abundant oxytalan fibres were present in all amnionic layers, while no elastic fibres were found. Oxytalan microfibrils formed a broad sub-epithelial layer and were intermingled with collagen fibrils in the subjacent compact layer and in the amnionic mesoderm. Light microscopically, bunches containing orcein-stained oxytalan and collagen-type-IV-immuno-stained microfibrils were seen rising from the amnionic mesoderm perpendicularly towards the epithelial layer, where they obviously inserted. It can be assumed that the subepithelial microfibrillar layer and the following compact layer form an anchoring zone between the amnionic mesoderm and the epithelium that may contribute to the maintenance of strength. The ultrastructure of the bunches clearly showed collagen fibrils mixed with oxytalan microfibrils. No collagen type I-immunostaining was found in the bunches. After pretreatment of cryostat sections with elastase, oxytalan-orcein-staining was absent, but collagen type IV-immunoreactivity was not altered. Furthermore, after oxytalan-orcein-staining resp. anti-collagen type IV incubation, all positive fibres revealed an identical morphological pattern. We propose that oxytalan and collagen type IV may represent further members of the microfibril complex.

Adult↗