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PubMed1989

The elastic tissue of Bruch's membrane. Connections to choroidal elastic tissue and the ciliary epithelium of the rabbit and human eyes.

Ultrastructural observations on the elastic lamina of Bruch's membrane of the rabbit and human eyes revealed connections to the ciliary epithelium and choroidal elastic tissue. The connections to the ciliary epithelium are in the form of bundles of microfibrils that peel off the anterior extension of Bruch's membrane beyond the ora serrata and insert into the basement membrane of the pigmented epithelium of the pars plana. The connections to the choroidal elastic tissue are in the form of bundles of microfibrils (in the rabbit) or elastin and microfibrils (in the human) that cross the tissue space between the choriocapillaris and join bundles of choroidal elastic tissue. These connections suggest that the elasticity of Bruch's membrane exerts its influence distant from the membrane itself. The connections onto the pars plana of the ciliary body implicate Bruch's membrane in disaccommodation when the ciliary muscle relaxes.

Animals↗
PubMed1997

HNK-1 epitope in the lens-ciliary zonular region in normal and pseudoexfoliative eyes. Immunohistochemistry and ultrastructure.

OBJECTIVE: To determine the specific binding sites for the HNK-1 adhesion molecule epitope in the lens-ciliary zonular region in normal and pseudoexfoliative (PSX) eyes. METHODS: Normal and PSX eyes and adjacent tissues from individuals aged 10 months to 89 years were investigated for the HNK-1 epitope by immunohistochemistry and immunogold electron microscopy. RESULTS: Concentration of HNK-1 epitope was high in the anterior central lens capsule into old age, but it tapered earlier and progressively in the inner capsule and elsewhere. On zonular fibers, label was strongest at their lens and ciliary attachments and intense on related elastic microfibrils in adjacent ciliary stroma. Label was also strong on PSX fibers and above normal on PSX central capsule. In contrast, HNK-1 was absent on PSX aggregates in conjunctiva and skin and on normal elastic microfibrils in these tissues. CONCLUSIONS: The prominent HNK-1 epitope in lens capsule and zonule has age- and site-specific variations that favor adhesive roles in each. The high density of epitope on ocular PSX material suggests an aberrant increase in expression that may contribute to adhesiveness of these aggregates, HNK-1 negativity on extraocular elastic microfibrils and PSX aggregates indicates a unique difference in composition of intraocular and extraocular elastic tissue, of potential significance for ocular function in aging and lens-dislocating diseases.

Adolescent↗
PubMedDate not supplied

Immunohistochemical localization of fibrillin in developing macaque and term human placentas and fetal membranes.

The objective of this study was to examine the developmental appearance of the extracellular matrix glycoprotein fibrillin in macaque placentas and fetal membranes and to compare this distribution to that seen in term human placentas and fetal membranes. Standard immunoperoxidase methods were used on paraformaldehyde-fixed, paraffin-embedded tissues. At early gestational ages (26-30 days), fibrillin was found in cell columns and cytotrophoblastic shell, with weak staining in the villous stroma. Staining was abundant in the shell and columns at 53 days as well, and stronger staining was seen in the stroma of the chorionic plate and stem villi. Staining in the shell and remnants of the cell columns in later gestation continued to be positive, though variable. Generally, the strongest staining was present in the distal cytotrophoblastic shell. Stroma in the tips of anchoring villi was also strongly positive. Later in gestation, fibrillin was observed around the multilayered cytotrophoblast of the chorionic plate. Fibrillin was abundant in the stromal cores of human term placental villi. In early macaque amnion, fibrillin staining was abundant in a layer beneath the amniotic epithelium. Later in gestation, macaque chorioamnion staining was generally similar to human term chorioamnion staining, with the heaviest staining in portions of the compact and reticular layers. Fibrillin was sometimes localized in regions known to be rich in connective tissue microfibrils, but, in other regions known to have abundant microfibrils, fibrillin staining was weak. This suggests that some microfibrils in placenta may be composed predominantly of some other protein(s). The function of fibrillin in the various placental compartments is unknown at present. It may provide attachment points for cells while at the same time providing a strong, yet flexible, matrix to accommodate growth particularly in areas subject to shear stress.

Animals↗
PubMed1978

Ultrastructural identification of collagen and glycosaminoglycans in notochordal extracellular matrix in vivo and in vitro.

Notochordal extracellular matrix consists of a continuous basal lamina, amorphous materials and microfibrils embedded in the ground substance of low electron density. Together they comprise the notochord sheath and are of considerable interest because of their suspected role in early embryonic tissue interactions. The notochord is particularly well-suited to morphological investigation of extracellular matrix because it is one of the few embryonic epithelia which produces ultrastructurally recognizable stroma in vitro without the advantage of a collagenous substratum. Furthermore, these matrix components produced in vitro are morphologically identical to those observed in vivo. The present study used ruthenium red staining to demonstrate that notochordal microfibrils exhibit collagen-like cross-banding patterns both in vivo and in vitro. Collagenase and testicular hyaluronidase digestion studies designed to localize collagen and glycosaminoglycans show a reduction of microfibrillar diameters by 30-35%. Furthermore, these enzyme treatments frequently result in enhanced striations of microfibrils. When cis-hydroxyproline (a proline analog) or beta-aminoproprionitrile (BAPN, a lathyrogenic compound) is added to the culture medium, a similar reduction in microfibrillar diameters is seen. Moreover, increased ruthenium red-positive surface coats and large collagen fibrils are frequently present in BAPN-treated cultures, implying a stimulatory metabolic effect. We conclude that most, if not all, notochordal extracellular matrix components are composed of both collagen and glycosaminoglycans and suggest that the entire extracellular matrix should be considered a macromolecular composite which acts in concert to induce or stabilize developmental interactions.

Aminopropionitrile↗
PubMed1988

Development of the notochord in human embryos: ultrastructural, histochemical, and immunohistochemical studies.

In the present study of the notochord, the specimens were 54 externally normal human embryos ranging between Carnegie stages 13 and 23. The following staining procedures were used: periodic acid-Schiff (PAS), modified method of PAS, alcian blue, colloidal iron, and toluidine blue. Routine electron microscopic techniques were used. Immunoreactivity of the notochord to alpha-enolase was also examined. The notochord cells were undifferentiated in stage 13 with few intracellular organelles. The microfibrils and deposition of acid mucopolysaccharides appeared in the notochordal sheath in stage 14. The characteristic relation of mitochondria with rough endoplasmic reticulum was observed. Golgi complexes increased in the perinuclear region in stage 15. The layer of microfibrils in the notochordal sheath initially separated from the notochord in stage 16. Glycogen, mucoprotein, neutral mucopolysaccharides, and glycolipids began to increase in the mesenchymal cells around the notochord, starting at stage 16. Acid mucopolysaccharides increased in the notochordal sheath and in the matrix of the precartilage area around the notochord as this embryonic stage advanced. It was also revealed that the immunoreactivity of the notochord to alpha-enolase remained constant during the embryonic period. The results show that the notochord is transformed from an apparently undifferentiated organ into an organ with secretory activity in stage 14, producing microfibrils and depositing acid mucoplysaccharides in the notochordal sheath. The immunoreactivity of the notochord to alpha- and gamma-enolase isoenzymes and the development of the notochord are discussed. This study was undertaken to provide additional information on the development of tumors of notochordal origin.

Embryo, Mammalian↗
PubMed1993

The fibrillin-Marfan syndrome connection.

A few years ago no one would have suspected that the well-known disorder of connective tissue, Marfan syndrome, could be caused by mutations in a recently discovered extracellular component, fibrillin. Likewise, nobody would have predicted that fibrillin represents a small family of proteins that are associated with several phenotypically overlapping disorders. The fibrillins are integral constituents of the non-collagenous microfibrils, with an average diameter of 10 nm. These aggregates are distributed in the extracellular matrix of virtually every tissue. Microfibrillar bundles provide the external coating to elastin in elastic fibers, and serve an anchoring function in non-elastic tissues. At higher resolution, individual microfibrils have a "beads-on-a-string" appearance resulting from the head-to-tail polymerization of multiple fibrillin aggregates. Structurally, fibrillin contains a series of repeated sequences homologous to the epidermal growth factor calcium-binding motif. Characterization of fibrillin mutations in Marfan syndrome patients, together with the elucidation of the structure of the fibrillin proteins, have provided new insights, and raised new questions, about the function of the 10 nm microfibrils. For example, it is possible that the fibrillins, in addition to serving a structural function, might also be involved in regulating cellular activities and morphogenetic programs. It is fitting that the long search for the Marfan syndrome gene has brought a novel group of proteins to the forefront of extracellular matrix biology.

Connective Tissue↗
PubMed2006

The xyloglucan-cellulose assembly at the atomic scale.

The assembly of cell wall components, cellulose and xyloglucan (XG), was investigated at the atomistic scale using molecular dynamics simulations. A molecular model of a cellulose crystal corresponding to the allomorph Ibeta and exhibiting a flexible complex external morphology was employed to mimic the cellulose microfibril. The xyloglucan molecules considered were the three typical basic repeat units, differing only in the size of one of the lateral chain. All the investigated XG fragments adsorb nonspecifically onto cellulose fiber; multiple arrangements are equally probable, and every cellulose surface was capable of binding the short XG molecules. The following structural effects emerged: XG molecules that do not have any long side chains tended to adapt themselves nicely to the topology of the microfibril, forming a flat, outstretched conformation with all the sugar residues interacting with the surface. In contrast, the XG molecules, which have long side chains, were not able to adopt a flat conformation that would enable the interaction of all the XG residues with the surface. In addition to revealing the fundamental atomistic details of the XG adsorption on cellulose, the present calculations give a comprehensive understanding of the way the XG molecules can unsorb from cellulose to create a network that forms the cell wall. Our revisited view of the adsorption features of XG on cellulose microfibrils is consistent with experimental data, and a model of the network is proposed.

Adsorption↗
PubMed2007

Analysis of structural changes in permanent waved human hair using Raman spectroscopy.

To investigate the mechanism leading to the reduction in tensile strength of permanent waved human hair, the structure of cross-sections at various depths of permanent waved white human hair was directly analyzed without isolating the cuticle and cortex, using Raman spectroscopy. The beta-sheet and/or random coil content (beta/R) and the Amide III(unordered) band intensity existing throughout the cortex region of virgin white human hair remarkably increased, while the alpha-helix (alpha) content slightly decreased by performing the permanent waving treatment. This suggests a secondary structural change from the alpha-helix form to the random coil form in the proteins existing in the microfibril of the cortex region. On the other hand, the S-S band intensity existing in the matrix of the cortex region almost did not change, despite the reduction in the tensile strength of the white human hair following the permanent waving treatment. Moreover, the transmission electron microscope observation shows that the macrofibril (the microfibril and matrix) existing in the cortex region of the virgin white human hair was remarkably disturbed, while the cuticle region was almost unchanged by performing the permanent waving treatment. From these experiments, the authors concluded that some of proteins existing in the cortex region (the microfibril and matrix) of the virgin white human hair were changed, thereby leading to the remarkable reduction in the tensile strength of the white human hair after the permanent waving treatment.

Amino Acids↗
PubMed1995

Truncated profibrillin of a Marfan patient is of apparent similar size as fibrillin: intracellular retention leads to over-N-glycosylation.

We studied profibrillin-1 (proFib) synthesis and microfibril formation in cultured fibroblasts from an individual with severe Marfan syndrome harboring a premature stop codon (W2756ter) in one FBN1 allele. Rotary shadowing analysis of extracellular matrix produced by these cells revealed the presence of only a very few intact microfibrils which showed marked disorganisation within the interbeaded domains. Metabolic pulse-chase studies identified intracellularly a population of truncated proFib molecules which were secreted more slowly than the normal proFib derived from the normal allele. Culture media contained strikingly reduced amounts of wild-type proFib in comparison to fibrillin (Fib). Our findings imply that (1) the truncated proFib is secreted and disturbs microfibril assembly; (2) the mutation is probably close to a putative cleavage site in the proFib C terminus necessary for the conversion of proFib to Fib; (3) the truncated proFib is over-N-glycosylated due to intracellular retention rather than incomplete cleavage of proFib with persistence of N-glycosylated sites; (4) not all potential N-glycosylation sites in proFib seem to be normally used, since we could produce over-N-glycosylated proFib in normal cells by brefeldin A mediated intracellular captivation and subsequent appearance of over-glycosylated Fib in culture medium upon removal of the compound. It is conceivable that post-translational over-modification might be important for modulating the phenotype of FBN1 mutations in Marfan syndrome.

Actin Cytoskeleton↗
PubMed1997

Diffraction contrast imaging of extracellular matrix components using zero-loss filtering.

The beta-chitin microfibrils from the deep-sea hydrothermal vent worm Riftia pachyptila were studied in both mature and fresh tubes experimentally obtained. The methods used were electron diffraction and electron diffraction contrast images, in conjunction with an electron-energy filter, operated in the zero-loss mode. In both studied samples, microfibrils are organized in successive layers, inside which they are parallel. However, the fresh tube is less densely packed and diffraction data show that these microfibrils may be in a partially hydrated state. These results indicate that a later step occurs in the compaction of the tube material once it has been extruded. Comparison of filtered and unfiltered diffraction patterns shows that zero-loss filtering significantly improves both working conditions and quality of diffraction recordings.

Actin Cytoskeleton↗
PubMed1977

The morphogenesis of elastic fibers.

Elastic fibers have been shown to contain two proteins, insoluble elastin and the elastic fiber microfibril, a glycoprotein. The microfibril has been suggested to play a morphogenetic role in determining the presumptive shape and direction of the forming elastic fiber. The principal alteration seen in individuals with the disease Pseudoxanthoma Elasticum is in insoluble elastin which loses its amorphous appearance and affinity for anionic stains, and takes on a finely granular appearance and shows increased affinity for cationic stains. Normal elastic fiber microfibrils are sometimes associated with this material; although, in general, these structures are not present in the elastic fibers that are markedly altered in this disease.

Animals↗
PubMed1977

The elastic system fibers.

Using the tannic acid-glutaraldehyde fixation it was possible to clearly visualize, with reproducible results, the elastic fiber amorphous material because of its density. The microfibrillar component was also evidenced with a good performance. With this technique the ultrastructural patterns of the oxytalan and elaunin fibers were also demonstrated. The oxytalan fibers appeared as a bundle of microfibrils similar to elastic microfibrils without amorphous material. The elaunin fibers presented a dispersed amorphous material intermingled among the microfibrils. It was suggested by ultrastructural evidences that oxytalan and elaunin fibers may represent interruption in successive phases in the development of the elastic fibers.

Elastic Tissue↗
PubMed1999

Chitin biosynthesis and structural organization in vivo.

Many organisms utilize chitin as a structural component of the protective cell walls or exoskeletons which surround them. These structures are light and resistant composites with specific structural and mechanical properties which allow them to fulfill their protective role. Chitin, in the form of microfibrils, is immersed in a matrix of proteins and other polysaccharides. Chitin microfibrils provide the high strength which allows them to resist tensions and modulus. The cementing compounds protect chitin from chemical attack; keep the microfibrils separate, preventing fracture; and provide support to tensions. The resulting structures adopt specific forms which are conserved during growth and are transmitted in a hereditary fashion. Synthesis of these complex structures involves the following steps: (i) synthesis of chitin either intracellularly or at the interphase with the extracellular medium; (ii) transport of the chitin molecules to the extracellular space; (iii) chemical modification of part of the noncrystallized chitin and association with other molecules; (iv) crystallization of the unmodified chitin which is covered by the rest of the components. The resulting supramolecular structure acquires viscoelastic mechanical properties; (v) maturation of the composite through formation of secondary covalent bonds among its components, and deposition of different substances.

Animals↗
PubMed1977

Extracellular matrix fibrils and cell contacts in the chick embryo. Possible roles in orientation of cell migration and axon extension.

The migration of neural crest and sclerotome cells and the extension of ventral root axons in chick embryos at stages 16-20 were studied by light microscopy as well as scanning and transmission electron microscopy at the leg bud level of fixed specimens. Extensive cellular movements take place in association with an extracellular matrix consisting of microfibrils. The neural crest and sclerotome cells migrate into the large matrix-filled extracellular space surrounding the neural tube and notochord, apparently using microfibril microfibril bundles as substratum. The cells exhibit pseudopodia which are closely associated with the matrix fibrils. The fibrils around the notochord show a spatial arrangement indicating that the sclerotome cells are contact-guided to their subsequent positions. Mutual cell contacts, including those established by cell processes, frequently show cytoplasmic electron dense plaques at adjacent membranes. These small "plaque contacts" might be correlated to contact inhibition of locomotion between the cells and participate in the guidance of cells. The growth cones of extending axons exhibit filopodia contacting both surrounding mesenchyme cells and extracellular fibrils. The orientation of the axons might thus be affected by contacts with cell surfaces as well as with extracellular material.

Animals↗
PubMed1984

Light and electron microscopic identification of elastic, elaunin and oxytalan fibers in human tracheal and bronchial mucosa.

The elastic fiber system in the human tracheal and bronchial mucosa was studied by light and electron microscopy. Elastic fibers, elaunin fibers, and oxytalan fibers were discerned. These fibers were identified by means of their staining characteristics (elastica stains, methods for disulfide-groups) and on account of their fine structural morphology. Elastic fibers consist of elastin and few "elastic-fiber microfibrils". The relative amount of elastin (compared to the amount of elastic-fiber microfibrils) is large in elastic fibers but small in elaunin fibers. Oxytalan fibers - by contrast - are pure bundles of microfibrils. In the light microscope a well-defined elastic lamina separates the lamina propria and the submucosa of the normal mucous membrane. The elastic lamina is formed by coarse strands of longitudinally running elastic fibers. A delicate network of elastica-positive fibers is attached to the basement membrane of the epithelial layer (subepithelial elastic layer). A few of these elastica-positive fibers branch out, traverse the region of the thickened basement membrane, and insert into the basal lamina of the epithelium. A loose network of elastica-positive fibers is present both in the lamina propria and in the submucosa. Plates of cartilage, glandular epithelium, and bundles of smooth muscle cells are enveloped by delicate elastica-positive fibers. Electron microscopy shows the lamina elastica to be predominantly composed of elastic fibers, whilst elaunin fibers form the subepithelial elastic layer. Fibers penetrating the thickened basement membrane of the epithelium are identified as oxytalan fibers. All three types of fibers are present throughout the lamina propria and in the submucosa.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1981

A new model for packing of type-I collagen molecules in the native fibril.

A specific fibril model is presented consisting of bundles of five-stranded microfibrils, which are usually disordered (except axially) but under lateral compression become ordered. The features are as follows (where D = 234 residues or 67 nm): (1) D-staggered collagen molecules 4.5 D long in the helical microfibril have a left-handed supercoil with a pitch of 400-700 residues, but microfibrils need not have helical symmetry. (2) straight-tilted 0.5-D overlap regions on a near-hexagonal lattice contribute the discrete x-ray diffraction reflections arising from lateral order, while the gap regions remain disordered. (3) The overlap regions are equivalent, but are crystallographically distinguished by systematic displacements from the near-hexagonal lattice. (4) The unit cell is the same as in a recently proposed three-dimensional crystal model, and calculated intensities in the equatorial region of the x-ray diffraction pattern agree with observed values.

Animals↗
PubMed1981

A mixed packing model for bone collagen.

A wide variety of physical properties, including sonic velocity, dimensional changes between wet and dried stages, anisotropy of the tissue properties, density, X-ray diffraction, differential microcalorimetry, dielectric constant, and composition (water, mineral, organic content) for the mineralized and demineralized tissue was used to develop a model for the superlattice structure of bone collagen. A mixed model is suggested where the collagen molecules are in register as in SLS type of aggregation within the microfibril, and the microfibrils are staggered in D unit steps according to the Hodge-Petruska scheme. A square packing model with 4 or more molecules per microfibril best fits the HP scheme with the effective molecular diameter of the wet collagen molecule, and allows for the regular array of axial gap filling microcrystallites of 5 nm or larger diameter. It is concluded that: 1. Macroscopic dimensional changes of adult bovine bone matrix closely match molecular dimensional changes of collagen superlattice. 2. Effective molecular diameter of dry collagen is 1.09 nm and that of wet bone collagen is 1.42-1.45 nm. 3. Water layer of the wet bone collagen molecule is 0.16 nm thick. 4. Water in the bone collagen molecule is distributed in 5 regimes much like in the tendon collagen molecule. 5. "Hidden" water, 0.10 g water per dry collagen of regimes I and II, is within the triple helix. 6. "External" water incorporated in the collagen molecule provides transition between the highly structured collagen molecule and the intermolecular medium. 7. Water incorporated in the mineralized bone collagen molecule is less than in demineralized bone matrix. 8. For adult bovine cortical bone, 25% by volume is water, 32% dry organic, 43% mineral; 28% by volume of the mineral is axial gap filling, 58% radial intrafibrillar, and 14% radial extrafibrillar.

Animals↗
PubMed1984

Papulacandin B: inhibitor of biogenesis of (1----3)-beta-D-glucan fibrillar component of the cell wall of Saccharomyces cerevisiae protoplasts.

The effect of papulacandin B on regenerating protoplasts of Saccharomyces cerevisiae was studied by light and electron microscopy. In liquid media it inhibited the biogenesis of (1----3)-beta-D-glucan fibrillar nets; as a result, the protoplasts did not grow polarly but only spherically. The effect was reversible. Instead of the nets the inhibited protoplasts synthesized only individual microfibrils soluble in hydroxide; these were not joined in the nets and were partially masked by amorphous material. The microfibrils disintegrated after lysis and did not maintain the shape of protoplasts. Protoplasts inhibited in solid media grew spherically up to 25 micron but they did not divide or revert, in spite of forming cell walls. These walls were amorphous and fragile and they disintegrated during preparation. Papulacandin B did not decrease the viability of protoplasts and did not interfere with their growth, biogenesis of alkali-soluble glucan microfibrils or amorphous wall matrix. It inhibited specifically the synthesis of alkali-insoluble branched (1----3)-beta-D-glucan, a necessary building unit required for the formation of the fibrillar component of the cell wall responsible for the cell wall shape, its rigidity and tensile strength.

Aminoglycosides↗