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PubMed2000

An ultrastructural study of connective tissue in mollusc integument: I. Bivalvia.

The ultrastructure of the subepidermal connective tissue (SEC) in different areas of the integument of the bivalves Callista chione, Pecten jacobaeus, Mytilus galloprovincialis and Ostrea edulis was studied by transmission electron microscopy. The main organisation of the SEC was broadly similar in all species: the SEC was connected to the epidermis by a basement membrane and merged directly with the deeper connective tissue surrounding muscles. The SEC was not differentiated into layers like the papillary and reticular dermis of mammals, however, the architecture, thickness and shape of the basement membrane varied from species to species, as well as within species (in the foot, central or marginal zones of the mantle). The ultrastructure of the lamina densa was broadly similar to that in mammals: although basotubules and double pegs were absent, proteoglycans and rod-like units homologous to 'double tracks' were always abundant. A zone similar to the lamina lucida was irregularly present and was shot thorough with small protrusions of the lamina densa that connected with the epithelial hemidesmosomes or focal adhesions. Nevertheless zones were observed where the lamina densa fuse directly to the epithelial plasmamembrane. This variability of connection may be related to the various types of epidermal cell. A lamina fibroreticularis was not recognized since anchoring fibrils and microfibrils were not present; lamina densa protrusions into the extracellular matrix (ECM) of SEC characterize the connection between basement membrane and SEC. Collagen fibrils were small and of constant diameter and were never organised into fibres. Anchoring devices - similar to the anchoring plaques of mammalian dermis - were abundant and scattered between SEC collagen fibrils. The orange-pink pigmentation of C. chione seems due to electron-dense granules embedded within the connective ECM.

Animals↗
PubMed1977

Infantile Gaucher's disease: neuropathology, acid hydrolase activities and negative staining observations.

A case of infantile Gaucher's disease with widespread cerebral degenerative changes is presented. Neuropathological features included perivascular Gaucher cell infiltrates accompanied by periadventitial fibrogliosis, focal neuronophagia, Purkinje cell vacuolation and diffuse astrocytosis of cerebellar white matter, brain stem and spinal paracentral grey matter. Gaucher cell tubules were isolated from formalin fixed material. Negative staining confirmed the appearance of a coiled helical structure, 200--400 A in diameter composed of microfibrils. A relative deficiency of acid beta-glucosidase was found in spleen homogenate accompanied by a considerable increase in acid phosphohydrolase, N-acetylglucosaminidase, beta-glucuronidase and beta-galactosidase.

Brain↗
PubMed1990

[Electron microscopy studies of the collagen fiber structure of the human tympanic membrane in an adhesive process].

In an EM study, the collagen fiber arrangement of the lamina propria in adhesive otitis media was investigated. Nine biopsies of the tympanic membrane were taken intraoperatively, and compared with two normal ones. The physiological specimens showed a regular arrangement of collagen fibrils and fibers, the typical network of the lamina propria. This confirmed results reported previously. In all adhesive otitis media samples the regular structure of the fiber arrangement was disturbed. Degenerative processes were to be found in the form of hyaline changes, with the network character of the fibers no longer in evidence. In one specimen a mass of microfibrils was observed, which was possibly a sign of reparative processes. The pathohistological findings in adhesive otitis media may be due to mechanical stresses (tubal function). Aside from that, they may also be caused by the biochemical influence of specific collagenases, which have been found by several authors in secretory otitis was well as in cholesteatoma.

Biopsy↗
PubMed1990

Immunohistologic abnormalities of the microfibrillar-fiber system in the Marfan syndrome.

BACKGROUND: Indirect-immunofluorescence studies of skin and cultured dermal fibroblasts from patients with the Marfan syndrome demonstrate apparent deficiency of one element of connective tissue--the microfibrillar-fiber system--in assays using specific antibodies against fibrillin, a major microfibrillar protein. This study was designed to test whether these immunostaining abnormalities are consistent and diagnostic features of the disease. METHODS: We studied patients with either the Marfan syndrome or various other inherited connective-tissue disorders and normal subjects according to a single-blind protocol in which coded samples of skin, fibroblast cultures, or both were analyzed without knowledge of the clinical diagnosis and classified as "Marfan" or "non-Marfan" before the sample codes were broken. RESULTS: Of the 27 patients with the Marfan syndrome, 24 were correctly identified by the decreased content of microfibrillar fibers in their skin, cultured fibroblasts, or both; in contrast, 19 of 25 patients with other heritable disorders of connective tissue and all 13 normal subjects were correctly classified as "non-Marfan" by these assays (P less than 0.001). CONCLUSIONS: These results document consistent, relatively specific abnormalities of microfibrillar fibers in the Marfan syndrome. The biomechanical incompetence of these structural elements, due to quantitative or qualitative abnormalities, may account for the pleiotropic clinical manifestations of the disease. Therefore, various defects in the expression, structure, assembly, or degradation of the constituent structural glycoprotein (or glycoproteins) of microfibrils may be implicated in the causation of the Marfan syndrome.

Actin Cytoskeleton↗
PubMed1992

Genetic linkage of the Marfan syndrome, ectopia lentis, and congenital contractural arachnodactyly to the fibrillin genes on chromosomes 15 and 5. The International Marfan Syndrome Collaborative Study.

BACKGROUND: The large glycoprotein fibrillin is a structural component of elastin-containing microfibrils found in many tissues. The Marfan syndrome has been linked to the fibrillin gene on chromosome 15, but congenital contractural arachnodactyly, which shares some of the physical features of the syndrome, has been linked to the fibrillin gene on chromosome 5. METHODS: Using specific markers for the fibrillin genes, we performed genetic linkage analysis in 28 families with the Marfan syndrome and 8 families with four phenotypically related disorders--congenital contractural arachnodactyly (3 families), ectopia lentis (2), mitral-valve prolapse syndrome (2), and annuloaortic ectasia (1). RESULTS: Genetic linkage was established between the Marfan syndrome and only the fibrillin gene on chromosome 15, with a maximum lod score of 25.6 (odds for linkage, 10(25.6):1). Ectopia lentis was also linked to the fibrillin gene on chromosome 15, whereas congenital contractural arachnodactyly was linked to the fibrillin gene on chromosome 5. There was no linkage of mitral-valve prolapse to the fibrillin gene on chromosome 5; studies of chromosome 15 were not informative. Annuloaortic ectasia was not linked to either fibrillin gene. CONCLUSIONS: The Marfan syndrome appears to be caused by mutations in a single fibrillin gene on chromosome 15. Diagnosis of the Marfan syndrome by genetic linkage and analysis is now feasible in many families.

Base Sequence↗
PubMed1986

Monoclonal antibodies to a subfraction of merino wool high-tyrosine proteins.

Monoclonal antibodies were prepared which react with members of the high-tyrosine type proteins from Merino wool. Specificity was confirmed by the use of Western transfer immunoassays and by enzyme-linked immunosorbent assay on purified fractions. Immunofluorescent staining of sections of wool follicles using the antibodies showed that the proteins were present in the developing wool shaft but that staining was asymmetric, indicating specific location of the proteins in the orthocortex of the fibres. Immunogold-electron microscopy confirmed that one of the antibodies bound to the keratin microfibril bundles.

Animals↗
PubMed1973

Ethylene in plant growth.

Ethylene inhibits cell division, DNA synthesis, and growth in the meristems of roots, shoots, and axillary buds, without influencing RNA synthesis. Apical dominance often is broken when ethylene is removed, apparently because the gas inhibits polar auxin transport irreversibly, thereby reducing the shoot's auxin content just as if the apex had been removed. A similar mechanism may underly ethylene-induced release from dormancy of buds, tubers, root initials, and seeds. Often ethylene inhibits cell expansion within 15 min, but delays differentiation so that previously expanding cells eventually grow to enormous size. These cells grow isodiametrically rather than longitudinally because their newly deposited cellulose microfibrils are laid down longitudinally rather than radially. Tropistic responses are inhibited when ethylene reversibly and rapidly prevents lateral auxin transport. In most of these cases, as well as certain other instances, ethylene action is mimicked by application of an auxin, since auxins induce ethylene formation. Regulation by ethylene extends to abscission, to flower formation and fading, and to fruit growth and ripening. Production of ethylene is controlled by auxin and by red light, auxin acting to induce a labile enzyme needed for ethylene synthesis and red light to repress ethylene production. Numerous cases in which a response to red light requires an intervening step dependent upon inhibition of ethylene production have been identified. Ethylene action requires noncovalent binding of the gas to a metal-containing receptor having limited access, and produces no lasting product. The action is competitively inhibited by CO(2), and requires O(2). Ethylene is biosynthesized from carbons 3 and 4 of methionine, apparently by a copper-containing enzyme in a reaction dependent upon an oxygen-requiring step with a K(m) = 0.2% O(2). The oxidative step appears to be preceded by an energy-requiring step subsequent to methionine formation.

Journal Article↗
PubMed1976

Cellulose biosynthesis in Acetobacter xylinum: visualization of the site of synthesis and direct measurement of the in vivo process.

In vivo synthesis of cellulose by Acetobacter xylinum was monitored by darkfield light microscopy. Cellulose is synthesized in the form of a ribbon projecting from the pole of the bacterial rod. The ribbon elongates at a rate of 2 mum min-1. The ribbon consists of approximately 46 microfibrils which average 1.6 X 5.8 nm in cross section. The observed microfibrillar elongation rate corresponds to 470 amol of glucose/cell per hr assimilated into cellulose. Electron microscopy of the process using negative staining, sectioning, and freeze-etching indicated the presence of approximately 50 individual synthetic sites organized in a row along the longitudinal axis of the bacterial rod and in close association with the outer envelope. The process of cellulose synthesis in Acetobacter is compared with that in eukaryotic plant cells.

Cellulose↗
PubMed1979

Roles of actin during sporocarp culmination in the simple mycetozoan Planoprotostelium aurantium.

Developing unicellular fruiting bodies of the protostelid Planoprotostelium aurantium examined by electron microscopy are shown to have a cortical zone of microfilaments that surrounds the lower portion of the sporogenic cell and extends into a cytoplasmic plug that fills the lumen of the tubular, microfibrillar stalk. Labeling with the S-1 fragment of myosin indicates that the microfilaments are actin. A model is proposed in which the actin is involved both in a contractile process that serves to raise the sporogen off the substrate at the tip of the stalk and in a cytoskeletal role by either directly or indirectly localizing the synthesis and orientation of the stalk tube microfibrils. The process of culmination in protostelids is compared to that of the multicellular dictyostelid cellular slime molds.

Journal Article↗
PubMed1980

Deposition of fibronectin in the course of reverse transformation of Chinese hamster ovary cells by cyclic AMP.

The Chinese hamster ovary (CHO) cell, like other transformed cells, has lost the fibronectin deposit around its membrane. Treatment with cyclic AMP derivatives restores the typical fibroblastic deposit of fibronectin. Thus, the reverse transformation process induced by cyclic AMP (cAMP) in the CHO cell restores this important property as well as other morphological, biochemical, and growth behavioral characteristics of the normal fibroblastic state. The fibronectin deposit occurs significantly later in time than do other characteristics of the reverse transformation reaction and may therefore reflect a metabolic action that requires other cAMP effect to precede it. The restoration of fibronectin deposition in response to cAMP derivatives is also exhibited by vole cells transformed by avian sarcoma virus, but it is not by HeLa cell. Addition of Colcemid, which disrupts microtubules, to CHO cells containing a fibronectin deposit induced by cAMP derivatives causes little or no erosion of the deposit, but cytochalasin B, which disrupts 5-nm microfilaments, eliminates it completely. Thus, various features of the action of cAMP derivatives on CHO and related cells require integrity of the cellular microfibrils--in some cases microtubules only, in some cases 5-nm microfilaments only, and in some cases both classes of fibrils.

Animals↗
PubMed1994

Dynamic reorientation of cortical microtubules, from transverse to longitudinal, in living plant cells.

The direction in which plant tissue cells expand is reflected in the alignment of microtubules in the cortical array. When microtubules and coaligned wall microfibrils are arranged transversely around the cell, turgor pressure is chaneled into cell elongation. However, various agents (such as wounding, ethylene, abscisic acid) can cause the microtubules to reorientate by 90 degrees so that they become aligned parallel to the cell's long axis, allowing lateral expansion instead of elongation. The mechanism by which microtubules undergo rapid shifts of alignment is crucial to understanding growth control in plants, but because current models are derived from studies on fixed cells, nothing is known about the dynamics of converting one microtubule alignment to another. Cells tend to have one predominant microtubule alignment--transverse, oblique, or longitudinal--but it is not established whether each represents a stable independent set that only changes by rounds of complete de- and repolymerization, or whether reorientation is a more continuous process involving movement of stable or dynamic microtubules. By microinjecting pea (Pisum sativum) epidermal cells with rhodamine-conjugated brain tubulin and optically sectioning them by confocal laser scanning microscopy, we could follow labeled microtubules for up to 2 hr as they reorientate. Reorientation does not occur by complete depolymerization of microtubules in one orientation followed by polymerization of a new array in another orientation. Instead, increased numbers of discordant microtubules in nontransverse alignment appear in particular locations. Neighboring microtubules then adopt the new alignment, so that there is a stage during which different alignments coexist before the array on the outer tangential cell face finally adopts a uniform steeply oblique/longitudinal configuration. Rapid fluorescence recovery after photobleaching confirms that bundles of cortical microtubules are not stable but exhibit properties consistent with dynamic instability. Dynamic microtubules offer a mechanism for rapid growth responses to a range of physiological stimuli.

Journal Article↗
PubMed1994

Assembly of synthetic cellulose I.

Cellulose microfibrils with an electron diffraction pattern characteristic of crystalline native cellulose I have been assembled abiotically by means of a cellulase-catalyzed polymerization of beta-cellobiosyl fluoride substrate monomer in acetonitrile/acetate buffer. Substantial purification of the Trichoderma viride cellulase enzyme was found to be essential for the formation of the synthetic cellulose I allomorph. Assembly of synthetic cellulose I appears to be a result of a micellar aggregation of the partially purified enzyme and the substrate in an organic/aqueous solvent system favoring the alignment of glucan chains with the same polarity and extended chain conformation, resulting in crystallization to form the metastable cellulose I allomorph.

Acetates↗
PubMed1997

Expression of a divergent expansin gene is fruit-specific and ripening-regulated.

Expansins are proteins that induce extension in isolated plant cell walls in vitro and have been proposed to disrupt noncovalent interactions between hemicellulose and cellulose microfibrils. Because the plant primary cell wall acts as a constraint to cell enlargement, this process may be integral to plant cell expansion, and studies of expansins have focused on their role in growth. We report the identification of an expansin (LeExp1) from tomato that exhibits high levels of mRNA abundance and is specifically expressed in ripening fruit, a developmental period when growth has ceased but when selective disassembly of cell wall components is pronounced. cDNAs closely related to LeExp1 were also identified in ripening melons and strawberries, suggesting that they are a common feature of fruit undergoing rapid softening. Furthermore, the sequence of LeExp1 and its homologs from other ripening fruit define a subclass of expansin genes. Expression of LeExp1 is regulated by ethylene, a hormone known to coordinate and induce ripening in many species. LeExp1 is differentially expressed in the ripening-impaired tomato mutants Nr, rin, and nor, and mRNA abundance appears to be influenced directly by ethylene and by a developmentally modulated transduction pathway. The identification of a ripening-regulated expansin gene in tomato and other fruit suggests that, in addition to their role in facilitating the expansion of plant cells, expansins may also contribute to cell wall disassembly in nongrowing tissues, possibly by enhancing the accessibility of noncovalently bound polymers to endogenous enzymic action.

Amino Acid Sequence↗
PubMed1997

Parallel-up structure evidences the molecular directionality during biosynthesis of bacterial cellulose.

The "parallel-up" packing in cellulose Ialpha and Ibeta unit cells was experimentally demonstrated by a combination of direct-staining the reducing ends of cellulose chains and microdiffraction-tilting electron crystallographic analysis. Microdiffraction investigation of nascent bacterial cellulose microfibrils showed that the reducing end of the growing cellulose chains points away from the bacterium, and this provides direct evidence that polymerization by the cellulose synthase takes place at the nonreducing end of the growing cellulose chains. This mechanism is likely to be valid also for a number of processive glycosyltransferases such as chitin synthases, hyaluronan synthases, and proteins involved in the synthesis of nodulation factor backbones.

Bacteria↗
PubMed1995

Isolation of a novel latent transforming growth factor-beta binding protein gene (LTBP-3).

This paper reports the molecular cloning of a novel gene in the mouse that shows structural similarities to the microfibril protein fibrillin and to the latent transforming growth factor-beta (TGF-beta) binding protein (LTBP), a component of the latent TGF-beta complex. The gene was initially isolated during a low stringency polymerase chain reaction screen of a NIH 3T3 cell cDNA library using primers that amplify a human fibrillin-1 epidermal growth factor-like repeat. Three lines of evidence suggest that the mouse gene is a third member of the LTBP gene family, which we designate LTBP-3. First, the deduced polypeptide, which consists of 15 epidermal growth factor-like repeats, 3 TGF binding protein repeats, and 2 proline- and glycine-rich sequences, shows 38.4% identity with LTBP-1 but only 27% identity with fibrillin-1. Second, the gene appears to be co-expressed in developing mouse tissues with TGF-beta. Third, immunoprecipitation studies using mouse preosteoblast MC3T3-E1 cells and a specific anti-peptide polyclonal antiserum reveal that the mouse polypeptide forms a complex with the TGF-beta 1 precursor. Finally, we note that the LTBP-3 gene was recently localized to a distinct genetic locus (Li, X., Yin, W., Perez-Jurado, L., Bonadio, J., and Francke, U. (1995) Mamm. Genome 6, 42-45). Identification of a third binding protein provides further insight into a mechanism by which latent TGF-beta complexes can be targeted to connective tissue matrices and cells.

3T3 Cells↗
PubMed1995

Primary structure and developmental expression of Fbn-1, the mouse fibrillin gene.

Previous studies have reported > 10 kilobases of human fibrillin-1 cDNA sequence, but a consensus regarding the 5' end of the transcript remains to be worked out. One approach to developing a clear consensus would be to search for regions of evolutionary conservation in transcripts from a related species such as mouse. As reported here, the mouse fibrillin-1 transcript encodes a highly conserved polypeptide of 2,871 amino acids. The upstream sequence that flanks the ATG is considerably less well conserved, however. Indeed, the ATG codon (which occurs in the context of a Kozak consensus sequence and is located just upstream of a consensus signal peptide) signals the point where human and mouse fibrillin-1 sequences cease to be nearly identical. Together, these results are consistent with previous efforts by Pereira et al. (Pereira, L., D'Alessio, M., Ramirez, F., Lynch, J. R., Sykes, B., Pangilinan, T., and Bonadio, J. (1993) Human Mol. Genet. 2, 961-968) to identify the human fibrillin-1 translational start site. Sequences immediately upstream of the ATG are GC-rich and devoid of TATA and CCAAT boxes, which suggests that the mouse fibrillin-1 gene will be broadly expressed. A survey of expression in mouse embryo tissues is consistent with this hypothesis and suggests two novel functions for fibrillin-associated microfibrils in non-elastic connective tissues.

Amino Acid Sequence↗
PubMed1996

Model structure of decorin and implications for collagen fibrillogenesis.

The three-dimensional structure of human decorin, a secreted proteoglycan involved in the regulation of collagen fibrillogenesis and cellular growth, has been modeled based on the crystal structure of the porcine ribonuclease inhibitor. Both proteins contain leucine-rich repeats and share 18% identical residues. This model structure of decorin has an arch shape with the single glycosaminoglycan chain and the three N-linked oligosaccharides located on the same side of the molecule. Decorin was modeled as binding to a polar sequence of collagen type I found in the d band. The inner concave surface is the appropriate size and shape to accommodate only one collagen triple helix of approximately 3 nm in length. The binding of one collagen triple helix to decorin is proposed to play a major role in the formation of the staggered arrangement of collagen molecules within the microfibrils by preventing lateral fusion of collagen molecules.

Amino Acid Sequence↗
PubMed2000

Self-assembly and supramolecular organization of EMILIN.

The primary structure of human Elastin microfibril interface-located protein (EMILIN), an elastic fiber-associated glycoprotein, consists of a globular C1q domain (gC1q) at the C terminus, a short collagenous stalk, a long region with a high potential for forming coiled-coil alpha helices, and a cysteine-rich N-terminal sequence. It is not known whether the EMILIN gC1q domain is involved in the assembly process and in the supramolecular organization as shown for the similar domain of collagen X. By employing the yeast two-hybrid system the EMILIN gC1q domains interacted with themselves, proving for the first time that this interaction occurs in vivo. The gC1q domain formed oligomers running as trimers in native gels that were less stable than the comparable trimers of the collagen X gC1q domain since they did not withstand heating. The collagenous domain was trypsin-resistant and migrated at a size corresponding to a triple helix under native conditions. In reducing agarose gels, EMILIN also migrated as a trimer, whereas under non-reducing conditions it formed polymers of many millions of daltons. A truncated fragment lacking gC1q and collagenous domains assembled to a much lesser extent, thus deducing that the C-terminal domain(s) are essential for the formation of trimers that finally assemble into large EMILIN multimers.

Cell Line↗