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PubMed2002

Sequential exposure and assembly of cyst wall filaments on the surface of encysting Giardia duodenalis.

The mode of appearance and assembly of cyst wall filaments on the surface of Giardia duodenalis trophozoites committed to encyst was analysed by scanning and transmission electron microscopy (SEM and TEM) and by fluorescence microscopy (FM). SEM showed a progressive appearance of fibril patches, predominantly on the anterior area of ventral and dorsal surfaces, which then spread and coalesced. By TEM, ruthenium red (RR) displayed staining in encysting cells as rodlike spots of variable diameter (3-25 nm), possibly microfibril tips with polyanionic moieties, that displayed tangential associations and random orientations over the cell membrane. In FM assays, the 1,10-phenanthroline derivative of ruthenium red (RR/oPHE) was a specific ligand for these assembling fibrils and this staining was significantly blocked by N-acetylgalactosamine (GalNac) and galactosamine (GalN). Interestingly, RR staining was lost when the cyst wall was completely assembled and thickened as observed by TEM and FM. Kinetic FM assays, in which a mAb specific for a 26 kDa Giardia cyst wall polypeptide was used concomitantly with RR/oPHE staining, showed a differential pattern for the appearance and reactivity of polypeptide and assembling GalN/GalNac-rich moieties of Giardia cyst wall.

Animals↗
PubMed2006

Negative Poisson ratio of crystalline cellulose in kraft cooked Norway spruce.

The tensile properties of kraft cooked Norway spruce were studied by tensile testing with in situ X-ray diffraction (XRD). Samples were of earlywood, cooked for varying times. The total lignin content of the samples was between 21.7% and 9.3%. Tensile tests with XRD were performed on wet samples, without XRD on dry samples. The tensile strength, the modulus of elasticity (MOE), and the elongation at fracture/yield were determined. X-ray diffraction was used to determine the microfibril angle (MFA) and the deformation of crystalline cellulose by monitoring the reflections 200 and 004. The (X-ray) Poisson ratio of crystalline cellulose was calculated, both before and after the yield point. The tensile strength and the MOE of the wet samples were significantly lower than in the dry samples. The tensile properties of dry samples were similar to dry earlywood samples of untreated Norway spruce. The MFA only showed notable changes due to strain when it was initially large, when a diminishing effect was observed. The Poisson ratio of crystalline cellulose was negative. The average values ranged between -0.26 and -1.17 before the yield point and between -0.86 and -1.05 after the yield point.

Carbohydrate Conformation↗
PubMed2000

Comparison of the water-holding capacity of wheat bran products prepared by wet and dry smashing methods in vitro and effect on the gastrointestinal retention time in rats in vivo.

Microfibril wheat bran (MFW) prepared by wet smashing of wheat bran using a colloidal mill has the advantages of being more palatable than other wheat bran and easier to apply to various foods. In this study, we investigated water-holding capacity (WHC) and physiological effects of a novel food material, MFW, focusing on shortening of the retention time of the gastrointestinal contents compared to those of dry smashing of wheat bran (DWB) prepared by conventional method, and wheat bran (WB), which is the raw materials. The mean particle size of MFW was 35 microns, and WHC was 5.1 g/g. In contrast, those of DWB were 61 microns and 3.0 g/g, respectively. Those of WB were 420 microns and 5.0 g/g, respectively. The WHC of MFW was 1.7 times greater than that of DWB and comparable to that of WB. The dietary fiber content in MFW, DWB, and WB were 73.5, 66.9 and 70.2%, respectively. Six-week-old Fisher rats were divided into three groups, and fed for 20 days with AIN-76 chow supplemented with MFW, DWB, or WB to a dietary fiber content of 10%. On days 14-16 of the experimental period, the mean retention time (MRT) of gastrointestinal content and fecal weight were measured using solid phase and liquid phase markers. On day 20 of the experimental period, animals were killed, and the water content, pH, composition of short chain fatty acids (SCFAs) in the cecal content and total amounts of SCFAs in the cecum were investigated. MRT in the MFW group was 15.2 +/- 0.8 h in the solid phase, which was significantly shorter than that in the DWB group (18.0 +/- 0.9 h) (p < 0.05), and comparable to that in the WB (15.5 +/- 2.4 h). MRT in the liquid phase was almost the same as that in the solid phase: 14.7 +/- 1.0, 18.4 +/- 0.8, and 16.0 +/- 2.5 h in the MFW, DWB, and WB groups, respectively. The fecal weight, pH, the concentration of SCFA in the cecal content and total amounts of SCFAs in the cecum did not differ among the groups, but the cecal water content was in the order of MFW > WB > DWB, showing a significant difference between each group (p < 0.05). The above finding suggested that MFW is a novel food material with a greater WHC and the ability of shortening the retention time of the gastrointestinal contents compared to DWB.

Animals↗
PubMed2002

Development of oxytalan fibers in the rat molar periodontal ligament.

Although oxytalan fibers are known to be a ubiquitous component of the periodontal ligament, little information has been available concerning their organization in the developing periodontal ligament. In the present study, growth and distribution of oxytalan fibers were examined in the developing periodontal ligament of rat molars aged 11, 14, 19, 21 and 28 days. A quantitative analysis of the fibers was made and the spatial relationship between the fibers and blood vessels was studied by means of a three-dimensional reconstruction of serial sections. At the beginning of root formation, oxytalan fibers appeared at first as dot-like structures around the root sheath as well as in areas very close to blood vessels. These structures were resolved in the electron microscope to be made up of 12-nm-wide microfibrils in the vicinity of the surface of the cells of the root sheath. In the process of development, these dot-like structures elongated into entities with helical appearances. As the development further proceeded, longer oxytalan fibers were produced in the apico-occlusal direction along with blood vessels. Quantitative analysis showed that an increase in oxytalan fibers coincided with an increase in the density of the vascular network in the developing periodontal ligament. Based on the results of the present study, the role of oxytalan fibers in the developing periodontal ligament may be in the maintenance of the integrity of the vascular system as previously suggested.

Age Factors↗
PubMed2003

Solution structure and dynamics of a calcium binding epidermal growth factor-like domain pair from the neonatal region of human fibrillin-1.

Fibrillin-1 is a mosaic protein mainly composed of 43 calcium binding epidermal growth factor-like (cbEGF) domains arranged as multiple, tandem repeats. Mutations within the fibrillin-1 gene cause Marfan syndrome (MFS), a heritable disease of connective tissue. More than 60% of MFS-causing mutations identified are localized to cbEGFs, emphasizing that the native properties of these domains are critical for fibrillin-1 function. The cbEGF12-13 domain pair is within the longest run of cbEGFs, and many mutations that cluster in this region are associated with severe, neonatal MFS. The NMR solution structure of Ca(2+)-loaded cbEGF12-13 exhibits a near-linear, rod-like arrangement of domains. This observation supports the hypothesis that all fibrillin-1 (cb)EGF-cbEGF pairs, characterized by a single interdomain linker residue, possess this rod-like structure. The domain arrangement of cbEGF12-13 is stabilized by additional interdomain packing interactions to those observed for cbEGF32-33, which may help to explain the previously reported higher calcium binding affinity of cbEGF13. Based on this structure, a model of cbEGF11-15 that encompasses all known neonatal MFS missense mutations has highlighted a potential binding region. Backbone dynamics data confirm the extended structure of cbEGF12-13 and lend support to the hypothesis that a correlation exists between backbone flexibility and cbEGF domain calcium affinity. These results provide important insight into the potential consequences of MFS-associated mutations for the assembly and biomechanical properties of connective tissue microfibrils.

Amino Acid Sequence↗
PubMed2004

Importance of exposed aromatic residues in chitinase B from Serratia marcescens 2170 for crystalline chitin hydrolysis.

Chitinase B (ChiB) of S. marcescens has five exposed aromatic residues linearly aligned toward the catalytic cleft, Tyr481 and Trp479 in the C-terminal domain, and Trp252, Tyr240 and Phe190 in the catalytic domain. To determine the contribution of these residues to the hydrolysis of crystalline beta-chitin, site-directed mutagenesis, to replace them by alanine, was carried out. The Y481A, W479A, W252A, and Y240A mutations all decreased the binding activity and hydrolyzing activity toward beta-chitin microfibrils. Substitution of Trp residues affected the binding activity more severely than that of Tyr residues. The F190A mutation decreased neither the binding activity nor the hydrolyzing activity. None of the mutations decreased the hydrolyzing activity toward soluble substrates. These results suggest that ChiB hydrolyzes crystalline beta-chitin via a mechanism in which four exposed aromatic residues play important roles, similar to the mechanism of hydrolysis by ChiA of this bacterium, although the directions of hydrolysis of the two chitinases are opposite.

Catalysis↗
PubMed2005

Molecular genetics of Marfan syndrome.

PURPOSE OF REVIEW: Marfan syndrome, the founding member of connective tissue disorders, is characterized by involvement of three major systems (skeletal, ocular, and cardiovascular) due to alteration in microfibrils. FBN1 at 15q21.1 was found to cause Marfan syndrome in 1991, and in 2004 TGFBR2 at 3p24.1 was newly identified as the Marfan syndrome type II gene. Several studies implied that fibrillin-1 and transforming growth factor-beta (TGF-beta) signaling are functionally related in extracellular matrix. Identification of TGFBR2 mutations in Marfan syndrome type II provided the direct evidence of the relation in humans. RECENT FINDINGS: More than 500 FBN1 mutations have been found in Marfan syndrome, tentative genotype - phenotype correlations have emerged, and mouse models are providing insight into pathogenic mechanisms. TGFBR2 mutations are still limited, however, in 2005 were also reported to cause a new aneurysm syndrome. Functional association between fibrillin-1 and TGF-beta signaling in extracellular matrix has been presented. SUMMARY: This review focuses on recent molecular genetics advances in Marfan syndrome and overlapping connective tissue disorders. Mutation spectrum of FBN1 and TGFBR2 in relation to phenotype is presented. Functional relation between fibrillin-1 and TGF-beta signaling is discussed. Future prospects in the study of Marfan syndrome are presented.

Animals↗
PubMed2000

Ultrastructural study of direct bone formation induced by BMPs-collagen complex implanted into an ectopic site.

OBJECTIVE: Some authors have reported that direct bone formation is ectopically induced by bone morphogenetic proteins (BMPs) independently of cartilage formation when type I collagen is used as a carrier. This study ultrastructurally investigated the mechanism of direct bone formation by BMPs-collagen complex. MATERIALS AND METHODS: Partially purified BMPs were combined with atelopeptide type I collagen (AC) and were implanted into the calf muscles of rats (n = 20). Tissue specimens were removed on days 7, 10, 14, and 21 after implantation. RESULTS: Ultrastructurally, several regions near the pellet rim showed evidence of early calcification on day 10. In the uncalcified regions, mitochondrial calcification was seen in mesenchymal cells near AC fibers. The initially calcified regions contained numerous calcified granules deposited in the AC fibers. Some of these granules adhered to the cell membrane of osteogenic cells. In the highly calcified regions, some osteogenic cells secreted uncalcified matrix and deposited needle-like crystals and calcified collagen microfibrils on the AC fibers. CONCLUSION: This study suggests that the mesenchymal cells invading BMPs-AC complex closely contacted the AC fibers, differentiated into osteogenic cells, and deposited calcified matrix on the AC fibers, resulting in direct osteoinduction without cartilage formation.

Animals↗
PubMed2006

The molecular genetics of Marfan syndrome and related disorders.

Marfan syndrome (MFS), a relatively common autosomal dominant hereditary disorder of connective tissue with prominent manifestations in the skeletal, ocular, and cardiovascular systems, is caused by mutations in the gene for fibrillin-1 (FBN1). The leading cause of premature death in untreated individuals with MFS is acute aortic dissection, which often follows a period of progressive dilatation of the ascending aorta. Recent research on the molecular physiology of fibrillin and the pathophysiology of MFS and related disorders has changed our understanding of this disorder by demonstrating changes in growth factor signalling and in matrix-cell interactions. The purpose of this review is to provide a comprehensive overview of recent advances in the molecular biology of fibrillin and fibrillin-rich microfibrils. Mutations in FBN1 and other genes found in MFS and related disorders will be discussed, and novel concepts concerning the complex and multiple mechanisms of the pathogenesis of MFS will be explained.

Activin Receptors, Type I↗
PubMed2004

Evidence for a critical contribution of haploinsufficiency in the complex pathogenesis of Marfan syndrome.

Marfan syndrome is a connective tissue disorder caused by mutations in the gene encoding fibrillin-1 (FBN1). A dominant-negative mechanism has been inferred based upon dominant inheritance, mulitimerization of monomers to form microfibrils, and the dramatic paucity of matrix-incorporated fibrillin-1 seen in heterozygous patient samples. Yeast artificial chromosome-based transgenesis was used to overexpress a disease-associated mutant form of human fibrillin-1 (C1663R) on a normal mouse background. Remarkably, these mice failed to show any abnormalities of cellular or clinical phenotype despite regulated overexpression of mutant protein in relevant tissues and developmental stages and direct evidence that mouse and human fibrillin-1 interact with high efficiency. Immunostaining with a human-specific mAb provides what we believe to be the first demonstration that mutant fibrillin-1 can participate in productive microfibrillar assembly. Informatively, use of homologous recombination to generate mice heterozygous for a comparable missense mutation (C1039G) revealed impaired microfibrillar deposition, skeletal deformity, and progressive deterioration of aortic wall architecture, comparable to characteristics of the human condition. These data are consistent with a model that invokes haploinsufficiency for WT fibrillin-1, rather than production of mutant protein, as the primary determinant of failed microfibrillar assembly. In keeping with this model, introduction of a WT FBN1 transgene on a heterozygous C1039G background rescues aortic phenotype.

Abnormalities, Multiple↗
PubMed2002

Elastic fibres.

Elastic fibres are essential extracellular matrix macromolecules comprising an elastin core surrounded by a mantle of fibrillin-rich microfibrils. They endow connective tissues such as blood vessels, lungs and skin with the critical properties of elasticity and resilience. The biology of elastic fibres is complex because they have multiple components, a tightly regulated developmental deposition, a multi-step hierarchical assembly and unique biomechanical functions. However, their molecular complexity is at last being unravelled by progress in identifying interactions between component molecules, ultrastructural analyses and studies of informative mouse models.

Animals↗
PubMed2000

Elastic and collagenous networks in vascular diseases.

Supravalvular aortic stenosis (SVAS), Marfan syndrome (MFS) and Ehlers-Danlos syndrome type IV (EDS IV) are three clinical entities characterized by vascular abnormalities that result from mutations of structural components of the extracellular matrix (ECM). Analyses of naturally occurring human mutations and of artificially generated deficiencies in the mouse have provided insights into the pathogenesis of these heritable disorders of the connective tissue. SVAS is associated with haploinsufficiency of elastin, one of the two major components of the elastic fibers. SVAS is characterized by narrowing of the arterial lumen due to the failure of regulation of cellular proliferation and matrix deposition. Mutations in fibrillin 1 are the cause of dissecting aneurysm leading to rupture of the ascending aorta. Fibrillin-1 is the building block of the microfibrils that span the entire thickness of the aortic wall and are a major component of the elastic fibers that reside in the medial layer. The vascular hallmark of EDS IV is rupture of large vessels. The phenotype is caused by mutations in type III collagen. The mutations ultimately affect the overall architecture of the collagenous network and the biomechanical properties of the adventitial layer of the vessel wall. Altogether, these genotype-phenotype correlations document the diversified contributions of distinct extracellular macroaggregates to the assembly and function of the vascular matrix.

Animals↗
PubMed1999

From cellulose to cell.

The cell wall is often pictured as a more-or-less random feltwork of cellulose microfibrils in association with other polysaccharide and protein complexes. There is evidence from morphology, morphogenesis and mechanics that the structures in the cell wall are far more regular and that their interactions are driven by their chemical and morphological properties. In particular, a model based on liquid crystal structures has more than morphological implications.

Biomechanical Phenomena↗
PubMed2001

Cellulose in cyanobacteria. Origin of vascular plant cellulose synthase?

Although cellulose biosynthesis among the cyanobacteria has been suggested previously, we present the first conclusive evidence, to our knowledge, of the presence of cellulose in these organisms. Based on the results of x-ray diffraction, electron microscopy of microfibrils, and cellobiohydrolase I-gold labeling, we report the occurrence of cellulose biosynthesis in nine species representing three of the five sections of cyanobacteria. Sequence analysis of the genomes of four cyanobacteria revealed the presence of multiple amino acid sequences bearing the DDD35QXXRW motif conserved in all cellulose synthases. Pairwise alignments demonstrated that CesAs from plants were more similar to putative cellulose synthases from Anabaena sp. Pasteur Culture Collection 7120 and Nostoc punctiforme American Type Culture Collection 29133 than any other cellulose synthases in the database. Multiple alignments of putative cellulose synthases from Anabaena sp. Pasteur Culture Collection 7120 and N. punctiforme American Type Culture Collection 29133 with the cellulose synthases of other prokaryotes, Arabidopsis, Gossypium hirsutum, Populus alba x Populus tremula, corn (Zea mays), and Dictyostelium discoideum showed that cyanobacteria share an insertion between conserved regions U1 and U2 found previously only in eukaryotic sequences. Furthermore, phylogenetic analysis indicates that the cyanobacterial cellulose synthases share a common branch with CesAs of vascular plants in a manner similar to the relationship observed with cyanobacterial and chloroplast 16s rRNAs, implying endosymbiotic transfer of CesA from cyanobacteria to plants and an ancient origin for cellulose synthase in eukaryotes.

Amino Acid Sequence↗
PubMed2001

"Masked" pseudoexfoliation syndrome in unoperated eyes with circular posterior synechiae: clinical-electron microscopic correlation.

OBJECTIVE: To investigate the prevalence of "masked" pseudoexfoliation (PEX) syndrome in eyes with circular posterior synechiae receiving antiglaucomatous therapy with miotics. DESIGN: Cross-sectional prospective study. METHODS: Twenty-eight eyes of 27 consecutive patients with circular posterior synechiae and a history of miotic drug use without previous intraocular surgery, inflammation, or trauma, and without conventional signs of PEX material in the anterior chamber were included in the study. All eyes were investigated by slitlamp biomicroscopy and gonioscopy of the anterior chamber before extracapsular cataract surgery for the presence of typical PEX-associated iris pigment epithelial changes, such as peripupillary atrophy and trabecular meshwork melanin granule deposition. The anterior chamber depth, lens thickness, and axial lengths of the eyes were measured by A-scan immersion sonography. The excised anterior lens capsules obtained during extracapsular cataract surgery were investigated for the presence of precapsular fibrillar PEX deposits by electron microscopy. MAIN OUTCOME MEASURE: The prevalence of masked PEX syndrome in eyes with circular posterior synechiae receiving antiglaucomatous therapy with miotics. RESULTS: Transmission electron microscopy of unselected nonserial sections revealed a precapsular layer consisting of typical PEX fibers or microfibrils, which indicated early stages of PEX syndrome in 18 (64%) of 28 eyes with circular posterior synechiae. Melanin granules were frequently found adhering to the fibrillar layer. Eyes with precapsular fibrillar deposits showed significantly greater trabecular meshwork pigmentation than eyes without such deposits. Differences in age, lens thickness, axial length of the eye, anterior chamber depth, and degree of peripupillary atrophy were, however, not statistically significant between the groups with and without electron microscopic evidence of PEX deposits. CONCLUSIONS: Circular posterior synechiae were more frequently associated with manifest or early stages of PEX syndrome. However, the formation of broad posterior synechiae in miosis prevented a definite clinical diagnosis based on the classic changes of the anterior lens capsule. In eyes with spontaneous or miotic-induced circular posterior synechiae without other obvious cause, the masked variant of PEX syndrome should always be considered.

Aged↗
PubMed2001

Unilateral or asymmetric pseudoexfoliation syndrome? An ultrastructural study.

BACKGROUND: Clinically, most patients with pseudoexfoliation (PEX) syndrome reveal only unilateral ocular involvement. However, the generalized nature of the disorder suggests that PEX syndrome is clinically asymmetric rather than strictly unilateral. OBJECTIVE: To perform an ultrastructural study of the contralateral eyes in patients with unilateral PEX syndrome. METHODS: Five pairs of donor eyes with slitlamp microscopic, macroscopic, and light microscopic evidence of unilateral PEX syndrome and 6 normal control eyes were investigated by transmission electron microscopy and light and electron microscopic immunohistochemistry using antibodies against the human natural killer (HNK-1) epitope and against latent transforming growth factor beta1-binding protein, both markers for the identification of PEX deposits. RESULTS: Ultrastructural alterations were observed in anterior segment tissues of all apparently not involved fellow eyes. These included (1) deposits of typical PEX fibrils on the iris and ciliary epithelia and in the dilator muscle of the iris; (2) increased accumulation of extracellular matrix, including microfibrils and reduplicated basement membrane material in the periphery of iris vessels, in the dilator muscle and in the juxtacanalicular tissue of the trabecular meshwork; and (3) degenerative changes of the iris pigment epithelium and dilator muscle cells. Latent transforming growth factor beta1-binding protein- and HNK-1-positive deposits indicating PEX material accumulations were detected in the periphery of iris vessels and in the dilator muscle in all affected and contralateral eyes, but not in the control eyes. CONCLUSIONS: These subclinical alterations of contralateral eyes in clinically so-called unilateral PEX syndrome support the concept that PEX syndrome is a generalized basically bilateral disorder with a clinically marked asymmetric manifestation. The iris changes may account for the clinical signs characteristic of early stages, such as melanin dispersion, peripupillary atrophy, trabecular meshwork pigmentation, and insufficient asymmetric mydriasis. The findings should be considered in the clinical management of the patients. CLINICAL RELEVANCE: In view of the fact that PEX syndrome is the most common identifiable cause of open-angle glaucoma worldwide and as it is an important risk factor for a wide spectrum of ocular complications, particularly during cataract surgery, the potential involvement of both eyes in the PEX process is of clinical significance.

Aged↗
PubMed1983

Microfibrillar protein and phospholipid in granular corneal dystrophy.

Keratoplasty specimens from eight patients with granular corneal dystrophy (GCD) and age-matched control subjects were examined by combinations of immunohistological stains, transmission electron microscopy (TEM), and sodium dodecyl sulfate gel electrophoresis. Fresh frozen sections from corneas with GCD stained positively with antibodies to microfibrillar protein by immunofluorescence. Routine TEM disclosed that the granules had central electron-dense areas partially surrounded by 9- to 10-nm tubular microfibrils. Material eluted from corneas with GCD showed denser peptide bands at 65 and 110 kilo than in normal corneas. Stains were negative for elastin, amyloid, neutral lipids, cholesterol, and glycosaminoglycan. Luxol fast blue MBSN stain was strongly positive in the granules in all cases examined. Immunofluorescent stains were negative with antibodies to plasma fibronectin (cold insoluble globulin), laminin, collagens I to V, basement membrane proteoglycan, tropoelastin, and keratin. In two corneas with GCD an increased lipid content was found in every phospholipid class, although cholesterol content was unchanged. Alterations in the fatty acid profiles of phospholipids were also observed.

Contractile Proteins↗
PubMed1993

Anterior capsule opacification in monkey eyes with posterior chamber intraocular lenses.

OBJECTIVE: To examine the morphologic features of anterior capsule opacifications in pseudophakic monkey eyes. METHODS: Extracapsular lens extraction with implantation of posterior chamber intraocular lenses in six monkey eyes. Eyes were enucleated 2, 4, and 12 months after implantation and then studied with light and electron microscopy. Distribution of proteoglycans was also examined with cuprolinic blue staining. RESULTS: Anterior capsule opacifications were composed of proliferated cellular and extracellular matrix components situated between the anterior capsule and the optics of the intraocular lens. The morphologic features of the proliferated cells were consistent with epithelial cells, and these cells probably represented lens epithelial cells. The extracellular matrix, which consisted of collagen fibrils, basal lamina-like material, and microfibrils, was most prominent in the specimens obtained 12 months after lens implantation. The extracellular matrix contained proteoglycans that showed positive staining with cuprolinic blue. CONCLUSIONS: Anterior capsule opacifications consisted of proliferated lens epithelial cells and aberrant extracellular matrix.

Animals↗