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PubMedDate not supplied

Quantitative analysis of animal model lens anatomy: accommodative range is related to fiber structure and organization.

PURPOSE: The results of a recent study on accommodation in humans and baboons has revealed that lens fiber structure and organization are key components of the mechanism of accommodation. Dynamic focusing involves the controlled displacement and replacement, or realignment, of cortical fiber-ends at sutures as the mechanism of accommodation at the fiber level. This emended explanation of the mechanism of accommodation raises the following question: as the structure of crystalline lenses are only similar, not identical between species, is accommodative amplitude related to differences in the structure and organization of fibers between species? To address this question, we have quantitatively examined the structure and organization of fibers in a number of the more commonly used animal models (mice, cattle, frogs, rabbits and chickens) for lens research. MATERIALS AND METHODS: Lenses (a minimum of 12-18 lenses/species) from mice, cattle, frogs and rabbits were used for this study. Prior to fixation for structural analysis, measurements of the gross shape of the lenses (equatorial diameter, anterior and posterior minor radii [anterior + posterior minor radius = polar axis]) were taken directly through a stereo surgical dissecting microscope equipped with an ocular reticle. Lenses were then prepared for and examined by light (LM), transmission (TEM) and scanning electron microscopy (SEM). Scale computer-assisted drawings (CADs) of lenses and lens fibers were then constructed from quantitative data as described above and from quantitative data contained in micrographs. RESULTS: The differences in fiber structure and organization that effect accommodative range arise early in development and are continued throughout lifelong lens growth. In umbilical suture lenses (avian) secondary fibers develop with almost completely tapered anterior ends (85-90% reduction of their measures of width and thickness at the equator). By comparison, in lenses with line sutures (e.g. frogs and rabbits) secondary fibers develop with just a 50-60% reduction in anterior fiber taper. In lenses with Y sutures (mice and cattle), fiber width taper is only 25-40%. However, in all cases, while the taper of the posterior end width of fibers is just slightly less (approx. 15-20%) than that of anterior ends, posterior end thickness is only reduced by one half that of anterior thickness. CONCLUSIONS: In humans, the mechanism of accommodation at the fiber level involves the controlled realignment of very flattened and flared, rather than tapered fiber-ends at sutures. In this manner, the simultaneous increase in lens thickness and surface curvature in the accommodated state is the result of fiber-ends being overlapped along multiple (9-12) suture branches covering the majority of the anterior and posterior surfaces. The results of this animal study strongly suggest that accommodative range is directly related to quantitative differences in fiber structure and organization in the different suture types. The very broad accommodative range in birds is made possible, at least in part, by the almost complete tapering of fiber-ends at umbilical sutures. In contrast, the essentially negligible accommodative range of animals that have line- and Y-suture lenses is at least partially the result of the fact that these lenses have fibers with very little end taper. Thus, the blunt ends of fibers in line- and Y-suture lenses precludes any significant overlap of end segments to effect accommodation.

Amphibians↗
PubMed1989

Effect of swim exercise training on human muscle fiber function.

This study examined the effect of a typical collegiate swim-training program and an intensified 10-day training period on the peak tension (Po), negative log molar Ca2+ concentration (pCa)-force, and maximal shortening speed (Vmax) of the slow-twitch type I and fast-twitch type II fibers of the deltoid muscle. Over a 10-wk period, the swimmers averaged 4,266 +/- 264 m/day swimming intermittent bouts of front crawl, kicking, or pulling. The training program induced an almost twofold increase in the mitochondrial marker enzyme citrate synthase. Po of the single fibers was not altered by either the training or 10-day intensive training programs, and no significant differences were observed in the Po (kg/cm2) of type I compared with the type II fibers. The type II fiber diameters were significantly larger than the type I fibers (94 +/- 4 vs. 80 +/- 2 microns), and although fiber diameters were unaffected by the training, the 10-day intensive training significantly reduced the type II fiber diameter. The type I fibers from the trained swimmers showed pCa-force curves shifted to the right such that higher free Ca2+ levels were required to elicit a given percent of Po (for values less than 0.5 Po). The activation threshold (pCa) for the onset of tension and the pCa required to elicit one-half maximal tension were not altered by the training in either fiber type. Fiber Vmax (measured by the slack test) was fivefold higher in type II compared with type I fibers (4.85 +/- 0.50 vs. 0.86 +/- 0.04 fiber lengths/s). The exercise-training program significantly increased and decreased the Vmax of the slow and fast fibers, respectively. The 10 days of intensified training produced a further significant decrease in the Vmax of the type II fibers. After a period of detraining, the Vmax of both fiber types returned to the control level. The force-velocity relation was not significantly altered in either fiber type by the swim training; however, the intensified training significantly depressed the velocity of the type II fiber at all loads studied. The Vmax changes with exercise training are likely explained by an exercise-induced expression of fast myosin in slow fibers and slow myosin in fast fibers.

Adult↗
PubMed1994

Relation of regional cross-fiber shortening to wall thickening in the intact heart. Three-dimensional strain analysis by NMR tagging.

BACKGROUND: The mechanism by which small amounts of myofiber shortening lead to extensive wall thickening is unknown. When isolated fibers shorten, they thicken in the two orthogonal directions. In situ fibers, however, vary in their orientation through the wall, and each is tethered to near or distant neighbors, which allows shortening to occur both in the direction of the fibers and also perpendicular to them. This "cross-fiber" shortening may enable the wall to shorten in two directions and thereby thicken extensively in the third. METHODS AND RESULTS: Nuclear magnetic resonance tagging is a noninvasive method of labeling and tracking myocardium of the entire heart in three dimensions that does not interfere with myocardial motion. To investigate the presence and importance of cross-fiber shortening in the intact left ventricle, 10 closed-chest dogs were studied by nuclear magnetic resonance tagging. Five short-axis and four long-axis images were acquired to reconstruct 32 cubes of myocardium in each dog at end diastole and end systole. Pathological dissection was performed to determine the fiber direction at the epicardium, midwall, and endocardium of each cube. Strain was computed from the three-dimensional cube coordinates in the fiber and cross-fiber directions for epicardial and endocardial surfaces, and thickening of the full wall and its epicardial and endocardial halves was determined. Shear deformations were also calculated. Fiber strain at the epicardium and endocardium was -6.4 +/- 0.7% and -8.5 +/- 0.6% (mean +/- SEM), respectively (difference, P > .05). Cross-fiber strain at epicardium and endocardium was -0.6 +/- 0.5% and -25 +/- 0.6%, respectively (difference, P < .05). Thickening of the full wall reached 32.5 +/- 1.0%, composed of epicardial thickening of 25.5 +/- 0.6% and endocardial thickening of 43.3 +/- 1.0% (difference, P < .05). Fiber/cross-fiber shear strain was small (< 3%). Significant regional differences were present in all strains. A significant correlation was found between the extents of regional thickening and cross-fiber shortening. CONCLUSIONS: Cross-fiber shortening at the endocardium, therefore, far exceeds cross-fiber shortening at the epicardium and fiber shortening at both epicardium and endocardium. Since no active shortening can occur locally in the cross-fiber direction, the extensive endocardial cross-fiber shortening must result from interaction with differently aligned fibers at a distance. The correlation between regional thickening and cross-fiber shortening supports the hypothesis that this interaction is the mechanism for amplifying small amounts of fiber shortening to cause extensive endocardial thickening.

Animals↗
PubMed1992

Expression of type-specific MHC isoforms in rat intrafusal muscle fibers.

Myosin heavy chain (MHC) expression by intrafusal fibers was studied by immunocytochemistry to determine how closely it parallels MHC expression by extrafusal fibers in the soleus and tibialis anterior muscles of the rat. Among the MHC isoforms expressed in extrafusal fibers, only the slow-twitch MHC of Type 1 extrafusal fibers was expressed along much of the fibers. Monoclonal antibodies (MAb) specific for this MHC bound to the entire length of bag2 fibers and the extracapsular region of bag1 fibers. The fast-twitch MHC isoform strongly expressed by bag2 and chain fibers had an epitope not recognized by MAb to the MHC isoforms characteristic of developing muscle fibers or the three subtypes (2A, 2B, 2X) of Type 2 extrafusal fibers. Therefore, intrafusal fibers may express a fast-twitch MHC that is not expressed by extrafusal fibers. Unlike extrafusal fibers, all three intrafusal fiber types bound MAb generated against mammalian heart and chicken limb muscles. The similarity of the fast-twitch MHC of bag2 and chain fibers and the slow-tonic MHC of bag1 and bag2 fibers to the MHC isoforms expressed in avian extrafusal fibers suggests that phylogenetically primitive MHCs might persist in intrafusal fibers. Data are discussed relative to the origin and regional regulation of MHC isoforms in intrafusal and extrafusal fibers of rat hindlimb muscles.

Aging↗
PubMed1994

Comparative investigations of the biodurability of mineral fibers in the rat lung.

The biodurability of various glass fibers, rockwool, and ceramic fibers was examined in rat lungs and compared with natural mineral fibers. Experiments were based on studies that have shown that the biodurability of fibers is one of the essential factors of the carcinogenic potency of these materials. Sized fractions of fibers were instilled intratracheally into Wistar rats. The evenness of distribution of fibers in the lung was checked by scanning electron microscopy (SEM) or careful examination of the fiber suspension before treatment. After serial sacrifices up to 24 months after treatment, the fibers were analyzed by SEM following low temperature ashing of the lungs. Parameters measured included number of fibers, diameter, and length distribution at the various sacrifice dates, so that analyses could be made of the elimination kinetics of fibers from the lung in relation to fiber length (FL). Size selective plots of the fiber elimination correlated with fiber diameters enables the mechanism of the fiber elimination (dissolution, fiber breakage, physical clearance) to be interpreted. The half-time of fiber elimination from the lung ranges from about 10 days for wollastonite to more than 300 days for crocidolite. The biodurability of man-made vitreous fibers (MMVF) is between these values and is dependent on the chemical composition of the fibers and the diameter and length distribution. Results indicate that the in vivo durability of glass fibers is considerably longer than expected from extrapolation of published data on their in vitro dissolution rates.

Animals↗
PubMed1997

[Age-related development of the arrangement of connective tissue fibers in the lamina propria of the human vocal folds--scanning electron microscopic examination with digestion method].

The lamina propria of the human vocal fold consists of a superficial, intermediate, and deep layer. This stratified structure is thought to facilitate phonation. Each layer has different physical properties based on different alignment and distribution of collagen and elastic fibers. In the present study, developmental changes in vocal fold structure were studied in human fetuses, infants, and children, with special reference to the pattern of distribution of collagen and elastic fibers. Vocal fold specimens were obtained at autopsy from 5 fetuses, 7 neonates, 3 infants, 3 children at the age of 1 year, 3 children at 3 years, 3 children at 5 years, 3 children at 12 years, and 5 subjects at ages ranging from 15 to 22 years. Prior to the examination of collagen fibers, elastic fibers and cells were dissolved with 10% sodium hydroxide treatment. Prior to the examination of elastic fibers, collagen fibers and cells were dissolved by treatment with 90% formic acid. The specimens were then dehydrated, dried, ion-coated with platinum, and examined with a scanning electron microscope. In fetuses and infants, thin, coiled fibers were found distributed densely in the anterior, posterior, and deep parts of the lamina propria, while irregular thick fibers were sparsely seen in the superficial layer of the vocal fold. In children aged 1 to 3 years, the dense fibers in the deep part decreased, and the longitudinal fibers in the superficial layer increased. In children at 5 years of age, longitudinal collagen and elastic fibers were noted in all of the layers of the vocal fold. The distribution of fibers was uniform irrespective of the depth. At 12 years of age, thin, coiled fibers were noted in the superficial layer, while thin, irregular fibers were found in the deep layer. At 17 years, differentiation of the superficial and deep layers was more evident. In male subjects after adolescence the curvature of curly collagen fibers decreased, and the diameter of fibers increased. The present findings suggest that the development of the vocal fold in childhood occurs in two steps. In the first step, dense fibers in the anterior, posterior, and deep parts of the lamina propria found in fetuses and infants shift to the anterior and posterior ends of the vocal fold, between which longitudinal fibers appear. During this step only simple phonation is possible. In the second step, differentiation of the superficial and deep layers occurs, and the stratified structure of the vocal fold appears in the teens. This step is probably related to the complicated modality of phonation in this age group. In males, the development of the vocal fold is completed after changes in collagen fibers during the mutation.

Adolescent↗
PubMed1976

Fiber types and size in equine skeletal muscle.

Frozen sections of equine musculus semitendinosus were examined for myosin adenosine triphosphatase (ATPase) and reduced nicotinamide adenine dinucleotide-tetrazolium reductase (NADH-TR), using standard histochemical procedures, and the proportions of the various fiber types and average fiber sectional size were determined. With ATPase staining, approximately 70% of the fibers were classified as alpha fibers (ATPase positive), and 30%, as beta fibers (ATPase negative). In addition, 2 populations of alpha fibers could be readily distinguished on the basis of the intensity of the ATPase reaction, and these were designated alpha positive and alpha intermediate. The relationship of this difference in ATPase reaction to contraction speed of the fibers is not known. With NADH-TR staining, fibers were classified as either red fibers (positive) having aerobic metabolism or white fibers (negative) having primarily anaerobic metabolism. All beta fibers were red by NADH-TR; thus, they conformed to the criteria for beta R fibers. All alpha positive fibers were white by NADH-TR, as were most of the alpha intermediate fibers, and would be classified alpha W. Some of the alpha intermediate fibers gave an intermediate reaction with NADH-TR and could be classified as alpha R fibers which have not transformed to alpha W fibers. The alpha positive fibers were 7 to 10 mum larger in diameter than either beta or alpha intermediate fibers.

Adenosine Triphosphatases↗
PubMed2000

Human cytomegalovirus IE1 promoter/enhancer drives variable gene expression in all fiber types in transgenic mouse skeletal muscle.

BACKGROUND: Versatile transgenic manipulation of skeletal muscle requires knowledge of the expression profiles of diverse promoter/enhancer elements in the transcriptionally specialized fiber types of which muscle is composed. "Universal" viral promoters/enhancers, e.g., cytomegalovirus IE1 (CMV IE1), are of interest as reagents that may drive broad expression. However, a previous study noted a marked heterogeneity of CMV IE1-driven transgene expression among muscle fibers, raising the possibility of fiber-type-restricted expression. The purpose of the present study was to characterize CMV IE1-driven expression in terms of fiber type. RESULTS: We produced two lines of transgenic mice carrying the CMV IE1/ beta-galactosidase construct CMVLacZ, and analyzed transgene expression and fiber type by histochemical analysis of hindlimb muscle sections. In both lines CMVLacZ was expressed in all four major fiber types: type I (slow) and types IIA, IIB and IIX (fast). There was no unique pattern of fiber-type-preferential expression; fiber-type quantitative differences were observed but details varied between muscle regions and between lines. Both lines showed similar fiber-type-independent regional differences in overall expression levels, and a high level of within-fiber-type variability of expression, even among nearby fibers. The soleus muscle showed strong expression and comparatively little within-fiber-type or between-fiber-type variability. CONCLUSIONS: The CMV IE1 promoter/enhancer is not fiber-type-restricted and can be useful for driving germ-line transgene expression in all four fiber types. However, not all fibers express the gene at high levels due in part to regional differences in overall expression levels, and to a high level of within-fiber-type variability. Given the multinucleate syncitial nature of muscle fibers, it is not likely that this variability is due to variegating heterochromatinization. The soleus muscle would make a suitable subject for near-uniform experimental gene expression driven by CMV IE1 elements.

Animals↗
PubMed1997

Transitory expression of alpha cardiac myosin heavy chain in a subpopulation of secondary generation muscle fibers in the pig.

Unlike the random distribution of fiber types seen in skeletal muscles of most mammals, pig muscle exhibits a rosette pattern consisting of islets of slow fibers surrounded by concentric circles of type IIA and IIB fibers. Within each islet of slow fibers, one of the central fibers is a primary myofiber, whereas all others are secondary fibers. The present study demonstrates that a subpopulation of the slow secondary fibers transiently expresses alpha-myosin heavy chain (MHC). Two cDNA libraries were made from longissimus dorsi skeletal muscle of 14-day-old piglet and adult pig atrium; the latter muscle is mainly composed of alpha-MHC. Screening of the libraries with a human anti-alpha-MHC mAb (F8812F8) demonstrated the presence of positive MHC clones in both libraries; the nucleotide sequence of the 3'-untranslated region (3'-UTR) was identical in both libraries. As this MHC 3'-UTR had 75% homology with the human alpha-MHC, it was identified as pig alpha-MHC. Using specific cRNA probes and mAbs against pig alpha-cardiac and beta/slow/type I MHC, we studied the expression of these MHCs in developing pig semitendinosus muscle by combining in situ hybridization and immunocytochemistry on serial sections at 90 days of gestation, and at 1, 6, 35 days and 6 months of age. The results showed that a subpopulation of secondary fibers that directly abut primary fibers, transiently produced alpha-MHC, both at the levels of the protein and its transcript. Subsequently, these fibres expressed beta-MHC. At 1 day, immunocytochemistry showed that 16% of the secondary fibers expressed alpha-MHC, among which 20% did not yet express beta-MHC. At 6 days, alpha- and beta-MHCs were mostly present in the same fibers, i.e., 23% of the secondary fibers. Thereafter, the proportion of secondary fibers reacting with alpha-MHC mAb decreased to 10% at 5 weeks and 0% at 6 months, whereas beta-MHC was still accumulating in about 38% of the secondary fibers. During the period studied, the distribution of alpha- and beta-MHC transcripts closely matched that of the corresponding proteins. Expression of alpha-MHC was not detected in primary type I muscle fibers and slow type I secondary fibers at the periphery of the rosettes of slow fibers. This study is the first unequivocal demonstration of a transitory expression of alpha-MHC in a subpopulation of secondary fibers in a limb skeletal muscle during mammalian development.

Amino Acid Sequence↗
PubMed1991

A WGA-HRP study of the fiber arrangement in the cat optic radiation: a demonstration via three-dimensional reconstruction.

The fiber arrangement of the optic radiation was investigated in fourteen adult cats. The retinotopies of the lateral geniculate nucleus (LGN) were first identified electrophysiologically, and thereafter, wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was iontophoretically injected into defined positions of the LGN. These corresponded to the central (medial LGN), horizontal peripheral (lateral LGN), dorsal (rostral LGN), and ventral (caudal LGN) retina. Geniculocortical fibers from the each position of the LGN and corticogeniculate fibers projecting to these positions were always labeled reciprocally. Labeled terminals were found massively in layer IV with some extending to the lower part of layer III, but layers VI and I also contained substantial numbers. Although most of the labeled neurons were localized in layer VI, some neurons were labeled in layer V and transsynaptically in layer IV. Labeled fibers were superimposed in three-dimensionally reconstructed maps of the white matter for the easy understanding of the pathways connecting the LGN and the visual cortex. They were localized in certain zones in the white matter without wide dispersion; however, we did not obtain any findings which suggested clearly different populations of geniculocortical and corticogeniculate fibers. In agreement with previous studies, fibers from the rostral LGN and the caudal LGN projected to the striate cortex in a regular order, rostrocaudally, and fibers from the medial LGN and the lateral LGN projected to the striate cortex inversely (i.e. lateromedially). This inverse projection resulted because fibers from the lateral LGN traversed fibers from the medial LGN in a lateromedial direction; however, there was only partial crossing of these two pathways. The distribution of geniculocortical fibers together with corticogeniculate fibers formed topographic zones arrayed mediolaterally in the white matter. Thus, fibers of the medial LGN were positioned in the intermediate zone, and fibers of the rostral LGN and the lateral LGN were positioned in the rostral and caudal parts of the lateral zone, respectively. Fibers of the caudal LGN were found in the medial zone. This fiber arrangement displayed a rough centroperipheral retinotopy in that fibers representing the central area were placed between fibers representing the peripheral retina. Finally, this fiber arrangement was compared with that of the optic nerve and optic tract.

Animals↗
PubMed2006

Parallel mechanisms for resting nucleo-cytoplasmic shuttling and activity dependent translocation provide dual control of transcriptional regulators HDAC and NFAT in skeletal muscle fiber type plasticity.

Skeletal muscle fibers exhibit plasticity of their physiological and biochemical properties in response to the firing pattern from the innervating motor neuron. In particular, the gene expression pattern generally characteristic of a slow twitch fiber can be induced in a fast twitch fiber by chronic slow fiber type electrical stimulation. We have studied the nucleo-cytoplasmic distribution of two transcriptional regulators of slow fiber type genes, HDAC4 and NFATc1, both in response to slow fiber type stimulation and in resting conditions using cultured fast twitch skeletal muscle fibers. HDAC4 is present in both cytoplasm and nuclei of resting fibers, and moves out of the nuclei in response to slow fiber type stimulation. The stimulation-dependent nuclear efflux of HDAC4 requires activation of nuclear CaMKII, which phosphorylates nuclear HDAC4 and thus allows its exit of the nucleus. In unstimulated resting fibers, a balance of nuclear efflux and influx of HDAC4 establishes the resting level of nuclear HDAC4. However, the nuclear efflux of HDAC4 in resting fibers does not involve CaMKII. Slow fiber type stimulation also causes NFATc1 translocation from the cytoplasm into muscle fiber nuclei following dephosphorylation by calcineurin (CaN) activated by the elevated cytosolic Ca2+ accompanying fiber stimulation. In resting fibers, NFATc1 exhibits balanced shuttling between cytoplasm and nucleus, but during this shuttling NFATc1 influx does not require CaN and NFATc1 efflux does not require the kinases involved in removing nuclear NFATc1 following prior activity. Thus different enzymes are responsible for HDAC4 nuclear efflux in resting and active fibers, and different pathways mediate NFATc1 nuclear influx and efflux in resting and active fibers. Such dual mechanisms for resting shuttling and active movements provide the potential for the resting level and the rate of translocation during fiber stimulation to be controlled independently for both of the transcriptional regulators HDAC4 and NFATc1.

Animals↗
PubMed1991

Calcium absorption in elderly subjects on high- and low-fiber diets: effect of gastric acidity.

In vitro studies suggest that the effect of fiber in inhibiting calcium absorption is pH dependent. In nine normal, elderly control subjects and eight elderly subjects with achlorhydria, 47Ca was ingested with three test meals: a low-fiber meal (0.5 g dietary fiber), a high-fiber meal (10.5 g), and a high-fiber meal with 120 mL of 0.1 mol HC/L. In control subjects calcium retention, measured in a whole-body counter, was 25.7 +/- 4.0% (mean +/- SD) with the low-fiber meal, 19.1 +/- 1.9% with the high-fiber meal (P less than 0.002 vs low fiber), and 18.9 +/- 3.3% with the high-fiber-plus-acid meal (P less than 0.002 vs low fiber, NS vs high fiber). Calcium absorption in achlorhydric subjects was not different from control subjects: 26.2 +/- 8.0% with low fiber, 19.6 +/- 4.1% with high fiber (P less than 0.04 vs low fiber), and 21.0 +/- 5.8% with high fiber plus acid (P less than 0.04 vs low fiber, NS vs high fiber). We conclude that, in humans, the reduction in calcium absorption with high fiber intake is unaffected by gastric pH.

Absorption↗
PubMed1996

Composition and size of type I, IIA, IID/X, and IIB fibers and citrate synthase activity of rat muscle.

A population of muscle fibers containing a myosin heavy-chain isoform IId (or 2x) has recently been identified in rat muscle. The purpose of this study was to histochemically determine the relative population and size of muscle fibers composed of type IID/X fibers as well as type I, IIA, and IIB fibers to estimate the absolute mass of the different types of fibers in rat muscle. In addition, muscle citrate synthase activity was measured to determine the relationship between fiber composition and muscle oxidative capacity. Seventy-six muscles or muscle parts from the face, neck, shoulder, arm, trunk, hip, thigh, and leg of three adult (4.5-5 mo of age) male Sprague-Dawley rats were removed, weighed, and frozen for histochemical and biochemical analyses. The data demonstrated that type IIB fibers make up 71% of the total muscle mass, type IID/X fibers 18%, type IIA fibers 5%, and type I fibers 6%. The mean cross-sectional area across all muscles was 5,078 +/- 175 microns 2 for type IIB fibers, 3,078 +/- 105 microns2 for type IID/X fibers, 2,045 +/- 80 microns2 for type IIA fibers, and 1,898 +/- 90 microns2 for type I fibers. Citrate synthase activity, an indicator of muscle mitochondrial content, was most closely related to the population of type IIA fibers and was in the rank order of type IIA > I > IID/X > IIB. NADH-tetrazolium reductase staining intensity also confirmed this order. These data demonstrate that type IID/X fibers make up a significant portion of the adult rat muscle mass and are intermediate to type IIA and IIB fibers in regard to fiber size and oxidative potential.

Aerobiosis↗
PubMed2006

Denervation effects on myonuclear domain size of rat diaphragm fibers.

Denervation (DNV) of rat diaphragm muscle (DIAm) leads to selective atrophy of type IIx and IIb fibers, whereas the cross-sectional area of type I and IIa fibers remains unchanged or slightly hypertrophied. DIAm DNV also increases satellite cell mitotic activity and myonuclear apoptosis. Similar to other skeletal muscles, DIAm fibers are multinucleated, and each myonucleus regulates the gene products in a finite fiber volume, i.e., myonuclear domain (MND). MND size varies across DIAm fiber types in rank order, I < IIa < IIx < IIb [fiber type based on myosin heavy chain isoform expression]. We hypothesized that, after DNV, the total number of myonuclei per fiber does not change and, accordingly, that MND changes proportionately to the change in fiber size regardless of fiber type. Adult rats underwent unilateral (right side) DIAm DNV, and after 2 wk single fibers were dissected. Fiber cross-sectional area, myonuclear number, and MND were measured by confocal microscopy, and these values in DNV DIAm were compared with those obtained in controls. After DNV, type I fibers hypertrophied, type IIa fiber size was unchanged, and type IIx and IIb fibers atrophied compared with control. The total number of myonuclei per fiber was not affected by DNV. Accordingly, after DNV, type I fiber MND increased by 25%, whereas it decreased in type IIx and IIb fibers by 50 and 70%, respectively. These results suggest that MND is not maintained after DNV-induced DIAm fiber hypertrophy or atrophy. These results are interpreted with respect to consequent effects of DNV on myonuclear transcriptional activity and protein turnover.

Animals↗
PubMed2000

Muscle fiber type composition and morphometric properties of denervated rat extensor digitorum longus muscle.

AIM: Analysis of fiber type composition and fiber size of extensor digitorum longus (EDL) muscle in rats during 30 days of denervation. METHODS: Fiber types were defined immunohistochemically using monoclonal antibodies specific for slow (type I) and fast fibers (type IIA, IIX, and IIB). Antibodies were applied on transverse sections of denervated extensor digitorum longus muscles 6, 12, and 30 days after denervation. Cross sectional area of muscle fibers was analyzed morphometrically by computerized image analysis. RESULTS: Control EDL muscle was composed of 41% of type IIB, 32% of IIA, 23% of IIX, and 4% of type I muscle fibers. The most profound effect of denervation was observed 30 days after the transection of the sciatic nerve. Denervation decreased the percentage of both type IIB and type IIX muscle fibers to 36% and 13% of the control muscle, respectively (p?0.001 for both), and increased the percentage of types IIA and type I muscle fibers to 42% and 9% of the control, respectively (p<0.001 for both). Morphometric analysis revealed progressive atrophy of all fast muscle fibers, which started 6 days after denervation (p<0.001). Thirty days after the sciatic nerve transection, a strong reduction in fiber size of type IIA, IIX, and IIB muscle fibers was observed (p<0.001 for each type). Type I muscle fibers initially showed the reduction in fiber size (p<0.001) but regained the size of control fibers until day 30. CONCLUSION: Denervation decreased the percentage of type IIX and IIB muscle fibers, with concomitant increase in type IIA and type I muscle fibers. The reduction in fiber size was observed in type IIA, IIX, and IIB muscle fibers.

Animals↗
PubMedDate not supplied

[Isolation by suppression-subtractive hybridization of genes preferentially expressed during early and late fiber development stages in cotton].

As a main natural fiber source, cotton plays an important role in human life. To identify genes preferentially expressed during early and late cotton fiber development, we constructed two fiber subtracted libraries on the basis of PCR-selected subtraction using a pool of nonfiber tissues as the same driver and 10 days postanthesis (DPA) and 20 DPA fiber cells as testers, respectively. Through differential screening, 292 clones in both libraries were identified as being preferentially expressed during fiber development. Sequence analysis showed that 31 unique sequences were found in the library of 10 DPA fibers and 48 unique sequences were obtained in the library of 20 DPA fibers. In addition, there were 13 unique clones in common in both libraries. Many previously reported cotton fiber-related genes were included in both libraries. Northern hybridization was performed to further confirm the differential expression and to determine the pattern of mRNA accumulation of selected clones. As a result, all selected cDNAs showed highly preferential expression in developing cotton fibers. Four genes-putative gibberellin-regulated protein, putative tonoplast intrinsic protein, putative plasma membrane intrinsic protein, and Gossypium hirsutum putative membrane protein-were identified in 10 DPA fiber subtracted library, and they were found to be expressed a lot during early fiber development. On the other hand, those genes screened out of 20 DPA fiber subtracted library, like arabinogalactan protein and fiber glycosyl hydrolase family 19 protein, were found highly expressed in fibers with the maximal transcription level during developmental switch from elongation to cellulose deposition. By subtraction between fibers and five nonfiber tissues, two sets of genes were identified, and their fiber-specific or fiber-preferential expression indicated that they are involved in the network that controls cotton fiber development.

Cloning, Molecular↗
PubMed1987

Dietary fiber: classification, chemical analyses, and food sources.

Dietary fiber's role in the prevention and treatment of constipation has long been known, but now fiber is touted as a cure for many of the ills in Western countries. Although some data exist to relate dietary fiber intake to certain diseases, lack of agreement on what dietary fiber is and how it should be measured make interpreting the data difficult. Further, not all dietary fiber is created equal. Water-soluble fibers, such as pectin and gums, have little effect on stool weight and hence are not appropriate treatment for patients with constipation. Water-insoluble fibers, such as cellulose and hemicellulose, are most effective in aiding laxation but may also limit absorption of minerals and possibly vitamins. Wheat bran is a good source of hemicellulose; vegetables supply cellulose to the diet. Most agencies are recommending a doubling or tripling of dietary fiber intake. Typical recommendations are set at 25 to 50 grams of dietary fiber daily. Different analytical methods for dietary fiber yield conflicting fiber values, and dietary fiber values do not exist for many foods, making fiber recommendations controversial and difficult to achieve. Fiber in the diet should ideally be increased by the consumption of unrefined breads and cereals and more fruits and vegetables. Vegetarians routinely consume 40 to 50 gm dietary fiber daily without ill effect. Fiber supplements may be appropriate for some patients, but the composition of the fiber should be known and be appropriate for the disease being treated. Before fiber supplements are marketed, clinical trials should be conducted to support the use of the supplements in the prevention and treatment of disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary Fiber↗
PubMed1983

Abnormal distribution of fiber types in the slow-twitch soleus muscle of the C57BL/6J dy2J/dy2J dystrophic mouse during postnatal development.

The postnatal development of extrafusal fibers in the slow-twitch soleus muscle of genetically dystrophic C57BL/6J dy2J/dy2J mice and their normal age-matched controls was investigated by histochemical and quantitative methods at selected ages of 4, 8, 12, and 32 weeks. The majority of fibers in the soleus consisted of two kinds, fast-twitch oxidative-glycolytic (FOG) and slow-twitch oxidative (SO), according to reactions for alkaline-stable and acid-stable myosin ATPase and the oxidative enzyme, NADH-tetrazolium reductase. A minor population of fibers, stable for both alkaline- and acid-preincubated ATPase, but variable in staining intensity for NADH-TR, were designated "atypical" fibers. With age, the normal soleus exhibited a gradual increase in the number and proportion of SO fibers and a reciprocal, steady decline in the percentage of FOG fibers. Atypical fibers were numerous at 4 weeks, but were substantially diminished at later ages. Since total extrafusal fiber number remained relatively constant between the periods examined, this change in relative proportions reflects an adaptive transformation of fiber types characteristic of normal postnatal growth. A striking alteration in the number and distribution of fiber types was associated with the dystrophic soleus. At 4 weeks an 18% reduction in total fiber number was already noted. Subsequently, by 32 weeks a further 22% diminution in overall fiber number had occurred. With age, the absolute number and proportion of dystrophic SO fibers were drastically reduced. In contrast, the percentage of dystrophic FOG fibers increased significantly while their absolute numbers between 4 and 32 weeks remained relatively constant. Atypical fibers in the dystrophic solei were found in elevated numbers at all age groups, particularly at 12 weeks. They may, in part, represent attempts at regeneration or an intermediate stage in fiber-type transformation. Microscopically, both of the major fiber types appeared affected, albeit differently, by the dystrophic process. We suggest that a failure or retardation in the normal postnatal conversion of fiber types within the soleus muscle occurs in this murine model for muscular dystrophy.

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