Cross-striated Fibers Research Articles

A Multifunction Muscle in Squid

Some striated muscles are multifunctional; they serve several different roles during locomotion and movement, including acting as motors, brakes, struts, or springs. The few multifunctional muscles that have been reported occur in the cross-striated muscles of animals with complex, jointed, skeletal support systems. In the comparatively simple muscular system of a cephalopod mollusc, we identified an obliquely striated muscle, the nuchal retractor muscle, which appears to be multifunctional. The nuchal retractor is composed of two different fiber types, mitochondria-rich (MR) and mitochondria-poor (MP) fibers; shortening of these fibers retracts the head toward the mantle. Synchronized measurements of head movement (as a proxy for nuchal retractor length) and muscle activation revealed that, while the MP nuchal retractor muscle fibers were activated only for head retractions that occurred during escape jet locomotion, the MR fibers were activated 1) as the head retracted during escape jets and a few jets used during slow swimming, 2) during brief periods of head stasis as the animal changed swimming direction, and 3) during the rapid head extensions that followed an escape jet. Our results suggest that the nuchal retractor muscle may function as a motor, a brake, and, occasionally, a strut. More broadly, our findings suggest that multifunctionality is not restricted to cross-striated fibers or to the muscles of animals with jointed skeletal support systems.

The Musculature of Coleoid Cephalopod Arms and Tentacles.

The regeneration of coleoid cephalopod arms and tentacles is a common occurrence, recognized since Aristotle. The complexity of the arrangement of the muscle and connective tissues of these appendages make them of great interest for research on regeneration. They lack rigid skeletal elements and consist of a three-dimensional array of muscle fibers, relying on a type of skeletal support system called a muscular hydrostat. Support and movement in the arms and tentacles depends on the fact that muscle tissue resists volume change. The basic principle of function is straightforward; because the volume of the appendage is essentially constant, a decrease in one dimension must result in an increase in another dimension. Since the muscle fibers are arranged in three mutually perpendicular directions, all three dimensions can be actively controlled and thus a remarkable diversity of movements and deformations can be produced. In the arms and tentacles of coleoids, three main muscle orientations are observed: (1) transverse muscle fibers arranged in planes perpendicular to the longitudinal axis; (2) longitudinal muscle fibers typically arranged in bundles parallel to the longitudinal axis; and (3) helical or obliquely arranged layers of muscle fibers, arranged in both right- and left-handed helixes. By selective activation of these muscle groups, elongation, shortening, bending, torsion and stiffening of the appendage can be produced. The predominant muscle fiber type is obliquely striated. Cross-striated fibers are found only in the transverse muscle mass of the prey capture tentacles of squid and cuttlefish. These fibers have unusually short myofilaments and sarcomeres, generating the high shortening velocity required for rapid elongation of the tentacles. It is likely that coleoid cephalopods use ultrastructural modifications rather than tissue-specific myosin isoforms to tune contraction velocities.

Ontogenetic development and functioning of the anterior end of Cossura pygodactylata Jones, 1956 (Annelida: Cossuridae)

Juvenile and adult Cossura pygodactylata Jones 1956 from the White Sea were studied using confocal laser scanning microscopy, light microscopy, scanning and transmission electron microscopy. Transformations of the anterior musculature and digestive tract during ontogenesis were investigated. The early juveniles were shown to be lecithotrophic; their pharyngeal cavities were not connected to the intestines, which contained yolk granules. The juveniles bore prototrochs, which are used for movement, although juveniles had parapodial musculature similar to that of the adults. The juveniles presumably inhabit the upper semi-liquid layer of the silt. The muscles of the prostomium and circumbuccal complex change dramatically during ontogenesis. The ultrastructure of the buccal tentacles is redescribed. The tentacles consist of outer ciliated epithelial cells and an inner cylinder formed by epithelio-muscle cells. The blood sinus is situated between the central cylinder and the epithelium. Both juveniles and adults have developed circulatory systems. The whole dorsal vessel forms the heart with walls that consist of cells with circular cross-striated muscular fibres. The inner lumen is occluded by the heart body which is formed by a single row of cells that are tightly pressed together and connected by adherens junctions along their anterior and posterior surfaces. They contain granules and vesicles and bear numerous processes on the outer surface. The heart body most likely has a secretory haemopoetic function. A hypothetical mechanism of protraction and retraction of the buccal tentacles is suggested, and the participation of muscle contraction and relaxation in these movements is described. It is proposed that the protraction of the tentacles is provided by cell rigidity and increases in the blood volume in the tentacles blood sinuses. The development of the circulatory system is likely related to the need to keep the tentacles exposed during feeding while the anterior part of the body cavity is filled with muscle cell processes and there is no coelomic liquid flow. The proposed mechanism of feeding inside the sediment contrasts with that of surface feeding suggested by Tzetlin (Mem Mus Natl Hist Nat 162:137–143, 1994).

Uniaxial Cyclic Strain Drives Assembly and Differentiation of Skeletal Myocytes

Ex vivo engineering of skeletal muscle represents an exciting new area of biotechnology. Although the ability of skeletal muscle cells to sense and respond to mechanical forces is well known, strategies based on the use of mechanical stimuli to optimize myogenesis in vitro remain limited. In this work, we describe a simple but powerful method based on uniaxial cyclic tensile strain (CTS) to induce assembly and differentiation of skeletal myocytes in vitro. Confluent mouse myoblastic precursors cultured on flexible-bottomed culture plates were subjected to either uniaxial or equibiaxial CTS. The uniaxial CTS protocol resulted in a highly aligned array of cross-striated fibers, with the major axis of most cells aligned perpendicularly to the axis of strain. In addition, a short period of myogenin activation and significant increase in the myotube/myoblast ratio and percentage of myosin-positive myotubes was found, indicating an enhanced cell differentiation. In contrast, cells under equibiaxial strain regimen had no clear orientation and displayed signs of membrane damage and impaired differentiation. These results, thus, demonstrate that the selection of a proper paradigm is a key element when discussing the relevance of mechanical stimulation for myogenesis in vitro. This study provides a rational framework to optimize engineering of functional skeletal muscle.

Ultrastructure of the Blood System in the Phoronid Phoronopsis harmeri Pixell, 1912: 1. Capillaries

Four types of blood capillaries of the phoronid Phoronopsis harmeri are described. These are capillaries of the tentacles, of the body, of the stomach plexus, and of the vasoperitoneal tissue. The wall of capillary consists of cells of the coelomic lining, a layer of extracellular matrix, and separate endothelial cells. Myoepithelial coelomic cells of tentacle capillaries contain cross-striated fibers. In capillaries of the body and the stomach plexus, the myofilaments are smooth. In the cells of the wall of vasoperitoneal tissue capillaries, myofilaments are lacking. The cells of the vessel wall of the tentacles, the body, and the vasoperitoneal tissue bear a single cilium. The cells of capillaries of the stomach plexus lack a cilium. The ultrastructure of erythrocytes and amebocytes is described. In the cytoplasm of erythrocytes, there is a basal body. It is assumed that erythrocytes originated from the ciliary cells of the wall of the blood vessels.

The synaptonemal complex protein SCP3 can form multistranded, cross-striated fibers in vivo.

The synaptonemal complex protein SCP3 is part of the lateral element of the synaptonemal complex, a meiosis-specific protein structure essential for synapsis of homologous chromosomes. We have investigated the fiber-forming properties of SCP3 to elucidate its role in the synaptonemal complex. By synthesis of SCP3 in cultured somatic cells, it has been shown that SCP3 can self-assemble into thick fibers and that this process requires the COOH-terminal coiled coil domain of SCP3, as well as the NH2-terminal nonhelical domain. We have further analyzed the thick SCP3 fibers by transmission electron microscopy and immunoelectron microscopy. We found that the fibers display a transversal striation with a periodicity of approximately 20 nm and consist of a large number of closely associated, thin fibers, 5-10 nm in diameter. These features suggest that the SCP3 fibers are structurally related to intermediate filaments. It is known that in some species the lateral elements of the synaptonemal complex show a highly ordered striated structure resembling that of the SCP3 fibers. We propose that SCP3 fibers constitute the core of the lateral elements of the synaptonemal complex and function as a molecular framework to which other proteins attach, regulating DNA binding to the chromatid axis, sister chromatid cohesion, synapsis, and recombination.

Dimensional and numerical growth of helical fibers in leeches: An unusual pattern

This study examines two different aspects of the growth mechanism of helical muscle fibers in adult leeches. The muscle is striated and together with cross-striated fibers shares the precise and rigorous spatial organization of actin and myosin filaments. Leeches continue to grow throughout their life. They have two suckers, which limits growth mainly to the central metameres. Each metamere increases in length and diameter. Each muscle fiber increases by inserting wedge-shaped sarcomeres between complete sarcomeres and by dividing. Before mitosis, the fiber accumulates a large amount of glycogen, and in the area of division the myofilaments change their orientation. The sarcolemma invaginates, and the cytoplasmic core containing organules is divided into two parts. Mitotic figures were observed, but indirect evidence was used as well to confirm this unusual mechanism. J. Exp. Zool. 281:171–187, 1998. © 1998 Wiley-Liss, Inc.

Contractile Properties of Obliquely Striated Muscle from the Mantle of Squid (Alloteuthis Subulata) and Cuttlefish (Sepia Officinalis)

The mechanical properties of obliquely striated muscle fibres were investigated using thin slices of mantle from squid Alloteuthis subulata and cuttlefish Sepia officinalis. Brief tetani or twitch stimuli were used as this pattern is likely to occur during jetting of the intact animal. The length­active force relationship for twitches and tetani (0.1s, 50Hz) was similar to that of vertebrate cross-striated fibres. Passive force at the length giving maximum tetanic force was 0.13±0.05P0 (mean ± s.e.m., N=6, where P0 is maximum isometric tetanus force) and increased steeply at longer lengths. Peak force in a brief isometric tetanus (0.2s, 100­150Hz) was 262±16mNmm-2 cross-sectional area of wet tissue (N=6) for squid, and 226±19mNmm-2 (N=7) for cuttlefish. The force­velocity relationship for isotonic shortening during twitches of squid mantle slices was a 'double hyperbolic' relationship as described for cross-striated fibres by Edman. Fitting Edman's equation to the results gave: P*=1.18±0.07, Vmax=2.43±0.11Ltws-1 and 1/G=0.69±0.13 (N=8), where P* is the intercept on the force axis expressed relative to Ptw, peak isometric twitch force, Vmax is the intercept on the velocity axis, Ltw is the length at which Ptw is produced and G is the constant expressing curvature. The large values of 1/G indicate that the force­velocity relationship is not very curved. Maximum power was produced during shortening at 0.45±0.03Ptw (N=8). Maximum power during twitch contraction was 18.3±1.7mWg-1wetmass or, expressed in relative units, (V/Vmax)(P/Ptw), where V is the velocity during shortening and P is the force during shortening, was 0.16±0.01 (N=8), which is higher than that of many cross-striated locomotor muscles.

Chapter 44 Purification of SF-Assemblin

Publisher Summary Basal apparatuses of many flagellate organisms have with non-contractile cross-striated fibers. In the green algae these fibers have been termed system I fibers, or striated microtubule-associated fibers. System I fibers have been isolated from the biflagellate green alga Spermatozopsis similis . Axonemes and basal body-associated microtubules are removed after homogenization, and basal apparatuses are enriched by differential centrifugation. The isolated basal apparatuses contain two system I fibers that are unequal in length and connected at their proximal ends in such a way as to appear as a single continuous fiber. High-salt extraction and mechanical disintegration of isolated basal apparatuses yield single system I fibers. Dialysis of these extracts against 150m M KCI yields paracrystals that closely resemble the native fibers in filament arrangement and cross-striation pattern. A polyclonal antiserum raised against SF-assemblin from S. similis labels the system I fibers in S. similis and several other flagellate green algae ( Chlamydomonas reinhardtii, Polytomella parva , and Dunaliella bioculata ) by indirect immunofluorescence. Proteins of the same apparent size as SF-assemblin are detected by immunoblotting in C. reinhardtii , P. parva , and Nephroselms olivacea , whereas in D.bioculata a 31-kDa protein is immunoreactive. Analysis of the amino acid sequence and the predicted secondary structure of SF-assemblin shows that the protein has two structural domains: a31-residue-long NH 2 -terminal, nonhelical domain rich in proline, and α-helical rod domain of 253 residues that forms a segmented coiled coil with a 29-residue repeat pattern based on four heptads followed by a skip residue. SF-assembling belongs to a widespread protein family forming microtubule-associated fibers of 2-nm filaments in eukaryotic cells. SF-assembling can be enriched after several cycles of disassembly and reassembly, this chapter is an alternative purification procedure using anion-exchange chromatography. There are details on materials, preparation of basal apparatuses, isolation of system I fibers, in vitro reassembly of system I fibers, and anion-exchange chromatography.

Life cycle and ultrastructure of Lagotia minor dons, 1948 (Ciliophora, Heterotrichia) revealing new characters for folliculinid classification

The morphology, behavior, trophont ultrastructure, and life cycle of the folliculinid species, Lagotia minor, is described. Lagotia minor has a simple lorica, a rounded macronucleus, broad and stiff peristomial wings, and a deep buccal cavity. The behavior of the swarmer and its mode of lorica secretion differ from these events in Eufolliculina and Metafolliculina. The ultrastructural investigations reveal further differences between the genera, e.g., in Lagotia minor the somatic dikinetids are associated with a cross-striated fiber which runs along the postciliary ribbon. The peristome of L. minor is supported from ladder-like nemadesmata which originate from opposite sides of the wings. Based on these results and on light microscopical observations on other folliculinid genera, new characters for folliculinid classification are discussed.

Transmission electron microscopic appearance of dentin matrix in type II dentin dysplasia

Dentin matrix of demineralized primary and permanent teeth with type II dentin dysplasia was studied by transmission electron microscopy. The coronal dentin of a maxillary third molar exhibited a normal structure. In the radicular dentin, tubules were few in number; the major part of the dentin was composed of thick, curvy bundles of cross-striated collagen fibers. In the most aberrant areas of the radicular dentin, coarse collagen fibers measuring up to 140 nm in thickness were observed. The dentin of the primary tooth showed a similar, but somewhat less irregular, structure.

Differentiation in dystrophic muscle cultures from mice of different ages.

Muscle from dystrophic (129 ReJ dy/dy) mice, aged 1, 2, 3, 4, and 6 months, was cocultured with normal embryonic mouse spinal cord. Cultures were scored for regeneration (myotubes) and differentiation (cross-striated or contracting fibers) over a 28-day period. Although muscle from dystrophic mice of all ages was able to regenerate, the ability to differentiate decreased with the increasing age of the mouse. Muscle from litter-mate control mice of different ages regenerated and differentiated equally well.

Muscles à striation oblique et à striation transversale chez les Annélides Polychètes

Abstract Ohlique- and cross-striated muscles in polichaetes. Most annelids, chiefly polychaetes, have muscles of oblique double striation or of helical striation. Yet special evolutionary processes may induce profound changes in the structure of muscles in two polychaete families, the Syllidae and Nereidae. At time of reproduction they can undergo somatic metamorphoses termed stolonisation and epitoky. Many of their muscles de-differentiate partly or wholly, and then they redifferentiate into epitokous fibres, characterized by thick, shorter filaments of smaller diameter, and rich in mitochondria and glycogen. Besides, there are some examples of muscle fibres non-helical in type worth investigating, for they show, first, an absence of a direct relation between phylogeny and fibre type (obliquely or transversely striated, or smooth), and, secondly, an absence of transitions between smooth and cross-striated fibres (the proventriculus in Syllidae), and between the latter and fibres of oblique simple striati...

Electron Microscopy of Fibrin Paris I

AbstractFibrinogen Paris I, a congenital fibrinogen abnormality, is characterized by delayed fibrin aggregation and poor clot retraction owing to the replacement of normal γ-chains by mutant γ-chains, which are termed γ-Paris I. Available evidence indicates that the structural abnormality involves the amino acid sequence near the COOH-terminus of the mutant chain and probably includes the region containing the normal γ-chain crosslinking site. Electron microscopy was carried out on Paris I fibrin. In place of the normally interwoven network of branching cross-striated fibers, negatively or positively contrasted Paris I fibrin was characterized by nonfibrous clumps of material connected by distinct fibrous strands tending to be thinner and more irregular in width than normal fibrin. Most Paris I fibrin fibers tended to be aperiodic, although cross-striations were observed occasionally in negatively contrasted specimens and rarely in positively contrasted specimens. In addition, Paris I fibrin frequently showed relatively short, abruptly terminating fibers. The gross ultrastructural differences between normal and Paris I fibrin suggest that for fibrin assembly to take place normally, a region(s) in the fibrin molecule near to or possibly overlapping the COOH-terminal γ-chain crosslinking site must be preserved or at least not sterically hindered.

Electron microscopy of fibrin Paris I

Fibrinogen Paris I, a congenital fibrinogen abnormality, is characterized by delayed fibrin aggregation and poor clot retraction owing to the replacement of normal gamma-chains by mutant gamma-chains, which are termed gamma-Paris I. Available evidence indicates that the structural abnormality involves the amino acid sequence near the COOH- terminus of the mutant chain and probably includes the region containing the normal gamma-chain crosslinking site. Electron microscopy was carried out on Paris I fibrin. In place of the normally interwoven network of branching cross-striated fibers, negatively or positively contrasted Paris I fibrin was characterized by nonfibrous clumps of material connected by distince fibrous strands tending to be thinner and more irregular in width than normal fibrin. Most Paris I fibrin fibers tended to the aperiodic, although cross-striations were observed occasionally in negatively contrasted specimens and rarely in positively contrasted specimens. In addition, Paris I fibrin frequently showed relatively short, abruptly terminating fibers. The gross ultrastructural differences between normal and Paris I fibrin suggest that for fibrin assembly to take place normally, a region(s) in the fibrin molecule near to or possibly overlapping the COOH-terminal gamma- chain crosslinking site must be preserved or at least not sterically hindered.

The ultrastructure of primary cilia in quiescent 3T3 cells

Electron microscopy was used to investigate primary cilia in quiescent 3T3 cells. As in the case of primary cilia of other cell types, their basal centriole was found to be a focal point of numerous cytoplasmic microtubules which terminate at the basal feet. There are also intermediate filaments which appear to converge at the basal centriole. Cross-striated fibers of microtubular diameter, reminiscent of striated rootlets of ordinary cilia, appear associated with the proximal end of the basal centriole. Usually less than nine cross-banded basal feet surround the basal centriole in a well-defined plane perpendicular to the centriolar axis. The ciliary shaft was found to be entirely enclosed in the cytoplasm of fully flattened cells. In rounded cells, it could be found extending to the outside of the cell. Periodic striations along the entire shaft were observed after preparing the cells in a special way. The tip of the shaft showed an electron-dense specialization. Several unusual forms of primary cilia were observed which were reminiscent of olfactory flagella or retinal rods. Using tubulin antibody for indirect immunofluorescence, a fluorescent rod is visible in the cells [18] which we demonstrate is identical with the primary cilium.

The fine structure of Gnathostomulid reproductive organs

The male copulatory organs of five species of Gnathostomulida Scleroperalia have been studied by TEM techniques. These observations provide a more solid basis for classification in the light microscope: inLabidognathia longicollis (fam. Mesognathariidae) the stylet is composed of eight, and inSemaeognathia sterreri, Gnathostomula jenneri, Gnathostomula mediterranea andGnathostomula microstyla (Gnathostomulidae) of ten stylet rods. Each rod consists of a microtubule-filled inner rod, and of an outer rod, filled with ‘crystallized inclusions’. The inner rods are continuous with eight — or ten — rod formation cells which are located in the proximal stylet sack. Bipartition of rods occurs by a longitudinal invagination of the basement lamina, underlying the rod cells and the gland cells and continuous with that of the body wall epithelium. InLabidognathia, the outer rods are interlocked, in Gnathostomulidae, the stylet rods are surrounded by an extracellular (‘cuticular’) tube-like stylet sheath of variable fine structure, which is believed to provide extra rigidity. In the species investigated, one single stylet gland, consisting of a monolayered epithelium showing different gland cell types, surrounds the stylet. In the apical gland cell portions, medially and distally membrane-bound secretory granules lie adjacent to the stylet sheath. In Gnathostomulidae, two anterior gland cells are seen in connection with the formation of the stylet sheath. In the muscular sheath the cross-striated fibers, basically derived from the longitudinal body wall musculature, show a tendency towards helical and circumferential arrangement. Musculature is especially prominent in the proximal stylet sack, which is rather a propulsive element than a sperm-storing vesicle, and lacks glands. InGnathostomula species, atrial cells underlie the distal tip of the stylet. The entrance into the male opening is lined with ciliary receptor cells and specialized gland cells. Stylet evolution in Scleroperalia is characterized by progressive differentiation of the muscular sheath, in particular of the proximal stylet sack, and of the stylet — the occurrence of a stylet sheath is seen in connection with increasing diversity of stylet shape.

Helical, striated rootlets in the midpiece of a teleost fish spermatozoon.

In the 45 μ long midpiece of the spermatozoon of Pantodon buchholzi nine helical, cross-striated fibers run from one end to the other and parallel nine helical mitochondrial threads; both fibers and mitochondrial threads surrounding the axoneme. The fibers have a major period about 750–900 A and are very similar to ciliary rootlets and other cross-striated structures in terms of which they are discussed.

Sarcosporidiosis-a review.

Sarcosporidia are protozoal parasites which develop in the cross-striated fibres of skeletal, tongue, oesophageal and cardiac muscle. The affection occurs in many species of vertebrate animals and birds, has a world-wide distribution, but rarely has any untoward effects on the host it parasitizes. The economic importance of the sarcosporidia is that carcases found severely infected on meat inspection are condemned.

Physiological studies during formation and development of rat neuromuscular junctions in tissue culture.

Developing neuromuscular junctions in tissue cultures of rat embryo spinal cord and muscle were studied with intracellular recording. Excitatory junctional potentials (ejps) were found during nerve or spinal cord stimulation, and also arising spontaneously. The time-course of the potentials tended to be shorter in cultures older than 9 days in vitro than in more recently innervated cultures. Evidence of multiple innervation was found in many cells. In order to test the hypothesis that transmitter was released in integral multiples of a quantal amount and according to a Poisson distribution, mean quantum content was calculated from the coefficient of variation of ejp amplitudes, the percentage of zero responses, and the ratio of mean amplitude to mean of the smallest class of amplitudes. The three independent measures were in fair or good mutual agreement, implying that the mechanism of transmitter release in newly developed junctions is the same as in the adult. In newly formed junctions, ejps were subthreshold for action potential generation, but afterwards mean quantum content increased and action potentials were generated by single ejps. In fibers developing both with and without innervation, the entire muscle cell surface was as sensitive to acetylcholine as the adult end plate region. Innervation was related to cross-striation: every cross-striated fiber tested was found to be innervated, and denervation in vitro led to loss of distinct cross-striations.