Ultrastructure of muscle cells from a few selected turbellarians: possible correlations between form and function

A comparative ultrastructural study of muscle cells from several turbellarian species revealed a basic smooth type of construction, with thick and thin myofilaments. However, the distribution of contractile elements, "dense bodies", smooth reticulum, mitochondria, as well as junctional specializations was found to vary within different systems. This variability is probably related to greater or lesser physical demands on the musculature. From a mechanical viewpoint, the most ‘powerful’ muscular system studied was represented by the pharyngeal bulb of Geocentrophora applanata, in which muscle fibers were organized into a compact, square reticulum, hemidesmosomes occurred in large numbers, and myofilaments were grouped in patches reminiscent of A and I bands of striated muscles. At the other extreme, muscular fibrils of the catenulids studied were thin and regularly spaced along the body wall, and the branched ends of radial myofibrils in the parenchyma were connected to the epithelial layer. This revised version was published online in July 2006 with corrections to the Cover Date.     

An ultrastructural study of mitotic division in differentiated gastric smooth muscle cells

Summary An ultrastructural examination of tissue from the gizzards of chicks just before and just after hatching showed numerous mitotic divisions in the well differentiated and functional smooth muscle. The nuclei in the very elongate, dividing cells were located centrally. The cytoplasm immediately adjacent to the nuclei contained the normal fully differentiated complement of myofilaments. During the active stages of division, after the breakdown of the nuclear membrane, myofilaments were shown to lie between the individual chromosomes. The process of division only occupied a small portion of the long muscle cells; the ultrastructural changes seen appeared similar to those described in other cell types.This work was supported by grants from the National Heart Foundation of Australia and the Australian Research Grants Committee. Part of this study was completed while J.L.S.C. was in receipt of a Queen Elizabeth II Research Fellowship. T. B. was supported by a Commonwealth Postgraduate Award.     

Ultrastructural changes in skeletal muscle of the tail of the lizard Hemidactylus mabouia immediately following autotomy

Araújo, T.H., Faria, F.P., Katchburian, E. and Freymüller, E. (2009). Ultrastructural changes in skeletal muscle of the tail of the lizard Hemidactylus mabouia immediately following autotomy. —Acta Zoologica (Stockholm) 91 : 440–446. Although autotomy and subsequent regeneration of lizard tails has been extensively studied, there is little information available on ultrastructural changes that occur to the muscle fibers at the site of severance. Thus, in the present study, we examine the ultrastructure of the musculature of the remaining tail stump of the lizard Hemidactylus mabouia immediately after autotomy. Our results show that exposed portions of the skeletal muscle fibers of the stump that are unprotected by connective tissue bulge to produce large mushroom‐like protrusions. These exposed portions show abnormal structure but suffer no leakage of cytoplasmic contents. Many small and large vesicular structures appeared between myofibrils in the interface at this disarranged region (distal) and the other portion of the fibers that remain unchanged (proximal). These vesicles coalesce, creating a gap that leads to the release of the mushroom‐like protrusion. So, our results showed that after the macroscopic act of autotomy the muscular fibers release part of the sarcoplasm as if a second and microscopic set of autotomic events takes place immediately following the macroscopic act of autotomy. Presumably these changes pave the way for the formation of a blastema and the beginning of regeneration.     

Comparative body wall musculature and muscle fibre ultrastructure in branchiobdellidans (Annelida: Clitellata), and their phylogenetic significance

The body wall muscles in five species of branchiobdellidans are all arranged in the oligochaete pattern and the muscle fibres are obliquely striated. The structure of the circular muscle fibres do vary to some degree. The longitudinal muscle fibres in Ankyrodrilus legaeus, Branchiobdella kozarovi, and Xironogiton instabilis all are round circomyarian and thus double-obliquely striated. These species represent three of the four genera composing the family Branchiobdellidae. Although Bdellodrilus illuminatus and Cambarincola fallax, from the families Bdellodrilidae and Cambarincolidae, respectively, also possess a few round circomyarian fibres, most are polyplatymyarian comparable to single-obliquely striated fibres. A similar division of branchiobdellidan families is obtained based on the number of anterior nephridial pores. The muscular structure in the branchiobdellidans shows both similarities and differences with the leeches and the lumbriculid oligochaetes. One phylogenetic explanation for this is that the branchiobdellidans separated from the common clitellate ancestor before the oligochaetes and leeches became recognizable taxa.     

Fine structure of the epistome in Phoronis ovalis: significance for the coelomic organization in Phoronida

Abstract. The hypothesis of a common ancestry of the lophophorate taxa Brachiopoda, Bryozoa, Phoronida, and the Deuterostomia can be traced back to the late 19th century when Masterman recognized a tripartite organization of the body consisting of pro-, meso-, and metasome, along with coelomic body cavities in each compartment, as characteristic for Echinodermata, Pterobranchia, Phoronida, and Brachiopoda. This idea became quite popular under the name archicoelomate concept. The organization of the phoronids, and especially of their transparent actinotroch larva, has for a long time been used as a touchstone for the validity of this concept. As a coelomic lining can reliably be recognized only on the ultrastructural level, this technique has been applied for adults of Phoronis ovalis , which is assumed to be a sister species to all other phoronids. Phoronis ovalis contains only two coelomic compartments, a posterior coelom inside the trunk (metasoma), occupying the space between the trunk epidermis and the digestive epithelium, and an anterior lophophoral coelom inside and basal to the tentacular crown (mesosoma). There is no coelomic cavity inside the epistome (prosoma). This part of the body is filled with myoepithelial cells, which are continuous with the epithelial lining of the lophophore cavity. These cells form a lumenless bilayer and possess long, tiny myofilamentous processes, which are completely embedded in an extracellular matrix. A comparison with data on P. muelleri shows that there is no need to assume three different coelomic cavities in Phoronida, in contrast to the predictions of the archicoelomate concept. At least for this taxon, a correspondence to the situation in deuterostomes can hardly be found.     

Exceptional preservation of nerve and muscle tissues in Late Devonian placoderm fish and their evolutionary implications

In this paper, we show exceptional three-dimensionally preserved fossilized muscle tissues in 380–384Myr old placoderm fish (Late Devonian), offering new morphological evidence supporting the hypothesis that placoderms are the sister group to all other gnathostomes. We describe the oldest soft tissue discovered in gnathostomes, which includes striated muscle fibres, circulatory and nerve tissues, preserved as phosphatized structures precipitated by microbial infilling of small, protected areas under the headshield of the arthrodire, Eastmanosteus calliaspis. Muscle impressions have also been found in the ptyctodontid, Austroptyctodus gardineri. The specimens display primitive vertebrate muscle structures; in particular, shallow W-shaped muscle blocks such as those observed in lampreys. New information from fossilized soft tissues thus elucidates the affinities of the placoderms and provides new insights into the evolution and radiation of gnathostomes.     

Culture and characterization of fetal human atrial and ventricular cardiac muscle cells

Summary Atrial and ventricular cardiac muscle cells isolated from 14- to 18-wk old fetal human hearts were grown in culture and characterized. Once established in culture the flattened cells contracted spontaneously and possessed differentiated ultrastructural characteristics including organized sarcomeres, intercalated discs, and transverse tubules with couplings. Atrial granules were present in the cultured atrial cells. Some cultured ventricular myocytes also contained electron-dense granules associated with Golgi cisternae, which were similar in size and appearance to atrial granules. The cultured ventricular myocytes divided and expressed the genes for thymidine kinase, histone H4, myosin heavy chain, muscle-specific creatine kinase, atrial natriuretic factor, and insulin-like growth factor II. These results establish that differentiated fetal human heart muscle cells can be cultured in sufficient quantities for biochemical, molecular, and morphological analyses. This work was supported by a postdoctoral fellowship from the American Heart Association, Louisiana Affiliate (JBD) and the National Institutes of Health, Bethesda, MD (HL-35632) (WCC).     

Development and characterization of primary cultures of smooth muscle cells from the fibromuscular stroma of the guinea pig prostate

Summary Primary cultures of smooth muscle cells (SMCs) were obtained by a two-step enzymatic digestion of guinea pig prostatic stroma. Ultrastructural morphology and growth characteristics of these cells conformed to those reported for SMCs isolated from vascular and visceral tissue sources. Electron microscopic examination indicated that the cells assumed modified myofibroblastoid features in culture. Microfilaments with associated dense bodies were markedly depleted in cultured smooth muscle cells, in comparison with those of the parent tissue. Cultured cells also possessed increased content of rough endoplasmic reticulum indicating the increased secretory or protein-synthetic capacity of the cells. Immunoperoxidase staining for cytoskeletal markers using monoclonal antibodies to desmin and vimentin supported the ultrastructural observations, suggesting a decline in desmin-staining intermediate filaments during “modulation” to the myofibroblastoid form. Despite this depletion of smooth muscle-specific differentiation markers and reversion to more general mesenchymal properties, the cells retained the ability to contract on challenge with norepinephrine, and grew in the characteristic “hill and valley” pattern on attaining confluence. Inasmuch as the estrogen and androgen receptor expression of the parent stromal tissue is also retained, these primary cell cultures should provide a useful model to study regulation of prostatic development. This work was supported by research grants from the National Health and Medical Research Council of Australia, the Anti Cancer Foundation of the Universities of South Australia, and the Flinders Medical Centre Research Foundation.     

饥饿和交配对小地老虎飞行肌发育的影响

小地老虎Agrotis ypsilon(Rottemburg)成虫飞行肌的发育常受一些因素影响而发生变化,为探讨饥饿和交配行为对飞行肌发育的影响,通过电子显微镜对雌虫飞行肌(背纵肌)的肌原纤维、线粒体结构进行观察,结果显示:4日龄饥饿雌虫,肌原纤维直径、肌节长度、肌原纤维体积均显著(P<0.05)小于取食的。7日龄饥饿雌虫肌原纤维直径、肌节长度、肌原纤维体积分数较4日龄的差异均不显著(P≥0.05),而7日龄饥饿的肌原纤维直径显著(P<0.05)大于7日龄取食的;羽化10 d后,饥饿雌虫肌节长度显著(P<0.05)大于取食雌虫的,而肌纤维体积分数和线粒体体积分数均却小于后者。7、10、13日龄交配雌虫肌原纤维横切直径分别显著(P<0.05)小于同日龄非交配的;7、10、13日龄交配雌虫肌原纤维体积分数显著(P<0.05)小于非交配的,线粒体体积分数虽然无差异(P≥0.05),但是交配雌虫的早在4日龄便已明显(P<0.05)减小。上述结果表明:正常取食的小地老虎飞行肌4日龄后会发生降解现象;饥饿抑制飞行肌前期发育和中期的降解,而促进成虫末期肌原纤维的分解;交配能促进飞行肌的降解。     

Unloading of the soleus in tail-suspended rats increases the number of intrafusal fibers in muscle spindles

Transmission electron microscopy was used to study the ultrastructure of muscle spindles (encapsulated stretch receptors) in m. soleus of adult Wistar rats after repeated hindlimb unloading. It was shown that the unloaded soleus contained not only spindles with a typical number of intrafusal fibers (four) but also spindles with five or six fibers. The increase in the number of intrafusal fibers in muscle spindles of the unloaded animals is likely to be caused by the proliferation of their satellite cells (myoblasts).     

The effects of S-carboxymethylcysteine and N-acetylcysteine on the adherence of Moraxella catarrhalis to human pharyngeal epithelial cells

We investigated the effects of two mucoregulating drugs, S-carboxymethylcysteine (S-CMC) and N-acetylcysteine (NAC), on the attachment of Moraxella catarrhalis (M. catarrhalis) to pharyngeal epithelial cells. The attachment of M. catarrhalis decreased (33-57%) significantly (P<0.01) in a dose-dependent manner in cells treated with mucoregulating drugs as compared to the control. There was a significant (P<0.01) decrease (35-45%) in the attachment of M. catarrhalis to pharyngeal cells after oral administration of S-CMC. By electron microscopic observation, it was found that there was a fine, granular, electron-dense, ruthenium red-positive layer on the surface of pharyngeal epithelial cells; this layer was absent on cell surfaces treated with mucoregulating drugs. Possibly, this layer contained the portion of M. catarrhalis receptor which is responsible for the attachment of this bacteria to pharyngeal epithelial cells. From the above results, it may be concluded that one of the mechanisms of mucoregulating drugs to decrease the episode of respiratory infections in patients with chronic respiratory diseases is by inhibiting the attachment of bacteria to the upper respiratory tract.     

A new variant of the neodermatan-type spermiogenesis in a parasitic 'turbellarian', Notentera ivanovi (Platyhelminthes) and the origin of the Neodermata

Spermiogenesis is characterized by fully incorporated (in the testes of mature worms) or partially free (submature worms) axonemes in spermatids. Formation of free flagella correlates with tight arrangement of cells in the testes and small size of the zone of differentiation and vice versa . In both cases the axonemes elongate within the growing shaft, so that the organization of the resulting spermatids is different only with regard to the distal end. In late spermatids, the nucleus occupies the proximal half, the two mitochondria and the axonemes directed distally lie in the distal half. After detachment of the spermatid, a migration of the nucleus takes place. In the resulting mature sperm, the proximal (anterior) half is occupied by the mitochondria and axonemes the basal bodies of which lie at the anterior end of the spermatozoon; the nucleus occupies the distal (posterior) half. Because of the distal orientation of the axonemes and a peculiar mode of the migration of the nucleus, the spermiogenesis of Notentera should be classified as a new variant of the type characteristic of the Neodermata (parasitic Platyhelminthes). Based on the analysis of the available morphological and other relevant data it is argued (i) that a high-ranked taxon, the Fecampiida, should be established within the Neoophora to include Notentera and the closely related Fecampiidae and (ii) that all the Platyhelminthes with neodermatan-type spermiogenesis form a monophyletic taxon, the Revertospermata, which includes the sister groups Fecampiida and Mediofusata.     

Distinction between smooth muscle,fibroblasts and endothelial cells in culture by the use of fluoresceinated antibodies against smooth muscle actin

Summary FITC-labelled antibodies against native actin from chicken gizzard smooth muscle (Gröschel-Stewart et al., 1976) have been used to stain cultures of guinea-pig vas deferens and taenia coli, rabbit thoracic aorta, rat ventricle and chick skeletal muscle. The I-band of myofibrils of cardiac muscle cells and skeletal muscle myotubes stains intensely. In isolated smooth muscle cells, the staining is located exclusively on long, straight, non-interrupted fibrils which almost fill the cell. Smooth muscle cells which have undergone morphological dedifferentiation to resemble fibroblasts with both phase-contrast microscopy and electronmicroscopy still stain intensely with the actin antibody. In those muscle cultures which contain some fibroblasts or endothelial cells, the non-muscle cells are not stained with the actin antibody even when the reactions are carried out at 37° C for 1 h or after glycerination. Prefusion skeletal muscle myoblasts also do not stain with this antibody.It is concluded that the actin antibody described in this report is directed against a particular sequence of amino acids in muscle actin which is not homologous with non-muscle actin. The usefulness of this antibody in determining the origin of cells in certain pathological conditions such as atherosclerosis is discussed.This work was supported by the Life Insurance Medical Research Fund of Australia and New Zealand, the National Heart Foundation of Australia, the Deutsche Forschungsgemeinschaft and the Wellcome Trust (London). We thank Janet D. McConnell for excellent technical assistance     

The pedal muscle of the land snail Megalobulimus oblongus (Gastropoda, Pulmonata): an ultrastructure approach

M. Cristina Faccioni-Heuser, Denise M. Zancan, Christiane Q. Lopes and Matilde Achaval. 1999. The pedal muscle of the land snail Megalobulimus oblongus (Gastropoda, Pulmonata): an ultrastructure approach. — Acta Zoologica (Stockholm) 80: 325–337
The ultrastructure of the pedal muscle of the Megalobulimus oblongus is described. This muscle consists of transverse, longitudinal and oblique bundles ensheathed in collagenous tissue. Each muscle cell is also ensheathed by collagen. The smooth muscle cells contain thin and thick filaments; the thin filaments are attached to dense bodies. These cells contain a simple system of sarcoplasmic reticulum, subsarcolemmal caveolae and mitochondria with dense granules in the matrix, and glycogen. Three types of muscle cells were identified. Type A cells exhibited densely packed myofilaments, abundant glycogen rosettes, numerous mitochondria and sarcoplasmic reticulum profiles. Type B cells exhibited scanty glycogen and mitochondria, few cisternae of sarcoplasmic reticulum and large intermyofibrillar spaces. Type C cells exhibited intermediate characteristics between type A and type B cells. Neither nexus nor desmosomes were observed between the muscle cell membranes. The muscle contains well developed connective tissue and blood vessels. These structures and the distribution of muscle cells are probably involved in the muscular-hydrostat system. The muscle is richly innervated, having neuromuscular junctions with clear and electron-dense synaptic vesicles. The clear vesicles probably contain acetylcholine because the axons to which they are connected arise from acetylcholinesterase positive neurones of the pedal ganglion. The other vesicles may secrete monoamines such as serotonin and/or neuropeptides such as substance P.     

On the fine structure of the creeping larva of Loxosomella murmanica: additional evidence for a clade of Kamptozoa (Entoprocta) and Mollusca

The creeping larva of the kamptozoan (entoproct) Loxosomella murmanica was investigated using transmission electron microscopy. The late larva exhibits a prominent apical organ connected to the ‘cerebral’ commissure of large cerebral ganglia, which supply the paired frontal organ. From the cerebral ganglia two paired nerve cords project backwards, closely resembling the tetraneuralian pattern of basal molluscs. In addition, a neural ring supplying the prototroch is present. The epidermis is composed of myoepithelial cells. Dorsally its cuticle is covered by granules of unknown composition. The prototroch consists of two ciliary rings; a downstream collecting system is not present. Although there is a one‐way gut with a lumen throughout, the larva obviously does not feed. A single pair of protonephridia is present. The foot sole shares distinct similarities with basic molluscs, particularly with those of the aplacophoran Solenogastres: The anterior part shows a huge, subepidermal pedal gland and several bundles of cirri consisting of compound cilia. The posterior part is ciliated with intraepithelial mucous cells interspersed. The dorsoventral muscle fibres show the mollusc‐like ventral intercrossing. The present results and previous findings, in particular the chitinous, non‐moulted cuticle, the sinus circulatory system, and a number of neural features shared by Kamptozoa and Mollusca, provide substantial evidence for a direct sister‐group relationship between these phyla. In addition, the basal position of the Solenogastres (Neomeniomorpha) within the Mollusca is corroborated.     

Precocious in vitro development of satellite cells from dystrophic chicken muscle

Summary Satellite cells, liberated from pectoral muscle of juvenile dystrophic chickens by sequential treatment with collagenase, hyaluronidase, and trypsin and preplated to remove fibroblasts and cultured on gelatin proliferated rapidly, fused and formed confluent muscle cultures within 6 d in vitro with minimal contamination by fibroblasts. When identical isolation and culturing techniques were applied to muscle from age-mateched normal chickens proliferation and differentiation were slower, contamination with fibroblasts was much greater, and only a small number of myotubes were formed. After injection of the myotoxic anesthetic marcaine into normal pectoral muscle for 5 consecutive days, myotube formation was accelerated in satellite cell cultures, but the rate of differentiation was not as rapid as that occurring in cells from dystrophic muscle. This research was supported by a grant from the Muscular Dystrophy Association of Canada.