Ultrastructure and differentiation of the larval esophageal muscle cells of the starfish Pisaster ochraceus

The muscle cells that cause constriction of the starfish larval esophagus (esophageal muscle cells) are one of the first cell types to express their differentiated morphological characteristics during development. Ultrastructurally these muscle cells resemble vertebrate and invertebrate smooth muscles. They contain a nucleus, a Golgi apparatus, contractile myofilaments, hemidesmosome-like structures, and what appears to be a simple sarcoplasmic reticulum. In asteroid embryos, this muscle layer originates during mouth formation when mesenchyme cells migrate from the tips of the coeloms to the esophagus. Once there, they elongate, forming processes. Over the next few days, the processes become filled with arrays of longitudinally arranged thick and thin myofilaments and thin sacs of smooth endoplasmic reticulum. The latter appear between the bundles of contractile filaments and the cell membranes. Contractile activity begins at approximately this time. The cisternae may represent a sarcoplasmic reticulum that is required for contraction. The majority of the esophageal muscle cell processes extend around the circumference of the developing esophagus, but occasional cells may be oriented in other directions. The latter cells are always farther away from the basal lamina and probably have little or no contact with it. Contact with basal lamina may serve to direct the migration of the cells and the orientation of the processes. J. Morphol. 237:1–18, 1998. © 1998 Wiley-Liss, Inc.     

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.     

Role of lipooligosaccharide in the attachment of Moraxella catarrhalis to human pharyngeal epithelial cells

The goal of this study was to determine the role of lipooligosaccharide in the attachment of Moraxella catarrhalis to human pharyngeal epithelial cells. Strain 2951 and its P(k) mutant strain 2951 galE were used in this study. This study suggests that the P(k) epitope of LOS is not an adhesin for M. catarrhalis, but plays a crucial role by its surface charge in the initial stage of attachment.     

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.     

Formation and function of the “Xestoleberis‐spot” in Xestoleberis hanaii (Crustacea: Ostracoda)

The crescent sculpture of the so‐called “Xestoleberis‐spot” develops inside the calcified valve of the family Xestoleberididae. Electron microscopic observations on both, intermoult and postmoult stages of Xestoleberis species reveal that the “Xestoleberis‐spot” system consists of three elements; two calcified chambers, a vesicle of electron‐dense material and an uncalcified procuticle. The formation and function of the “Xestoleberis‐spot” system are discussed. In conclusion, the “Xestoleberis‐spot” system functions as the muscle attachment site for several antennal muscles, and provides the material for chitinous fibers in the exocuticle of outer lamella. The unique cuticular structures of the family Xestoleberididae are due to the “Xestoleberis‐spot” system.     

The fine structure of the muscle system in the female of the orthonectid Intoshia variabili (Orthonectida)

The contractile system of the female Intoshia variabili (Orthonectida) consists of smooth muscles. The attachment of the longitudinal muscle fibres at the anterior and the posterior tips of the body is rather peculiar, accomplished by means of elongated terminal muscle cells piercing through several ciliated cells. In the last ciliated cell, the muscle cell invaginates the ciliated cell basal membrane almost up to the ciliated cell surface. Here, around the protrusion terminus, there is an electron‐dense zone in contact with the cilia rootlets.     

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.     

Quantitative microanatomy of jaw muscle attachment in extant diapsids

Muscular reconstructions in vertebrate paleontology have often relied heavily on the presence of "muscle scars" and similar osteological correlates of muscle attachment, a practice complicated by the fact that approximately half of tendinous muscle attachments to bone in extant vertebrates do not leave readily interpretable scars. Microanatomical and histological correlates of tendinous muscle attachment are much less ambiguous. This study examines the microanatomical correlates of muscle attachment for the mandibular adductors in six species of diapsids. Most prominent tendinous or aponeurotic muscle attachments display a high density of extrinsic fibers (similar to Sharpey's fibers). There is also some indication that the density of extrinsic fibers at an attachment may be directly related to the amount of stress exerted on that attachment. The presence of comparable densities of extrinsic fibers in fossil tissue constitutes strong and readily interpretable positive evidence for the presence of adjacent fibrous connective tissue in life. Microanatomy and histology provide reliable data about muscle attachments that cannot be gleaned from gross observation alone. These additional data, when coupled with existing muscular reconstruction techniques, may be essential to the resolution of ambiguous character states, and will provide more severe tests for long-standing hypotheses of musculature in extinct diapsids. Increasing the accuracy and precision of muscular reconstructions lends greater strength to any phylogenetic, paleobiological, or paleoecological inferences that draw upon these reconstructions as important lines of evidence.     

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.     

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.     

Phylogeny of Itaquasconinae in the light of the evolution of the flexible pharyngeal tube in Tardigrada

The family Hypsibiidae comprises four subfamilies, among which Itaquasconinae are the most abundant in genera. Although being morphologically diverse and cosmopolitan, itaquasconins are scarcely reported and their taxonomy is entangled. Here, we present a phylogeny based on three DNA markers and morphological clues obtained from a detailed scanning electron microscopy analysis of bucco-pharyngeal apparatuses of 25 species representing seven genera. Our study revealed that (a) the polyphyletic Adropion consists of at least three evolutionary lineages, with Guidettion gen. nov. being the sister group of all remaining itaquasconins; (b) stylet supports were independently lost in Astatumen and Insulobius gen. nov.; (c) pharyngeal tube annulation can be divided into two general types, simple and complex, and is stable at the genus level, but being homoplasious (similarly to the apophyses for the insertion of stylet muscles and the shape of the claw bases), it is not useful in inferring phyletic relationships within the subfamily; and (d) Astatumen and Platicrista contain numerous similar species, challenging the current taxonomic classification; moreover, (e) three new taxa are proposed to accommodate the newly recognised lineages: Guidettion gen. nov. (the former Adropion prorsirostre group), Insulobius gen. nov. (for a new Malayan species with a mixture of Astatumen and Itaquascon traits), and Raribius gen. nov. (former Itaquascon spp. with an elongated and narrowed pharyngeal tube terminating with a spherical pharynx). The simple type of annulation is synapomorphic to Hypsibiidae, with single reversals to the uniform buccal tube in Parascon (Itaquasconinae) and in Hypsibiinae. The pharyngeal tube evolved convergently several times, and is of different character in classes Heterotardigrada and Eutardigrada.     

Sensitivity of muscle and intervertebral disc force computations to variations in muscle attachment sites

Abstract

The current paper aims at assessing the sensitivity of muscle and intervertebral disc force computations against potential errors in modeling muscle attachment sites. We perturbed each attachment location in a complete and coherent musculoskeletal model of the human spine and quantified the changes in muscle and disc forces during standing upright, flexion, lateral bending, and axial rotation of the trunk. Although the majority of the muscles caused minor changes (less than 5%) in the disc forces, certain muscle groups, for example, quadratus lumborum, altered the shear and compressive forces as high as 353% and 17%, respectively. Furthermore, percent changes were higher in the shear forces than in the compressive forces. Our analyses identified certain muscles in the rib cage (intercostales interni and intercostales externi) and lumbar spine (quadratus lumborum and longissimus thoracis) as being more influential for computing muscle and disc forces. Furthermore, the disc forces at the L4/L5 joint were the most sensitive against muscle attachment sites, followed by T6/T7 and T12/L1 joints. Presented findings suggest that modeling muscle attachment sites based on solely anatomical illustrations might lead to erroneous evaluation of internal forces and promote using anatomical datasets where these locations were accurately measured. When developing a personalized model of the spine, certain care should also be paid especially for the muscles indicated in this work.     

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。     

Transformation methods for estimation of subject-specific scapular muscle attachment sites

The parameters that describe the soft tissue structures are among the most important anatomical parameters for subject-specific biomechanical modelling. In this paper, we study one of the soft tissue parameters, namely muscle attachment sites. Two new methods are proposed for transformation of the muscle attachment sites of any reference scapula to any destination scapula based on four palpable bony landmarks. The proposed methods as well as one previously proposed method have been applied for transformation of muscle attachment sites of one reference scapula to seven other scapulae. The transformation errors are compared among the three methods. Both proposed methods yield significantly less (p < 0.05) prediction error as compared to the currently available method. Furthermore, we investigate whether there exists a reference scapula that performs significantly better than other scapulae when used for transformation of muscle attachment sites. Seven different scapulae were used as reference scapula and their resulting transformation errors were compared with each other. In the considered statistical population, no such a thing as an ideal scapula was found. There was, however, one outlier scapula that performed significantly worse than the other scapulae when used as a reference. The effect of perturbations in both muscle attachment sites and other muscle properties is studied by comparing muscle force predictions of a musculoskeletal model between perturbed and non-perturbed versions of the model. It is found that 10 mm variations in muscle attachments have more significant effect on muscle force predictions than 10% variations in any of the other four analysed muscle properties.