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.     

The structure of the muscular and nervous systems of the male Intoshia linei (Orthonectida)

Orthonectida is a small group of parasites, which, according to recent studies, may be phylogenetically close to Annelida. Here, we describe the musculature and serotonin-like immunoreactive (SLIR) nervous system of male adults of Intoshia linei (Orthonectida) using immunohistochemistry and confocal laser scanning microscopy. The whole muscular system consists of four outer longitudinal and eight pairs of inner semicircular muscle fibres. Immunohistochemistry revealed six serotonin-like cells at the anterior part of the body, and two backward lateral longitudinal nerves, merging at the posterior end. Compared to females, the organization of the nervous system is modified and its progenetic origin seems unlikely. The general neuromuscular organization corresponds to the pattern of small-sized annelids, suggesting their possible phylogenetic affinity. Free-living males and females of the orthonectid I. linei may present a good example of a highly simplified Bilaterian with fully functioning nervous and muscular systems. This simplicity is secondary and is caused by two factors—the parasitic life style and miniaturization of free-living sexual stages.     

Smooth muscle actin expression during rat gut development and induction in fetal skin fibroblastic cells associated with intestinal embryonic epithelium

Abstract. Cytodifferentiation of smooth muscle cells has been analyzed immunocytochemically during rat intestinal development and in chimaeric intestines by using monoclonal antibodies reacting specifically with smooth muscle actin species ( CGA7 [10] and anti-α SM-1 [40]). As development proceeds, the various intestinal muscle layers differentiate in the following order: (1) cells expressing smooth muscle actin appear within the mesenchyme of the 15-day fetal rat intestine, in the circular muscle-forming area, the differentiation of cells in the presumptive longitudinal muscle layer starting with a 48-h delay; (2) smooth muscle fibers appear within the connective tissue core of the villi shortly after birth, in parallel with a progressive formation of the muscularis mucosae, which becomes clear-cut only in the course of the 2nd week after birth; (3) a distinct cell layer in the innermost part of the circular muscle layer arises during the perinatal period. Thereafter, the fluorescence pattern remains unchanged until the adult stage. Chimaeric intestines were constructed by the association of 14-day fetal intestinal epithelium and cultured fetal rat or human skin fibroblasts. These fibroblastic cells did not express actin at the time at which they were associated. The immunocytochemical analysis of smooth muscle actin in the hybrid intestines, which had developed as intracoelomic grafts for 12 days, revealed that the skin fibroblastic cells had been induced by the intestinal epithelial cells to differentiate into smooth muscle cells. Such a result was also obtained with allantoic endoderm. It was not obvious in cocultures of intestinal epithelium with skin fibroblastic cells. However, when intestinal epithelial cells were cocultured with intestinal mesenchymal cells, actin expression was stimulated in the latter cell population.     

Histologic, morphometric, and immunocytochemical analysis of myometrial development in rats and mice: I. Normal development

Myometrial development from the prenatal to adult period was examined in rats and mice 1) by histologic and immunocytochemical methods with anti-actin, -vimentin, and -laminin to assess cytodifferentiation of smooth muscle and fibroblastic cells; and 2) by morphometric procedures to assess quantitatively the expression of cellular orientation in the emerging inner circular myometrial layer. Uterine mesenchymal cells initially were uniformly vimentin-positive, undifferentiated, and randomly oriented during the late fetal period. By the early neonatal period, three mesenchymal layers became recognizable histologically, the middle one of which (prospective circular myometrium) developed distinct circular orientation and differentiated into a layer composed of actin-positive smooth muscle cells. The cells of the inner mesenchymal layer initially exhibited radial orientation. By 10 days postpartum, the outer longitudinal mesenchymal layer differentiated into bundles of smooth muscle cells representing the longitudinal myometrium. The inner mesenchymal layer remained vimentin-positive and differentiated into the randomly ordered endometrial stroma. The cells of the middle and outer mesenchymal layers that were destined to form myometrium initially expressed vimentin throughout and then coexpressed vimentin and actin, but with time vimentin staining disappeared in the maturing smooth muscle cells as they expressed actin.     

黄胫小车蝗受精囊的亚显微结构

利用组织学方法,观察了黄胫小车蝗Oedaleus infernalis 受精囊的显微与亚显微结构。结果表明,黄胫小车蝗受精囊为单个,由高度卷曲的受精囊管和蚕豆状的端囊构成。受精囊壁主要由表皮层、上皮层、基膜和肌肉层构成;上皮层包含上皮细胞、导管细胞和腺细胞。上皮细胞在靠表皮层的边缘有大量的微绒毛,两相邻上皮细胞的细胞膜相互嵌入,并有细微的突起延伸在导管细胞及腺细胞之间,直到基膜,达基膜处的上皮细胞膜折叠,与腺细胞膜的折叠,一起形成迷宫样的指状突起,附着在基膜上。导管细胞有一个较大的核和分泌导管,连接于腺细胞的细胞腔和受精囊腔,将腺细胞中分泌物运输到受精囊腔中。腺细胞具有典型的分泌细胞特征： 含发达内质网、高尔基复合体及不同大小的囊泡。肌肉层位于受精囊最外层,附在基膜上。在受精囊不同部位的结构有差异。在交配前和交配后,受精囊腺细胞的亚显微结构也有差异。     

BMPs signal alternately through a SMAD or FRAP-STAT pathway to regulate fate choice in CNS stem cells

The ability of stem cells to generate distinct fates is critical for the generation of cellular diversity during development. Central nervous system (CNS) stem cells respond to bone morphogenetic protein (BMP) 4 by differentiating into a wide variety of dorsal CNS and neural crest cell types. We show that distinct mechanisms are responsible for the generation of two of these cell types, smooth muscle and glia. Smooth muscle differentiation requires BMP-mediated Smad1/5/8 activation and predominates where local cell density is low. In contrast, glial differentiation predominates at high local densities in response to BMP4 and is specifically blocked by a dominant-negative mutant Stat3. Upon BMP4 treatment, the serine-threonine kinase FKBP12/rapamycin-associated protein (FRAP), mammalian target of rapamycin (mTOR), associates with Stat3 and facilitates STAT activation. Inhibition of FRAP prevents STAT activation and glial differentiation. Thus, glial differentiation by BMP4 occurs by a novel pathway mediated by FRAP and STAT proteins. These results suggest that a single ligand can regulate cell fate by activating distinct cytoplasmic signals.     

Fine structure of the male accessory glands in Aedes triseriatus

The paired accessory glands of the male mosquito, Aedes triseriatus, consisted of a single layer of columnar epithelial cells enclosed by a richly-nucleated circular muscle layer. Each accessory gland is divided into an anterior gland (AG) with one type of secretory cell, and a posterior gland (PG) with two types. The cells of the AG and those of the anterior region of the PG showed macroapocrine secretion. The mucus secreting cells located at the posterior region of the PG, however, released their contents into the lumen of the gland by rupturing the apical membrane of the cell. The secretion from all cells was in the form of membrane-bound granules which had distinct electron-dense and electron-lucent areas.     

Orthonectida's life cycle

Analysis of original and literary data permits to conclude that the life cycle in Orthonectida may be characterized as a monohost--monoxenous one, including regular interchange of three generations: asexual and parthenogenetic ones, which are represented by parasitic plasmodiums, and sexual generation, represented by free living and non-feeding males and females or, rarely, hermaphrodites. The sexual individuals are bilaterial, while the parasitic ones are anaxonic. The life cycle of Orthonectida includes the agamic reproduction, apomictic parthenogenesis and sexual reproduction regularly following one another. The life cycle of Orthonectida can be considered as a combination of metagenesis and heterogony. So far, such combination has not been described in any group of metazoan parasites.     

Structural analysis of functionally different smooth muscles

Summary The ultrastructure of the longitudinal and circular muscle cells of the guinea pig stomach which show different contractile responses was compared. The extracellular space within the muscle bundles is about 12.1% in the longitudinal layer and about 4.4% in the circular layer. Nexuses were consistently found in the circular muscle layer but not in the longitudinal muscle layer. Numbers of both mitochondria and microtubules per unit area of smooth muscle cell are larger in the longitudinal than in the circular muscle. Cellular area occupied by sarcoplasmic reticulum is about 4.7% in the longitudinal muscle, 2.3% in the circular muscle. The numbers of caveolae are almost the same in both tissues. The most distinct difference between the two types of smooth muscle is the appearance of the thick filaments. The circular muscle cell contains approximately 50 thick filaments per 0.5 m² of cytoplasmic area, while the longitudinal muscle cell has only about 25 filaments which were usually much thinner than those of the circular muscle. These results indicate that the contractile apparatus itself is different in longitudinal and circular smooth muscles of the guinea pig stomach.We are grateful to Dr. Y. Furukawa, Physical Section, Institute of Low Temperature Science, Hokkaido University, for help in the use of their film analyzing system. We are also indebted to the Department of Pathology of our college, for the use of a Photo Pattern Analyzer throughout this experiment.     

Muscle development in the grasshopper embryo. II. Syncytial origin of the extensor tibiae muscle pioneers

The extensor tibiae muscle (ETi) in the metathoracic leg of the grasshopper, which powers the jump, is among the most studied insect muscles. In contrast to many insect muscles which are simple (consisting of only a single bundle of muscle fibers), the ETi is a complex muscle which consists of an array of bundles of muscle fibers, each with a separate site of insertion on the body wall ectoderm and on the ETi apodeme ectoderm. Here we describe the embryonic development of this complex muscle. The ETi muscle develops from a single muscle pioneer (MP) which connects the initial invagination of the ETi apodeme to the wall of the femur. This MP then dramatically expands around the developing apodeme to form a large horseshoe-shaped, multinucleate cell, called the supramuscle pioneer (supra-MP); the number of nuclei in the supra-MP increases by cell fusion rather than by nuclear division. The arms of the supra-MP grow steadily longer and their outer edges begin to appear scalloped, certain areas remaining tightly apposed to the ectoderm of the wall of the leg while adjacent areas lose their adhesion and are pulled away. By about 50% of embryonic development the ETi supra-MP consists of a periodic series of bridges (cytoplasmic extensions) connecting the leg wall ectoderm with the apodeme, and linked into a giant syncytium near their inner, apodeme surface by a thin layer of cytoplasm containing hundreds of nuclei. Each bridge is surrounded by a cluster of many smaller mesoderm cells. Next the syncytium begins to divide such that by 60% the periodic bridges of the supra-MP have lost syncytial contact with each other and now themselves form an array of smaller, individual, multinucleate MPs connecting the body wall to the apodeme, each surrounded by a mass of undifferentiated mesoderm cells. This initial cycle of fusion and division is followed by a second similar cycle in which the individual mesoderm cells surrounding each MP fuse with the MP. At the same time, the MP divides into the initial bundle of smaller muscle fibers. Coincident with this division into muscle fibers is the further development of thick and thin filaments and the T-tubule system.     

Ultrastructural analysis of the morphology and function of the spermatheca of the pulmonate snail,Sonorella santaritana

The ultrastructure of the spermatheca of the reproductive tract in the pulmonate snail, Sonorella santaritana, was investigated. This organ has a debris-filled lumen and an outer wall which can be divided into three distinct layers. The cell layer adjacent to the lumen is comprised of two cell types, tall columnar epithelial cells with microvilli and cells lacking microvilli. The next layer also has two cell types, muscle cells and apparent pigment cells. The most distant layer is an adventitia of large glycogen-containing cells. The lumen of the spermatheca contains a core of partially digested sperm and related materials. The luminal contents and the cellular morphology of this organ suggest that the spermathecal functions are both digestive and absorptive. It is proposed that excess sperm and related materials are transported to the spermatheca, digested, and the usable products are reabsorbed.     

Embryonic chicken gizzard: smooth muscle and non-muscle myosin isoforms

Antibodies to smooth muscle and non-muscle myosin allow the development of smooth muscle and its capillary system in the embryonic chicken gizzard to be followed by immunofluorescent techniques. Although smooth muscle development proceeds in a serosal to luminal direction, angiogenetic cell clusters develop independently at the luminal side close to the epithelial layer, and the presumptive capillaries invade the developing muscle in a luminal to serosal direction. The smooth muscle and non-muscle myosin heavy chains in this avian system cannot be separated by SDS polyacrylamide gel electrophoresis and do not show isoform specificity in immunoblotting, unlike the system found in mammals. Only two myosin heavy chains with M_r of 200 and 196 kDa were separable and considerable immunological cross-reactivity was found between the denatured myosin isoform heavy chains.     

人胎胃壁内NOS阳性神经元发育的研究

研究用NADPH-d组织化学法对第3个月胎龄至足月人胎胃壁内NOS阳性神经元的分化,迁移和生长发育进行了观察。结果表明：第5个月龄时,肌层神经节处的圆形细胞出现一氧化氮合酶（nitric oxide synthase,NOS)阳性反应。第6个月龄时,NOS阳性细胞分化演变成NOS阳性神经细胞,细胞呈圆形或椭圆形,核大,细胞质极少,由细胞发出短小的6个月龄时,NOS阳性细胞分化演变成NOS阳性神经细胞,细胞呈圆形或椭圆形,核大,细胞质极少,由细胞发出短小的突起,有部分NOS阳性细胞分化演变成梭形的NOS阳性神经细胞,呈条索状排列和粘膜下层延伸,吸的到达粘膜层,在粘膜层形成网状细胞,第7个月龄时,神经元细胞明显增大,细胞质增多,染色加深,在肌层形成神经节,神经节细胞突起投射到整个肌层,第8-10个月龄时,肌层和粘膜下层神经元日趋成熟,细胞质增多,染色强度加深,肌层神经纤维分布密度增加,大多数神经纤维增粗,有的呈弹簧样弯曲,其走向与肌纤维长轴平行。结果提示;人胎胃壁内NOS阳性神经元来源于胚胎早期肌层神经节处的圆形细胞,通过分化,生长发育形成成熟的NOS阳性神经元。     

Drosophila Anaplastic Lymphoma Kinase regulates Dpp signalling in the developing embryonic gut

The Drosophila melanogaster gene Anaplastic Lymphoma Kinase (Alk) regulates a signal transduction pathway required for founder cell specification within the visceral muscle of the developing embryonic midgut. During embryonic development, the midgut visceral muscle is lined by the endodermal cell layer. In this paper, we have investigated signalling between these two tissues. Here, we show that Alk function is required for decapentaplegic (Dpp) expression and subsequent signalling via the Mad pathway in the developing gut. We propose that not only does Alk signalling regulate founder cell specification and thus fusion in the developing visceral muscle, but that Alk also regulates Dpp signalling between the visceral muscle and the endoderm. This provides an elegant mechanism with which to temporally coordinate visceral muscle fusion and later events in midgut development.     

Endothelial cell behavior inside myoblast sheets with different thickness

Using a cell sheet stacking method, we developed an in vitro culture system in which green fluorescent protein expressing human umbilical vein endothelial cells (GFP-HUVECs) were cultured under human skeletal muscle myoblast (HSMM) sheets with different layer numbers. Our aim in developing this system was to examine the different endothelial behaviors in the cell sheet. During 96 h of incubation, in monolayer HSMM sheet, HUVECs quickly reached the top of the cell sheet and detached. In three-layered HSMM sheet, HUVECs also migrated to the top layer and formed island-shaped aggregates. In five-layered HSMM sheet, HUVECs migrated into the middle of the cell sheet and formed net-shaped aggregates. In seven-layered HSMM sheet, HUVECs migrated in the basal of the cell sheet and formed sparse net-shaped aggregates. The thickness of the HSMM sheet, which can be controlled by the layer number of the cell sheet, is therefore an important parameter that affects the migration time, encounters, localization, and morphology of HUVECs inside the HSMM sheet.     

Fine structure of anterior terminus of apical sense organ in Macracanthorhynchus hirudinaceus (Acanthocephala)

The apex of the proboscis of Macracanthorhynchus hirudinaceus is crowned by a cone-shaped projection with a small opening in its center. The bottom of this opening is the anterior terminus of the apical sensory organ. When viewed in transverse section, the anterior terminus of this organ appears as a series of distinct layers that encircle a central cone enclosing a complex arrangement of nerves and a sensory support cell duct. Four membrane-defined layers encircle the cone area. The outermost glycocalyx is morphologically identical with that described on the metasoma. The second layer, or tegument, is similar in appearance to that observed on the trunk except for the greater abundance of keratinlike bundles throughout. These bundles are also organized into a loose network along the inner tegumental membrane. The third layer, a latticework of fine filaments containing few organelles, has an erratic boundary that occasionally extends into layer 4. The area adjacent to the inner and outer boundary contains numerous vesicles. Layer 4 has 2 distinct zones. The outer contains filaments arranged as in circular muscle; whereas, the medial lacks such filaments but consists of a finely grained matrix. Radiating throughout both zones are numerous osmiophilic bundles of fibers. The cone at this level contains 8 branches of the apical sensory nerves that interdigitate with the duct from the sensory support cell. Numerous filaments and vesicles are associated with this complex.     

Vascular smooth muscle cells spontaneously adopt a skeletal muscle phenotype: a unique Myf5(-)/MyoD(+) myogenic program.

Smooth and skeletal muscle tissues are composed of distinct cell types that express related but distinct isoforms of the structural genes used for contraction. These two muscle cell types are also believed to have distinct embryological origins. Nevertheless, the phenomenon of a phenotypic switch from smooth to skeletal muscle has been demonstrated in several in vivo studies. This switch has been minimally analyzed at the cellular level, and the mechanism driving it is unknown. We used immunofluorescence and RT-PCR to demonstrate the expression of the skeletal muscle-specific regulatory genes MyoD and myogenin, and of several skeletal muscle-specific structural genes in cultures of the established rat smooth muscle cell lines PAC1, A10, and A7r5. The skeletal muscle regulatory gene Myf5 was not detected in these three cell lines. We further isolated clonal sublines from PAC1 cultures that homogeneously express smooth muscle characteristics at low density and undergo a coordinated increase in skeletal muscle-specific gene expression at high density. In some of these PAC1 sublines, this process culminates in the high-frequency formation of myotubes. As in the PAC1 parental line, Myf5 was not expressed in the PAC1 sublines. We show that the PAC1 sublines that undergo a more robust transition into the skeletal muscle phenotype also express significantly higher levels of the insulin-like growth factor (IGF1 and IGF2) genes and of FGF receptor 4 (FGFR4) gene. Our results suggest that MyoD expression in itself is not a sufficient condition to promote a coordinated program of skeletal myogenesis in the smooth muscle cells. Insulin administered at a high concentration to PAC1 cell populations with a poor capacity to undergo skeletal muscle differentiation enhances the number of cells displaying the skeletal muscle differentiated phenotype. The findings raise the possibility that the IGF signaling system is involved in the phenotypic switch from smooth to skeletal muscle. The gene expression program described here can now be used to investigate the mechanisms that may underlie the propensity of certain smooth muscle cells to adopt a skeletal muscle identity.(J Histochem Cytochem 48:1173-1193, 2000)     

人胎大肠氮能神经元发育的研究

用NADPH-d组织化学法对人胎大肠氮能神经元的发育进行了观察.结果表明第5个月胎龄时,肌间神经节处圆形细胞中部分细胞出现一氧化氮合酶(NOS)阳性反应,并分化成氮能神经细胞.第6个月胎龄时,氮能神经元胞体增大,突起伸长,在肌层、粘膜下层和肠腺基部出现氮能神经纤维分布.第7个月胎龄时,氮能神经元生长发育达到高峰,肌间神经节细胞数目增多,环肌层神经纤维分布密度增加,膨体结构明显.第8-10个月胎龄时,氮能神经元染色强度加深,其胞体分布以肌间神经节最多,粘膜下层和内环肌层较少.氮能神经纤维的分布密度以内环肌层最高,粘膜下层和外纵肌层次之,粘膜层较低.本研究揭示了大肠氮能神经元发育的变化规律.     

Ultrastructure of the dorsal hemal vessel in the sea-cucumber Parastichopus tremulus (Echinodermata: Holothuroidea)

The dorsal hemal vessel in Parastichopus consists of three distinct layers: An outer flagellated epithelium, an intermediate circular muscle layer and an inner connective tissue layer which nearly fills the lumen. Between the outer and intermediate layer runs strands of nerve fibers. Each coelomic epithelial cell has one flagellum and some microvilli. It contains a number of different vacuoles and a few bundles of tonofilaments. One special type of vacuole which contains well organized myofilaments is described. Each muscle cell contains one myofibril of a non-striated type consisting of thick and thin filaments and no dense bodies. The sarcoplasmic reticulum is poorly developed, but peripheral coupling are frequently found. The muscle cells in the dorsal hemal vessel of Parastichopus are compared with other muscles in echinoderms and muscle types described in other phyla.