Participation of the coelomic epithelium of the body wall in muscle regeneration in <Emphasis Type="Italic">Apostichopus japonicus</Emphasis> (Holothuroidea: Aspidochirota)

The cellular sources of regeneration of longitudinal muscles were studied in the holothurian Apostichopus japonicus. An autoradiographic method tracing the distribution of cells labeled with tritiated thymidine (³HT) revealed that the majority of ³HT-cells, which were initially localized in the coelomic epithelium of muscles and the body wall at the beginning of active morphogenesis, were then found in the structure of new muscular bundles during subsequent terms of restoration. Thus, the coelomic epithelium of the body wall participated in the regeneration of muscle tissue concurrently with the coelomic epithelium of muscle, contributing to the recruitment of a pool of myogenic cells.     

Ultrastructure of the coelomic lining in the podium of the starfish Stylasterias forreri

Summary Ultrastructural examination of the podium of the asteroid echinoderm Stylasterias forreri reveals that cells of the coelomic epithelium and cells of the retractor muscle are, in fact, components of a single epithelium. The basal lamina of this unified epithelium adjoins the connective tissue layer of the podium.The principal epithelial cells in the coelomic lining are the flagellated adluminal cells and the myofilament-bearing retractor cells. Adluminal cells interdigitate extensively with each other and form zonular intermediate and septate junctions at their apicolateral surfaces. The adluminal cells emit processes which extend between the underlying retractor cells and terminate on the basal lamina of the epithelium. Retractor cells exhibit unregistered arrays of thick and thin myofilaments. The periphery of the retractor cell is characteristically thrown into keel-like folds which interdigitate with the processes of neighboring cells. Specialized intermediate junctions bind the retractor cells to each other and anchor the retractor cells to the basal lamina of the epithelium. The retractor cells are not surrounded by external laminae or connective tissue envelopes.It is concluded that the coelomic lining in the podium of S. forreri is a bipartite epithelium and that the retractor cells of the podium are myoepithelial in nature. There are no detectable communicating (gap) junctions between the epithelial cells of the coelomic lining.This investigation was supported by general research funds from the Department of Anatomy of the University of Southern California (R.L.W.) and by Research Operating Grant A0484 from the Natural Sciences and Engineering Research Council of Canada (M.J.C.). Ms. Aileen Kuda and Mr. Steve Osborne provided technical assistance. A portion of this study was conducted at the Friday Harbor Laboratories of the University of Washington, and the authors gratefully acknowledge the cooperation and hospitality of the Director, Dr. A.O. Dennis Willows     

The fine structure of the ovary of the feather star Nemaster rubiginosa (Echinodermata: Crinoidea)

The outer layer of the crinoid ovary consists of coelomic epithelium, smooth muscles, and nerve cell processes. The middle layer of the ovary contains non-germinal accessory cells, small germinal cells (either oogonia or pre-leptotene primary oocytes), and post-pachytene primary oocytes; all these cells are completely embedded in a haemal matrix of 200 A-diameter granules. The primary oocytes larger than 20mu in diameter have abundant invaginations in the plasma membrane, suggesting uptake of materials from the haemal matrix. The innermost layer of the ovary is a ciliated epithelium lining the cell-free ovarian lumen.     

Structure of the Digestive Tube in the Holothurian Eupentacta fraudatrix (Holothuroidea: Dendrochirota)

In the holothurian Eupentacta fraudatrix,the gut wall exhibits trilaminar organization. It consists of an inner digestive epithelium, a middle layer of connective tissue, and an outer mesothelium (coelomic epithelium). The pharynx, esophagus, and stomach are lined with a cuticular epithelium composed of T-shaped cells. The lining epithelium of the intestine and cloaca lacks a cuticle and consists of columnar vesicular enterocytes. Mucocytes are also encountered in the digestive epithelium. The connective tissue layer is composed of a ground substance, which houses collagen fibers, amoebocytes, morula cells, and fibroblasts. The gut mesothelium is a pseudostratified epithelium, which is dominated by peritoneal and myoepithelial cells and also includes the perikarya and processes of the neurons of the hyponeural plexus and vacuolated cells.     

Fine Structure of Tentacles,Arms and Associated Coelomic Structures of Cephalodiscus gracilis (Pterobranchia,Hemichordata)

The tentacles of the pterobranch Cephalodiscus, a hemisessile ciliary feeder, originate from the lateral aspects of the arms and are covered by an innervated epithelium, the majority of its cells bearing microvilli. Each side of a tentacle has two rows of ciliated cells and additional glandular cells. The coelomic spaces in the tentacles are lined by cross-striated myoepithelial cells, allowing rapid movements of the tentacles. One, possibly two, blood vessels accompany the coelomic canal. On their outer sides the arms are covered by a simple ciliated epithelium with intra-epithelial nerve fibres; the inner side is covered by vacuolar cells. On both sides different types of exocrine cells occur. The collar canals of the mesocoel are of complicated structure. Ventrally their epithelium is pseudostratified and ciliated; dorsally it is lower and forms a fold with specialized cross-striated myoepithelial cells of the coelomic lining. Arms, tentacles, associated coelomic spaces and the collar canal of the mesocoel are considered to be functionally interrelated. It is assumed that rapid regulation of the pore width is possible and even necessary when the tentacular apparatus is retracted, which presumably leads to an increase of hydrostatic pressure in the coelom.     

The Ulrastructure of the Gill of the Lugworm Arenicola marina (L.) (Annelida,Polychaeta)

Arenicola marina gills are hollow, branched, body outgrowths with a central coelomic cavity and afferent and efferent vessels. The gill surface area per unit body weight is about 4 cm²/g wet weight. The blood vascular system anatomy differs from the tip to the base of the gill. In the distal branches of the gill the superficial afferent and efferent vessels are joined by connecting vessels. All vessels arise as spacings between the basal laminae of the thin epidermis and of the coelomic myoepithelium. The contractile part of this epithelium mainly borders the afferent and efferent vessels, whereas pedicel-like cytoplasmic processes extend from the cell bodies and mainly line the connecting vessels. In the proximal branches of the gill the afferent and efferent vessels located in the coelomic cavity are surrounded by the coelomic myoepithelium, and a peripheral blood plexus is present below the epidermis. The gill epidermis is everywhere thin and does not exhibit the characters of a transporting epithelium. The gill coelomic myoepithelium has several functions: (i) periodic contractions of the gill, propelling blood and coelomic fluid toward the central vascular and coelomic compartments; (ii) blood ultrafilration toward the coelomic cavity; (iii) probably transport, suggested by the specialized structures of the lateral membranes of the cells.     

The basiepithelial nerve plexus of the viscera and coelom of eleutherozoan echinodermata

Summary The organisation of the basiepithelial nerve plexus in the alimentary canal of a starfish and the water vascular system of a sea-urchin is described. The plexus contains varicose aminergic neurones which terminate adjacent to the ciliated epithelial cells. It is proposed that the basiepithelial plexus innervates these cells and controls ciliary beating. The distribution of the basiepithelial plexus in various tissues described by other workers is dicscussed particularly in relation to whether it is the coelomic epithelium or the luminal epithelium which is innervated. It is concluded that where there is both an endothelium and a coelomic epithelium only one is innervated. The muscles, where present, of the viscera are innervated by a separate nervous system. The muscles are always on the opposite side of the non-cellular connective tissue sheath to the basiepithelial plexus.     

The Development of the Brachiopod Crania (Neocrania) anomala (O. F. Müller)and its Phylogenetic Significance

The freely spawned eggs of Crania go through radial cleavage, embolic gastrulation, and the posteroventral part of the archenteron forms mesoderm through modified enterocoely. The blastopore closes in the posterior end of the larva. The ciliated, lecithotrophic larva has four pairs of coelomic pouches and three pairs of dorsal setal bundles. At metamorphosis, the larva curls ventrally by contraction of a pair of midventral muscles, which are extensions of the first pair of coelomic sacs; the larva attaches by the epithelium just behind the closed blastopore. The brachial valve is secreted by the middle part of the dorsal epithelium and the pedicle valve is secreted by the attachment epithelium. The second pair of coelomic sacs develop small attachment areas at the edge of the dorsal valve and become the lophophore coelom (mesocoel); the third pair of coelomic sacs become the body coelom (metacoel) with the adductor muscles. The posterior position of the closing blastopore is characteristic of deuterostomes. The ventral curving of the settling larva and the formation of both valves from dorsal epithelial areas indicate that the brachiopods have a very short ventral side as opposed to the phoronids. It is concluded that both groups have originated from a creeping ancestor with a straight gut.     

Differentiation of hemangioblasts from embryonic mesothelial cells? A model on the origin of the vertebrate cardiovascular system

The existence of the hemangioblast, a common progenitor of the endothelial and hematopoietic cell lineages, was proposed at the beginning of the century. Although recent findings seem to confirm its existence, it is still unknown when and how the hemangioblasts differentiate. We propose a hypothesis about the origin of hemangioblasts from the embryonic splanchnic mesothelium. The model is based on observations collected from the literature and from our own studies. These observations include: (1) the extensive population of the splanchnic mesoderm by mesothelial-derived cells coinciding with the emergence of the endothelial and hematopoietic progenitors; (2) the transient localization of cytokeratin, the main mesothelial intermediate filament protein, in some embryonic vessels and endothelial progenitors; (3) the possible origin of cardiac vessels from epicardial-derived cells; (4) the origin of endocardial cells from the splanchnic mesoderm when this mesoderm is an epithelium; (5) the evidence that mesothelial cells migrate to the hemogenic areas of the dorsal aorta. (6) Biochemical and antigenic similarities between mesothelial and endothelial cells. We suggest that the endothelium-lined vascular system arose as a specialization of the phylogenetically older coelomic cavities. The origin of the hematopoietic cells might be related to the differentiation, reported in some invertebrates, of coelomocytes from the coelomic epithelium. Some types of coelomocytes react against microbial invasion and other types transport respiratory pigments. We propose that this phylogenetic origin is recapitulated in the vertebrate ontogeny and explains the differentiation of endothelial and blood cells from a common mesothelial-derived progenitor.     

Two distinct origins for Leydig cell progenitors in the fetal testis

During the differentiation of the mammalian embryonic testis, two compartments are defined: the testis cords and the interstitium. The testis cords give rise to the adult seminiferous tubules, whereas steroidogenic Leydig cells and other less well characterized cell types differentiate in the interstitium (the space between testis cords). Although the process of testis cord formation is essential for male development, it is not entirely understood. It has been viewed as a Sertoli-cell driven process, but growing evidence suggests that interstitial cells play an essential role during testis formation. However, little is known about the origin of the interstitium or the molecular and cellular diversity within this early stromal compartment. To better understand the process of mammalian gonad differentiation, we have undertaken an analysis of developing interstitial/stromal cells in the early mouse testis and ovary. We have discovered molecular heterogeneity in the interstitium and have characterized new markers of distinct cell types in the gonad: MAFB, C-MAF, and VCAM1. Our results show that at least two distinct progenitor lineages give rise to the interstitial/stromal compartment of the gonad: the coelomic epithelium and specialized cells along the gonad–mesonephros border. We demonstrate that both these populations give rise to interstitial precursors that can differentiate into fetal Leydig cells. Our analysis also reveals that perivascular cells migrate into the gonad from the mesonephric border along with endothelial cells and that these vessel-associated cells likely represent an interstitial precursor lineage. This study highlights the cellular diversity of the interstitial cell population and suggests that complex cell–cell interactions among cells in the interstitium are involved in testis morphogenesis.     

Comparative analysis of behavior and proliferative activity in culture of cells of coelomic fluid and of cells of various tissues of the sea star <Emphasis Type="Italic">Asterias rubens</Emphasis> L. Isolated from normal and injured animals

The sources of coelomocytes in Asteroidea are suggested to be the coelomic epithelium, the axial organ, or Tiedemann’s bodies. To study the problem of whether the cells are replenished at the expense of divisions, we analyzed the incorporation of bromodeoxyuridine (BrdU) in vivo into cells from different tissues of the sea star Asterias rubens L. To study differentiation in vitro, methods of isolating and cultivating cells from various tissues were elaborated and an analysis of the behavior and incorporation of BrdU in culture was performed. The reproduced BrdU incorporation was detected in coelomic epithelial cells. The behavior of coelomocytes and the coelomic epithelial cells in culture depended on the time after the injury of the animals in which the cells were isolated, whereas, for the axial organ and Tiedemann’s bodies, no differences were revealed. After 2 months of cultivation, the formation of BrdU-incorporating, colony-like cells with high nuclear-cytoplasmic ratios was characteristic of coelomic epithelial cells. Thus, the most prospective object for studying the processes of A. rubens cell differentiation in vitro seems to be the coelomic epithelium.     

Electron microscopic studies of the digestive tract and absorption from the gut lumen of a feather star,oligometra serripinna (Echinodermata)

Summary The gut of a crinoid echinoderm is described for the first time by transmission electron microscopy. The gut comprises a short esophagus, a relatively long intestine and a short rectum. From the luminal side to the coelomic side, the layers of the gut wall are an inner epithelium, an epineural plexus (much reduced or absent in the intestine and rectum), haemal fluid, smooth muscles mixed with a hyponeural plexus, and a visceral peritoneum. The inner epithelium of the esophagus consists of numerous flagellated enterocytes and some mucous cells containing abundant mucous granules. The luminal surface of the esophagus, but not that of the other gut regions, is covered by a conspicuous cuticle. The inner epithelium of the intestine consists of some exocrine cells, presumably exporting digestive enzymes to the gut lumen, and numerous vesicular enterocytes that are flagellated and contain a few apical mucous granules. The inner epithelium of the rectum is made up entirely of vesicular enterocytes most of which lack a flagellum. The uptake of macromolecules from the gut lumen was demonstrated by feeding the feather stars food mixed with ferritin. By 4 h after feeding, ferritin was identified in presumed secondary lysosomes within the enterocytes of the esophagus and within the vesicular enterocytes of the intestine and rectum. The functional implications of the new fine structural results are discussed.     

Organization of the coelomic lining and a juxtaposed nerve plexus in the suckered tube feet of Parastichopus californicus (Echinodermata: Holothuroida)

The coelomic lining of the water-vascular canal in a suckered tube foot from the sea cucumber, Parastichopus californicus, is a pseudostratified myoepithelium consisting of flagellated adluminal cells and myofilament-bearing retractor cells. The bodies of adluminal cells flank the water-vascular canal and send basal processes between the underlying retractor cells to confront the podial connective tissue. Retractor cells have a contractile apparatus of unregistered thick and thin myofilaments. The contractile apparatus is confined to the medullary sarcoplasm and oriented parallel to the primary axis of a tube foot. The bodies and processes of retractor cells intermingle with the basal processes of adluminal cells at the basal lamina of the coelomic lining. A ganglionated nerve plexus in the podial connective tissue approximates the basal lamina. Neuronal connectives link the ganglia to one another and to the nerve plexus in deep sectors of the podial epidermis. External laminae enveloping the ganglia and connectives in the podial connective tissue are continuous with the basal lamina of the epidermis. The adventitial nerve plexus, since it merges with the epidermal nerve plexus, is a component of the ectoneural division of the echinoderm nervous system.     

Post-autotomy regeneration of respiratory trees in the holothurian Apostichopus japonicus (Holothuroidea, Aspidochirotida)

Specialised respiratory organs, viz. the respiratory trees attached to the dorsal part of the cloaca, are present in most holothurians. These organs evolved within the class Holothuroidea and are absent in other echinoderms. Some holothurian species can regenerate their respiratory trees but others lack this ability. Respiratory trees therefore provide a model for investigating the origin and evolution of repair mechanisms in animals. We conducted a detailed morphological study of the regeneration of respiratory trees after their evisceration in the holothurian Apostichopus japonicus. Regeneration of the respiratory trees occurred rapidly and, on the 15th day after evisceration, their length reached 15–20 mm. Repair involved cells of the coelomic and luminal epithelia of the cloaca. Peritoneocytes and myoepithelial cells behaved differently during regeneration: the peritoneocytes kept their intercellular junctions and migrated as a united layer, whereas groups of myoepithelial cells disaggregated and migrated as individual cells. Although myoepithelial cells did not divide during regeneration, the peritoneocytes proliferated actively. The contractile system of the respiratory trees was assumed to develop during regeneration by the migration of myoepithelial cells from the coelomic epithelium of the cloaca. The luminal epithelium of the respiratory trees formed as a result of dedifferentiation, migration and transformation of cells of the cloaca lining. The mode of regeneration of holothurian respiratory trees is discussed. This work was funded by a grant from the Russian Foundation for Basic Research (project no. 08–04–00284) to I.Y.D. and by a grant from the Far Eastern Branch of the Russian Academy of Sciences and the Russian Foundation for Basic Research (project no. 09–04–98547) to T.T.G.     

Small coelomic epithelial cells of the starfish Asterias rubens L. that are able to proliferate in vivo and in vitro

Echinoderms, due to their outstanding potential for regeneration, are widely used as experimental models for research in regenerative biology. One of the main problems in this field concerns identification and characterization of cells responsible for the restoration of lost body parts and organs in adult animals. In this study, we analyze the probable candidates for this role in the starfish Asterias rubens L., namely, small coelomic epithelial cells with a high nuclear–cytoplasmic ratio that have the ability to proliferate. These cells are one of several cell types common to the coelomic epithelium (CE) and coelomic fluid (CF). They are analyzed with respect to morphology, proportion in the total cell pool, dynamics after injury and distribution between CE and CF. The results of whole-mount and scanning electron microscopy provide evidence that these small cells occupy a boundary position between CE and CF. Moreover, a novel subpopulation of CE cells is identified that is enriched (up to 50 %) with small epitheliocytes capable of migrating from CE into the CF. As shown in experiments with BrdU incorporation and anti-phospho-histone H3 antibody staining, small epitheliocytes cultured on laminin retain proliferative activity for at least 1 month and can form colony-like aggregates. Two types of small proliferating cells are distinguished by their behavior in culture: some cells remain attached to the substrate and form aggregates, while others detach from the substrate during culturing. The morphology of small epitheliocytes, their proliferative activity in vivo and in vitro and the ability to migrate suggest that they possess certain properties characteristic of stem cells.     

Ultrastructure of tentacles in the sipunculid worm <Emphasis Type="Italic">Thysanocardia nigra</Emphasis> Ikeda, 1904 (Sipuncula)

The ultrastructure of the tentacles was studied in the sipunculid worm Thysanocardia nigra. Flexible digitate tentacles are arranged into the dorsal and ventral tentacular crowns at the anterior end of the introvert of Th. nigra. The tentacle bears oral, lateral, and aboral rows of cilia; on the oral side, there is a longitudinal groove. Each tentacle contains two oral tentacular canals and an aboral tentacular canal. The oral side of the tentacle is covered by a simple columnar epithelium, which contains large glandular cells that secrete their products onto the apical surface of the epithelium. The lateral and aboral epithelia are composed of cuboidal and flattened cells. The tentacular canals are lined with a flattened coelomic epithelium that consists of podocytes with their processes and multiciliated cells. The tentacular canals are continuous with the radial coelomic canals of the head and constitute the terminal parts of the tentacular coelom, which shows a highly complex morphology. Five tentacular nerves and circular and longitudinal muscle bands lie in the connective tissue of the tentacle wall. Similarities and differences in the tentacle morphology between Th. nigra and other sipunculan species are discussed.Original Russian Text Copyright © 2005 by Biologiya Morya, Maiorova, Adrianov.     

Juxtaligamental cells in the arm of the brittlestar <Emphasis Type="Italic">Amphipholis kochii</Emphasis> Lütken, 1872 (Echinodermata: Ophiuroidea)

We found that ligaments connecting the skeletal elements in the arm of the brittlestar Amphipholis kochii, consisted of mutable collagenous tissue (MCT), whose basichistological character is that of numerous processes of juxtaligamental cells penetrating the extracellular matrix. These cells are located in the hyponeural neuroepithelium associated with hyponeural nerves, and were also recorded in the spine ganglia and basiepithelial nervous plexus in the coelomic epithelium. The distinctive feature of juxtaligamental cells is the presence of electron-dense granules in their cytoplasm and a well developed synthetic apparatus. Based on personal and literature data it is concluded that juxtaligamental cells are a part of the nervous system, and their basic function is related to providing MCT with innervation.     

Biochemical and pathogenic properties of the natural isolate of Shewanella algae from Peter the Great Bay, Sea of Japan

Pathogenic properties of the natural isolate of Shewanella algae from the coelomic fluid of the sea cucumber Apostichopus japonicus (Peter the Great Bay, Sea of Japan) were investigated. The isolate had oxydative metabolism, was positive for ornithine decarboxylase, cytochrome oxidase, catalase, DNase and gelatinase, hemolytically active, did not produce acid from carbohydrates, and did not hydrolyze urea and esculin. The strain was resistant to penicillin, amoxicillin, and ampicillin and susceptible to tetracycline and carbenicillin. Among cellular fatty acids, 13:0-i, 15:0-i, 16:0, 16:1(n-7), 17:0-i, and 17:0-ai dominated. These biochemical properties made it possible to attribute the isolated bacteria to the genus Shewanella and identified as S. algae. The cells of this bacterium were introduced into the coelomic cavity of another echinoderm, the sea urchin Strongylocentrotus nudus. As a result, in about 24 h the animals became slow and 3-8 days after the inoculation died. Dividing bacteria were being found during the experiment in the coelomic fluid as well as in the phagosomes of amoebocytes, i.e. cells acting as phagocytes in the coelomic fluid. The studies of the invasive properties of strain 156 showed that bacterial cells entered the subcuticular space of S. nudus and A. japonicus through the cuticle and stayed there for a long time without penetrating epithelium and exerting toxic effect upon the organisms of the laboratory animals. Pathogenic effect of S. algae can be manifested only if the cutaneous epithelium is destroyed permitting it to penetrate the lower tissue layers. The toxicity of S. algae is confirmed by in vitro experiments. The inoculation of the embryonic cells of S. nudus with samples of this bacterium caused the death of 10% of cells within an hour and 100% of cells within 12 h after inoculation. The results of the investigations demonstrate that S. algae could produce opportunistic infection in the sea cucumber A. japonicus and the sea urchin S. nudus, which may be natural reservoirs of this human pathogen.