Chlamydial symbionts in the enigmatic Xenoturbella (Deuterostomia)

Ultrastructural observations of the gastrodermal cells in the enigmatic Xenoturbella revealed numerous chlamydiae. They are related to "Candidatus Fritschea" and Simkania (Simkaniaceae) based on 16S and 23S rRNA. Their 23S rRNA gene contains an intron encoding a putative homing endonuclease. The chlamydiae were pleomorphic and formed intravacuolar colonies. They have flattened disk-shaped elementary bodies, either oval or bow tie-shaped in cross-section, and reticulate bodies that are spherical, polygonal or irregularly shaped. All stages have five-layered cell wall with rippled appearance. Bacteria were not observed in the nuclei. The association between the chlamydiae and Xenoturbella is characterized by absence of cytopathological effects; limited host cell response against the chlamydiae; the confinement of the chlamydiae to inclusions in some part of the host cell; and complete and uniform infection of all examined hosts.     

Feeding ecology of Xenoturbella bocki (phylum Xenoturbellida) revealed by genetic barcoding

The benthic marine worm Xenoturbella is frequently contaminated with molluscan DNA, which had earlier caused confusion resulting in a suggested bivalve relationship. In order to find the source of the contaminant, we have used molluscan sequences derived from Xenoturbella and compared them to barcodes obtained from several individuals of the nonmicroscopic molluscs sharing the same environment as Xenoturbella. Using cytochrome oxidase 1, we found the contaminating sequences to be 98% similar to the bivalve Ennucula tenuis. Using the highly variable D1-D2 region of the large ribosomal subunit in Xenoturbella, we found three distinct species of contaminating molluscs, one of which is 99% similar to the bivalve Abra nitida, one of the most abundant bivalves in the Gullmarsfjord where Xenoturbella was found, and another 99% similar to the bivalve Nucula sulcata. These data clearly show that Xenoturbella only contains molluscan DNA originating from bivalves living in the same environment, refuting former hypotheses of a bivalve relationship. In addition, these data suggest that Xenoturbella feeds specifically on bivalve prey from multiple species, possibly in the form of eggs and larvae.     

Ultrastructural aspects of the 'statocyst' of Xenoturbella (Deuterostomia) cast doubt on its function as a georeceptor

The "statocyst" in the enigmatic worm Xenoturbella is a structure containing motile flagellated cells. It is situated inside the subepidermal membrane complex (between epidermis and muscular layers) in the anterior end of the body. The motile cells contain a lipophilic refractile body ("statolith"), and a series of vesicles from small dense core vesicles presumably formed from the refractile body to large vesicles with dense aggregates of filamentous tubules that become exocytized through secretion. It is unlikely that the statocyst is a georeceptor (true statocyst); maybe it has an endocrine function.     

A new method for isolating primary mesenchyme cells of the sea urchin embryo : Panning on wheat germ agglutinin-coated dishes

This paper describes a rapid and efficient way to isolate primary mesenchyme cells (PMCs) of the sea urchin embryo. The procedure involves three simple steps: Dissociation of mesenchyme blastulae in calcium-free artificial seawater. Incubation of the resulting cell suspension on dishes that have been coated with wheat germ agglutinin (WGA), to which the PMCs adhere more firmly than do other cell types. Gentle rinsing of the dishes to remove loosely attached cells, followed by more vigorous rinsing to remove PMCs. This panning procedure has been applied to embryos of three species of sea urchins, Lytechinus variegatus, L. pictus and Arbacia punctulata, and yields populations of PMCs that are 95-99% pure as determined by the proportion of cells that stain with fluorescein isothiocynate (FITC)-WGA and with a monoclonal antibody that binds specifically to PMCs. The yield of PMCs is 4-5 X 10(6) cells/100-mm dish, or 1-2 X 10(7) PMCs/ml of packed embryos. The principal advantages of this procedure are that it can be carried out rapidly and simply, and it yields pure populations of PMCs.     

The ciliated epidermis of Xenoturbella bocki (Platyhelminthes, Xenoturbellida) with some phylogenetic considerations

The epidermis of Xenoturbella bocki Westblad was studied by scanning and transmission electron microscopy. Two cell types predominate in the epidermis: multiciliated epidermal cells and non-ciliated or monociliated gland cells. A conspicuous feature is the dense ciliary coverage and the numerous gland cell openings. Xenoturbella has a characteristic pattern of axonemal filament termination in the distal tips of their cilia. Each epidermal cilium has the typical 9 + 2 patten through the major part of its shaft. Near the tip there is a shelf at which doublets 4–7 terminate. Doublets 1, 2, 3, 8 and 9 continue into the thinner distal part of the cilium. A similar shelf in cilia is known only from the turbellarian orders Nemertodermatida and Acoela, and hence may be an apomorphic feature which indicates a close relationship between Xenoturbellida, Nemertoder-matida and Acoela. The basal body is provided with a so-called basal foot which has a cross-striated appearance and an expanded distal plate that seems to act as a microtubule organizing center. Approximately 15–25 microtubuli radiate from the endplate of the basal foot to the basal bodies caudally. The arrangement of basal foot and ciliary rootlets in Xenoturbella differs from that of Acoela and related orders in that there are two striated rootlets only (an anterior and a posterior one), rather than one main rootlet and two lateral rootlets.     

Cell lineage conversion in the sea urchin embryo

The mesoderm of the sea urchin embryo conventionally is divided into two populations of cells; the primary mesenchyme cells (PMCs), which produce the larval skeleton, and the secondary mesenchyme cells (SMCs), which differentiate into a variety of cell types but do not participate in skeletogenesis. In this study we examine the morphogenesis of embryos from which the PMCs have been removed microsurgically. We confirm the observation of Fukushi (1962) that embryos lacking PMCs form a complete skeleton, although in a delayed fashion. We demonstrate by microsurgical and cell marking experiments that the appearance of skeletogenic cells in such PMC-deficient embryos is due exclusively to the conversion of other cells to the PMC phenotype. Time-lapse video recordings of PMC-deficient embryos indicate that the converting cells are a subpopulation of late-ingressing SMCs. The conversion of these cells to the skeletogenic phenotype is accompanied by their de novo expression of cell surface determinants normally unique to PMCs, as shown by binding of wheat germ agglutinin and a PMC-specific monoclonal antibody. Cell transplantation and cell marking experiments have been carried out to determine the number of SMCs that convert when intermediate numbers of PMCs are present in the embryo. These experiments indicate that the number of converting SMCs is inversely proportional to the number of PMCs in the blastocoel. In addition, they show that PMCs and converted SMCs cooperate to produce a skeleton that is correct in both size and configuration. This regulatory system should shed light on the nature of cell-cell interactions that control cell differentiation and on the way in which evolutionary processes modify developmental programs.     

Skeletogenesis by transfated secondary mesenchyme cells is dependent on extracellular matrix-ectoderm interactions in Paracentrotus lividus sea urchin embryos

In the sea urchin embryo, primary mesenchyme cells (PMCs) are committed early in development to direct skeletogenesis, provided that a permissive signal is conveyed from adjacent ectoderm cells. We showed that inhibition of extracellular matrix (ECM)-ectoderm cells interaction, by monoclonal antibodies (mAb) to Pl-nectin, causes an impairment of skeletogenesis and reduced expression of Pl-SM30, a spicule-specific matrix protein. When PMCs are experimentally removed, some secondary mesenchyme cells (SMCs) switch to skeletogenic fate. Here, for the first time we studied SMC transfating in PMC-less embryos of Paracentrotus lividus. We observed the appearance of skeletogenic cells within 10 h of PMCs removal, as shown by binding of wheat germ agglutinin (WGA) to cell surface molecules unique to PMCs. Interestingly, the number of WGA-positive cells, expressing also msp130, another PMC-specific marker, doubled with respect to that of PMCs present in normal embryos, though the number of SM30-expressing cells remained constant. In addition, we investigated the ability of SMCs to direct skeletogenesis in embryos exposed to mAbs to Pl-nectin after removal of PMCs. We found that, although phenotypic SMC transfating occurred, spicule development, as well as Pl-SM30-expression was strongly inhibited. These results demonstrate that ectoderm inductive signals are necessary for transfated SMCs to express genes needed for skeletogenesis.     

Interactions of pathogen‐containing compartments with the secretory pathway

A subgroup of intracellular pathogens reside and replicate within membrane‐bound compartments often termed pathogen‐containing compartments (PCC). PCCs navigate around a wide range of host cell vesicles and organelles. In light of the perils of engaging with vesicles of the endocytic pathway, most PCCs modulate their interactions with endocytic vesicles while a few avoid those interactions. The secretory pathway constitutes another important grouping of vesicles and organelles in host cells. Although the negative consequences of engaging with the secretory pathway are not known, there is evidence that PCCs interact differentially with vesicles and organelles in this pathway as well. In this review, we consider three prokaryote pathogens and two protozoan parasites for which there is information on the interactions of their PCCs with the secretory pathway. Current understandings of the molecular interactions as well as the metabolic benefits that accompany those interactions are discussed. Not unexpectedly, our understanding of the extent of these interactions is variable. An underlying theme that is brought to the fore is that PCCs establish preferential interactions with distinct compartments of the secretory pathway.     

革胡子鲇原生殖细胞和早期间质细胞主动迁移时的超微结构

用电镜观察了革胡子鲇原生殖细胞和早期间质细胞主动迁移时的超微结构．这两种细胞具有伪足,伪足内有线粒体．两种细胞周围的间质细胞的排列比较疏松．在这两种细胞主动迁移时,细胞周围的空隙内分布有丰富的纤维状的结构,这种纤维状结构与这两种细胞的主动迁移有密切的联系．     

Localized VEGF signaling from ectoderm to mesenchyme cells controls morphogenesis of the sea urchin embryo skeleton

During development, cell migration plays an important role in morphogenetic processes. The construction of the skeleton of the sea urchin embryo by a small number of cells, the primary mesenchyme cells (PMCs), offers a remarkable model to study cell migration and its involvement in morphogenesis. During gastrulation, PMCs migrate and become positioned along the ectodermal wall following a stereotypical pattern that determines skeleton morphology. Previous studies have shown that interactions between ectoderm and PMCs regulate several aspects of skeletal morphogenesis, but little is known at the molecular level. Here we show that VEGF signaling between ectoderm and PMCs is crucial in this process. The VEGF receptor (VEGFR) is expressed exclusively in PMCs, whereas VEGF expression is restricted to two small areas of the ectoderm, in front of the positions where the ventrolateral PMC clusters that initiate skeletogenesis will form. Overexpression of VEGF leads to skeletal abnormalities, whereas inhibition of VEGF/VEGFR signaling results in incorrect positioning of the PMCs, downregulation of PMC-specific genes and loss of skeleton. We present evidence that localized VEGF acts as both a guidance cue and a differentiation signal, providing a crucial link between the positioning and differentiation of the migrating PMCs and leading to morphogenesis of the embryonic skeleton.     

A germ cell specific gene of the ARGONAUTE family is essential for the progression of premeiotic mitosis and meiosis during sporogenesis in rice

The rice (Oryza sativa) genome contains 18 copies of genes of the ARGONAUTE (AGO) family. Although AGO members play important roles in RNA-mediated silencing during plant development, a family member that is specifically involved in sexual reproduction has not been identified in plants. We identified the rice AGO gene MEIOSIS ARRESTED AT LEPTOTENE1 (MEL1) from the analysis of seed-sterile mutants. In the mel1 mutant, chromosome condensation was arrested at early meiotic stages and irregularly sized, multinucleated, and vacuolated pollen mother cells (PMCs) frequently appeared in developing anthers. In addition, histone H3 lysine-9 dimethylation of pericentromeres was rarely reduced and modification of the nucleolar-organizing region was altered in mel1 mutant PMCs. The mutation also affected female germ cell development. These results indicate that the germ cell-specific rice MEL1 gene regulates the cell division of premeiotic germ cells, the proper modification of meiotic chromosomes, and the faithful progression of meiosis, probably via small RNA-mediated gene silencing, but not the initiation and establishment of germ cells themselves.     

Cytomixis and its possible evolutionary role in a Kuwaiti population of Diplotaxis harra (Brassicaceae)

During a cytotaxonomical study of a Kuwaiti diploid (2 n  = 26) population of Diplotaxis harra (Forssk.) Boiss (Brassicaceae), cytomixis and aneuploidy were found in 1.5% and 7.8% of the pollen mother cells (PMCs), respectively. Cytomictic cells revealed wide variability as far as the number of involved PMCs and their stage of division were concerned. The cytoplasmic channels, which were of different sizes, contained migrating chromosomes in a few cases. In some PMCs, the location of some of the chromosomes was clearly indicative of an imminent migration from a donor to its attached recipient cell. At metaphase I and anaphase I, PMCs showed variable degree of chromosomal transfer. In addition to a genetic control of the phenomenon, stress factors such as high temperature or drought in certain periods of the growing season may have contributed to the incidence of cytomixis in the material. A possible relationship between cytomixis and detected aneuploid PMCs, as well as a reconsideration of an evolutionary role of cytomixis is discussed.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 169–175.     

The epidermal ciliary rootlets of Xenoturbella bocki (Xenoturbellida) revisited: new support for a possible kinship with the Acoelomorpha (Platyhelminthes)

Ultrastructural studies of epidermal locomotory ciliary structures of Xenoturbella bocki , i.e. the basal part of the axaneme, the basal body and the ciliary rootlets, have revealed characters supporting the hypothesis of a close relationship between Xenoturbella and the Acoelomorpha. Some of the most prominent of these possibly synapomorphic characters are a cup-shaped structure at the base of the axoneme, a proximally hollow rootlet arising on the anterior face of the basal body and bundles of microtubules extending from the basal foot to the main rootlets in the next hind row. Other views in the recent literature places Xenoturbella as closely related to the Mollusca or to the stem species of the Bilateria. As such, the phylogenetic affinities of Xenoturbella remain highly debateable. A review of recent reports on the subject is given here, together with a discussion of combinations of current phylogeny hypotheses.     

Current and voltage responses in instant photosynthetic microbial cells with Spirulina platensis

The electrical response of photosynthetic microbial cells (PMCs) containing Spirulina platensis was investigated to assess the feasibility of using these PMCs as instant-use and portable devices. The PMCs were constructed without membranes, mediators, or any additive organic substrates. Once S. platensis was attached to an anode, voltage was instantly obtained and ready for application. Since no additional substrate was required as fuel for electricity generation, these PMCs were different from typical microbial fuel cells. PMCs were examined under various operating conditions, and they performed under high open circuit voltage (OCV) with high power output in the dark, short electrode spacing (2 cm), low pH value (5.5), and high temperature (40 °C) conditions. According to Ohm's Law and the Nernst equation, the superior OCV and power output were caused by high ionic strength, low internal resistance, and high temperature. Additionally, two equal-sized PMCs were arranged in serial and parallel configurations. The former yielded higher voltage while the latter yielded higher current density.     

MCP-1 in pleural injury: CCR2 mediates haptotaxis of pleural mesothelial cells

Pleural injury results in the death of mesothelial cells and denudation of the mesothelial basement membrane. Repair of the mesothelium without fibrosis requires proliferation and migration of mesothelial cells into the injured area. We hypothesized that monocyte chemoattractant protein-1 (MCP-1) induces proliferative and haptotactic responses in pleural mesothelial cells (PMCs) and that the MCP-1 binding receptor CCR2 mediates the pleural repair process. We demonstrate that PMCs exhibited MCP-1-specific immunostaining on injury. MCP-1 induced proliferative and haptotactic responses in PMCs. PMCs express CCR2 in a time-dependent manner. Fluorescence-activated cell sorting analysis demonstrated that interleukin (IL)-2 upregulated CCR2 protein expression in PMCs, whereas lipopolysaccharide (LPS) downregulated the response at the initial period compared with that in resting PMCs. However, the inhibitory potential of LPS was lost after 12 h and showed a similar response at 24 and 48 h. Haptotactic migration was upregulated in PMCs that were cultured in the presence of IL-2. The increased haptotactic capacity of mesothelial cells in the presence of IL-2 correlated with increased CCR2 mRNA expression. PMCs cultured in the presence of LPS showed decreased haptotactic activity to MCP-1. Blocking the CCR2 with neutralizing antibodies decreased the haptotactic response of PMCs to MCP-1. These results suggest that the haptotactic migration of mesothelial cells in response to MCP-1 are mediated through CCR2, which may play a crucial role in reepithelialization of the denuded basement membrane at the site of pleural injury and may thus contribute to the regeneration of the mesothelium during the process of pleural repair.     

Phenotypic and functional characteristics of porcine peritoneal mesothelial cells

The objective of this study was to establish a technique to isolate porcine mesothelial cells (PMCs) from omental tissue and to compare them to human mesothelial cells (HMCs). The PMCs were dispersed by collagenase digestion and isolated on a Ficoll layer. Their morphologic and ultrastructural features were assessed at confluence by light and electronic microscopy, and they were characterized by immunohistochemistry using specific HMC markers. PMC proliferation was studied in the presence of growth factors platelet-derived growth factor (PDGF), epidermal growth factor (EGF) or transforming growth factors beta1, beta2, or beta3 (TGF). Fibrinolytic PMC activity was detected by zymography for tissue plasminogen activator (tPA) and by reverse zymography for plasminogen activator inhibitor-1 (PAI-1). The recalcification time of cell lysates was used to define PMC procoagulant activity, and gelatinase zymography was used to detect metalloproteinase production. At confluence, PMCs formed typical cobblestone monolayers and exhibited structural features characteristic of HMCs. Weibel Palade bodies were never seen. Specific HMC markers (HBME1, ME1, WT1) cross-reacted with PMCs. As HMCs and PMCs coexpressed cytokeratin and vimentin, and also expressed vinculin and alpha-actin. Addition of PDGF or EGF to the culture medium stimulated PMC proliferation. PMCs constitutively expressed fibrinolytic and procoagulant activity and secreted MMP9 and MMP2. The technique described in this study allows isolation of mesothelial cells from porcine omental tissue. These porcine cells exhibit a mesothelial phenotype and functional properties similar to those of HMCs. Our data warrant an evaluation of mesothelial cells as targets in several therapeutic strategies with porcine models.     

Cancer cells arise from bacteria

Background

The origin of cancer cells is the most fundamental yet unresolved problem in cancer research. Cancer cells are thought to be transformed from the normal cells. However, recent studies reveal that the primary cancer cells (PCCs) for cancer initiation and secondary cancer cells (SCCs) for cancer progression are formed in but not transformed from the senescent normal and cancer cells, respectively. Nevertheless, the cellular mechanism of PCCs/SCCs formation is unclear. Here, based on the evidences (1) the nascent PCCs/SCCs are small and organelle-less resembling bacteria; (2) our finding that the cyanobacterium TDX16 acquires its algal host DNA and turns into a new alga TDX16-DE by de novo organelle biogenesis, and (3) PCCs/SCCs formations share striking similarities with TDX16 development and transition, we propose the bacterial origin of cancer cells (BOCC).

Presentation of the hypothesis

The intracellular bacteria take up the DNAs of the senescent/necrotic normal cells/PCCs and then develop into PCCs/SCCs by hybridizing the acquired DNAs with their own ones and expressing the hybrid genomes.

Testing the hypothesis

BOCC can be confirmed by testing BOCC-based predictions, such as normal cells with no intracellular bacteria can not “transform” into cancer cells in any conditions.

Implications of the hypothesis

According to BOCC theory: (1) cancer cells are new single-celled eukaryotes, which is why the hallmarks of cancer are mostly the characteristics of protists; (2) genetic changes and instabilities are not the causes, but the consequences of cancer cell formation; and (3) the common role of carcinogens, infectious agents and relating factors is inducing or related to cellular senescence rather than mutations. Therefore, BOCC theory provides new rationale and direction for cancer research, prevention and therapy.

     

Pancreatic cancer cells activate CCL5 expression in mesenchymal stromal cells through the insulin-like growth factor-I pathway

Mesenchymal stromal cells (MSCs) have a critical role in cancer progression and metastasis. Despite extensive studies of the physiological responses in cancer cells, the molecular mechanisms regulating gene expression in MSCs by cancer cells remain undefined. Here we demonstrate that CC chemokine ligand 5 (CCL5) expression was increased in MSCs co-cultured with pancreatic cancer cells (PCCs), and this activation was dependent on extracellular insulin-like growth factor (IGF-I). Moreover, CCL5 induction in MSCs was required for the activation of IGF-I pathway in PCCs. These results reveal a link between the IGF-I pathway in PCCs and CCL5 pathway in MSCs through the interaction of those cells.