p53 Superfamily proteins in marine bivalve cancer and stress biology

Microplastic induces mitochondrial pathway mediated cellular apoptosis in mussel (Mytilus galloprovincialis) via inhibition of the AKT and ERK signaling pathway

Microplastics (MPs) is an escalating aquatic environmental crisis that poses significant threats to marine organisms, especially mussels. Here, we compare the cumulative toxic effects of the two most abundant morphotypes of MPs in the environment, microspheres, and microfibers, on the gill and digestive gland (DG) of Mytilus galloprovincialis in a dose-dependent (1, 10, and 100 mg/L) and time-dependent (1, 4, 7, 14, 21 days exposure) manner. DNA fragmentation assessment through TUNEL assay revealed consistency in the pattern of morphological disturbance degree and cell apoptosis proportions indicated by histopathological analysis. Upon the acute phase of exposure (day 1-4), gill and DG treated with low MPs concentration exhibited preserved morphology and low proportion of TUNEL+ cells. At higher concentrations, spherical and fibrous MP-induced structural impairments and DNA breakage occurred at distinct levels. 100 mg/L microfibers was lethal to all mussels on day 21, indicating the higher toxicity of the fibrous particles. During the chronic phase, both morphological abnormalities degree and DNA fragmentation level increased over time and with increasing concentration, but the differentials between the spherical and fibrous group was gradually reduced, particularly diminished in 10 and 100 mg/L in the last 2 weeks. Furthermore, analysis of transcriptional activities of key genes for apoptosis of 100 mg/L-day 14 groups revealed the upregulation of both intrinsic and extrinsic apoptotic induction pathway and increment in gene transcripts involving genotoxic stress and energy metabolism according to MP morphotypes. Overall, microfibers exert higher genotoxic effects on mussel. In response, mussels trigger more intense apoptotic responses together with enhanced energy metabolism to tolerate the adverse effects in a way related to the accumulation of stimuli.

Toward invasive mussel genetic biocontrol: Approaches, challenges, and perspectives

Invasive freshwater mussels, such as the zebra (Dreissena polymorpha), quagga (Dreissena rostriformis bugensis), and golden (Limnoperna fortunei) mussel have spread outside their native ranges throughout many regions of the North American, South American, and European continents in recent decades, damaging infrastructure and the environment. This review describes ongoing efforts by multiple groups to develop genetic biocontrol methods for invasive mussels. First, we provide an overview of genetic biocontrol strategies that have been applied in other invasive or pest species. Next, we summarize physical and chemical methods that are currently in use for invasive mussel control. We then describe the multidisciplinary approaches our groups are employing to develop genetic biocontrol tools for invasive mussels. Finally, we discuss the challenges and limitations of applying genetic biocontrol tools to invasive mussels. Collectively, we aim to openly share information and combine expertise to develop practical tools to enable the management of invasive freshwater mussels.

The expanded inhibitor of apoptosis gene family in oysters possesses novel domain architectures and may play diverse roles in apoptosis following immune challenge

Background

Apoptosis plays important roles in a variety of functions, including immunity and response to environmental stress. The Inhibitor of Apoptosis (IAP) gene family of apoptosis regulators is expanded in molluscs, including eastern, Crassostrea virginica, and Pacific, Crassostrea gigas, oysters. The functional importance of IAP expansion in apoptosis and immunity in oysters remains unknown.

Results

Phylogenetic analysis of IAP genes in 10 molluscs identified lineage specific gene expansion in bivalve species. Greater IAP gene family expansion was observed in C. virginica than C. gigas (69 vs. 40), resulting mainly from tandem duplications. Functional domain analysis of oyster IAP proteins revealed 3 novel Baculoviral IAP Repeat (BIR) domain types and 14 domain architecture types across gene clusters, 4 of which are not present in model organisms. Phylogenetic analysis of bivalve IAPs suggests a complex history of domain loss and gain. Most IAP genes in oysters (76% of C. virginica and 82% of C. gigas), representing all domain architecture types, were expressed in response to immune challenge (Ostreid Herpesvirus OsHV-1, bacterial probionts Phaeobacter inhibens and Bacillus pumilus, several Vibrio spp., pathogenic Aliiroseovarius crassostreae, and protozoan parasite Perkinsus marinus). Patterns of IAP and apoptosis-related differential gene expression differed between the two oyster species, where C. virginica, in general, differentially expressed a unique set of IAP genes in each challenge, while C. gigas differentially expressed an overlapping set of IAP genes across challenges. Apoptosis gene expression patterns clustered mainly by resistance/susceptibility of the oyster host to immune challenge. Weighted Gene Correlation Network Analysis (WGCNA) revealed unique combinations of transcripts for 1 to 12 IAP domain architecture types, including novel types, were significantly co-expressed in response to immune challenge with transcripts in apoptosis-related pathways.

Conclusions

Unprecedented diversity characterized by novel BIR domains and protein domain architectures was observed in oyster IAPs. Complex patterns of gene expression of novel and conserved IAPs in response to a variety of ecologically-relevant immune challenges, combined with evidence of direct co-expression of IAP genes with apoptosis-related transcripts, suggests IAP expansion facilitates complex and nuanced regulation of apoptosis and other immune responses in oysters.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08233-6.

MDM2 is involved in the regulation of p53 expression in the immune response of oyster Crassostrea hongkongensis

MDM2 (mouse double-minute) and p53 form a negative feedback loop and play a prominent role in preventing the induction of uncontrolled apoptosis. To better understand their potential roles in oyster Crassostrea hongkongensis, MDM2 and p53 homologs were first isolated and cloned in C. hongkongensis (named ChMDM2 and Chp53), and their mRNA expression patterns in tissues and developmental stages were analyzed. Multiple sequence alignment analysis and phylogenetic analysis of ChMDM2 and Chp53 displayed a high degree of homology and conservation. In addition, exposure to Vibrio coralliilyticus resulted in DNA damage and apoptosis in the hemocytes of C. hongkongensis, and found that the mRNA expression level of ChMDM2 was decreased, while the relative expression of Chp53 was significantly increased in the hemocytes and gills. Furthermore, fluorescence from ChMDM2-EGFP and Chp53-Red were found to be distributed in the nucleus of HEK293T cells. Besides, dual-luciferase reporter assays showed that ChMDM2 antagonized with Chp53 and participates in p53 signaling pathway. In addition, the interaction between ChMDM2 and Chp53 was confirmed strongly by Co-immunoprecipitation assays. Furthermore, the results of RNAi showed that ChMDM2 and Chp53 participated in apoptosis which induced infection of V. coralliilyticus. Taken together, our results characterized the features of ChMDM2 and Chp53, which played a critical role in apoptosis of C. hongkongensis.

Between the Devil and the Deep Blue Sea: Non-Coding RNAs Associated with Transmissible Cancers in Tasmanian Devil, Domestic Dog and Bivalves

Currently there are nine known examples of transmissible cancers in nature. They have been observed in domestic dog, Tasmanian devil, and six bivalve species. These tumours can overcome host immune defences and spread to other members of the same species. Non-coding RNAs (ncRNAs) are known to play roles in tumorigenesis and immune system evasion. Despite their potential importance in transmissible cancers, there have been no studies on ncRNA function in this context to date. Here, we present possible applications of the CRISPR/Cas system to study the RNA biology of transmissible cancers. Specifically, we explore how ncRNAs may play a role in the immortality and immune evasion ability of these tumours.

Phylogenetic analysis of the caspase family in bivalves: implications for programmed cell death, immune response and development

BACKGROUND

Apoptosis is an important process for an organism's innate immune system to respond to pathogens, while also allowing for cell differentiation and other essential life functions. Caspases are one of the key protease enzymes involved in the apoptotic process, however there is currently a very limited understanding of bivalve caspase diversity and function.

RESULTS

In this work, we investigated the presence of caspase homologues using a combination of bioinformatics and phylogenetic analyses. We blasted the Crassostrea gigas genome for caspase homologues and identified 35 potential homologues in the addition to the already cloned 23 bivalve caspases. As such, we present information about the phylogenetic relationship of all identified bivalve caspases in relation to their homology to well-established vertebrate and invertebrate caspases. Our results reveal unexpected novelty and complexity in the bivalve caspase family. Notably, we were unable to identify direct homologues to the initiator caspase-9, a key-caspase in the vertebrate apoptotic pathway, inflammatory caspases (caspase-1, - 4 or - 5) or executioner caspases-3, - 6, - 7. We also explored the fact that bivalves appear to possess several unique homologues to the initiator caspase groups - 2 and - 8. Large expansions of caspase-3 like homologues (caspase-3A-C), caspase-3/7 group and caspase-3/7-like homologues were also identified, suggesting unusual roles of caspases with direct implications for our understanding of immune response in relation to common bivalve diseases. Furthermore, we assessed the gene expression of two initiator (Cg2A, Cg8B) and four executioner caspases (Cg3A, Cg3B, Cg3C, Cg3/7) in C. gigas late-larval development and during metamorphosis, indicating that caspase expression varies across the different developmental stages.

CONCLUSION

Our analysis provides the first overview of caspases across different bivalve species with essential new insights into caspase diversity, knowledge that can be used for further investigations into immune response to pathogens or regulation of developmental processes.

The Genome of the Softshell Clam Mya arenaria and the Evolution of Apoptosis

Apoptosis is a fundamental feature of multicellular animals and is best understood in mammals, flies, and nematodes, with the invertebrate models being thought to represent a condition of ancestral simplicity. However, the existence of a leukemia-like cancer in the softshell clam Mya arenaria provides an opportunity to re-evaluate the evolution of the genetic machinery of apoptosis. Here, we report the whole-genome sequence for M. arenaria which we leverage with existing data to test evolutionary hypotheses on the origins of apoptosis in animals. We show that the ancestral bilaterian p53 locus, a master regulator of apoptosis, possessed a complex domain structure, in contrast to that of extant ecdysozoan p53s. Further, ecdysozoan taxa, but not chordates or lophotrochozoans like M. arenaria, show a widespread reduction in apoptosis gene copy number. Finally, phylogenetic exploration of apoptosis gene copy number reveals a striking linkage with p53 domain complexity across species. Our results challenge the current understanding of the evolution of apoptosis and highlight the ancestral complexity of the bilaterian apoptotic tool kit and its subsequent dismantlement during the ecdysozoan radiation.

Transmissible Cancers in an Evolutionary Perspective

Inter-individual transmission of cancer cells represents an intriguing and unexplored host-pathogen system, with significant ecological and evolutionary ramifications. The pathogen consists of clonal malignant cell lines that spread horizontally as allografts and/or xenografts. Although only nine transmissible cancer lineages in eight host species from both terrestrial and marine environments have been investigated, they exhibit evolutionary dynamics that may provide novel insights into tumor-host interactions particularly in the formation of metastases. Here we present an overview of known transmissible cancers, discuss the necessary and sufficient conditions for cancer transmission, and provide a comprehensive review on the evolutionary dynamics between transmissible cancers and their hosts.

Chemical modulation of apoptosis in molluscan cell cultures

This study focused on the alterations that occur in larval molluscan cells after administration of apoptotic inducers and inhibitors used in mammalian cells in response to cold stress. This is the first report on apoptosis modulation in molluscan cells assessed by flow cytometry. Mitochondrial activity, general caspase activation, and membrane integrity of control molluscan cells were compared to those processes in frozen-thawed molluscan cells, primary mouse embryonic fibroblasts, and human colon tumor cells prior to treatment and after incubation with apoptotic inducers or inhibitors. We tested three apoptotic inducers (staurosporine, camptothecin, and mitomycin C, routinely used for the chemical induction of apoptosis in different mammalian cells) and found that only staurosporine resulted in an evident apoptotic increase in molluscan cell cultures: 9.06% early apoptotic cells in comparison with 5.63% in control frozen-thawed cells and 20.6% late apoptotic cells in comparison with 10.68% in controls. Camptothecin did not significantly induce molluscan cell apoptosis but did cause a slight increase in the number of active cells after thawing. Mitomycin C produced similar results, but its effect was less pronounced. In addition, we hypothesize that the use of the apoptotic inhibitors could reduce apoptosis, which is significant after cryopreservation in molluscan cells; however, our attempts failed. Development in this direction is important for understanding the mechanisms of marine organisms' cold susceptibility.

From the raw bar to the bench: Bivalves as models for human health

Bivalves, from raw oysters to steamed clams, are popular choices among seafood lovers and once limited to the coastal areas. The rapid growth of the aquaculture industry and improvement in the preservation and transport of seafood have enabled them to be readily available anywhere in the world. Over the years, oysters, mussels, scallops, and clams have been the focus of research for improving the production, managing resources, and investigating basic biological and ecological questions. During this decade, an impressive amount of information using high-throughput genomic, transcriptomic and proteomic technologies has been produced in various classes of the Mollusca group, and it is anticipated that basic and applied research will significantly benefit from this resource. One aspect that is also taking momentum is the use of bivalves as a model system for human health. In this review, we highlight some of the aspects of the biology of bivalves that have direct implications in human health including the shell formation, stem cells and cell differentiation, the ability to fight opportunistic and specific pathogens in the absence of adaptive immunity, as source of alternative drugs, mucosal immunity and, microbiome turnover, toxicology, and cancer research. There is still a long way to go; however, the next time you order a dozen oysters at your favorite raw bar, think about a tasty model organism that will not only please your palate but also help unlock multiple aspects of molluscan biology and improve human health.

An Evolutionary Perspective of Neoplastic Diseases in the Universe

The existence of exoplanets orbiting low mass-stars is one of the most significant discoveries of our time. Especially intriguing to us is the possibility that Earth-sized exoplanets within a habitable zone might harbor life-forms that resemble our own RNA/DNA-based species. We further narrow this theoretical possibility with the following question: if alien life does indeed exist elsewhere, would extraterrestrial life be burdened with earthly diseases? Given that the chemistry of the universe is subject to specific rules, restraints, and predictable outcomes, we argue that cancer-signaling pathways might be programmed into the life cycle of habitable exoplanets. This hypothetical prediction is also based on evolutionary convergence, the repeated emergence of biological similarity that occurs when disparate life-forms adapt to comparable selection pressures. The possibility that mutations and nucleotide base rearrangements that drive cancer growth might be fixed in the chemical hardware of alien life provides us with the opportunity to wonder and consider the origins, evolution, and ubiquity of disease beyond Earth.

The p53 gene with emphasis on its paralogues in mosquitoes

The p53 gene is highly important in human cancers, as it serves as a tumor-suppressor gene. Subsequently, two p53 homologues, i.e., p73 and p63, with high identity of amino acids were identified, leading to construction of the p53 family. The p53 gene is highly important in human cancer because it usually transcribes genes that function by causing apoptosis in mammalian cells. In contrast, p63 and p73 tend to be more important in modulating development than inducing cell death, even though they share similar protein structures. Relatively recently, p53 was also identified in mosquitoes and many other insect species. Uniquely, its structure lacks the sterile alpha motif domain which is a putative protein-protein interaction domain and exclusively exists at the C-terminal region in p73 and p63 in mammals. A phylogenetic analysis revealed that the p53 gene derived from mosquitoes is composed of two paralogues, p53-1 and p53-2. Of these, only p53-2 is responsively upregulated by dengue 2 virus (DENV2) in C6/36 cells which usually survive the infection. This indicates that the p53 gene is closely related to DENV infection in mosquito cells. The specific significance of p53-2's involvement in cell survival from virus-induced stress is described and briefly discussed in this report.

Effect of exposure time, particle size and uptake pathways in immune cell lysosomal cytotoxicity of mussels exposed to silver nanoparticles

Cytotoxicity evaluation of hemocytes (lysosomal membrane stability [LMS] assay) from Mytilus galloprovincialis Lamarck, exposed to a sublethal dose (100 μg/L) of two size of silver nanoparticles (AgNPs: <50 nm and <100 nm) - prior to and after inhibition of potential uptake pathways (i.e., clathrin- and caveolae-mediated endocytosis) within different times of exposure (3, 6, 12 h) - showed that there was a significant cytotoxic effect on immune cells of mussels exposed for different times to either AgNP size (p < 0.01); the greater effect was with the smaller size. However, hemocytes seemed more sensitive to the larger AgNP after clathrin-mediated endocytosis was blocked (p < 0.01); this was not so with inhibition of caveolae-mediated endocytosis. Dimethyl-sulfoxide (DMSO) did not impart a carrier-mediated effect despite an enhanced cytotoxicity when DMSO was present with AgNP. From these results, it is concluded that the immunotoxicity of AgNP in mussels was size-dependent as well as length of exposure-dependent. It was also clear that nanoparticles (NP) internalization mechanisms were a major factor underlying any toxicity.

Evidence of horizontal transmission of the cancer-associated Steamer retrotransposon among ecological cohort bivalve species

Bivalve specimens from legacy frozen tissue collections, and others freshly obtained, were surveyed for the presence of the Steamer long terminal repeat (LTR)-retrotransposon associated with disseminated hemic neoplasia of the soft-shelled clam Mya areneria. Of 22 species investigated using primers for the pol region, only Atlantic M. arenaria, Atlantic and North Sea razor clams Ensis directus, and Baltic clams Macoma balthica from the North Sea were found to possess copies of Steamer in their genomes. Notably, close relatives like Mya truncata and Siliqua patula did not exhibit evidence of Steamer. Amplified Steamer sequences were uniformly identical in all M. areneria specimens, and were highly variable across specimens of E. directus. Variation in the latter included nucleotide polymorphisms among and within individuals as well as length variation in 2 specimens corresponding to the deletion of a predicted stable hairpin structure. Results implicate Atlantic razor clams as the proximal source for horizontal transmission of Steamer among ecologically similar yet markedly distantly related bivalves. The consequences of cross-species transmission of the Steamer retrotransposon are unknown, and the finding of Steamer in 3 bivalve species suggests that further spread is possible.

Comparative genomics explains the evolutionary success of reef-forming corals

Transcriptome and genome data from twenty stony coral species and a selection of reference bilaterians were studied to elucidate coral evolutionary history. We identified genes that encode the proteins responsible for the precipitation and aggregation of the aragonite skeleton on which the organisms live, and revealed a network of environmental sensors that coordinate responses of the host animals to temperature, light, and pH. Furthermore, we describe a variety of stress-related pathways, including apoptotic pathways that allow the host animals to detoxify reactive oxygen and nitrogen species that are generated by their intracellular photosynthetic symbionts, and determine the fate of corals under environmental stress. Some of these genes arose through horizontal gene transfer and comprise at least 0.2% of the animal gene inventory. Our analysis elucidates the evolutionary strategies that have allowed symbiotic corals to adapt and thrive for hundreds of millions of years.

DOI:http://dx.doi.org/10.7554/eLife.13288.001

For millions of years, reef-building stony corals have created extensive habitats for numerous marine plants and animals in shallow tropical seas. Stony corals consist of many small, tentacled animals called polyps. These polyps secrete a mineral called aragonite to create the reef – an external ‘skeleton’ that supports and protects the corals.

Photosynthesizing algae live inside the cells of stony corals, and each species depends on the other to survive. The algae produce the coral’s main source of food, although they also produce some waste products that can harm the coral if they build up inside cells. If the oceans become warmer and more acidic, the coral are more likely to become stressed and expel the algae from their cells in a process known as coral bleaching. This makes the coral more likely to die or become diseased. Corals have survived previous periods of ocean warming, although it is not known how they evolved to do so.

The evolutionary history of an organism can be traced by studying its genome – its complete set of DNA – and the RNA molecules encoded by these genes. Bhattacharya et al. performed this analysis for twenty stony coral species, and compared the resulting genome and RNA sequences with the genomes of other related marine organisms, such as sea anemones and sponges. In particular, Bhattacharya et al. examined “ortholog” groups of genes, which are present in different species and evolved from a common ancestral gene. This analysis identified the genes in the corals that encode the proteins responsible for constructing the aragonite skeleton. The coral genome also encodes a network of environmental sensors that coordinate how the polyps respond to temperature, light and acidity.

Bhattacharya et al. also uncovered a variety of stress-related pathways, including those that detoxify the polyps of the damaging molecules generated by algae, and the pathways that enable the polyps to adapt to environmental stress. Many of these genes were recruited from other species in a process known as horizontal gene transfer.

The oceans are expected to become warmer and more acidic in the coming centuries. Provided that humans do not physically destroy the corals’ habitats, the evidence found by Bhattacharya et al. suggests that the genome of the corals contains the diversity that will allow them to adapt to these new conditions.

DOI:http://dx.doi.org/10.7554/eLife.13288.002

The evolutionary ecology of transmissible cancers

Transmissible tumours, while rare, present a fascinating opportunity to examine the evolutionary dynamics of cancer as both an infectious agent and an exotic, invasive species. Only three naturally-occurring transmissible cancers have been observed so far in the wild: Tasmanian devil facial tumour diseases, canine transmissible venereal tumour, and clam leukaemia. Here, we define four conditions that are necessary and sufficient for direct passage of cancer cells between either vertebrate or invertebrate hosts. Successful transmission requires environment and behaviours that facilitate transfer of tumour cells between hosts including: tumour tissue properties that promote shedding of large numbers of malignant cells, tumour cell plasticity that permits their survival during transmission and growth in a new host, and a 'permissible' host or host tissue. This rare confluence of multiple host- and tumour cell-traits both explains the rarity of tumour cell transmission and provides novel insights into the dynamics that both promote and constrain their growth.

Applying genotoxicology tools to identify environmental stressors in support of river management

Although bioassay approaches are useful for identifying chemicals of potential concern, they provide little understanding of the mechanisms of chemical toxicity. Without this understanding, it is difficult to address some of the key challenges that currently face aquatic ecotoxicology. To overcome this, the toxicity potential of the water samples was assessed and surviving organisms (Physa acuta) were used for protein activity measurements and gene expression profiling by making use of complementary DNA amplified fragment length polymorphism (cDNA-AFLP) analysis. From the data it was evident that the impacts of specific pollutants (e.g. sewage) on organisms at the cellular level could be identified, and that the expressed stressor genes can be used as bioindicators/markers/genetic signatures or fingerprints during identification of point source pollution. From an ecosystem management point of view these insights could assist with the forecasting and reduction of environmental risks on catchment level by implementing suitable management interventions.

Lipid unsaturation per se does not explain the physical state of mitochondrial membranes in Mytilus galloprovincialis

Through a multiple approach, the present study on the mitochondrial membranes from mussel gills and swine heart combines some biochemical information on fatty acid composition, sterol pattern, and temperature dependence of the F1FO-ATPase activity (EC 3.6.3.14.) with fluorescence data on mitochondrial membranes and on liposomes obtained from lipid extracts of mitochondria. The physical state of mussel gills and swine heart was investigated by Laurdan steady state fluorescence. Quite surprisingly, the similar temperature dependence of the F1FO complex, illustrated as Arrhenius plot which in both mitochondria exhibits the same discontinuity at approximately 21°C and overlapping activation energies above and below the discontinuity, is apparently compatible with a different composition and physical state of mitochondrial membranes. Accordingly, mussel membranes contain highly unsaturated fatty acids, abundant sterols, including phytosterols, while mammalian membranes only contain cholesterol and in prevalence shorter and less unsaturated fatty acids, leading to a lower membrane unsaturation with respect to mussel mitochondria. As suggested by fluorescence data, the likely formation of peculiar microdomains interacting with the membrane-bound enzyme complex in mussel mitochondria could produce an environment which somehow approaches the physical state of mammalian mitochondrial membranes. Thus, as an adaptive strategy, the interaction between sterols, highly unsaturated phospholipids and proteins in mussel gill mitochondria could allow the F1FO-ATPase activity to maintain the same activation energy as the mammalian enzyme.

The effect of environmental chemicals on the tumor microenvironment

Potentially carcinogenic compounds may cause cancer through direct DNA damage or through indirect cellular or physiological effects. To study possible carcinogens, the fields of endocrinology, genetics, epigenetics, medicine, environmental health, toxicology, pharmacology and oncology must be considered. Disruptive chemicals may also contribute to multiple stages of tumor development through effects on the tumor microenvironment. In turn, the tumor microenvironment consists of a complex interaction among blood vessels that feed the tumor, the extracellular matrix that provides structural and biochemical support, signaling molecules that send messages and soluble factors such as cytokines. The tumor microenvironment also consists of many host cellular effectors including multipotent stromal cells/mesenchymal stem cells, fibroblasts, endothelial cell precursors, antigen-presenting cells, lymphocytes and innate immune cells. Carcinogens can influence the tumor microenvironment through effects on epithelial cells, the most common origin of cancer, as well as on stromal cells, extracellular matrix components and immune cells. Here, we review how environmental exposures can perturb the tumor microenvironment. We suggest a role for disrupting chemicals such as nickel chloride, Bisphenol A, butyltins, methylmercury and paraquat as well as more traditional carcinogens, such as radiation, and pharmaceuticals, such as diabetes medications, in the disruption of the tumor microenvironment. Further studies interrogating the role of chemicals and their mixtures in dose-dependent effects on the tumor microenvironment could have important general mechanistic implications for the etiology and prevention of tumorigenesis.

The complexity of apoptotic cell death in mollusks: An update

Apoptosis is a type of programmed cell death that produces changes in cell morphology and in biochemical intracellular processes without inflammatory reactions. The components of the apoptotic pathways are conserved throughout evolution. Caspases are key molecules involved in the transduction of the death signal and are responsible for many of the biochemical and morphological changes associated with apoptosis. Nowadays, It is known that caspases are activated through two major apoptotic pathways (the extrinsic or death receptor pathway and the intrinsic or mitochondrial pathway), but there are also evidences of at least other alternative pathway (the perforin/granzyme pathway). Apoptosis in mollusks seems to be similar in complexity to apoptosis in vertebrates but also has unique features maybe related to their recurrent exposure to environmental changes, pollutants, pathogens and also related to the sedentary nature of some stages in the life cycle of mollusks bivalves and gastropods. As in other animals, apoptotic process is involved in the maintenance of tissue homeostasis and also constitutes an important immune response that can be triggered by a variety of stimuli, including cytokines, hormones, toxic insults, viruses, and protozoan parasites. The main goal of this work is to present the current knowledge of the molecular mechanisms of apoptosis in mollusks and to highlight those steps that need further study.

Cancer across the tree of life: cooperation and cheating in multicellularity

Multicellularity is characterized by cooperation among cells for the development, maintenance and reproduction of the multicellular organism. Cancer can be viewed as cheating within this cooperative multicellular system. Complex multicellularity, and the cooperation underlying it, has evolved independently multiple times. We review the existing literature on cancer and cancer-like phenomena across life, not only focusing on complex multicellularity but also reviewing cancer-like phenomena across the tree of life more broadly. We find that cancer is characterized by a breakdown of the central features of cooperation that characterize multicellularity, including cheating in proliferation inhibition, cell death, division of labour, resource allocation and extracellular environment maintenance (which we term the five foundations of multicellularity). Cheating on division of labour, exhibited by a lack of differentiation and disorganized cell masses, has been observed in all forms of multicellularity. This suggests that deregulation of differentiation is a fundamental and universal aspect of carcinogenesis that may be underappreciated in cancer biology. Understanding cancer as a breakdown of multicellular cooperation provides novel insights into cancer hallmarks and suggests a set of assays and biomarkers that can be applied across species and characterize the fundamental requirements for generating a cancer.

Applications of biological tools or biomarkers in aquatic biota: A case study of the Tamar estuary, South West England

Biological systems are the ultimate recipients of pollutant-induced damage. Consequently, our traditional reliance on analytical tools is not enough to assess ecosystem health. Biological responses or biomarkers are therefore also considered to be important tools for environmental hazard and risk assessments. Due to historical mining, other anthropogenic activities, and its conservational importance (e.g. NATURA sites, SACs), the Tamar estuary in South West England is an ideal environment in which to examine applications of such biological tools. This review presents a thorough and critical evaluation of the different biological tools used in the Tamar estuary thus far, while also discussing future perspectives for biomarker studies from a global perspective. In particular, we focus on the challenges which hinder applications of biological tools from being more readily incorporated into regulatory frameworks, with the aim of enabling both policymakers and primary stakeholders to maximise the environmental relevance and regulatory usefulness of such tools.

ChBax/Bak as key regulators of the mitochondrial apoptotic pathway: cloned and characterized in Crassostrea hongkongensis

Apoptosis has been primarily investigated in mammals, and little is known about apoptosis in mollusks. The proteins Bax and Bak play critical roles in the mitochondrial apoptosis pathway and in determining cell fate. In this study, ChBax and ChBak, homologs of the well-known Bax and Bak proteins, were identified from the oyster Crassostrea hongkongensis. The ChBax/Bak proteins consist of 207/232 amino acids with the typical domains found in BCL-2 family members. ChBax and ChBak mRNA expression were detected in all 8 of the selected oyster tissues and at the different stages of development. Fluorescence microscopy revealed that the full-length proteins of ChBax/Bak were located in the cytoplasm and mitochondrial outer membrane, of HEK293T cells, respectively. Furthermore, both of the genes' expression levels were found to increase in the hemocytes of oysters challenged with pathogens. The over-expression of ChBax or ChBak activates the p53-Luc reporter gene in HEK293T cells in a dose-dependent manner. These results indicate that ChBax and ChBak may play important roles in the mitochondrial apoptotic pathway in oysters.

Activation of transcription and retrotransposition of a novel retroelement, Steamer, in neoplastic hemocytes of the mollusk Mya arenaria

Bivalve mollusks of the North Atlantic, most prominently the soft shell clam Mya arenaria, are afflicted with an epidemic transmissible disease of the circulatory system closely resembling leukemia. The disease is characterized by a dramatic expansion of blast-like cells in the hemolymph with high mitotic index. Examination of hemolymph of diseased clams revealed high levels of reverse transcriptase activity, the hallmark of retroviruses and retroelements. By deep sequencing of RNAs from hemolymph, we identified transcripts of a novel retroelement, here named Steamer. The DNA of the element is marked by long terminal repeats and encodes a single large protein with similarity to mammalian retroviral Gag-Pol proteins. Steamer mRNA levels were specifically elevated in diseased hemocytes, and high expression was correlated with disease status. DNA copy number per genome was present at enormously high levels in diseased hemocytes, indicative of extensive reverse transcription and retrotransposition. Steamer activation in M. arenaria is an example of a catastrophic induction of genetic instability that may initiate or advance the course of leukemia.

Effects of murine double minute 2 polymorphisms on the risk and survival of osteosarcoma: a systemic review and meta-analysis

Murine double minute 2 (MDM2) plays an important role in the carcinogenesis of many cancers including osteosarcoma. We performed a systemic review and meta-analysis to assess the effects of MDM2 polymorphisms on osteosarcoma risk and survival of patients with osteosarcoma. PubMed, Web of Science, and Wanfang databases were searched for eligible studies on the associations of MDM2 polymorphisms with osteosarcoma risk and survival of patients with osteosarcoma. Pooled odds ratio (OR) or hazard ratio (HR) with 95 % confidence intervals (95 % CIs) was used to assess the effects of MDM2 polymorphisms on osteosarcoma risk and survival of patients with osteosarcoma. Overall, MDM2 rs2279744 polymorphism was associated with a risk of osteosarcoma (allele model, OR = 1.60, 95 % CI 1.23-2.07, P < 0.001; codominant model, OR = 2.47, 95 % CI 1.46-4.19, P = 0.001; recessive model, OR = 2.13, 95 % CI 1.32-3.46, P = 0.002; dominant model, OR = 1.61, 95 % CI 1.12-2.33, P = 0.01). MDM2 rs1690916 polymorphism was also associated with a risk of osteosarcoma (OR = 0.60, 95 % CI 0.46-0.77, P < 0.001). However, MDM2 rs2279744 polymorphism was not associated with the overall survival of patients with osteosarcoma (codominant model, HR = 1.01, 95 % CI 0.53-1.91, P = 0.98; recessive model, HR = 1.07, 95 % CI 0.54-2.11, P = 0.85; dominant model, HR = 1.04, 95 % CI 0.65-1.66, P = 0.87). The meta-analysis suggests that MDM2 polymorphisms have some effects on the risk of osteosarcoma but have no effect on the survival of patients with osteosarcoma. Future studies are needed to further assess the effects of MDM2 polymorphisms on the risk and survival of osteosarcoma.

Transcriptome analysis of neoplastic hemocytes in soft-shell clams Mya arenaria: Focus on cell cycle molecular mechanism

In North America, a high mortality of soft-shell clams Mya arenaria was found to be related to the disease known as disseminated neoplasia (DN). Disseminated neoplasia is commonly recognized as a tetraploid disorder related to a disruption of the cell cycle. However, the molecular mechanisms by which hemocytes of clams are transformed in the course of DN remain by far unknown. This study aims at identifying the transcripts related to DN in soft shell clams' hemocytes using next generation of sequencing (Illumina HiSeq2000). This study mainly focuses on transcripts and molecular mechanisms involved in cell cycle. Using Illumina next generation of sequencing, more than 95,399,159 reads count with an average length of 45  bp was generated from three groups of hemocytes: (1) a healthy group with less than 10% of tetraploid cells; (2) an intermediate group with tetraploid hemocytes ranging between 10% and 50% and (3) a diseased group with more than 50% of tetraploid cells. After the reads were cleaned by removing the adapters, de novo assembly was performed on the sequences and more than 73,696 contigs were generated with a mean contig length estimated at 585 bp ranging from 189 bp to 14,773 bp. Once a Blastx search against NCBI Non Redundant database was performed and the duplicates removed, 18,378 annotated sequences matched known sequences, 3078 were hypothetical and 9002 were uncharacterized sequences. Fifty percent and 41% of known sequences match sequences from Mollusca and Gastropoda respectively. Among the bivalvia, 33%, 17%, 17% and 15% of the contigs match sequences from Ostreoida, Veneroida, Pectinoida and Mytiloida respectively. Gene ontology analysis showed that metabolic, cellular, transport, cell communication and cell cycle represent 33%, 15%, 9%, 8.5% and 7% respectively of the total biological process. Approximately 70% of the component process is related to intracellular process and 15% is linked to protein and ribonucleoprotein complex. Catalytic activities and binding molecular processes represent 39% and 33% of the total molecular functions. Interestingly, nucleic acid binding represents more than 18% of the total protein class. Transcripts involved in the molecular mechanisms of cell cycle are discussed providing new avenues for future investigations.

Cytomorphology and PCNA expression pattern in bivalves Mytilus galloprovincialis and Cerastoderma edule with haemic neoplasia

Haemic neoplasia (HN) is a pathologic condition reported in several bivalve species in different geographic areas. In this study we describe the cytomorphological features and the proliferative behaviour, assessed by the proliferating cell nuclear antigen (PCNA), of HN in common cockle Cerastoderma edule and Mediterranean mussel Mytilus galloprovicialis. In mussels the presence of at least 5 types of atypical haemocytes was detected, including A- and B-type cells, previously described in M. edulis and Mytilus sp., with predominance of A-type cells in early phases of the disease and B-type cells in more advanced stages. PCNA immunostaining was positive for 97 to 100% of the neoplastic cells, with both cytoplasmic (A cells) and nuclear patterns (B cells). Conversely, in C. edule there was no distinctive morphological cell sub-population, and staining atypical haemocytes with PCNA (range 93 to 100%) showed nuclear expression in early phases of disease and cytoplasmic expression in more advanced stages. The above findings suggest distinct histo-pathogenetic pathways for HN in mussels and common cockles.

Molluscan cells in culture: primary cell cultures and cell lines

In vitro cell culture systems from molluscs have significantly contributed to our basic understanding of complex physiological processes occurring within or between tissue-specific cells, yielding information unattainable using intact animal models. In vitro cultures of neuronal cells from gastropods show how simplified cell models can inform our understanding of complex networks in intact organisms. Primary cell cultures from marine and freshwater bivalve and gastropod species are used as biomonitors for environmental contaminants, as models for gene transfer technologies, and for studies of innate immunity and neoplastic disease. Despite efforts to isolate proliferative cell lines from molluscs, the snail Biomphalaria glabrata Say, 1818 embryonic (Bge) cell line is the only existing cell line originating from any molluscan species. Taking an organ systems approach, this review summarizes efforts to establish molluscan cell cultures and describes the varied applications of primary cell cultures in research. Because of the unique status of the Bge cell line, an account is presented of the establishment of this cell line, and of how these cells have contributed to our understanding of snail host-parasite interactions. Finally, we detail the difficulties commonly encountered in efforts to establish cell lines from molluscs and discuss how these difficulties might be overcome.

Genes of the mitochondrial apoptotic pathway in Mytilus galloprovincialis

Bivalves play vital roles in marine, brackish, freshwater and terrestrial habitats. In recent years, these ecosystems have become affected through anthropogenic activities. The ecological success of marine bivalves is based on the ability to modify their physiological functions in response to environmental changes. One of the most important mechanisms involved in adaptive responses to environmental and biological stresses is apoptosis, which has been scarcely studied in mollusks, although the final consequence of this process, DNA fragmentation, has been frequently used for pollution monitoring. Environmental stressors induce apoptosis in molluscan cells via an intrinsic pathway. Many of the proteins involved in vertebrate apoptosis have been recognized in model invertebrates; however, this process might not be universally conserved. Mytilus galloprovincialis is presented here as a new model to study the linkage between molecular mechanisms that mediate apoptosis and marine bivalve ecological adaptations. Therefore, it is strictly necessary to identify the key elements involved in bivalve apoptosis. In the present study, six mitochondrial apoptotic-related genes were characterized, and their gene expression profiles following UV irradiation were evaluated. This is the first step for the development of potential biomarkers to assess the biological responses of marine organisms to stress. The results confirmed that apoptosis and, more specifically, the expression of the genes involved in this process can be used to assess the biological responses of marine organisms to stress.

Expression of RAS-like family members, c-jun and c-myc mRNA levels in neoplastic hemocytes of soft-shell clams Mya arenaria using microsphere-based 8-plex branched DNA assay

The molecular mechanisms by which disseminated neoplasia (DN) is developed in soft shell clams Mya arenaria remain largely unknown. This study aims at quantifying Rho-like GTPase, RAS-Rho, RAS-related C3 botulinum (RAS C3), c-jun as well as c-myc transcript levels in clams sampled at North River (Charlottetown, Prince Edward Island, Canada). The transcripts were quantified using multiplex gene analysis (Quantigene(®) 2 Plex, Affymetrix) in 3 groups of clams: (1) Group C (healthy clams considered as control) with a low percentage of tetraploid hemocytes (<10%); (2) Group D (disease in development): individuals presenting a percentage of tetraploid cells ranging between 10% and 50%; (3) Group E (established disease): clams with a high percentage of tetraploid hemocytes (>50%). Data showed a down-regulation of Rho-like GTPase, Rho-like subfamily, RAS C3, c-jun and an up-regulation of c-myc gene expression. It is believed that a deregulation of the expression of these genes could partly unravel the molecular mechanisms involved in the development of DN in soft shell clams Mya arenaria. Further investigations should be pursued to determine the role of these gene products in clams' hemocytes.