Gonadal neoplasms in hard shell clams Mercenaria spp., from the Indian River, Florida: occurrence, prevalence, and histopathology

Epidemiological insight into disseminated neoplasia in Mytilus chilensis from southern Chile

This study investigates the prevalence and characteristics of disseminated neoplasia (DN) in Mytilus chilensis in the Los Lagos Region of southern Chile. DN is a malignant proliferative disease that has been described in several species of the genus Mytilus. More than 4.000 adult mussels, both cultured and natural, collected between 2016 and 2022 in different geographical areas (Calbuco-Hueihue, Castro, Quellón) and seasons (winter-spring, summer-autumn) were histologically analysed. The prevalence was assessed and three levels of severity of DN were defined, based on number of neoplastic cells and organs invaded. Morphology and morphometry of neoplastic cells and hemocytes were evaluated. Cell and nucleus diameters and the nucleus/cytoplasm ratio of granulocytes and hyalinocytes were analysed in healthy and neoplastic individuals. The size of neoplastic cells was significantly larger in stage 3 of neoplasia than in stage 1. The overall mean prevalence of DN in M. chilensis was 3.4%, significant differences were found between sites, being higher in Calbuco-Hueihue (5.59%) than in Castro (3.78%) and Quellón (1.40%). The prevalence was significantly higher in the winter-spring season (7.79%) than in the summer-autumn season (3.95%) in Calbuco-Hueihue. The sex, gametogenic stage, and Adipogranular (ADG) cells status were recorded for each mussel, and related to the severity stages of DN. For stages 1 and 2 of DN, females and males could be recognized, but in stage 3 almost no evidence of sex remained. The same trend was identified for the gonadal status, the advanced stages of DN were associated with castration of the mussels. The ADG cells status was highest at stage 1 of DN, declining in number and staining till stage 3. The sex ratio of healthy mussels was 53.5% female, 43.7% male, 1.6% hermaphrodite, and 1.3% indeterminate, for mussels with DN it was 34.1% female, 16% male, 2.2% hermaphrodite and 47.8% indeterminate. Occurrence of DN was higher in females, but the severity stages affected equally female and male mussels. Although the overall prevalence is low, there are some potential risks that warrant continued monitoring and further study of disseminated neoplasia in M. chilensis. This study provides important data on the epidemiology of DN in M. chilensis, which will inform future research and management strategies in aquaculture.

The Pacific oyster reproduction is affected by early-life exposure to environmental pesticide mixture: A multigenerational study

Pesticides threat marine organisms worldwide. Among them, the Pacific oyster is a bivalve mollusc model in marine ecotoxicology. A large body of literature already stated on the multiple-scale effects pesticides can trigger in the Pacific oyster, throughout its life cycle and in a delayed manner. In particular, reproductive toxicity is of major concern because of its influence on population dynamics. However, past studies mostly investigated pesticide reprotoxicity as a direct effect of exposure during gametogenesis or directly on gametes and little is known about the influence of an early embryo exposure on the breed capacity. Therefore, we studied delayed and multigenerational consequences through gametogenesis features (i.e. sex ratio, glycogen content, gene expression) and reproductive success in two consecutive oyster generations (F0 and F1) exposed to an environmentally-relevant pesticide mixture (sum nominal concentration: 2.85 μg.L-1) during embryo-larval development (0-48 h post fertilization, hpf). In the first generation, glycogen content increased in exposed individuals and the expression of some gametogenesis target genes was modified. The reproductive success measured 48 hpf was higher in exposed individuals. A multigenerational influence was observed in the second generation, with feminisation, acceleration of gametogenesis processes and the sex-specific modification of glycogen metabolism in individuals from exposed parents. This study is the first to highlight the delayed effects on reproduction induced by an early exposure to pesticides, and its multigenerational implications in the Pacific oyster. It suggests that environmental pesticide contamination can have impacts on the recruitment and the dynamics of natural oyster populations exposed during their embryo-larval phase.

Disseminated neoplasia in cultured hard clams (Mercenaria mercenaria)

Marine bivalves are commonly affected by disseminated neoplasia of presumed hemocytic origin (i.e., hemic neoplasia and hemocytic neoplasia). Histopathology of 520 cultured hard clams (Mercenaria mercenaria) from Florida was performed for health surveillance over a consecutive 13-month period. Disseminated neoplasia was identified in 9 of 520 animals (1.7%). The neoplasia was characterized by the presence of large, round to oval, anaplastic cells within hemolymphatic vessels and sinusoids with variable infiltration into adjacent connective tissues of the visceral mass, mantle, foot, and/or adductor muscles. Frequent involvement and/or infiltration of the gill was also identified (5/9). Disseminated neoplasia in other species of clams, mussels, and cockles is considered a transmissible disease. At this time, it is unknown if these hard clams represent de novo development of the disease or potential transmission; however, this report expands both the geographic and host range for this condition.

The Bcl-2 Family: Ancient Origins, Conserved Structures, and Divergent Mechanisms

Intrinsic apoptosis, the response to intracellular cell death stimuli, is regulated by the interplay of the B-cell lymphoma 2 (Bcl-2) family and their membrane interactions. Bcl-2 proteins mediate a number of processes including development, homeostasis, autophagy, and innate and adaptive immune responses and their dysregulation underpins a host of diseases including cancer. The Bcl-2 family is characterized by the presence of conserved sequence motifs called Bcl-2 homology motifs, as well as a transmembrane region, which form the interaction sites and intracellular location mechanism, respectively. Bcl-2 proteins have been recognized in the earliest metazoans including Porifera (sponges), Placozoans, and Cnidarians (e.g., Hydra). A number of viruses have gained Bcl-2 homologs and subvert innate immunity and cellular apoptosis for their replication, but they frequently have very different sequences to their host Bcl-2 analogs. Though most mechanisms of apoptosis initiation converge on activation of caspases that destroy the cell from within, the numerous gene insertions, deletions, and duplications during evolution have led to a divergence in mechanisms of intrinsic apoptosis. Currently, the action of the Bcl-2 family is best understood in vertebrates and nematodes but new insights are emerging from evolutionarily earlier organisms. This review focuses on the mechanisms underpinning the activity of Bcl-2 proteins including their structures and interactions, and how they have changed over the course of evolution.

Putative histiocytic sarcoma in redfin needlefish Strongylura notata (Beloniformes: Belonidae) in Florida, USA

Redfin needlefish Strongylura notata from Florida coastal waters were observed with unusual neoplastic lesions. Affected specimens were collected from 1 Atlantic estuary (Indian River Lagoon, prevalence = 0.32%, n = 5314) and 2 Gulf of Mexico estuaries (Tampa Bay, prevalence = 0.02%, n = 10762; Charlotte Harbor, prevalence = 0.02%, n = 5112) during routine fisheries-independent monitoring surveys conducted from 1999-2009. Grossly, each lesion manifested as a large (18-30 mm × 20-50 mm), raised (approximately 10 mm), white, creamy, or pinkish nodule on the flank, dorsal trunk, base of the pectoral fin, or head. Multiple small (<5 mm) nodules possessing poorly demarcated borders with neighboring tissues on the external jaw surface and at the base of the teeth were also observed. Histopathologically, neoplastic cells were found in the dermis, beneath the skeletal muscle, and in the soft tissue at the base of teeth of the premaxilla and the dentary jaw processes. Neoplastic cells usually had prominently invaded among the myosepta of the skeletal muscle. Neoplastic parenchymal cells had the basic characteristics of atypical, mononuclear, round, histiocytic cells with an eccentric, reniform nucleus and abundant cytoplasmic vacuolation, while some exhibited bizarre nuclear pleomorphism. Transmission electron microscopy revealed that neoplastic cells had a grooved nucleus and cytoplasmic organelles with rough endoplasmic reticulum, mitochondria, Golgi apparatus, and lysosomes. Neoplastic cells had possibly metastasized to liver, spleen, and kidney. Positive immunohistochemical staining with Ki67, p53, S-100, and CD163 support neoplastic features and a putative diagnosis of histiocytic sarcoma.

Invertebrate Oncology: Diseases, Diagnostics, and Treatment

Neoplasia is a documented occurrence across invertebrate taxa, but challenges remain with regard to tumor diagnosis and treatment. Literature reports of neoplasia are frequent in mollusks and insects, infrequent in Cnidaria and crustaceans, and are yet to be documented in Porifera and echinoderms. A significant contribution could be made by veterinary practitioners documenting and treating neoplasms in invertebrates. Traditional methods of veterinary diagnosis are encouraged, but the anatomy and tissue biology of each invertebrate species need to be considered. Most neoplasms described in the invertebrate literature have been considered benign, making external lesions potentially amenable to surgical resection.

A la Pêche aux Moules

In a recent manuscript, Goff and collaborators (Metzger et al. 2016) reported data arguing for the spread of contagious cancer cells among different species of shellfish. Although horizontal transmission of cancer cells has been observed in a few cases in higher organisms, it appears to be rather frequent among molluscs. Recent evidence supports the concept of inter-species horizontal infectious transmission of cancer cells both in molluscs but also in mammals, including humans.

Field and laboratory transmission studies of haemic neoplasia in the soft-shell clam, Mya arenaria, from Atlantic Canada

A two-year laboratory and field study was initiated in 2001 in response to mass mortalities associated with haemic neoplasia (HN) in 1999 in Prince Edward Island (PEI) soft-shell clams, Mya arenaria. A laboratory proximity experiment (cohabitation) and an inoculation challenge were conducted with clams and mussels (Mytilus edulis). Three field exposure experiments were also conducted, in which naive clams were held in sediment (in trays) or out of sediment (in mesh bags) at three high HN prevalence sites on PEI. There was a conversion to HN positive in clams in the proximity experiment and in clams injected with whole blood and cell-free homogenate, but not at statistically significant levels. No mussels or control clams became HN positive. There was a significant conversion to HN positive in as little as 24 and 58 days after transfer with clams held out of sediment and in sediment, respectively. The laboratory and field experiments' results suggest that HN-infected clams are spreading the disease through water from infected clams to naïve individuals and via transplantation from affected to unaffected sites. Some environmental conditions (e.g. abnormally high water temperature and hypoxia-induced sea lettuce [Ulva lacteus] invasion) may make clams susceptible to infections or exacerbate the proliferation of HN.

Emerging risks from ballast water treatment: the run-up to the International Ballast Water Management Convention

Uptake and discharge of ballast water by ocean-going ships contribute to the worldwide spread of aquatic invasive species, with negative impacts on the environment, economies, and public health. The International Ballast Water Management Convention aims at a global answer. The agreed standards for ballast water discharge will require ballast water treatment. Systems based on various physical and/or chemical methods were developed for on-board installation and approved by the International Maritime Organization. Most common are combinations of high-performance filters with oxidizing chemicals or UV radiation. A well-known problem of oxidative water treatment is the formation of disinfection by-products, many of which show genotoxicity, carcinogenicity, or other long-term toxicity. In natural biota, genetic damages can affect reproductive success and ultimately impact biodiversity. The future exposure towards chemicals from ballast water treatment can only be estimated, based on land-based testing of treatment systems, mathematical models, and exposure scenarios. Systematic studies on the chemistry of oxidants in seawater are lacking, as are data about the background levels of disinfection by-products in the oceans and strategies for monitoring future developments. The international approval procedure of ballast water treatment systems compares the estimated exposure levels of individual substances with their experimental toxicity. While well established in many substance regulations, this approach is also criticised for its simplification, which may disregard critical aspects such as multiple exposures and long-term sub-lethal effects. Moreover, a truly holistic sustainability assessment would need to take into account factors beyond chemical hazards, e.g. energy consumption, air pollution or waste generation.

Histological survey of symbionts and other conditions of pod razor clam Ensis siliqua (Linnaeus, 1758) in Galicia (NW Spain)

The aim of the present study was to carry out a survey of parasites and other conditions affecting pod razor clam populations, Ensis siliqua, in two beds from Galicia (NW Spain). In Galicia, the production of E. siliqua has increased in recent years due to the development of specific plans for its exploitation, however few and quite recent pathological studies have been carried out in this species. The results of this study showed the presence of different protozoa as the more prevalent group, especially Nematopsis sp. gregarines, unidentified branchial protozoa, renal coccidia and Trichodina sp. ciliates. Larval stages of trematodes and neoplastic disorders were also observed with lower prevalences. Furthermore, an ultrastructural analysis of two types of unidentified basophilic inclusions, both found in the digestive gland, revealed the presence of icosahedral viral particles and prokaryotic organisms, respectively. None of the parasites detected in E. siliqua from this study was notifiable to the World Organisation for Animal Health (OIE) and the majority of the symbionts and conditions observed in their tissues did not cause host damage. Nevertheless, parasites like bucephalid digenean sporocysts, viral inclusions, prokaryotic infections, disseminated neoplasm or germinoma detected in some samples could cause moderate or severe damage to the host depending on the intensity of infection.

Minchinia mercenariae n. sp. (Haplosporidia) in the hard clam Mercenaria mercenaria: implications of a rare parasite in a commercially important host

During routine histopathology of 180 juvenile hard clams, Mercenaria mercenaria, from a site in Virginia, USA, in 2007, we discovered a single individual heavily infected with a parasite resembling a haplosporidian, some members of which cause lethal bivalve diseases. Scanning electron microscopy of spores and sequencing of small subunit ribosomal DNA confirmed a new species: Minchinia mercenariae n. sp. Further sampling of clams at the site found prevalences up to 38% using polymerase chain reaction (PCR). No parasites were found in routine histological screening of the same individuals, but re-examination of clams judged positive by in situ hybridization (ISH) revealed very faintly staining plasmodia. No unusual mortalities have occurred among the sampled groups. Analysis of clams from Massachusetts to Florida by PCR failed to detect the parasite, but a haplosporidian found in a clam from New Jersey in 2001 was subsequently identified by ISH as M. mercenariae. No other haplosporidians have been reported in thousands of hard clams from the US east coast examined histologically since the mid-1980s. The discovery underscores critical questions about how to assess the risks associated with parasites in groups known to be lethal, but that themselves are not considered a problem.

Germinoma in razor clam Ensis arcuatus (Jeffreys, 1865) in Galicia (NW Spain)

Germinoma is a gonadal neoplasm originating from progenitor cells in germinal epithelium. Over the last four decades it has been diagnosed in several species of marine bivalve molluscs but most consistently in some populations of Mercenaria mercenaria and Mya arenaria in North America. Tissue sections of gonads from Ensis arcuatus (family Pharidae--superfamily Solenacea), collected in Ría de Vigo (Galicia-NW Spain), revealed germinoma in both males and females. Proliferating, undifferentiated, germ cells, with no evidence of maturation, had formed discrete masses in the walls and lumens of gonadal follicles. This is the first report of germinoma in superfamily Solenacea.

Genotoxicological studies in aquatic organisms: an overview

Substantial progress has been made in the lat two decades to evaluate the impact of physical and chemical genotoxins in aquatic organisms. This overview (a) summarises the major high lights in this stimulating area of research, (b) compares the developments in this field with the developments in mammalian genotoxicological studies, where appropriate, (c) introduces 18 different articles presented in this special issue of Mutation Research in the backdrop of main advances and , (d) hypothesises on future directions of research in this exciting field.

A new cytochrome P450 (CYP30) family identified in the clam, Mercenaria mercenaria

A full-length clone with sequence similarity to genes in the cytochrome P450 superfamily was isolated from a cDNA library prepared from female Mercenaria mercenaria gonadal tissue. This clone was isolated while screening an expression library with an antibody prepared against a peptide sequence within the ligand-binding region of the murine Ah receptor. Comparison of the predicted amino acid sequence of this clone to those of other cytochrome P450 genes indicated that the closest overall sequence similarity (38%) was to proteins predicted from genes in the CYP3 family. Northern blots indicated the presence of a transcript of the appropriate size (3.0 kb) with homology to the clam cytochrome P450. In vitro translation of the cDNA clone produced a 50.7-kDa protein as determined by SDS-polyacrylamide gel electrophoresis. The in vitro translated protein was not recognized on Western blots by two polyclonal antibodies specific for members of the CYP3 family. Since the degree of similarity to existing cytochrome P450 families was below the 40% level required for membership, and the expressed protein was not recognized by CYP3-specific antibodies, this clam cytochrome P450 cDNA has been placed in a new family, cytochrome P450 30 (CYP30).

The ecotoxicological significance of genotoxicity in marine invertebrates

Attention is drawn to the goals of genetic ecotoxicology, in particular, the need to relate genotoxicity in individuals to population and community level consequences. The evidence for pollutant-induced genotoxicity in marine invertebrates is reviewed. Neoplasia is apparently rare in marine invertebrates and only limited evidence is available to suggest that chemical genotoxins act as causative agents. It is unknown why marine invertebrates exhibit low tumour incidences and are much more tolerant of ionising radiation than their vertebrate counterparts. The importance of the genotoxic disease syndrome is highlighted. Disentangling phenotypic manifestations of genotoxic damage and that due to direct metabolic toxicity provides a major challenge for the future. Further work is required to assess the significance of interspecific and interindividual variability in susceptibility to genotoxicity, especially with regard to the evolution of resistant populations and communities of marine organisms at contaminated sites. Only by addressing the issues highlighted above can proper risk assessments of genotoxic agents be performed to minimise threats to human and ecosystem health.

Environmental effects and aquatic organisms: investigations of molecular mechanisms of carcinogenesis

Cancers of the reproductive system are among the leading causes of mortality in women in the United States. While both genetic and environmental factors have been implicated in their etiology, the extent of the contribution of environmental factors to human diseases remains controversial. To better address the role of environmental exposures in cancer etiology, there has been an increasing focus on the development of nontraditional, environmentally relevant models. Our research involves the development of one such model. Gonadal tumors have been described in the softshell clam (Mya arenaria) in Maine and the hardshell clam (Mercenaria spp.) from Florida. Prevalence of these tumors is as high as 40% in some populations in eastern Maine and 60% in some areas along the Indian River in Florida. The average tumor prevalence in Maine and Florida is approximately 20 and 11%, respectively. An association has been suggested between the use of herbicides and the incidence of gonadal tumors in the softshell clam in Maine. The role of environmental exposures in the development of the tumors in Mercenaria in Florida is unknown; however, there is evidence that genetic factors may contribute to its etiology. Epidemiologic studies of human populations in these same areas show a higher than average mortality rate due to cancers of the reproductive system in women, including both ovarian and breast cancer. The relationship, if any, among these observations is unknown. Our studies on the molecular basis of this disease in clams may provide additional information on environmental exposures and their possible link to cancer in clams and other organisms, including humans.