A prokineticin-like protein responds to immune challenges in the gastropod pest Pomacea canaliculata

Clodronate Liposome-Mediated Phagocytic Hemocyte Depletion Affects the Regeneration of the Cephalic Tentacle of the Invasive Snail, Pomacea canaliculata

After amputation, granular hemocytes infiltrate the blastema of regenerating cephalic tentacles of the freshwater snail Pomacea canaliculata. Here, the circulating phagocytic hemocytes were chemically depleted by injecting the snails with clodronate liposomes, and the effects on the cephalic tentacle regeneration onset and on Pc-Hemocyanin, Pc-transglutaminase (Pc-TG) and Pc-Allograft Inflammatory Factor-1 (Pc-AIF-1) gene expressions were investigated. Flow cytometry analysis demonstrated that clodronate liposomes targeted large circulating hemocytes, resulting in a transient decrease in their number. Corresponding with the phagocyte depletion, tentacle regeneration onset was halted, and it resumed at the expected pace when clodronate liposome effects were no longer visible. In addition to the regeneration progress, the expressions of Pc-Hemocyanin, Pc-TG, and Pc-AIF-1, which are markers of hemocyte-mediated functions like oxygen transport and immunity, clotting, and inflammation, were modified. After the injection of clodronate liposomes, a specific computer-assisted image analysis protocol still evidenced the presence of granular hemocytes in the tentacle blastema. This is consistent with reports indicating the large and agranular hemocyte population as the most represented among the professional phagocytes of P. canaliculata and with the hypothesis that different hemocyte morphologies could exert diverse biological functions, as it has been observed in other invertebrates.

The Eco-Immunological Relevance of the Anti-Oxidant Response in Invasive Molluscs

Reactive oxygen species (ROS) are volatile and short-lived molecules playing important roles in several physiological functions, including immunity and physiological adaptation to unsuitable environmental conditions. In an eco-immunological view, the energetic costs associated with an advantageous metabolic apparatus able to cope with wide changes in environmental parameters, e.g., temperature range, water salinity or drought, could be further balanced by the advantages that this apparatus may also represent in other situations, e.g., during the immune response. This review provides an overview of molluscs included in the IUCN list of the worst invasive species, highlighting how their relevant capacity to manage ROS production during physiologically challenging situations can also be advantageously employed during the immune response. Current evidence suggests that a relevant capacity to buffer ROS action and their damaging consequences is advantageous in the face of both environmental and immunological challenges, and this may represent a trait for potential invasiveness. This should be considered in order to obtain or update information when investigating the potential of the invasiveness of emerging alien species, and also in view of ongoing climate changes.

Study on the Synergistic Molluscicidal Effect of Pedunsaponin A and Niclosamide

Niclosamide (NI) is the main molluscicide used to control Pomacea canaliculata (Lamarck) (Architaenioglossa: Ampullariidae). However, NI failed to inhibit snail climbing during the treatment process. In this study, we examined the effect of NI combined with pedunsaponin A at an ineffective concentration. The molluscicidal effect of Pedunsaponin A on NI was evidently synergistic after 48 h, and the synergism ratio (SR) was 1.82 after treatment for 72 h at 0.8 mg·L^-1. Examination of the climbing adhesion effect showed that a high concentration of Pedunsaponin A (0.4 mg·L^-1 and 0.8 mg·L^-1) combined with NI significantly inhibited the climbing of P. canaliculata. We further studied the synergism mechanism; the results of histopathological observation showed that the siphon appeared cavities, the muscle fibers of the ventricular were severely dissolved, and kidney tubule arrangement was distorted after NI adding Pedunsaponin A. In addition, the hemocyte survival rate and the content of hemocyanin decreased significantly. According to the results of our study, the synergism mechanism may hinder oxygen transport of P. canaliculata, influencing the supply of energy; the ability of immune defense and excretion and metabolic detoxification decreased, prolonging the action time of NI in the body.

A Dissenters’ View on AppleSnail Immunobiology

We stand as dissenters against the acceptance of scientific knowledge that has not been built on empirical data. With this in mind, this review synthesizes selected aspects of the immunobiology of gastropods and of apple snails (Ampullariidae) in particular, from morphological to molecular and “omics” studies. Our trip went through more than two centuries of history and was guided by an evo-devo hypothesis: that the gastropod immune system originally developed in the mesenchymal connective tissue of the reno-pericardial complex, and that in that tissue some cells differentiated into hematopoietically committed progenitor cells that integrate constitutive hemocyte aggregations in the reno-pericardial territory, whether concentrated in the pericardium or the kidney in a species-specific manner. However, some of them may be freed from those aggregations, circulate in the blood, and form distant contingent aggregations anywhere in the body, but always in response to intruders (i.e., pathogens or any other immune challenge). After that, we reviewed the incipient immunology of the Ampullariidae by critically revising the findings in Pomacea canaliculata and Marisa cornuarietis, the only ampullariid species that have been studied in this respect, and we attempted to identify the effectors and the processes in which they are involved. Particularly for P. canaliculata, which is by far the most studied species, we ask which hemocytes are involved, in which tissues or organs are integrated, and what cellular reactions to intruders this species has in common with other animals. Furthermore, we wondered what humoral factors could also integrate its internal defense system. Among the cellular defenses, we give an outstanding position to the generation of hemocyte nodules, which seems to be an important process for these snails, serving the isolation and elimination of intruders. Finally, we discuss hematopoiesis in apple snails. There have been contrasting views about some of these aspects, but we envision a hematopoietic system centered in the constitutive hemocyte islets in the ampullariid kidney.

CgATP synthase β subunit involved in the regulation of haemocytes proliferation as a CgAstakine receptor in Crassostrea gigas

Astakine is considered as an endogenous cytokine-like factor of prokineticin homologue in invertebrate. Recently, an astakine homologue (CgAstakine) has been identified and characterized in oyster Crassostrea gigas. In the present study, a CgATP synthase β subunit was identified as the receptor of CgAstakine in C. gigas. There was an ATP-synt_ab_N domain and an AAA domain in the CgATP synthase β subunit protein. The mRNA transcripts of CgATP synthase β subunit were detected in all tested tissues, with the highest expression level in hepatopancreas and gills, which was 109.11-fold (p < 0.01) and 97.21-fold (p < 0.01) of that in labial palps, respectively. After rCgAstakine stimulation, the mRNA transcripts of CgATP synthase β subunit in agranulocytes and semi-granulocytes were significantly increased at 24 h (2.44-fold, and 9.01-fold of that in control group, p < 0.01), and those in granulocytes were significantly increased at 6 h (1.83-fold, p < 0.01), 12 h (1.92-fold, p < 0.01) and 24 h (3.47-fold, p < 0.01). The expression level of CgATP synthase β subunit protein in agranulocytes and granulocytes was also significantly increased after rCgAstakine stimulation, which was 1.64-fold (p < 0.05) and 1.85-fold (p < 0.05) of that in control group, respectively, while there were no significant changes in semi-granulocytes. The immunofluorescence assay showed that CgATP synthase β subunit positive signals were mainly located on the membrane of haemocytes. The number of haemocytes with EdU positive signals was significantly increased after rCgAstakine stimulation (2.04-fold of seawater group, p < 0.01), while significantly decreased after the RNA interference (RNAi) of CgATP synthase β subunit, which was 0.28-fold of that in NC group (p < 0.01). Bio-layer interferometry (BLI) assay confirmed in vitro interaction between rCgAstakine and rCgATP synthase β subunit. There results suggested that CgATP synthase β subunit acts as the receptor of CgAstakine and plays important roles in CgAstakine induced renewal of haemocytes in C. gigas.

Pomacea canaliculata Ampullar Proteome: A Nematode-Based Bio-Pesticide Induces Changes in Metabolic and Stress-Related Pathways

Pomacea canaliculata is a freshwater gastropod known for being both a highly invasive species and one of the possible intermediate hosts of the mammalian parasite Angiostrongylus cantonensis. With the aim of providing new information concerning P. canaliculata biology and adaptability, the first proteome of the ampulla, i.e., a small organ associated with the circulatory system and known as a reservoir of nitrogen-containing compounds, was obtained. The ampullar proteome was derived from ampullae of control snails or after exposure to a nematode-based molluscicide, known for killing snails in a dose- and temperature-dependent fashion. Proteome analysis revealed that the composition of connective ampulla walls, cell metabolism and oxidative stress response were affected by the bio-pesticide. Ultrastructural investigations have highlighted the presence of rhogocytes within the ampullar walls, as it has been reported for other organs containing nitrogen storage tissue. Collected data suggested that the ampulla may belong to a network of organs involved in controlling and facing oxidative stress in different situations. The response against the nematode-based molluscicide recalled the response set up during early arousal after aestivation and hibernation, thus encouraging the hypothesis that metabolic pathways and antioxidant defences promoting amphibiousness could also prove useful in facing other challenges stimulating an oxidative stress response, e.g., immune challenges or biocide exposure. Targeting the oxidative stress resistance of P. canaliculata may prove helpful for increasing its susceptibility to bio-pesticides and may help the sustainable control of this pest's diffusion.

A New Protocol of Computer-Assisted Image Analysis Highlights the Presence of Hemocytes in the Regenerating Cephalic Tentacles of Adult Pomacea canaliculata

In humans, injuries and diseases can result in irreversible tissue or organ loss. This well-known fact has prompted several basic studies on organisms capable of adult regeneration, such as amphibians, bony fish, and invertebrates. These studies have provided important biological information and helped to develop regenerative medicine therapies, but important gaps concerning the regulation of tissue and organ regeneration remain to be elucidated. To this aim, new models for studying regenerative biology could prove helpful. Here, the description of the cephalic tentacle regeneration in the adult of the freshwater snail Pomacea canaliculata is presented. In this invasive mollusk, the whole tentacle is reconstructed within 3 months. Regenerating epithelial, connective, muscular and neural components are already recognizable 72 h post-amputation (hpa). Only in the early phases of regeneration, several hemocytes are retrieved in the forming blastema. In view of quantifying the hemocytes retrieved in regenerating organs, granular hemocytes present in the tentacle blastema at 12 hpa were counted, with a new and specific computer-assisted image analysis protocol. Since it can be applied in absence of specific cell markers and after a common hematoxylin-eosin staining, this protocol could prove helpful to evidence and count the hemocytes interspersed among regenerating tissues, helping to unveil the role of immune-related cells in sensory organ regeneration.

Both quiescent and proliferating cells circulate in the blood of the invasive apple snail Pomacea canaliculata

Gastropod hematopoiesis occurs at specialized tissues in some species, but the evidence also suggests that hemocyte generation is maybe widespread in the connective tissues or the blood system in others. In Ampullariidae (Caenogastropoda), both the kidney and the lung contain putative hematopoietic cells, which react to immune challenges. In the current study, we wanted to explore if hematopoiesis occurs in the blood of Pomacea canaliculata. Thus, we obtained circulating hemocytes from donor animals and tested their ability to proliferate in the blood of conspecific recipients. We tracked cell proliferation by labeling the donors' hemocytes with the fluorescent cell proliferation marker carboxyfluorescein diacetate succinimidyl ester (CFSE). Transferred CFSE-labeled hemocytes survived and proliferated into the recipients' circulation for at least 17 days. We also determined the cell cycle status of circulating hemocytes by using the propidium iodide (PI) and acridine orange (AO) staining methods. Flow cytometry analyses showed that most PI-stained hemocytes were in the G1 phase (~96%), while a lower proportion of cells were through the G2/S-M transition (~4%). When we instead used AO-staining, we further distinguished a subpopulation of cells (~5%) of low size, complexity-granularity, and RNA content. We regarded this subpopulation as quiescent cells. In separate experimental sets, we complemented these findings by assessing in circulating hemocytes two evolutionary conserved features of quiescent, undifferentiated cells. First, we used JC-1 staining to determine the mitochondrial membrane potential (Ψ_m) of circulating hemocytes, which is expected to be low in quiescent cells. Most hemocytes (~87%) showed high aggregation of JC-1, which indicates a high Ψ_m. Besides that, a small hemocyte subpopulation (~11%) showed low aggregation of the dye, thus indicating a low Ψ_m. It is known that the transition from a quiescent to a proliferating state associates with an increase of the Ψ_m. The specificity of these changes was here controlled by membrane depolarization with the Ψ_m disruptor CCCP. Second, we stained hemocytes with Hoechst33342 dye to determine the efflux activity of ABC transporters, which participate in the multixenobiotic resistance system characteristic of undifferentiated cells. Most hemocytes (>99%) showed a low dye-efflux activity, but a small proportion of cells (0.06-0.12%) showed a high dye-efflux activity, which was significantly inhibited by 100 and 500 μM verapamil, and thus is indicative of an undifferentiated subpopulation of circulating hemocytes. Taken together, our results suggest that, among circulating hemocytes, there are cells with the ability to proliferate or to stay in a quiescent state and behave as progenitor cells later, either in the circulation or the hematopoietic tissues/organs.

The Immune Response of the Invasive Golden Apple Snail to a Nematode-Based Molluscicide Involves Different Organs

Simple Summary

Sustainable solutions to the spreading of invasive species are difficult to find due to the absence of biological information about basic immune mechanisms of the target pests. Here, we present evidence of the effects of a commercially available roundworm, Phasmarhabditis hermaphrodita, against the invasive apple snail Pomacea canaliculata. The effects are principally evaluated in terms of snail survival and immune activation. Via molecular and microscopy-based approaches, we demonstrate that dosage and temperature are critical in determining the effects of the roundworm, and that the apple snail response to this immune challenge involves different organs. To our knowledge, these findings are the first demonstration that a P. hermaphrodita-based molluscicide can effectively kill P. canaliculata and that the snail can mount a multi-organ response against this pathogenic roundworm.

Abstract

The spreading of alien and invasive species poses new challenges for the ecosystem services, the sustainable production of food, and human well-being. Unveiling and targeting the immune system of invasive species can prove helpful for basic and applied research. Here, we present evidence that a nematode (Phasmarhabditis hermaphrodita)-based molluscicide exerts dose-dependent lethal effects on the golden apple snail, Pomacea canaliculata. When used at 1.7 g/L, this biopesticide kills about 30% of snails within one week and promotes a change in the expression of Pc-bpi, an orthologue of mammalian bactericidal/permeability increasing protein (BPI). Changes in Pc-bpi expression, as monitored by quantitative PCR (qPCR), occurred in two immune-related organs, namely the anterior kidney and the gills, after exposure at 18 and 25 °C, respectively. Histological analyses revealed the presence of the nematode in the snail anterior kidney and the gills at both 18 and 25 °C. The mantle and the central nervous system had a stable Pc-bpi expression and seemed not affected by the nematodes. Fluorescence in situ hybridization (FISH) experiments demonstrated the expression of Pc-bpi in circulating hemocytes, nurturing the possibility that increased Pc-bpi expression in the anterior kidney and gills may be due to the hemocytes patrolling the organs. While suggesting that P. hermaphrodita-based biopesticides enable the sustainable control of P. canaliculata spread, our experiments also unveiled an organ-specific and temperature-dependent response in the snails exposed to the nematodes. Overall, our data indicate that, after exposure to a pathogen, the snail P. canaliculata can mount a complex, multi-organ innate immune response.

The Damaging Effects of Pedunsaponin A on Pomacea canaliculata Hemocytes

Pomacea canaliculata hemocytes are the main functional cells in the immune defense system, and hemocyte destruction disrupts the immune response mechanism of P. canaliculata, resulting in abnormal growth, development, reproduction, and even death. Our previous study found that Pedunsaponin A significantly affects P. canaliculata hemocyte structure. This study further investigated the damaging effects of Pedunsaponin A on P. canaliculata hemocytes. The cell mortality rate results showed that the hemocyte mortality was significantly increased after treatment with Pedunsaponin A, and the mortality rate exhibited a significant positive correlation with treatment time and dose. The membrane potential results showed that the cell membranes of P. canaliculata hemocytes exhibited time-dependent membrane depolarization after 40 mg/L Pedunsaponin A treatment. At 36 h, the cell depolarization rate in the Pedunsaponin A treatment group was 41.43%, which was significantly greater than the control group (6.24%). The cytoskeleton results showed that Pedunsaponin A led to disordered and dispersed arrangement of microfilaments and changes in the cytoskeletal structure. The apoptosis and cell cycle results showed that Pedunsaponin A induced apoptosis and influenced the cell cycle to some extent. These results showed that the cell membrane and cytoskeleton of P. canaliculata hemocytes were damaged after treatment with Pedunsaponin A, which led to an increase in cell mortality, dysfunction, cell cycle abnormalities and apoptosis. This study provides a foundation for further identification of the site of Pedunsaponin A activity on hemocytes.

Assessment of the kidney and lung as immune barriers and hematopoietic sites in the invasive apple snail Pomacea canaliculata

Knowledge on the immune system of Pomacea canaliculata is becoming increasingly important, because of this gastropod's role as intermediate host and vector of Angiostrongylus cantonensis, the etiologic agent of eosinophilic meningitis in humans and domestic animals. Immune defenses of this gastropod comprise both humoral and cellular components, but they may also involve organs that act as immune barriers to prevent the spread of alien molecules and organisms. Both the kidney and lung are here shown to serve this function, because of (1) their positions in blood circulation, (2) the intricate architecture of their blood spaces, and (3) the proliferative and nodulation reactions of hemocytes to an immune challenge. However, these organs differ in that only the kidney shows permanent hemocyte aggregations. Microcirculation in the kidney was found to flow through an intricate vascular bed containing the permanent aggregations, which occurred either as hemocyte islets anchored by cytoplasmic projections of the renal epithelium or as perivascular accretions. Within 96 h of the injection of yeast cells, hemocyte nodules were formed both in the kidney and lung. Moreover, cell proliferation in renal hemocyte islets was measured by bromodeoxyuridine (BrdU) incorporation. The proportion of BrdU positive nuclei increased 48 h after injection. Signs of nodule regression (apoptotic bodies, lipofuscin-like deposits) and a decrease in the proportion of BrdU positive nuclei were found at 96 h. In addition, the area of renal hemocyte islets was significantly increased 96 h after injection. Nevertheless, the high complexity of the small vascular chambers that constitute the lung's respiratory lamina would also facilitate hemocyte-antigen contacts, required to elicit cellular aggregation, and hence, nodulation. To our knowledge, this paper includes the first quantitative indication of hemocyte proliferation after an immune challenge among Caenogastropoda.

An adaptable chromosome preparation methodology for use in invertebrate research organisms

Background

The ability to efficiently visualize and manipulate chromosomes is fundamental to understanding the genome architecture of organisms. Conventional chromosome preparation protocols developed for mammalian cells and those relying on species-specific conditions are not suitable for many invertebrates. Hence, a simple and inexpensive chromosome preparation protocol, adaptable to multiple invertebrate species, is needed.

Results

We optimized a chromosome preparation protocol and applied it to several planarian species (phylum Platyhelminthes), the freshwater apple snail Pomacea canaliculata (phylum Mollusca), and the starlet sea anemone Nematostella vectensis (phylum Cnidaria). We demonstrated that both mitotically active adult tissues and embryos can be used as sources of metaphase chromosomes, expanding the potential use of this technique to invertebrates lacking cell lines and/or with limited access to the complete life cycle. Simple hypotonic treatment with deionized water was sufficient for karyotyping; growing cells in culture was not necessary. The obtained karyotypes allowed the identification of differences in ploidy and chromosome architecture among otherwise morphologically indistinguishable organisms, as in the case of a mixed population of planarians collected in the wild. Furthermore, we showed that in all tested organisms representing three different phyla this protocol could be effectively coupled with downstream applications, such as chromosome fluorescent in situ hybridization.

Conclusions

Our simple and inexpensive chromosome preparation protocol can be readily adapted to new invertebrate research organisms to accelerate the discovery of novel genomic patterns across the branches of the tree of life.