Intestinal microbiome in crayfish: Its role upon growth and disease presentation

The intestine-associated microbiota in crustaceans are considered a key element for maintaining homeostasis and health within the organisms. Recently, efforts have been made to characterize bacterial communities of freshwater crustaceans, including crayfish, and their interplay with the host's physiology and the aquatic environments. As a result, it has become evident that crayfish intestinal microbial communities display high plasticity, which is strongly influenced by both the diet, especially in aquaculture, and the environment. Moreover, studies regarding the characterization and distribution of the microbiota along the gut portions led to the discovery of bacteria with probiotic potential. The addition of these microorganisms to their food has shown a limited positive correlation with the growth and development of crayfish freshwater species. Finally, there is evidence that infections, particularly those from viral etiology, lead to low diversity and abundance of the intestinal microbial communities. In the present article, we have reviewed data on the crayfish' intestinal microbiota, highlighting the most frequently observed taxa and emphasizing the dominance of phylum within this community. In addition, we have also searched for evidence of microbiome manipulation and its potential impact on productive parameters, and discussed the role of the microbiome in the regulation of diseases presentation, and environmental perturbations.

Blood cell formation in crustaceans

In crustacean animals the hemocytes are key players in immunity and of crucial importance for the health of the animals. Hemocytes are mainly produced in the hematopoietic tissue and from there released into the circulation where they finally mature. In this review we summarize the latest findings about crustacean hemocyte formation. The role of the extracellular matrix and crosslinking enzyme transglutaminase is discussed. Moreover, important growth factors, transcriptional regulation and recent findings about inducers of hematopoiesis are covered. Finally, we discuss the use of different markers for classification of crustacean hemocytes.

Characterization of hemocytes and hematopoietic cells of a freshwater crayfish based on single-cell transcriptome analysis

Crustaceans constitute a species-rich and ecologically important animal group, and their circulating blood cells (hemocytes) are of critical importance in immunity as key players in pathogen recognition, phagocytosis, melanization, and antimicrobial defense. To gain a better understanding of the immune responses to different pathogens, it is crucial that we identify different hemocyte subpopulations with different functions and gain a better understanding of how these cells are formed. Here, we performed single-cell RNA sequencing of isolated hematopoietic tissue (HPT) cells and hemocytes from the crayfish Pacifastacus leniusculus to identify hitherto undescribed hemocyte types in the circulation and show that the circulating cells are more diversified than previously recognized. In addition, we discovered cell populations in the HPT with clear precursor characteristics as well as cells involved in iron homeostasis, representing a previously undiscovered cell type. These findings may improve our understanding of hematopoietic stem cell regulation in crustaceans and other animals.

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Single-cell RNA sequencing of hematopoietic cell types reveals new cell types

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One cell type contains iron homeostasis-associated transcripts

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Hemocytes and hematopoietic cells differ in their transcript profiles

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Prophenoloxidase is only expressed in hemocytes

Gut microbiome alterations in the crustacean Pacifastacus leniusculus exposed to environmental concentrations of antibiotics and effects on susceptibility to bacteria challenges

Gut-associated microbiota in crustaceans are recognized as a key element for maintaining homeostasis and health in the animal. Since the richness of these microbial communities is strongly influenced by the local environment, especially in aquatic organisms, it is important to address to what extent environmental variations can affect these communities. In the present study, we used high-throughput 16S rRNA sequencing technology to study the composition of gut-associated microbiota of the crayfish Pacifastacus leniusculus after exposure to environmentally-relevant concentrations of an antibiotic, namely sulfamethoxazole. Also, we examined if alterations of microbiota caused by environmentally-relevant concentrations of this antibiotic affected the host susceptibility to bacterial diseases, including Vibrio species. As a result, we found high individual variability of bacterial abundance and composition in the intestinal microbiome of crayfish, in both antibiotic-exposed and antibiotic-free crayfish. However, an increase of chitinolytic bacteria including Vibrio spp. was detected in some animals exposed to the antibiotic. Moreover, when crayfish susceptibility to bacterial infections was tested, the antibiotic-exposed crayfish survived longer than the control crayfish group. This study represents the first approach for investigating the interplay between crayfish and intestinal bacteria during antibiotic-pollution scenarios. Results herein should be considered by scientists before planning experiments under laboratory conditions, especially to study environmental effects on aquatic animals' intestinal health and immune status.

Early Changes in Crayfish Hemocyte Proteins after Injection with a β-1,3-glucan, Compared to Saline Injected and Naive Animals

Early changes in hemocyte proteins in freshwater crayfish Pacifastacus leniusculus, in response to an injection with the fungal pattern recognition protein β-1,3-glucan (laminarin) were investigated, as well as changes after saline (vehicle) injection and in naïve animals. Injection of saline resulted in rapid recruitment of granular hemocytes from surrounding tissues, whereas laminarin injection on the other hand induced an initial dramatic drop of hemocytes. At six hours after injection, the hemocyte populations therefore were of different composition. The results show that mature granular hemocytes increase in number after saline injection as indicated by the high abundance of proteins present in granular cell vesicles, such as a vitelline membrane outer layer protein 1 homolog, mannose-binding lectin, masquerade, crustin 1 and serine protease homolog 1. After injection with the β-1,3-glucan, only three proteins were enhanced in expression, in comparison with saline-injected animals and uninjected controls. All of them may be associated with immune responses, such as a new and previously undescribed Kazal proteinase inhibitor. One interesting observation was that the clotting protein was increased dramatically in most of the animals injected with laminarin. The number of significantly affected proteins was very few after a laminarin injection when compared to uninjected and saline-injected crayfish. This finding may demonstrate some problematic issues with gene and protein expression studies from other crustaceans receiving injections with pathogens or pattern recognition proteins. If no uninjected controls are included and no information about hemocyte count (total or differential) is given, expressions data for proteins or mRNAs are very difficult to properly interpret.

Sexual conflict drives micro- and macroevolution of sexual dimorphism in immunity

BACKGROUND

Sexual dimorphism in immunity is believed to reflect sex differences in reproductive strategies and trade-offs between competing life history demands. Sexual selection can have major effects on mating rates and sex-specific costs of mating and may thereby influence sex differences in immunity as well as associated host-pathogen dynamics. Yet, experimental evidence linking the mating system to evolved sexual dimorphism in immunity are scarce and the direct effects of mating rate on immunity are not well established. Here, we use transcriptomic analyses, experimental evolution and phylogenetic comparative methods to study the association between the mating system and sexual dimorphism in immunity in seed beetles, where mating causes internal injuries in females.

RESULTS

We demonstrate that female phenoloxidase (PO) activity, involved in wound healing and defence against parasitic infections, is elevated relative to males. This difference is accompanied by concomitant sex differences in the expression of genes in the prophenoloxidase activating cascade. We document substantial phenotypic plasticity in female PO activity in response to mating and show that experimental evolution under enforced monogamy (resulting in low remating rates and reduced sexual conflict relative to natural polygamy) rapidly decreases female (but not male) PO activity. Moreover, monogamous females had evolved increased tolerance to bacterial infection unrelated to mating, implying that female responses to costly mating may trade off with other aspects of immune defence, an hypothesis which broadly accords with the documented sex differences in gene expression. Finally, female (but not male) PO activity shows correlated evolution with the perceived harmfulness of male genitalia across 12 species of seed beetles, suggesting that sexual conflict has a significant influence on sexual dimorphisms in immunity in this group of insects.

CONCLUSIONS

Our study provides insights into the links between sexual conflict and sexual dimorphism in immunity and suggests that selection pressures moulded by mating interactions can lead to a sex-specific mosaic of immune responses with important implications for host-pathogen dynamics in sexually reproducing organisms.

Vibrio areninigrae as a pathogenic bacterium in a crustacean

The occurrence of infectious diseases poses a significant threat to the aquaculture industry worldwide. Therefore, characterization of potentially harmful pathogens is one of the most important strategies to control disease outbreaks. In the present study, we investigated for the first time the pathogenicity of two Vibrio species, Vibrio metschnikovii, a foodborne pathogen that causes fatalities in humans, and Vibrio areninigrae, a bacteria isolated from black sand in Korea, using a crustacean model, the signal crayfish Pacifastacus leniusculus. Mortality challenges indicated that injection of V. metschnikovii (10⁸ CFU/crayfish) has a mortality percentage of 22% in crayfish. In contrast, injection of P. leniusculus with 10⁸ or 10⁷ CFU of V. areninigrae resulted in 100% mortality within one and two days post-injection, respectively. V. areninigrae was successfully re-isolated from hepatopancreas of infected crayfish and caused 100% mortality when reinjected into new healthy crayfish. As a consequence of this infection, histopathological analysis revealed nodule formation in crayfish hepatopancreas, heart, and gills, as well as sloughed cells inside hepatopancreatic tubules and atrophy. Moreover, extracellular crude products (ECP's) were obtained from V. areninigrae in order to investigate putative virulence factors. In vivo challenges with ECP's caused >90% mortalities within the first 24 h. In vitro challenges with ECP's of hemocytes induced cytotoxicity of hemocytes within the first hour of exposure. These findings represent the first report that V. areninigrae is a highly pathogenic bacterium that can cause disease in crustaceans. On the contrary, V. metschnikovii could not represent a threat for freshwater crayfish.

A transcription factor glial cell missing (Gcm) in the freshwater crayfish Pacifastacus leniusculus

The transcription factor glial cell missing, Gcm, is known to be an important protein in the determination of glial cell fate as well as embryonic plasmatocyte differentiation in Drosophila melanogaster. So far, no function for Gcm in crustaceans has been reported. In this study, we show the cDNA sequence of a Gcm homologue in the freshwater crayfish Pacifastacus leniusculus. The P. leniusculus Gcm transcript is expressed exclusively in brain and nervous tissue, and by in situ hybridization we show that the expression is restricted to a small number of large cells with morphology similar to neurosecretory cells. Furthermore, we show that the expression of Gcm coincides with the expression of a Repo homologue, that is induced in expression by Gcm in Drosophila. Moreover, the Gcm transcript is increased shortly and transiently after injection of cystamine, a substance that inhibits transglutaminase and also strongly affects the movement behavior of crayfish. This finding of Gcm transcripts in a subpopulation of brain cells in very low numbers may enable more detailed studies about Gcm in adult crustaceans.

Transglutaminase 1 and 2 are localized in different blood cells in the freshwater crayfish Pacifastacus leniusculus

In the present study we show that hemocytes in the freshwater crayfish Pacifastacus leniusculus express two different transglutaminases. We describe the sequence of a previously unknown TGase (Pl_TGase1) and named this as Pl_TGase2 and compared this sequence with similar sequences from other crustaceans. The catalytic core domain is similar to the previously described TGase in P. leniusculus, but Pl_TGase2 has significant differences in the N-terminal and C-terminal domains. Further, we show conclusive evidences that these different transglutaminases are specific for different hemocyte types so that Pl_TGase1 is expressed in the hematopoietic tissue and in the cytoplasm of semigranular hemocytes, while Pl_TGase2 is expressed in vesicles in the granular hemocytes. By in situ hybridization we show that both Pl_TGase1 and Pl_TGase2 mRNA are present only in a subset of the respective hemocyte population. This observation indicates that there may be different subtypes of semigranular as well as granular hemocytes which may have different specific functions.

The N-terminal peptide generated after activation of prophenoloxidase affects crayfish hematopoiesis

The circulating hemocytes of invertebrates are important mediators of immunity, and hemocyte homeostasis is of high importance for survival and health of crustaceans. The prophenoloxidase (proPO)-activating system is one of the most essential immune reactions, which can be activated by pattern recognition proteins from microorganisms. Activation of proPO by the proPO activating enzyme generates an N-terminal peptide, with cleavage site after Arg176, as well as the active enzyme phenoloxidase, which is the key enzyme for melanization. In the present study we demonstrate a role for the N-terminal proPO-peptide in hematopoiesis. Injection of this proPO-peptide increased the number of circulating hemocytes and especially granular hemocytes. We also show that the reactive oxygen species (ROS) production in the anterior proliferative center was enhanced after proPO peptide injection, which is a prerequisite for rapid hemocyte release from the hematopoietic tissue. Moreover, this peptide had an effect on ROS production in in vitro cultured hematopoietic cells and induced spreading of these cells within 72 h. Taken together, our findings show a role of the N-terminal proPO peptide in stimulation of hematopoiesis in crayfish, Pacifastacus leniusculus.

Environmental concentrations of sulfamethoxazole increase crayfish Pacifastacus leniusculus susceptibility to White Spot Syndrome Virus

Antibiotics used for humans and livestock are emerging as pollutants in aquatic environments. However, little is known about their effect on aquatic organisms, especially in crustaceans. In the present study, the freshwater crayfish Pacifastacus leniusculus was exposed during 21 days to environmental concentrations of sulfamethoxazole (SMX) (100 ng/L and 1 μg/L). Subsequently, the crayfish susceptibility to infection was evaluated by using White Spot Syndrome Virus (WSSV) challenge, a well-known crustacean pathogen. The median survival time of the infected crayfish exposed to 100 ng/L SMX was one day, whereas the control and the group exposed to 1 μg/L SMX survived for two and three days, respectively. In order to elucidate the effect of SMX upon the crayfish immune response, new sets of crayfish were exposed to the same SMX treatments to evaluate mRNA levels of immune-related genes which are expressed and present in hemocytes and intestine, and to perform total and differential hemocyte counts. These results show a significant down-regulation of the antimicrobial peptide (AMP) Crustin 3 in hemocytes from the 100 ng/L SMX group, as well as a significant up-regulation of the AMP Crustin 1 in intestines from the 1 μg/L SMX group. Semigranular and total hemocyte cell number were observed to be significantly lower after exposure to 100 ng/L SMX in comparison with the control group. The present study demonstrates that environmentally relevant SMX concentrations in the water at 100 ng/L led to an increased WSSV susceptibility, that may have been caused by a reduction of circulating hemocytes. Nevertheless, SMX concentrations of 1 μg/L could marginally and for a few days have an immunostimulatory effect.

Astakine1 forms protein complex in plasma

Astakine 1 is a small cytokine-like peptide which is directly involved in hematopoiesis in crustaceans. Astakines are present in many different invertebrate groups primarily in arthropods. In this study we found that astakine1 was present as a high molecular weight (HMW) complex in plasma. It is known that calcium concentration are fluctuating in several crustaceans especially during the molting process. This HMW-complex was formed under low calcium concentrations in plasma and could be partially reversed provided calcium was added. The biological function of the naïve astakine1 and that in the HMW complex was about the same, but if the protein is to be isolated or studied for its function it is important to know about this property of astakine1 which may previously have hampered isolation and functional studies in other animals than freshwater crayfish.

A comparative global proteomic analysis of the hematopoietic lineages in the crustacean Pacifastacus leniusculus

In crustaceans as in other arthropods, the circulating hemocytes are vital for protecting the animal against attacking microorganisms. As many hemocytes are destroyed early during an infection, new hemocytes must fast get in place to prevent disperse of a pathogenic microbe, In order to understand the hematopoietic process in more detail we here report a complete proteomic analysis from purified cell types from the APC of the hematopoietic tissue, via the remaining parts of the HPT to the mature semigranular and granular hemocytes. Several possible cell type specific proteins are detected and new putative biomarkers within the crayfish hematopoietic lineage that can be used to increase the understanding of how the differentiation process is regulated is described.

Transglutaminase inhibition stimulates hematopoiesis and reduces aggressive behavior of crayfish, Pacifastacus leniusculus

Transglutaminase (TGase) is a Ca²⁺-dependent cross-linking enzyme, which has both enzymatic and nonenzymatic properties. TGase is involved in several cellular activities, including adhesion, migration, survival, apoptosis, and extracellular matrix (ECM) organization. In this study, we focused on the role of the TGase enzyme in controlling hematopoiesis in the crayfish, Pacifastacus leniusculus We hypothesized that a high TGase activity could mediate an interaction of progenitor cells with the ECM to maintain cells in an undifferentiated stage in the hematopoietic tissue (HPT). We found here that the reversible inhibitor cystamine decreases the enzymatic activity of TGase from crayfish HPT, as well as from guinea pig, in a concentration-dependent manner. Cystamine injection decreased TGase activity in HPT without affecting production of reactive oxygen species. Moreover, the decrease in TGase activity in the HPT increased the number of circulating hemocytes. Interestingly the cystamine-mediated TGase inhibition reduced aggressive behavior and movement in crayfish. In conclusion, we show that cystamine-mediated TGase inhibition directly releases HPT progenitor cells from the HPT into the peripheral circulation in the hemolymph and strongly reduces aggressive behavior in crayfish.

Transfection of crayfish hematopoietic tissue cells

Transfection is a powerful tool useful for studying gene function. Establishing transfection methods that enable highly efficient DNA uptake has become increasingly important. The crayfish hematopoietic tissue (Hpt) cell cultures have been proven to be suitable for studies on immunity and cell differentiation in crustaceans including shrimps, but no efficient gene transfer and expression method is available for these cells. Here we report a novel and highly efficient DNA transfection system based on electroporation. This method depends on a recombinant plasmid with the promoter from white spot syndrome virus immediate-early gene wsv249. This plasmid could be introduced into primary cells and efficiently express foreign genes by electroporation. By optimizing different electroporation parameters, more than 30% transfection efficiency could be achieved with the relative viability of cells around 50%. This is the first report of gene introduction to crayfish Hpt cells and will be useful for the expanding our research on crustacean immunity.

Characterization of a cold-active transglutaminase from a crayfish, Pacifastacus leniusculus

Transglutaminase (TGase) from signal crayfish (Pacifastacus leniusculus) and its activity at low temperatures was studied. TGase is an abundant protein in the hematopoietic (HPT) cells and this tissue was used for TGase enzyme preparation. The optimal temperature and pH for the activity of crayfish TGase were determined. We found that TGase activity at 4 °C showed nearly the same activity as at a temperature of 22 °C. TGase activity from crayfish was compared with guinea pig liver TGase activity at 4 °C and the crayfish TGase displayed a higher activity while guinea pig liver TGase had a very low activity at this low temperature. By comparing kinetic parameters to guinea pig liver TGase, the results showed that a high activity of crayfish TGase was due to a decreasing K_m value for pentylamine as a substrate, while it did not affect the k_cat value (at 22 °C). The amino acid sequences of a krill and a crayfish TGase, which both are cold adapted, do not give any clue to why these two enzymes are cold-adapted. These results demonstrate that crayfish TGase is adapted to have significant activity at low temperatures and since crayfish are living in quite cold waters this is an interesting adaptation of this enzyme.

Astakines in arthropods-phylogeny and gene structure

Astakine1 was isolated as a hematopoietic cytokine in the freshwater crayfish Pacifastacus leniusculus. In this study we detect and compare 79 sequences in GenBank, which we consider to be possible astakine orthologs, among which eleven are crustacean, sixteen are chelicerate and 52 are from insect species. Available arthropod genomes are searched for astakines, and in conclusion all astakine sequences in the current study have a similar exon containing CCXX(X), thus potentially indicating that they are homologous genes with the structure of this exon highly conserved. Two motifs, RYS and YP(N), are also conserved among the arthropod astakines. A phylogenetic analysis reveals that astakine1 and astakine2 from P. leniusculus and Procambarus clarkii are distantly related, and may have been derived from a gene duplication occurring early in crustacean evolution. Moreover, a structural comparison using the Mamba intestinal toxin (MIT1) from Dendroaspis polylepis as template indicates that the overall folds are similar in all crustacean astakines investigated.

Clotting protein - An extracellular matrix (ECM) protein involved in crustacean hematopoiesis

Hematopoietic progenitor cells in crustaceans are organized in lobule-like structures surrounded by different types of cells and extracellular matrix (ECM) proteins in a Hematopoietic tissue (HPT). Here we show that the clotting protein (CP) is part of the ECM in HPT and is secreted during HPT cell culture. The formation of a filamentous network of CP was observed in HPT cell culture. A high amount of CP protein was detected at the surfaces of undifferentiated cells (round-shaped) compared with migrating cells (spindle shaped). Co-localization of the CP protein and TGase activity was observed on the cell surface and filamentous network between cells. A role for CP together with collagen was revealed in a 3D culture in which a collagen-I matrix was immobilized with CP or supplemented with CP. The results showed possible functions of CP, collagen, TGase and the cytokine Ast1 in the regulation of HPT progenitor cell behavior. This is the first study to provide insight into the role of CP, which probably not only participates in clot formation but also functions as an ECM component protein controlling hematopoietic stem cell behavior.

Role of astakine1 in regulating transglutaminase activity

Transglutaminase (TGase) has been implicated in maintaining the undifferentiated stage of hematopoietic stem cells (HSC) in the crayfish Pacifastacus leniusculus. TGase activity has been reported to be regulated by astakine1, an essential crayfish cytokine for inducing new hemocyte synthesis in hematopoietic tissue (HPT). Here, the role of astakine1 in TGase activity regulation and clotting protein (CP) cross-linking was characterized. A reduction in TGase activity was observed by the addition of purified astakine1 in vitro for both endogenous crayfish TGase and a commercial purified guinea pig liver TGase. As a result, we observed that astakine1 inhibits TGase enzyme activity and acts as a non-competitive inhibitor for the TGase enzyme. Additionally, the clotting reaction was impaired in the presence of astakine1. A decrease in TGase-mediated crosslinking of ε(γ-glutamyl)-lysine bonds was also observed in the presence of astakine1. In conclusion, this study shows that astakine1 acts as an inhibitor of TGase activity and that it also affects CP cross-linking during crayfish hematopoiesis.

PDGF/VEGF-Related Receptor Affects Transglutaminase Activity to Control Cell Migration During Crustacean Hematopoiesis

The platelet-derived growth factor (PDGF) receptor, a tyrosine kinase (TK) receptor whose ligand is PDGF, is crucial in the transduction of extracellular signals into cells and mediates numerous processes, such as cell proliferation, differentiation, survival, and migration. We demonstrate the important roles of a receptor TK related to the PDGF/VEGF family protein (PVR) in controlling hematopoietic progenitor cell migration by affecting extracellular transglutaminase (TGase) activity. Pl_PVR1, GenBank accession No. KY444650, is highly expressed in hemocytes and the hematopoietic tissue (HPT). Sunitinib malate was used to block the PVF/PVR downstream pathway in HPT cell culture. The addition of Sunitinib also caused the HPT cells to increase in size and begin spreading. An increase in extracellular TGase activity on the HPT cell membrane was observed in a dose-dependent manner after treatment with Sunitinib malate. The presence of crude Ast1 provided a combinatorial beneficial effect that enhanced the number of spreading cells after inhibition of the Pl_PVR downstream signaling cascade. In addition, an increased immunoreactivity for β-tubulin and elongation of β-tubulin filaments were found in Pl_PVR signaling-inhibited cells. The potential roles of PVF/PVR signaling in controlling progenitor cell activity during hematopoiesis in crayfish were investigated and discussed.

A Pacifastacus leniusculus serine protease interacts with WSSV

Serine proteases are involved in many critical physiological processes including virus spread and replication. In the present study, we identified a new clip-domain serine protease (PlcSP) in the crayfish Pacifastacus leniusculus hemocytes, which can interact with the White Spot Syndrome Virus (WSSV) envelope protein VP28. It was characterized by a classic clip domain with six strictly conserved Cys residues, and contained the conserved His-Asp-Ser (H-D-S) motif in the catalytic domain. Furthermore, signal peptide prediction revealed that it has a 16-residue secretion signal peptide. Tissue distribution showed that it was mainly located in P. leniusculus hemocytes, and its expression was increased in hemocytes upon WSSV challenge. In vitro knock down of PlcSP decreased both the expression of VP28 and the WSSV copy number in hematopoietic stem (HPT) cells. Accordingly, these data suggest that the new serine protease may be of importance for WSSV infection into hematopoietic cells.

Characterization of a hemocyte homeostasis-associated-like protein (HHAP) in the freshwater crayfish Pacifastacus leniusculus

Hemocyte homeostasis-associated-like protein (HHAP) in the freshwater crayfish Pacifastacus leniusculus has a distinct role from that of its homolog PmHHAP in the shrimp Penaeus monodon. Knockdown of PlHHAP in vitro using double-stranded RNA (dsRNA) had no effect on the cell morphology of hematopoietic tissue (HPT) cells. The total hemocyte number and caspase activity were unchanged after PlHHAP knockdown in vivo, in contrast to the results found in shrimp. Moreover, suppression of PlHHAP both in vitro and in vivo did not change the mRNA levels of some genes involved in hematopoiesis and hemocyte homeostasis. Interestingly, bacterial count and scanning electron microscope revealed that depletion of PlHHAP in intestine by RNAi resulted in higher number of bacteria in the crayfish intestine. Together, these results suggest that PlHHAP is not involved in hemocyte homeostasis in the crayfish P. leniusculus but appears to affect the bacterial number in the intestine through an unknown mechanism. Since PlHHAP has different functions from PmHHAP, we therefore named it HHAP-like protein.

Reactive Oxygen Species Affect Transglutaminase Activity and Regulate Hematopoiesis in a Crustacean

Reactive oxygen species (ROS) serve as a prime signal in the commitment to hematopoiesis in both mammals and Drosophila In this study, the potential function of ROS during hematopoiesis in the crayfish Pacifastacus leniusculus was examined. The antioxidant N-acetylcysteine (NAC) was used to decrease ROS in both in vivo and in vitro experiments. An increase in ROS was observed in the anterior proliferation center (APC) after LPS injection. In the absence of NAC, the LPS-induced increase in ROS levels resulted in the rapid restoration of the circulating hemocyte number. In the presence of NAC, a delay in the recovery rate of the hemocyte number was observed. NAC treatment also blocked the spread of APC and other hematopoietic tissue (HPT) cells, maintaining these cells at an undifferentiated stage. Extracellular transglutaminase (TGase) has been shown previously to play a role in maintaining HPT cells in an undifferentiated form. In this study, we show that extracellular TGase activity increased when the ROS level in HPT or APC cells was reduced after NAC treatment. In addition, collagen, a major component of the extracellular matrix and a TGase substrate were co-localized on the HPT cell surface. Taken together, the results of this study show that ROS are involved in crayfish hematopoiesis, in which a low ROS level is required to maintain hematopoietic progenitor cells in the tissue and to reduce hemocyte release. The potential roles of TGase in this process are investigated and discussed.

Crustacean hematopoiesis

Crustacean hemocytes are important mediators of immune reactions, and the regulation of hemocyte homeostasis is of utmost importance for the health of these animals. This review discusses the current knowledge on the lineages, synthesis and differentiation of hemocytes in crustaceans. Hematopoietic tissues, their origins, and the regulation of hematopoiesis during molting, seasonal variation and infection are discussed. Furthermore, studies concerning the molecular regulation of hemocyte formation in crustaceans are also described, and the different lineages and their molecular markers are discussed and compared with several insect species. Signaling pathways and the regulation of hematopoiesis by transcription factors are typically conserved among these arthropods, whereas cytokines and growth factors are more variable and species specific. However, considering the great diversity among the crustaceans, one should be cautious in drawing general conclusions from studies of only a few species.

Cells from the immune system generate adult-born neurons in crayfish

Neurogenesis is an ongoing process in the brains of adult decapod crustaceans. However, the first-generation precursors that produce adult-born neurons, which reside in a neurogenic niche, are not self-renewing in crayfish and must be replenished. The source of these neuronal precursors is unknown. Here, we report that adult-born neurons in crayfish can be derived from hemocytes. Following adoptive transfer of 5-ethynyl-2'-deoxyuridine (EdU)-labeled hemocytes, labeled cells populate the neurogenic niche containing the first-generation neuronal precursors. Seven weeks after adoptive transfer, EdU-labeled cells are located in brain clusters 9 and 10 (where adult-born neurons differentiate) and express appropriate neurotransmitters. Moreover, the number of cells composing the neurogenic niche in crayfish is tightly correlated with total hemocyte counts (THCs) and can be manipulated by raising or lowering THC. These studies identify hemocytes as a source of adult-born neurons in crayfish and demonstrate that the immune system is a key contributor to adult neurogenesis.

Caspase-1-like regulation of the proPO-system and role of ppA and caspase-1-like cleaved peptides from proPO in innate immunity

Invertebrates rely on innate immunity to respond to the entry of foreign microorganisms. One of the important innate immune responses in arthropods is the activation of prophenoloxidase (proPO) by a proteolytic cascade finalized by the proPO-activating enzyme (ppA), which leads to melanization and the elimination of pathogens. Proteolytic cascades play a crucial role in innate immune reactions because they can be triggered more quickly than immune responses that require altered gene expression. Caspases are intracellular proteases involved in tightly regulated limited proteolysis of downstream processes and are also involved in inflammatory responses to infections for example by activation of interleukin 1ß. Here we show for the first time a link between caspase cleavage of proPO and release of this protein and the biological function of these fragments in response to bacterial infection in crayfish. Different fragments from the cleavage of proPO were studied to determine their roles in bacterial clearance and antimicrobial activity. These fragments include proPO-ppA, the N-terminal part of proPO cleaved by ppA, and proPO-casp1 and proPO-casp2, the fragments from the N-terminus after cleavage by caspase-1. The recombinant proteins corresponding to all three of these peptide fragments exhibited bacterial clearance activity in vivo, and proPO-ppA had antimicrobial activity, as evidenced by a drastic decrease in the number of Escherichia coli in vitro. The bacteria incubated with the proPO-ppA fragment were agglutinated and their cell morphology was altered. Our findings show an evolutionary conserved role for caspase cleavage in inflammation, and for the first time show a link between caspase induced inflammation and melanization. Further we give a more detailed understanding of how the proPO system is regulated in time and place and a role for the peptide generated by activation of proPO as well as for the peptides resulting from Caspase 1 proteolysis.

Melanization is an important reaction in most multicellular organisms, both animals and plants. The initiation steps of this reaction in invertebrates are catalyzed by the prophenoloxidase (proPO) activating system a proteolytic enzyme cascade, which primary function is to recognize cell wall products from microorganisms and respond by activation of the system and generation of immune effector molecules. This cascade requires careful regulation to achieve spatial and temporal control to avoid dangerous side effects. We here show that a Caspase1-like enzyme can inactivate proPO when ppA is not activating the proPO to avoid deleterious effects and further we show for the first time that the N-terminal peptide from ppA cleavage of proPO (activation of proPO) has an important biological function as also the Caspase1 cleaved fragments. Our results also show that Caspase 1-induced inflammatory response is evolutionarily conserved and is linked to melanization.

Circadian regulation of melanization and prokineticin homologues is conserved in the brain of freshwater crayfish and zebrafish

Circadian clock is important to living organisms to adjust to the external environment. This clock has been extensively studied in mammals, and prokineticin 2 (Prok2) acts as one of the messenger between the central nervous system and peripheral tissues. In this study, expression profiles of Prok1 and Prok2 were investigated in a non-mammalian vertebrate brain, zebrafish, and the expression was compared to the Prok homologues, astakines (Ast1 and Ast2) in crayfish. These transcripts exhibited circadian oscillation in the brain, and Ast1 had similar pattern to Prok2. In addition, the expression of tyrosinase, an enzyme which expression is regulated by E-box elements like in Prok2, was also examined in zebrafish brain and was compared with the expression of prophenoloxidase (proPO), the melanization enzyme, in crayfish brain. Interestingly, the expressions of both Tyr and proPO displayed circadian rhythm in a similar pattern to Prok2 and Ast1, respectively. Therefore, this study shows that circadian oscillation of prokineticin homologues and enzymes involved in melanization are conserved.

Recent advances in crayfish hematopoietic stem cell culture: a model for studies of hemocyte differentiation and immunity

Hematopoiesis is the process by which blood cells (hemocytes) mature and subsequently enter the circulation and we have developed a new technique to culture the hematopoietic progenitor cells in vitro. The reason for the successful culture was the isolation of a plasma protein that turned out to be a novel cytokine, astakine 1 (Ast1) containing a domain present in several vertebrates, so-called prokineticins. Now we have detected several astakines from other invertebrate species. Depending on our discovery of the cytokine Ast1 we have an opportunity to study in detail the differentiation of cells in the hematopoietic tissue of a crustacean, a tissue of evolutionary interest for studies of the connection between the vascular system and the nervous system. We have been able to isolate the entire hematopoietic tissue and for the first time detected a link between this tissue and the brain. We have further localized a proliferation center in the tissue and characterized its different parts. We have also used this system to isolate a new hematopoietic factor CHF that is important in the crossroad between apoptosis and hemocyte differentiation. Our technique for culture of crayfish hematopoietic stem cells provides a simple tool for studying the mechanism of hematopoiesis, but also enables detailed studies of immune defense reactions. Further, the culture system has been used for studies of viral defense and the system is suitable for gene silencing which allows functional characterization of different molecules involved in host defense as well as in hemocyte differentiation.

β-thymosins and hemocyte homeostasis in a crustacean

Thymosin proteins are well known for their actin-binding activity. Thymosin beta 4 (Tβ4) has been associated with biological activities in tissue repair and cell migration via interaction with ATP-synthase in vertebrates, while the information of similar thymosin functions in invertebrates is limited. We have shown previously that ATP-synthase is present on the surface of crayfish hematopoietic tissue (HPT) cells, and that astakine 1 (Ast1, an invertebrate cytokine) was found to interact with this β-subunit of ATP synthase. Here, we identified five different β-thymosins from Pacifastacus leniusculus, designated Pl-β-thymosin1-5. The two dominant isoforms in brain, HPT and hemocytes, Pl-β-thymosin1 and 2, were chosen for functional studies. Both isoforms could bind to the β-subunit of ATP-synthase, and Pl-β-thymosin1, but not Pl-β-thymosin2, significantly increased extracellular ATP formation. Moreover, Pl-β-thymosin1 stimulated HPT cell migration in vitro and Ast1 blocked this effect. Pl-β-thymosin2 increased the circulating hemocyte number at an early stage after injection. Additionally, in vivo injection of Pl-β-thymosin1 resulted in significant reduction of reactive oxygen species (ROS) production in crayfish HPT whereas Pl-β-thymosin2 had a similar but transient effect. Both Pl-β-thymosins induced the expression of Ast1 and superoxide dismutase (SOD) transcripts, while silencing of endogenous Pl-β-thymosin 1 and 2 by RNAi resulted in significant reduction of the Ast1 and SOD transcripts. The diverse effects exhibited by Pl-β-thymosin1 and Pl-β-thymosin2 indicates that these proteins are involved in a complex interaction that regulates the hematopoietic stem cell proliferation and differentiation.

Astakine 2--the dark knight linking melatonin to circadian regulation in crustaceans

Daily, circadian rhythms influence essentially all living organisms and affect many physiological processes from sleep and nutrition to immunity. This ability to respond to environmental daily rhythms has been conserved along evolution, and it is found among species from bacteria to mammals. The hematopoietic process of the crayfish Pacifastacus leniusculus is under circadian control and is tightly regulated by astakines, a new family of cytokines sharing a prokineticin (PROK) domain. The expression of AST1 and AST2 are light-dependent, and this suggests an evolutionarily conserved function for PROK domain proteins in mediating circadian rhythms. Vertebrate PROKs are transmitters of circadian rhythms of the suprachiasmatic nucleus (SCN) in the brain of mammals, but the mechanism by which they function is unknown. Here we demonstrate that high AST2 expression is induced by melatonin in the brain. We identify RACK1 as a binding protein of AST2 and further provide evidence that a complex between AST2 and RACK1 functions as a negative-feedback regulator of the circadian clock. By DNA mobility shift assay, we showed that the AST2-RACK1 complex will interfere with the binding between BMAL1 and CLK and inhibit the E-box binding activity of the complex BMAL1-CLK. Finally, we demonstrate by gene knockdown that AST2 is necessary for melatonin-induced inhibition of the complex formation between BMAL1 and CLK during the dark period. In summary, we provide evidence that melatonin regulates AST2 expression and thereby affects the core clock of the crustacean brain. This process may be very important in all animals that have AST2 molecules, i.e. spiders, ticks, crustaceans, scorpions, several insect groups such as Hymenoptera, Hemiptera, and Blattodea, but not Diptera and Coleoptera. Our findings further reveal an ancient evolutionary role for the prokineticin superfamily protein that links melatonin to direct regulation of the core clock gene feedback loops.

Most living organisms are able to sense the time and in particular time of day by their internal clocks. So-called clock proteins control these internal clockworks. BMAL1 and CLK are two important clock proteins, which together form a complex that serves as a transcription factor and controls the production of diurnal proteins. These diurnal proteins, in turn, inhibit the formation of clock proteins so that the concentration of the different proteins in the cell oscillates back and forth throughout the day. External factors may affect the balance of clock proteins, and one such important factor is light. Melatonin is a darkness hormone produced in the brain of most animals during the night, and here we show that melatonin controls the formation of a protein named AST2 in crayfish. AST2 belongs to a group of proteins found in many arthropods, such as spiders, scorpions, crustaceans, and some insects, whose function has been unknown until now. Now we demonstrate that AST2 is induced by melatonin at night and then functions in the internal biological clock by preventing BMAL1 and CLK to form a complex. In this way, AST2 acts as a link between melatonin and the internal biological clock.

A calreticulin/gC1qR complex prevents cells from dying: a conserved mechanism from arthropods to humans

The crossroad between cell death and proliferation is a general target for viral infections because viruses need to obstruct apoptosis to use cells for their own replication. Inducing immunogenic cell death in proliferating cells is also an important aim of anticancer chemotherapy. The C1q-binding proteins calreticulin (CRT) and gC1qR are highly conserved ubiquitous proteins, which are putative targets for viral manipulation and are associated with cancer. Here we show that these proteins form a complex in the cytoplasm as a response to viral infection resulting in apoptosis prevention. The formation of a cytosolic CRT/gC1qR complex prevents cell death by reducing gC1qR translocation into the mitochondria, and we provide evidence that this mechanism is conserved from arthropods to human cancer cells. Furthermore, we show that it is possible to prevent this complex from being formed in cancer cells. When the peptides of the complex proteins are overexpressed in these cells, the cells undergo apoptosis. This finding shows a causal link between virus and cancer and may be used to develop new tools in anticancer or antiviral therapy.

Invertebrate hematopoiesis: an anterior proliferation center as a link between the hematopoietic tissue and the brain

During evolution, the innate and adaptive immune systems were developed to protect organisms from non-self substances. The innate immune system is phylogenetically more ancient and is present in most multicellular organisms, whereas adaptive responses are restricted to vertebrates. Arthropods lack the blood cells of the lymphoid lineage and oxygen-carrying erythrocytes, making them suitable model animals for studying the regulation of the blood cells of the innate immune system. Many crustaceans have a long life span and need to continuously synthesize blood cells, in contrast to many insects. The hematopoietic tissue (HPT) of Pacifastacus leniusculus provides a simple model for studying hematopoiesis, because the tissue can be isolated, and the proliferation of stem cells and their differentiation can be studied both in vivo and in vitro. Here, we demonstrate new findings of a physical link between the HPT and the brain. Actively proliferating cells were localized to an anterior proliferation center (APC) in the anterior part of the tissue near the area linking the HPT to the brain, whereas more differentiated cells were detected in the posterior part. The central areas of HPT expand in response to lipopolysaccharide-induced blood loss. Cells isolated from the APC divide rapidly and form cell clusters in vitro; conversely, the cells from the remaining HPT form monolayers, and they can be induced to differentiate in vitro. Our findings offer an opportunity to learn more about invertebrate hematopoiesis and its connection to the central nervous system, thereby obtaining new information about the evolution of different blood and nerve cell lineages.

An insect TEP in a crustacean is specific for cuticular tissues and involved in intestinal defense

In an attempt to identify genes encoding thioester-containing proteins in the freshwater crayfish, Pacifastacus leniusculus, three different cDNAs were found. A phylogenetic analysis of these proteins indicates that they can be classified into two subfamilies: two alpha-2-macroglobulins (Pl-A2M1, Pl-A2M2) showing a close similarity to shrimp A2M, and one insect TEP-like protein (Pl-TEP). This is the first report of an insect TEP-like protein in a crustacean. Crayfish Pl-A2M1, Pl-A2M2 and Pl-TEP cDNAs encode proteins with 1480, 1586 or 1507 amino acids, respectively. Pl-A2M1, Pl-A2M2 and Pl-TEP have the basic domain structure and functionally important residues for each molecule, and their mRNA was detected in different parts of the body, suggesting that they may have different functions. Pl-A2M1 was mainly expressed in hemocytes and Pl-A2M2 was highly expressed in heart and nerve, while Pl-TEP was exclusively expressed in cuticular tissues such as gill and intestine. RNA interference of Pl-TEP in vivo resulted in that these animals were slightly less resistant when fed with the bacterium, Pseudomonas libanensis/gessardii. Furthermore, when TEP activity was blocked using methylamine followed by bacterial feeding, the animals were killed to a higher extent compared to a control group. Taken together, this indicates that Pl-TEP and/or Pl-A2M1, Pl-A2M2 may be important for the immune defense in crayfish intestine and function as a pattern recognition protein in crayfish cuticular tissues.

Inflammation in arthropods

The inflammatory process in arthropods includes primarily the recruitment of circulating hemocytes to wounds or sites of microbial infections. Melanization, capsule formation and clotting reactions will finally result in the sealing of wounds. In this review we will focus on recent research about hemolymph clotting and melanization reactions, and the recruitment of hemocytes to wounds and infections. We further describe in more detail new knowledge about crustacean hematopoiesis that is crucial for hemocyte recruitment to the site of an infection and there develop an inflammatory response. Moreover, we pay special attention to the gut as an important route of infection in arthropods. Since the gastrointestinal tract provides a first line of defense and regulation of the indigenous bacteria and the intestine often harbors loads of potential pathogenic microorganisms, the integrity of intestinal epithelium and to maintain the correct flora is crucial to animal health.

Two novel ficolin-like proteins act as pattern recognition receptors for invading pathogens in the freshwater crayfish Pacifastacus leniusculus

To isolate pathogen-associated molecular patterns (PAMPs)-binding molecules, the bacterium, Staphylococcus aureus was used as an affinity matrix to find bacteria-binding proteins in the plasma of the freshwater crayfish, Pacifastacus leniusculus. Two new bacteria-binding ficolin-like proteins (FLPs) were identified by 2-DE and MS analysis. The FLPs have a fibrinogen-related domain (FReD) in their C-terminal and a repeat region in their N-terminal regions with putative structural similarities to the collagen-like domain of vertebrate ficolins and mannose binding lectins (MBLs). Phylogenetic analysis shows that the newly isolated crayfish FLP1 and FLP2 cluster separately from other FReD-containing proteins. A tissue distribution study showed that the mRNA expression of FLP occurred mainly in the hematopoietic tissue (Hpt) and in the hepatopancreas. Recombinant FLPs exhibited agglutination activity of Gram-negative bacteria Escherichia coli and Aeromonas hydrophila in the presence of Ca(2+) . The FLPs could bind to A. hydrophila, E. coli as well as S. aureus as judged by bacteria adsorption. Moreover, the FLPs may help crayfish to clear Gram-negative bacteria, but not Gram-positive bacteria which had been injected into the hemolymph. When Gram-negative bacteria coated with FLPs were incubated with Hpt cells, a lower death rate of the cells was found compared with control treatment. Our results suggest that FLPs function as pattern recognition receptors in the immune response of crayfish.

Peptidoglycan activation of the proPO-system without a peptidoglycan receptor protein (PGRP)?

Recognition of microbial polysaccharide by pattern recognition receptors triggers the prophenoloxidase (proPO) cascade, resulting in melanin synthesis and its deposition on the surface of invading pathogens. Several masquerade-like proteins and serine proteinase homologues have been shown to be involved in the proPO activation in insects. In this study, a novel serine proteinase homologue, Pl-SPH2, was found and isolated as a 30kDa protein from hemocytes of the freshwater crayfish, Pacifastacus leniusculus, by its binding property to a partially lysozyme digested or TCA-treated insoluble Lysine (Lys)-type peptidoglycan (PGN) and soluble polymeric Lys-type PGN. Two other proteins, the Pl-SPH1 and lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) were also found in the several different PGN-binding assays. However no PGRP homologue was detected. Neither was any putative PGRP found after searching available crustacean sequence databases. If RNA interference of Pl-SPH2, Pl-SPH1 or LGBP in the crayfish hematopoietic tissue cell culture was performed, it resulted in lower PO activity following activation of the proPO-system by soluble Lys-type PGN. Taken together, we report for the first time that Lys-type PGN is a trigger of proPO-system activation in a crustacean and that two Pl-SPHs are involved in this activation possibly by forming a complex with LGBP and without a PGRP.

Melanization and pathogenicity in the insect, Tenebrio molitor, and the crustacean, Pacifastacus leniusculus, by Aeromonas hydrophila AH-3

Aeromonas hydrophila is the most common Aeromonas species causing infections in human and other animals such as amphibians, reptiles, fish and crustaceans. Pathogenesis of Aeromonas species have been reported to be associated with virulence factors such as lipopolysaccharides (LPS), bacterial toxins, bacterial secretion systems, flagella, and other surface molecules. Several mutant strains of A. hydrophila AH-3 were initially used to study their virulence in two animal species, Pacifastacus leniusculus (crayfish) and Tenebrio molitor larvae (mealworm). The AH-3 strains used in this study have mutations in genes involving the synthesis of flagella, LPS structures, secretion systems, and some other factors, which have been reported to be involved in A. hydrophila pathogenicity. Our study shows that the LPS (O-antigen and external core) is the most determinant A. hydrophila AH-3 virulence factor in both animals. Furthermore, we studied the immune responses of these hosts to infection of virulent or non-virulent strains of A. hydrophila AH-3. The AH-3 wild type (WT) containing the complete LPS core is highly virulent and this bacterium strongly stimulated the prophenoloxidase activating system resulting in melanization in both crayfish and mealworm. In contrast, the ΔwaaE mutant which has LPS without O-antigen and external core was non-virulent and lost ability to stimulate this system and melanization in these two animals. The high phenoloxidase activity found in WT infected crayfish appears to result from a low expression of pacifastin, a prophenoloxidase activating enzyme inhibitor, and this gene expression was not changed in the ΔwaaE mutant infected animal and consequently phenoloxidase activity was not altered as compared to non-infected animals. Therefore we show that the virulence factors of A. hydrophila are the same regardless whether an insect or a crustacean is infected and the O-antigen and external core is essential for activation of the proPO system and as virulence factors for this bacterium.

Proteinase inhibitory activities of two two-domain Kazal proteinase inhibitors from the freshwater crayfish Pacifastacus leniusculus and the importance of the P(2) position in proteinase inhibitory activity

Serine proteinase inhibitors are found ubiquitously in living organisms and involved in homeostasis of processes using proteinases as well as innate immune defense. Two two-domain Kazal-type serine proteinase inhibitors (KPIs), KPI2 and KPI8, have been identified from the hemocyte cDNA library of the crayfish Pacifastacus leniusculus. Unlike other KPIs from P. leniusculus, they are found specific to the hemocytes and contain an uncommon P(2) amino acid residue, Gly. To unveil their inhibitory activities, the two KPIs and their domains were over-expressed. By testing against subtilisin, trypsin, chymotrypsin and elastase, the KPI2 was found to inhibit strongly against subtilisin and weakly against trypsin, while the KPI8 was strongly active against only trypsin. With their P(1) Ser and Lys residues, the KPI2_domain2 and KPI8_domain2 were responsible for strong inhibition against subtilisin and trypsin, respectively. Mutagenesis of KPI8_domain1 at P(2) amino acid residue from Gly to Pro, mimicking the P(2) residue of KPI8_domain2, rendered the KPI8_domain1 strongly active against trypsin, indicating the important role of P(2) residue in inhibitory activities of the Kazal-type serine proteinase inhibitors. Only the KPI2 was found to inhibit against the extracellular serine proteinases from the pathogenic oomycete of the freshwater crayfish, Aphanomyces astaci.

Effects of manganese and hypoxia on coelomocyte renewal in the echinoderm, Asterias rubens (L.)

Manganese (Mn) is a naturally abundant metal and particularly so in soft-bottom oceanic sediments where it generally occurs bound in a four-valent colloidal state as MnO2. When hypoxic conditions occur in bottom waters, the metal reduces to the bioavailable ion Mn2+ and can reach concentrations known to have immunotoxic effects in the crustacean Nephrops norvegicus, reducing numbers of circulating haemocytes as a consequence. However, we have previously shown that Mn seems to have a contrasting effect on the echinoderm Asterias rubens in which it triggers the proliferation of haematopoietic cells and increases coelomocyte numbers. Since elevated Mn levels mostly co-occur with hypoxia in nature, here we investigated whether hypoxia has a negative effect on haematopoiesis. Proliferation and differentiation of coelomocytes and cells in the coelomic epithelium of A. rubens were compared after 3 days of exposure to realistic levels of Mn, hypoxia or a combination of these two parameters. We can confirm that Mn elevated numbers of coelomocytes and increased proliferation of epithelial cells, but hypoxia did not affect these levels. However, hypoxia did affect differentiation of these cells as judged by investigating the expression of a Runt domain transcription factor, which was also cloned and sequenced. Through comparative quantification using a real time PCR technique, we found that exposure to hypoxia had a clearly stimulating effect on mRNA expression of Runt gene in both coelomocytes and epithelial cells. These results indicate that during hypoxic conditions the composition of coelomocyte sub-populations changed.

Cloning and characterization of a melanization inhibition protein (PmMIP) of the black tiger shrimp, Penaeus monodon

Melanization is an important component of the innate immune responses in invertebrates and it is essential for defense against invading microorganism. Melanin formation, which is a result of activation of the so called prophenoloxidase activating system, needs to be controlled due to the dangerous effects of quinones and melanin which are produced during the process of melanization. Here, a cDNA for a melanization inhibition protein (MIP), named PmMIP, was identified from the black tiger shrimp, Penaeus monodon by RT-PCR using degenerated oligonucleotide primers and RACE-PCR. The complete sequence significantly matched MIP of the freshwater crayfish Pacifastacus leniusculus (PlMIP). PmMIP contains an N-terminal signal peptide and a fibrinogen related domain (FReD). RT-PCR was applied to examine the expression profiles of PmMIP in various tissues of juvenile P. monodon. PmMIP was expressed in all examined tissues except hemocytes and at very low levels in hepatopancreas and ovaries. The expression of this gene was very low during the larval stages and hardly present in egg and at the nauplius stage. A time-course expression analysis of PmMIP upon Vibrio harveyi challenge at protein levels in plasma was determined. The result shows that MIP protein in plasma was induced at 6 h and disappeared at 12 and 24 h and then the protein reappeared at 48 and 72 h post injection. These results suggest that upon bacterial infection the PmMIP protein is first released from tissues into hemolymph and then degraded to allow melanization to occur for fighting against bacteria.

Ancient cytokines, the role of astakines as hematopoietic growth factors

Hematopoiesis is the process by which hemocytes mature and subsequently enter the circulation. Vertebrate prokineticins (PKs) are known to take part in this process, as are the invertebrate prokineticin domain proteins, astakines. In Pacifastacus leniusculus, astakine 1 is essential for the release of new hemocytes into the open circulatory system of these animals. In addition to astakine 1, we have now cloned a homologue of astakine 1 with an insert of 13 amino acids, named as astakine 2. Both crustacean astakines lack the N-terminal AVIT motif, which is present in vertebrate PKs, and hence receptor binding differs from that of vertebrate PKs. We have found astakine-like sequences in 19 different invertebrate species, and the sequences show that some motifs are conserved among invertebrate groups. Previously we showed that astakine 1 is directly involved in hematopoiesis, and now we show that astakine 1 and astakine 2 have different roles in hemocyte lineage differentiation. Astakine 1 can stimulate proliferation of hematopoietic tissue (Hpt) cells (precursor of hemocytes) as well as specifically induce differentiation of Hpt cells along the semigranular cell lineage, whereas astakine 2 plays a role in granular cell differentiation. Moreover, we discuss the impact of the putative structures of different astakines in comparison with the vertebrate prokineticins.

Expression of immune-related genes in one phase of embryonic development of freshwater crayfish, Pacifastacus leniusculus

Crayfish do not have larval stage as other crustacean such as penaeid shrimp they spawn their eggs until hatching and what hatches out from the eggs are miniature crayfish known as juveniles. In order to address the question whether immune genes are initially expressed during the embryo development in the egg stage, the expression of some immune-related genes: prophenoloxidase (proPO), peroxinectin, hemocyanin, anti-lipopolysaccharide factor (ALF), plcrustin, astakine-1, 2 and transglutaminase (TGase) were determined in the middle phase of crayfish embryo development. Furthermore, immune challenge was used to determine the immune response of eggs by immersing them in a solution of the highly pathogenic bacterium Aeromonas hydrophila. Semi-quantitative RT-PCR analysis showed that all tested genes are present except proPO in this phase of crayfish embryo development and none of the genes tested changed their expression following immersion in A. hydrophila. The proPO transcript has been reported from hemocytes in crustaceans and it plays crucial roles in crustacean immune response. This may indicate that the development of immune-competent hemocytes in this stage of crayfish embryo is not completed and the egg shell as such plays an important role as a shield in protecting the embryo from bacteria and maybe also other pathogens.