Insights into hepatopancreatic functions for nutrition metabolism and ovarian development in the crab Portunus trituberculatus: gene discovery in the comparative transcriptome of different hepatopancreas stages

Molecular insights into reproduction regulation of female Oriental River prawns Macrobrachium nipponense through comparative transcriptomic analysis

The oriental river prawn, Macrobrachium nipponense, is an important commercial aquaculture resource in China. During breeding season, short ovary maturation cycles of female prawns cause multi-generation reunions in ponds and affect the growth of females representing individual miniaturization (known as autumn -propagation). These reproductive characteristics pose problems for in large - scale farming. To date, the molecular mechanisms of reproduction regulation of M. nipponense remain unclear. To address this issue, we performed transcriptome sequencing and gene expression analyses of eyestalk and cerebral ganglia of female M. nipponense during breeding and non-breeding seasons. Differentially expressed gene enrichment analysis results revealed several important reproduction related terms and signaling pathways, such as "photoreceptor activity", "structural constituent of cuticle" and "G-protein coupled receptor activity". The following six key genes from the transcriptome were predicted to mediate environmental factors regulating reproduction of M. nipponense: neuroparsin, neuropeptide F II, orcokinin II, crustacean cardioactive peptide, pigment-dispersing hormone 3 and tachykinin. These results will contribute to a better understanding of the molecular mechanisms of reproduction of oriental river prawns. Further detailed functional analyses of the candidate reproduction regulation related neuropeptides are needed to shed light on the mechanisms of reproduction of crustacean.

Effects of dietary lipids on the hepatopancreas transcriptome of Chinese mitten crab (Eriocheir sinensis)

Fish oil supplies worldwide have declined sharply over the years. To reduce the use of fish oil in aquaculture, many studies have explored the effects of fish oil substitutions on aquatic animals. To illustrate the effects of dietary lipids on Chinese mitten crab and to improve the use of vegetable oils in the diet of the crabs, 60 male juvenile Chinese mitten crabs were fed one of five diets for 116 days: fish oil (FO), soybean oil (SO), linseed oil (LO), FO + SO (1:1, FSO), and FO + LO (1:1, FLO). Changes in the crab hepatopancreas transcriptome were analyzed using RNA sequencing. There were a total 55,167 unigenes obtained from the transcriptome, of which the expression of 3030 was significantly altered in the FLO vs. FO groups, but the expression of only 412 unigenes was altered in the FSO vs. FO groups. The diets significantly altered the expression of many enzymes involved in lipid metabolism, such as pancreatic lipase, long-chain acyl-CoA synthetases, carnitine palmitoyltransferase I, acetyl-CoA carboxylase, fatty acid synthase, and fatty acyl Δ9-desaturase. The dietary lipids also affected the Toll-like receptor and Janus activated kinase-signal transducers and activators of transcription signaling pathways. Our results indicate that substituting fish oil with vegetable oils in the diet of Chinese mitten crabs might decrease the digestion and absorption of dietary lipids, fatty acids biosynthesis, and immunologic viral defense, and increase β-oxidation by altering the expression of the relevant genes. Our results lay the foundation for further understanding of lipid nutrition in Chinese mitten crab.

Purification and characterization of bioactive peptides RYamide and CCHamide in the kuruma shrimp Marsupenaeus japonicus

To understand the regulation systems of appetite, bioactive peptides from the kuruma shrimp Marsupenaeus japonicus (Mj) were isolated and purified by reverse pharmacological assays using CHO cells expressing the Drosophila melanogaster G-protein-coupled receptors (GPCRs) CG5811 (a RYamide receptor) or CG14593 (a CCHamide-2 receptor). Four peptides having binding activity to GPCRs were obtained and named Mj RYamide-1, Mj RYamide-2, Mj RYamide-3, and Mj CCHamide. Genes encoding the prepropeptides of these peptides were identified using kuruma shrimp transcriptome databases. The Mj prepro-RYamide gene encodes a 130-amino acid polypeptide containing Mj RYamide-1, Mj RYamide-2, and Mj RYamide-3, whereas the Mj prepro-CCHamide gene encodes a 119-amino acid polypeptide containing a single Mj CCHamide peptide. The expression of these genes was confirmed in various neuronal organs including the brain and ventral nerve cord. In addition, prepro-RYamide gene expression is significantly reduced in the brain after starvation. RYamides may thus be associated with regulation of feeding or digestion. Changes in kayak (the c-fos ortholog in invertebrates) gene expression after administration of synthetic peptides were also investigated. Mj kayak expression levels are upregulated in hepatopancreas after treatment with Mj RYamide-3 or CCHamide. Thus, the peptides isolated in this study may have some regulatory effect on cellular metabolism in aquacultured invertebrates.

Identification of ecdysteroid receptor-mediated signaling pathways in the hepatopancreas of the red swamp crayfish, Procambarus clarkii

The hepatopancreas of crustaceans plays an important role in lipid and carbohydrate metabolism, digestion of food, and biogenesis. In this study, the hepatopancreas transcriptome from the red crayfish Procambarus clarkii was characterized for the first time using high-throughput sequencing, producing approximately 41.4 million reads were obtained. After de novo assembly, 57,363 unigenes with an average length of 725bp were identified, Gene Ontology analysis categorized 22,580 as being involved in biological processes, among which metabolic process and cellular process groups were the most highly enriched. A total of 8034 unigenes were assigned to 223 metabolic pathways following mapping against the Kyoto encyclopedia of genes and genomes (KEGG) database. Ecdysteroid receptor (EcR)-mediated signaling pathways were investigated using digital gene expression (DGE) analysis following RNA interference targeting the EcR. A total of 529 differentially expressed genes (DEGs) were identified, including 322 downregulated and 207 upregulated unigenes. Of these, 445 (84.12%) were annotated successfully by alignment with known sequences, many of which were related to catalytic activity and binding functional categories. Using KEGG enrichment analysis, 183 DEGs were clustered into 78 pathways, and six significantly enriched pathways were predicted. The expression patterns of candidate genes identified by real-time PCR were consistent with the DGE results.

Two short peptidoglycan recognition proteins from Crassostrea gigas with similar structure exhibited different PAMP binding activity

Peptidoglycan recognition protein (PGRP) is an essential molecule in innate immunity for both invertebrates and vertebrates, owing to its prominent ability in specifically recognizing bacterial peptidoglycan (PGN) and eliminating the invading bacteria. In the present study, the full length cDNA of two PGRP genes, CgPGRPS2 and CgPGRPS4, were cloned from oyster Crassostrea gigas. Their amino acid sequences both contained one signal peptide, one typical PGRP/amidase domain with conserved catalytic residues responsible for amidase activity (55H, 90Y, 164H, 172C in CgPGRPS2, and 98H, 133Y, 207H, 215C in CgPGRPS4), and specific PGN recognition (84R, 85W, 104R, 109V in CgPGRPS2, and 127G, 128W, 147R, 152V in CgPGRPS4), and they shared 55.9% sequence similarity. The mRNA transcripts of CgPGRPS2 and CgPGRPS4 were constitutively expressed in all the examined tissues, including haemocytes, hepatopancreas, mantle, gonad, heart, adductor muscle and gill, with the highest expression level in adductor muscle and hepatopancreas, respectively. Both CgPGRPS2 and CgPGRPS4 proteins were mainly localized in the cytoplasma. The recombinant protein of CgPGRPS2 (rCgPGRPS2) could bind lipopolysaccharide (LPS), PGN and mannan (Man), as well as various microorganisms including Gram-negative bacteria Escherichia coli, Vibrio anguillarum, Gram-positive bacteria Staphylococcus aureus and fungi Yarrowia lipolytica. The recombinant protein of CgPGRPS4 (rCgPGRPS4) exhibited higher binding affinity to PGN, lower binding affinity to LPS, while no binding activity to Man and Y. lipolytica. The results indicated that CgPGRPS2 and CgPGRPS4 could function as pattern recognition receptors (PRR) in the innate immune response of oyster, and they exhibited a certain degree of functional differentiation in recognition of Man.

Oxidative Status Profile in Different Tissues of Parastacus brasiliensis promatensis (Crustacea, Decapoda, Parastacidae) over a Seasonal Cycle

The objective of this study was to assess annual redox balance by quantifying activity of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST), as well as measuring lipid peroxidation levels by determination of thiobarbituric acid-reactive substances, in different tissues of male and female crayfish collected from an area little affected by anthropogenic impacts. A total of 37 male and 32 female of Parastacus brasiliensis promatensis were collected over an annual cycle, and gill, muscle, hepatopancreas, and gonad samples were harvested and subjected to the aforementioned analyses via spectrophotometry. Comparison of the annual oxidative status response profile in gill and in hepatopancreas between males and females revealed differences only in SOD activity. In abdominal muscle, this comparison revealed a distinct profile of SOD and GST activity, as well as of lipid peroxidation. SOD activity in gonads of females increased in the summer when compared to autumn; conversely, CAT and GST levels did not differ over the year. During reproduction, a possible increase of the energy requirements led to an increase in lipid peroxidation in all tested tissues, in males and females alike. It was least evident in female gonad tissue, which suggests this tissue type is relatively protected; within this context, one may establish a tissue-specific grading of Lipid Peroxidation intensity in females of the species during the spring: gonads < muscle < gills < hepatopancreas. Our results show that the responses of the defenses analyzed antioxidants, as well as lipid peroxidation levels, were sex and tissue dependent and a clear pattern of seasonal variation.

Two novel LRR-only proteins in Chlamys farreri: Similar in structure, yet different in expression profile and pattern recognition

Leucine-rich repeat (LRR)-only proteins could mediate protein-ligand and protein-protein interactions and be involved in the immune response. In the present study, two novel LRR-only proteins, CfLRRop-2 and CfLRRop-3, were identified and characterized from scallop Chlamys farreri. They both contained nine LRR motifs with the consensus signature sequence LxxLxLxxNxL and formed typical horseshoe structure. The CfLRRop-2 and CfLRRop-3 mRNA transcripts were constitutively expressed in haemocytes, muscle, mantle, gill, haepatopancreas and gonad, with the highest expression level in haepatopancreas and gill, respectively. During the ontogenesis of scallop, the mRNA transcripts of CfLRRop-2 were kept at a high level in oocytes and embryos, while those of CfLRRop-3 were expressed at a rather low level from oocytes to blastula. Their mRNA transcripts were significantly increased after the stimulation of lipopolysaccharide (LPS), peptidoglycan (PGN), glucan (GLU) and polyinosinic-polycytidylic acid (poly I:C), and the mRNA expression of CfLRRop-2 rose more intensely than that of CfLRRop-3. After the suppression of CfTLR (previously identified Toll-like receptor in C. farreri) via RNA interference (RNAi), CfLRRop-3 mRNA transcripts increased more intensely and lastingly than those of CfLRRop-2. The rCfLRRop-3 protein could bind LPS, PGN, GLU and poly I:C, while rCfLRRop-2 exhibited no significant binding activity to them. Additionally, rCfLRRop-2 could significantly induce the release of TNF-α from the mixed primary cultured scallop haemocytes, but rCfLRRop-3 failed. These results collectively indicated that CfLRRop-2 might act as an immune effector or pro-inflammatory factor, while CfLRRop-3 would function as a pattern recognition receptor (PRR), suggesting the function of LRR-only protein family has differentiated in scallop.

A First Insight into the Genome of the Filter-Feeder Mussel Mytilus galloprovincialis

Mussels belong to the phylum Mollusca, one of the largest and most diverse taxa in the animal kingdom. Despite their importance in aquaculture and in biology in general, genomic resources from mussels are still scarce. To broaden and increase the genomic knowledge in this family, we carried out a whole-genome sequencing study of the cosmopolitan Mediterranean mussel (Mytilus galloprovincialis). We sequenced its genome (32X depth of coverage) on the Illumina platform using three pair-end libraries with different insert sizes. The large number of contigs obtained pointed out a highly complex genome of 1.6 Gb where repeated elements seem to be widespread (~30% of the genome), a feature that is also shared with other marine molluscs. Notwithstanding the limitations of our genome sequencing, we were able to reconstruct two mitochondrial genomes and predict 10,891 putative genes. A comparative analysis with other molluscs revealed a gene enrichment of gene ontology categories related to multixenobiotic resistance, glutamate biosynthetic process, and the maintenance of ciliary structures.

Transcriptome assembly and expression profiling of molecular responses to cadmium toxicity in hepatopancreas of the freshwater crab Sinopotamon henanense

Cadmium (Cd) pollution is a serious global problem, which causes irreversible toxic effects on animals. Freshwater crab, Sinopotamon henanense, is a useful environmental indicator since it is widely distributed in benthic habitats whereby it tends to accumulate Cd and other toxicants. However, its molecular responses to Cd toxicity remain unclear. In this study, we performed transcriptome sequencing and gene expression analyses of its hepatopancreas with and without Cd treatments. A total of 7.78 G clean reads were obtained from the pooled samples, and 68,648 unigenes with an average size of 622 bp were assembled, in which 5,436 were metabolism-associated and 2,728 were stimulus response-associated that include 380 immunity-related unigenes. Expression profile analysis demonstrated that most genes involved in macromolecular metabolism, oxidative phosphorylation, detoxification and anti-oxidant defense were up-regulated by Cd exposure, whereas immunity-related genes were down-regulated, except the genes involved in phagocytosis were up-regulated. The current data indicate that Cd exposure alters gene expressions in a concentration-dependent manner. Therefore, our results provide the first comprehensive S.henanense transcriptome dataset, which is useful for biological and ecotoxicological studies on this crab and its related species at molecular level, and some key Cd-responsive genes may provide candidate biomarkers for monitoring aquatic pollution by heavy metals.

Rapid immunochromatographic test strip to detect swimming crab Portunus trituberculatus reovirus

Swimming crab reovirus (SCRV) is the causative agent of a serious disease with high mortality in cultured Portunus trituberculatus. A rapid immunochromatographic assay (ICA) was developed in a competitive assay format and optimized for the detection of SCRV. The gold probe-based ICA test comprised SCRV antigen and goat anti-chicken egg yolk antibody (IgY) sprayed onto a nitrocellulose membrane as the test line and control line, respectively. IgY-gold complexes were deposited onto the conjugate pad as detector reagents. The method showed high specificity with no cross-reactivity with other related aquatic pathogens. The detection limit of the ICA strip was 50 µg ml⁻¹. To evaluate the performance of the ICA test, the strip and an enzyme-linked immunosorbent assay (ELISA) were applied to the same samples (n = 90 crabs). The strip successfully detected SCRV in all of the artificially infected samples. Furthermore, the ICA strip and ELISA tests had high consistency (98.28%). The strip assay requires no instruments and has a detection time of less than 10 min. It is portable and easy to perform in the field. These results indicated that the developed strip could be a promising on-site tool for screening pooled crabs to confirm SCRV infection or disease outbreaks.

Ovarian Transcriptome Analysis of Portunus trituberculatus Provides Insights into Genes Expressed during Phase III and IV Development

Enhancing the production of aquatic animals is crucial for fishery management and aquaculture applications. Ovaries are specialized tissues that play critical roles in producing oocytes and hormones. Significant biochemical changes take place during the sexual maturation of Portunus trituberculatus, but the genetics of this process has not been extensively studied. Transcriptome sequencing can be used to determine gene expression changes within specific periods. In the current study, we used transcriptome sequencing to produce a comprehensive transcript dataset for the ovarian development of P. trituberculatus. Approximately 100 million sequencing reads were generated, and 126,075 transcripts were assembled. Functional annotation of the obtained transcripts revealed important pathways in ovarian development, such as those involving the vitellogenin gene. Also, we performed deep sequencing of ovaries in phases III and IV of sexual maturation in P. trituberculatus. Differential analysis of gene expression identified 506 significantly differentially expressed genes, which belong to 20 pathway, transporters, development, transcription factors, metabolism of other amino acids, carbohydrate and lipid, solute carrier family members, and enzymes. Taken together, our study provides the first comprehensive transcriptomic resource for P. trituberculatus ovaries, which will strengthen understanding of the molecular mechanisms underlying the sexual maturation process and advance molecular nutritional studies of P. trituberculatus.

Transcriptomic variation of hepatopancreas reveals the energy metabolism and biological processes associated with molting in Chinese mitten crab, Eriocheir sinensis

Molting is a critical developmental process for crustaceans, yet the underlying molecular mechanism is unknown. In this study, we used RNA-Seq to investigate transcriptomic profiles of the hepatopancreas and identified differentially expressed genes at four molting stages of Chinese mitten crab (Eriocheir sinensis). A total of 97,398 transcripts were assembled, with 31,900 transcripts annotated. Transcriptomic comparison revealed 1,189 genes differentially expressed amongst different molting stages. We observed a pattern associated with energy metabolism and physiological responses during a molting cycle. In specific, differentially expressed genes enriched in postmolt were linked to energy consumption whereas genes enriched in intermolt were related to carbohydrates, lipids metabolic and biosynthetic processes. In premolt, a preparation stage for upcoming molting and energy consumption, highly expressed genes were enriched in response to steroid hormone stimulus and immune system development. The expression profiles of twelve functional genes detected via RNA-Seq were corroborated through real-time RT-PCR assay. Together, our results, including assembled transcriptomes, annotated functional elements and enriched differentially expressed genes amongst different molting stages, provide novel insights into the functions of the hepatopancreas in energy metabolism and biological processes pertaining to molting in crustaceans.

Molecular characterization and expression profile of three Fem-1 genes in Eriocheir sinensis provide a new insight into crab sex-determining mechanism

The FEM-1 protein of Caenorhabditis elegans plays a crucial role in the nematode sex-determination pathway. Here, we reported the characterization of three members of Fem-1 gene family in Eriocheir sinensis (designated EsFem-1a, EsFem-1b, and EsFem-1c), which were homologs of the nematode FEM-1 protein. The amino acid sequences of EsFem-1a, EsFem-1b, and EsFem-1c contained eight, nine, and eight ankyrin repeats, respectively. None of the ankyrin repeats had its own specific signature, and the evolution of ankyrin repeat was not completely independent. The predicted three-dimensional structure of EsFem-1 proteins exhibited highly similar superhelical conformation, especially the N-terminal six contiguous ankyrin repeats, which provided a binding surface for the protein-protein interaction. Phylogenetic tree based on the amino acid sequences revealed that EsFem-1a, EsFem-1b, and EsFem-1c were divided into three obvious separated clades. EsFem-1 genes were highly expressed in fertilized egg, 2-4 cell and blastula stage comparing with larval stage (P<0.01), which suggested they might be maternal genes. They also showed a certain degree of sexually dimorphic expression in some tissues. Notably, the highest expression of EsFem-1a was in the hepatopancreas, with EsFem-1b in testes and EsFem-1c in muscle (P<0.05), which indicated their potential role in a broad array of tissues. In addition, the genes initially involved in sex differentiation were not limited to those specifically expressed in the developing gonad. Taken together, these results suggested that EsFem-1 might function in crab early sex determination and late gonad development. The identification of Fem-1 gene family in E. sinensis provides a new insight into crab sex-determination mechanism.

De novo assembly of a transcriptome from juvenile blue crabs (Callinectes sapidus) following exposure to surrogate Macondo crude oil

Background

The blue crab, Callinectes sapidus, is economically and ecologically important in western Atlantic and Gulf of Mexico coastal estuaries. In 2010 blue crabs in the northern Gulf of Mexico were exposed to crude oil and chemical dispersants from the Deepwater Horizon oil spill. To characterize the blue crab transcriptome and identify genes that could be regulated in response to oil exposure we sequenced transcriptomes from hepatopancreas and gill tissues of juvenile blue crabs after exposing them to a water-accommodated fraction of surrogate Macondo crude oil in the laboratory and compared them to transcriptomes from an unexposed control group.

Results

Illumina sequencing provided 42.5 million paired-end sequencing reads for the control group and 44.9 million paired-end reads for the treatment group. From these, 73,473 transcripts and 52,663 genes were assembled. Comparison of control and treatment transcriptomes revealed about 100 genes from each tissue type that were differentially expressed. However, a much larger number of transcripts, approximately 2000 from each tissue type, were differentially expressed. Several examples of alternatively spliced transcripts were verified by qPCR, some of which showed significantly different expression patterns. The combined transcriptome from all tissues and individuals was annotated to assign putative gene products to both major gene ontology categories as well as specific roles in responses to cold and heat, metabolism of xenobiotic compounds, defence, hypoxia, osmoregulation and ecdysis. Among the annotations for upregulated and alternatively-spliced genes were candidates for the metabolism of oil-derived compounds.

Conclusions

Previously, few genomic resources were available for blue crabs or related brachyuran crabs. The transcriptome sequences reported here represent a major new resource for research on the biology of blue crabs. These sequences can be used for studies of differential gene expression or as a source of genetic markers. Genes identified and annotated in this study include candidates for responses of the blue crab to xenobiotic compounds, which could serve as biomarkers for oil exposure. Changes in gene expression also suggest other physiological changes that may occur as the result of exposure to oil.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1739-2) contains supplementary material, which is available to authorized users.

Marine invertebrate lipases: Comparative and functional genomic analysis

Lipases are key enzymes involved in lipid digestion, storage and mobilization of reserves during fasting or heightened metabolic demand. This is a highly conserved process, essential for survival. The genomes of five marine invertebrate species with distinctive digestive system were screened for the six major lipase families. The two most common families in marine invertebrates, the neutral an acid lipases, are also the main families in mammals and insects. The number of lipases varies two-fold across analyzed genomes. A high degree of orthology with mammalian lipases was observed. Interestingly, 19% of the marine invertebrate lipases have lost motifs required for catalysis. Analysis of the lid and loop regions of the neutral lipases suggests that many marine invertebrates have a functional triacylglycerol hydrolytic activity as well as some acid lipases. A revision of the expression profiles and functional activity on sequences in databases and scientific literature provided information regarding the function of these families of enzymes in marine invertebrates.

Identification of genes associated with reproduction in the Mud Crab (Scylla olivacea) and their differential expression following serotonin stimulation

The central nervous system (CNS) is often intimately involved in reproduction control and is therefore a target organ for transcriptomic investigations to identify reproduction-associated genes. In this study, 454 transcriptome sequencing was performed on pooled brain and ventral nerve cord of the female mud crab (Scylla olivacea) following serotonin injection (5 µg/g BW). A total of 197,468 sequence reads was obtained with an average length of 828 bp. Approximately 38.7% of 2,183 isotigs matched with significant similarity (E value < 1e⁻⁴) to sequences within the Genbank non-redundant (nr) database, with most significant matches being to crustacean and insect sequences. Approximately 32 putative neuropeptide genes were identified from nonmatching blast sequences. In addition, we identified full-length transcripts for crustacean reproductive-related genes, namely farnesoic acid o-methyltransferase (FAMeT), estrogen sulfotransferase (ESULT) and prostaglandin F synthase (PGFS). Following serotonin injection, which would normally initiate reproductive processes, we found up-regulation of FAMeT, ESULT and PGFS expression in the female CNS and ovary. Our data here provides an invaluable new resource for understanding the molecular role of the CNS on reproduction in S. olivacea.

In-depth transcriptome analysis of the red swamp crayfish Procambarus clarkii

The red swamp crayfish Procambarus clarkii is a highly adaptable, tolerant, and fecund freshwater crayfish that inhabits a wide range of aquatic environments. It is an important crustacean model organism that is used in many research fields, including animal behavior, environmental stress and toxicity, and studies of viral infection. Despite its widespread use, knowledge of the crayfish genome is very limited and insufficient for meaningful research. This is the use of next-generation sequencing techniques to analyze the crayfish transcriptome. A total of 324.97 million raw reads of 100 base pairs were generated, and a total of 88,463 transcripts were assembled de novo using Trinity software, producing 55,278 non-redundant transcripts. Comparison of digital gene expression between four different tissues revealed differentially expressed genes, in which more overexpressed genes were found in the hepatopancreas than in other tissues, and more underexpressed genes were found in the testis and the ovary than in other tissues. Gene ontology (GO) and KEGG enrichment analysis of differentially expressed genes revealed that metabolite- and immune-related pathway genes were enriched in the hepatopancreas, and DNA replication-related pathway genes were enriched in the ovary and the testis, which is consistent with the important role of the hepatopancreas in metabolism, immunity, and the stress response, and with that of the ovary and the testis in reproduction. It was also found that 14 vitellogenin transcripts were highly expressed specifically in the hepatopancreas, and 6 transcripts were highly expressed specifically in the ovary, but no vitellogenin transcripts were highly expressed in both the hepatopancreas and the ovary. These results provide new insight into the role of vitellogenin in crustaceans. In addition, 243,764 SNP sites and 43,205 microsatellite sequences were identified in the sequencing data. We believe that our results provide an important genome resource for the crayfish.

The invertebrate midintestinal gland ("hepatopancreas") is an evolutionary forerunner in the integration of immunity and metabolism

The immune system has an impact on the metabolic performance in vertebrates, thus the metabolic effects of immune cells are receiving intense attention today in the biomedical field. However, the evolutionary origin of the immunity-metabolism interaction is still uncertain. In this review, I show that mollusks and crustaceans integrate immune functions to a metabolic organ, the midintestinal gland ("hepatopancreas"). In these animals, the epithelial cells of the midintestinal gland are major sources of immune molecules, such as lectins, hemocyanin, ferritin, antibacterial and antiviral proteins, proteolytic enzymes and nitric oxide. There is crosstalk between midintestinal gland cells and phagocytes, which aids the initiation of the immune response and the clearance of pathogens. The midintestinal gland is thereby an integrated organ of immunity and metabolism. It is likely that immunity was the primary function of the midintestinal gland cells and that their role in the intermediate metabolism has evolved during the course of their further specialization.