The polymorphism of lysozyme gene in Zhikong scallop (Chlamys farreri) and its association with susceptibility/resistance to Listonella anguillarum

Characterization of TRAF genes and their responses to Vibrio anguillarum challenge in Argopecten scallops

The tumor necrosis factor receptor-related factor (TRAF) family has been reported to be involved in many immune pathways, such as TNFR, TLR, NLR, and RLR in animals. However, little is known about the roles of TRAF genes in the innate immune of Argopecten scallops. In this study, we first identified five TRAF genes, including TRAF₂, TRAF₃, TRAF₄, TRAF₆ and TRAF₇, but not TRAF₁ and TRAF₅, from both the bay scallop A. irradians (Air) and the Peruvian scallop A. purpuratus (Apu). The phylogenetic analysis showed that the TRAF genes in Argopecten scallops (AiTRAF) belong to the branch of molluscan TRAF family, which lacks TRAF₁ and TRAF₅. Since TRAF₆ is a key bridge factor in the tumor necrosis factor superfamily and plays an important role in innate and adaptive immunity, we cloned the ORFs of the TRAF₆ gene in both A. irradians and A. purpuratus, as well as in two reciprocal hybrids (Aip for the hybrid Air × Apu and Api for the hybrid Apu × Air). Differences in conformational and post-translational modification resulted from the variation in amino acid sequences may cause differences in activity among them. Analysis of conserved motifs and protein structural domains revealed that AiTRAF contains typical structural domains similar to those of other mollusks and has the same conserved motifs. Tissue expression of TRAF in Argopecten scallops challenged by Vibrio anguillarum was examined by qRT-PCR. The results showed that AiTRAF were higher in gill and hepatopancreas. When challenged by Vibrio anguillarum, the expression of AiTRAF was significantly increased compared with the control group, indicating that AiTRAF may play an important role in the immunity of scallops. In addition, the expression of TRAF was higher in Api and Aip than in Air when challenged by Vibrio anguillarum, suggesting that TRAF may have contributed to the high resistance of Api and Aip to Vibrio anguillarum. The results of this study may provide new insights into the evolution and function of TRAF genes in bivalves and ultimately benefit scallop breeding.

Immune diversity in lophotrochozoans, with a focus on recognition and effector systems

Lophotrochozoa is one of the most species-rich but immunologically poorly explored phyla. Although lack of acquired response in a narrow sense, lophotrochozoans possess various genetic mechanisms that enhance the diversity and specificity of innate immune system. Here, we review the recent advances of comparative immunology studies in lophotrochozoans with focus on immune recognition and effector systems. Haemocytes and coelomocytes are general important yet understudied player. Comparative genomics studies suggest expansion and functional divergence of lophotrochozoan immune reorganization systems is not as "homogeneous and simple" as we thought including the large-scale expansion and molecular divergence of pattern recognition receptors (PRRs) (TLRs, RLRs, lectins, etc.) and signaling adapters (MyD88s etc.), significant domain recombination of immune receptors (RLR, NLRs, lectins, etc.), extensive somatic recombination of fibrinogenrelated proteins (FREPs) in snails. Furthermore, there are repeatedly identified molecular mechanisms that generate immune effector diversity, including high polymorphism of antimicrobial peptides and proteins (AMPs), reactive oxygen and nitrogen species (RONS) and cytokines. Finally, we argue that the next generation omics tools and the recently emerged genome editing technicism will revolutionize our understanding of innate immune system in a comparative immunology perspective.

A functional polymorphism in the promoter of RhoB is associated with susceptibility to Vibrio anguillarum in turbot (Scophthalmus maximus)

As an isoform of Rho family GTPases, RhoB plays a pivotal role in cytoskeletal organization, cell proliferation, apoptosis and immune response. However, the regulatory mechanisms of RhoB expression in aquatic animals are still unknown. In the present study, we first construct Vibrio anguillarum infection model in S. maximus, including susceptible and resistant individuals. Then the temporal expression of RhoB was detected after V. anguillarum challenge using qRT-PCR and found that RhoB transcripts were significantly induced in the liver, gill and blood despite of differential expression levels and responsive time points. In addition, the mRNA levels of RhoB in resistant individuals were significantly higher than in susceptible ones. The length of 2083 bp sequences of RhoB promoter was cloned and characterized. Moreover, DNA methylation of the RhoB promoter was measured by bisulfite sequencing (BSP) and hypo-methylated was detected in the CpG islands. Three SNPs (-1590, -1575 and -1449) and two haplotypes in the promoter region of RhoB were identified to be associated with V. anguillarum resistance in turbot by association analysis in group 17-R and 17-S. Deletion analysis indicated that these SNPs could negatively mediate the activity of RhoB promoter. Site-directed mutagenesis and qRT-PCR of individuals with different genotypes demonstrated that -1575 T/A polymorphism affected promoter activity. Further study showed that this mutation altered the binding site of the transcription factor CREB. Co-transfection of SmCREB and RhoB promoter was performed in HEK293T cells which confirmed the -1575 allelic differences on transcriptional activity, with the susceptibility allele showing reduced activity. Taken together, our findings implicate that losing of binding of CREB to SmRhoB promoter due to -1575T/A polymorphisms enhances SmRhoB expression in resistant turbot, which provide insights into the effect of SmRhoB expression in response to V. anguillarum infection.

The polymorphism of chicken-type lysozyme gene in Japanese flounder (Paralichthys olivaceus) and its association with resistance/susceptibility to Listonella anguillarum

Lysozyme is a crucially spread hydrolase in organisms that can defend against bacterial infection in innate immunity. In this study, we successfully sequenced the coding region of chicken-type lysozyme gene (PoLysC) in Paralichthys olivaceus and identified nine single nucleotide polymorphisms (SNPs). We then amplified the 2500 bp promoter region of lysozyme and identified the eight sites of polymorphisms. All SNPs were genotyped between susceptible and resistance groups after Listonella anguillarum challenge. One of these SNP sites in the codon of PoLysC was genotyped and determined to be a significant marker by analyzing its distribution in the susceptible and resistant groups. As a nonsynonymous mutation, the frequency of 140G/C genotype in the resistant group was higher (67.74%) than that in the susceptible group (32.26%). The linkage between SNP140 and polymorphisms in the promoter region was also studied. Results revealed that the frequency of haplotype CC_-536/CC_-1200/GG₁₄₀ in the resistance group was significantly higher than that in the susceptible group. The quantitative expression of lysozyme gene in the resistant group was also higher than that in the susceptible group. This finding indicated that the linkage between polymorphism -536 and -1200 sites in promoter and SNP140 in codon sequence was associated with the resistance of P. olivaceus to L. anguillarum. All these results suggest that the mutations in promoter and coding region were related to changes in PoLysC for resisting L. anguillarum. The haplotype CC_-536/CC_-1200/GG₁₄₀ was a potential marker and can thus be applied to selective breeding for the disease resistance of P. olivaceus.

Infectious diseases of marine molluscs and host responses as revealed by genomic tools

More and more infectious diseases affect marine molluscs. Some diseases have impacted commercial species including MSX and Dermo of the eastern oyster, QPX of hard clams, withering syndrome of abalone and ostreid herpesvirus 1 (OsHV-1) infections of many molluscs. Although the exact transmission mechanisms are not well understood, human activities and associated environmental changes often correlate with increased disease prevalence. For instance, hatcheries and large-scale aquaculture create high host densities, which, along with increasing ocean temperature, might have contributed to OsHV-1 epizootics in scallops and oysters. A key to understanding linkages between the environment and disease is to understand how the environment affects the host immune system. Although we might be tempted to downplay the role of immunity in invertebrates, recent advances in genomics have provided insights into host and parasite genomes and revealed surprisingly sophisticated innate immune systems in molluscs. All major innate immune pathways are found in molluscs with many immune receptors, regulators and effectors expanded. The expanded gene families provide great diversity and complexity in innate immune response, which may be key to mollusc's defence against diverse pathogens in the absence of adaptive immunity. Further advances in host and parasite genomics should improve our understanding of genetic variation in parasite virulence and host disease resistance.

Polymorphism in a serine protease inhibitor gene and its association with the resistance of bay scallop (Argopecten irradians) to Listonella anguillarum challenge

Serine protease inhibitors (SPIs) play a crucial role in regulation of both host and bacterial serine protease. They are classified into several protein families, where Kazal-type inhibitors are one of families with multi-domain. In the present study, the polymorphism of AiSPI from Bay scallop Argopecten irradians was found to be associated with disease resistance of bay scallop against Listonella anguillarum. Nine single nucleotide polymorphisms (SNPs) were identified in the exon region of AiSPI, where five SNPs were non-synonymous mutation. Three of these mutations were located in "kazal-like 3"domain, two SNP loci positioned at +536, +1312 were selected for further association studies. For the locus +536, the genotype frequency of A/G in the resistant stock (12.8%) was significantly lower (p < 0.05) than that in the susceptible stock (35.1%), while, the genotype A/A in the resistant stock (87.2%) was significantly higher in comparison with susceptible stock (64.9%) (p < 0.05). The G allele frequencies were 6.4% and 17.6% in resistant stock and susceptible stock, respectively, and χ²-test revealed a significant difference in the frequency distribution between the two stocks (p < 0.05). But there was no significant association between the mutation C-T at locus +1312 with either resistant or susceptible group (p > 0.05). The genotype frequencies of T/T, T/C, C/C at locus +1312 were 94.6%, 2.7% and 2.7% respectively in the susceptible stock, while 100%, 0% and 0% respectively in the resistant stock. The amino acid change for the mutation at locus +536 A-G was from asparagine to serine, and the predicted homology model of this amino acid variation could affect its function as well as the structural integrity of the domain. In vitro elastase inhibition assay of the protein variants at locus +536 was conducted to explicate the effect of SNP. The increasing concentration of protein (0 mmol/L- 2.93 mmol/L) was incubated with 80 nmol/L elastase where the residual enzyme activity values for rAiSPI (N) with A variant and rAiSPI (S) with G variant were started to reduce from 0.40 to 0.215 and 0.435 to 0.356, respectively. The elastase inhibition ability of rAiSPI (N) variant was significantly higher than that of rAiSPI (S) (p < 0.01). The results suggested that the mutation at locus +536A/A significantly associated with disease resistance of bay scallop would shed light for selective breeding program.

The polymorphisms of a MIF gene and their association with Vibrio resistance in the clam Meretrix meretrix

Macrophage migration inhibitory factor (MIF) is an important proinflammatory cytokine that mediates both innate and adaptive immune responses. In this study, a homolog of MIF was identified in the clam Meretrix meretrix. Ten SNPs in the DNA partial sequence of MmMIF were found to be significantly associated with Vibrio resistance (P < 0.05). Distinct expression patterns of MmMIF among different haplotypes were observed after Vibrio challenge. The results showed that haplotypes did not affect MmMIF expression in the negative control group, while the expression of MmMIF in clams with Hap1 and Hap1/Hap2 was significantly lower than that with Hap2 at 24 h in the PBS-injected group but significantly higher than that with Hap2 in the Vibrio-injected group. The results also indicate that Hap1 and Hap1/Hap2 can specifically respond to mechanical stimulation while Hap2 can specifically respond to Vibrio infection. The effect of a missense mutation was detected by site-directed mutagenesis using fusion expression of the protein, which showed that the SNP g.737 (I > V) has no effect on redox activity and tautomerase activity. These studies identified a potential marker that is enriched in Vibrio-resistant clams that can be used for the genetic breeding of Meretrix meretrix.

The immune system and its modulation mechanism in scallop

Scallops are a cosmopolitan family of bivalves, and some of them are highly prized as dominant aquaculture species. In the past decades, there have been increasing studies on the basic biology and immunology of scallops, and this review summarizes the research progresses of immune system and its modulation mechanism in scallop. As invertebrate, scallops lack adaptive immunity and they have evolved an array of sophisticated strategies to recognize and eliminate various invaders by employing a set of molecules and cells. It is evident that basic immune reactions such as immune recognition, signal transduction, and effector synthesis involved in immune response are accomplished in a variety of ways. They rely upon an extensive repertoire of phagocytosis, apoptosis and encapsulation of the circulating hemocytes for eliminating invasive pathogens, as well as the production of immune effectors that are active against a large range of pathogens or sensitive for the environmental stress. Furthermore, the molecular constitutions, metabolic pathways and immunomodulation mechanisms of the primitive catecholaminergic, cholinergic, enkephalinergic system and NO system in scallop are also discussed, which can be taken as an entrance to better understand the origin and evolution of the neuroendocrine-immune regulatory network in lower invertebrates.

Development of Vibrio spp. infection resistance related SNP markers using multiplex SNaPshot genotyping method in the clam Meretrix meretrix

The clam Meretrix meretrix is a commercially important mollusc species in the coastal areas of South and Southeast Asia. In the present study, large-scale SNPs were genotyped by the Multiplex SNaPshot genotyping method among the stocks of M. meretrix with different Vibrio spp. infection resistance profile. Firstly, the AUTOSNP software was applied to mine SNPs from M. meretrix transcriptome, and 323 SNP loci (including 120 indels) located on 64 contigs were selected based on Uniprot-GO associations. Then, 38 polymorphic SNP loci located on 15 contigs were genotyped successfully in the clam stocks with different resistance to Vibrio parahaemolyticus infection (11-R and 11-S groups). Pearson's Chi-square test was applied to compare the allele and genotype frequency distributions of the SNPs between the different stocks, and seven SNP markers located on three contigs were found to be associated with V. parahaemolyticus infection resistance trait. Haplotype-association analysis showed that six haplotypes had significantly different frequency distributions in 11-S and 11-R (P < 0.05). With selective genotyping between 09-R and 09-C populations, which had different resistance to Vibrio harveyi infection, four out of the seven selected SNPs had significantly different distributions (P < 0.05) and therefore they were considered to be associated with Vibrio spp. infection resistance. Sequence alignments and annotations indicated that the contigs containing the associated SNPs had high similarity to the immune related genes. All these results would be useful for the future marker-assisted selection of M. meretrix strains with high Vibrio spp. infection resistance.

The polymorphisms in the promoter of HSP90 gene and their association with heat tolerance of bay scallop

The heat shock protein 90 (HSP90) is a highly abundant and ubiquitous molecular chaperone which plays essential roles in many cellular processes. In the present study, the messenger RNA (mRNA) expressions of HSP90 after acute heat stress were investigated in two bay scallop populations (Argopecten irradians irradians and Argopecten irradians concentricus). The heat-resistant scallop A. i. concentricus, which is distributed in Zhanjiang, China, exhibited significantly higher induction of HSP90 compared with that of the heat-sensitive scallop A. i. irradians, which is distributed in Qinhuangdao, China. The promoter sequence of HSP90 gene from bay scallop (AiHSP90) was cloned, and the polymorphisms within this region were investigated by sequencing to analyze their association with heat tolerance. A total of six single nucleotide polymorphisms (SNPs), including -1167 T-C, -1023 A-C, -799 C-T, -774 A-G, -686 C-T, and -682 A-C, were identified in the amplified promoter region, and most of them affected the putative transcription factor binding sites except for locus -1167. All the six SNP sites were found to be associated with heat tolerance after Hardy-Weinberg equilibrium (HWE) and association analysis. Moreover, haplotypes CACACC and TCTATC were also found to be associated with heat tolerance based on the result of linkage disequilibrium and association analysis. The results provided insights into the molecular mechanisms underlying the thermal adaptation of different congener endemic bay scallops, which suggested that the increased heat tolerance of A. i. concentricus (compared with A. i. irradians) was associated with the higher expression of AiHSP90. Meanwhile, the six genotypes (-1167 TT, -1023 CC, -799 TT, -774 GG, -686 CC, and -682 AA) and two haplotypes (CACACC and TCTATC) could be used as potential markers for scallop selection breeding with higher heat tolerance.

The polymorphism in the promoter of HSP70 gene is associated with heat tolerance of two congener endemic bay scallops (Argopecten irradians irradians and A. i. concentricus)

Background

The heat shock protein 70 (HSP70) is one kind of molecular chaperones, which plays a key role in protein metabolism under normal and stress conditions.

Methodology

In the present study, the mRNA expressions of HSP70 under normal physiological condition and after acute heat stress were investigated in gills of two bay scallop populations (Argopecten irradians irradians and A. i. concentricus). The heat resistant scallops A. i. concentricus showed significantly lower basal level and higher induction of HSP70 compared with that of the heat sensitive scallops A. i. irradians. The promoter sequence of HSP70 gene from bay scallop (AiHSP70) was cloned and the polymorphisms within this region were investigated to analyze their association with heat tolerance. Totally 11 single nucleotide polymorphisms (SNPs) were identified, and four of them (−967, −480, −408 and −83) were associated with heat tolerance after HWE analysis and association analysis. Based on the result of linkage disequilibrium analysis, the in vitro transcriptional activities of AiHSP70 promoters with different genotype were further determined, and the results showed that promoter from A. i. concentricus exhibited higher transcriptional activity than that from A. i. irradians (P<0.05).

Conclusions

The results provided insights into the molecular mechanisms underlying the thermal adaptation of different congener endemic bay scallops, which suggested that the increased heat tolerance of A. i. concentricus (compared with A. i. irradians) was associated with the higher expression of AiHSP70. Meanwhile, the −967 GG, −480 AA, −408 TT and −83 AG genotypes could be potential markers for scallop selection breeding with higher heat tolerance.

Acetylcholine modulates the immune response in Zhikong scallop Chlamys farreri

Acetylcholine (ACh) is an indispensable neurotransmitter and neuromodulator in the cholinergic nervous system and it is implicated in the dynamic modulation of immune response in vertebrates. Although ACh has also been identified in most invertebrates, the knowledge about its immunomodulation is still limited. In the present study, the immunoreactivities of ACh and acetylcholinesterase (AChE) were observed in all the tested tissues of scallop Chlamys farreri, including adductor muscle, mantle, gill, hepatopancreas, kidney and gonad. The ACh concentration in the supernate of scallop hemolymph increased from 11.59 ± 0.27 to 14.36 ± 0.17 μM L(-1) at 6 h after LPS (0.5 mg ml(-1)) stimulation, and increased to 15.51 ± 1.20 μM L(-1) at 3 h after the stimulation of tumor necrosis factor alpha (TNF-α) (50 ng ml(-1)). After LPS stimulation, the mRNA expression levels of superoxide dismutase (CfSOD), catalase (CfCAT) and lysozyme (CfLYZ) in hemocytes increased significantly at 3 h (P < 0.05), 6 h (P < 0.05) and 12 h (P < 0.05), respectively. Compared with the LPS treatment, the induction of CfSOD, CfCAT and CfLYZ expression in hemocytes was repressed effectively (P < 0.05) by the co-stimulation of LPS and ACh (5 × 10(-7) M) at 3 h (P < 0.05), 6 h (P < 0.05) and 12 h (P < 0.05), respectively. Furthermore, the expression level of CfCAT in hemocytes increased significantly after 12 h by the co-stimulation with LPS and ACh (P < 0.05). These results indicated collectively that the scallop cholinergic nervous system could be activated by immune stimulations, and it might play an essential role in immunomodulation of scallops.

Analysis of two lysozyme genes and antimicrobial functions of their recombinant proteins in Asian seabass

Lysozymes are important proteins of the innate immune system for the defense against bacterial infection. We cloned and analyzed chicken-type (c-type) and goose-type (g-type) lysozymes from Asian seabass (Lates calcarifer). The deduced amino acid sequence of the c-type lysozyme contained 144 residues and possessed typical structure residues, conserved catalytic residues (Glu⁵⁰ and Asp⁶⁷) and a “GSTDYGIFQINS” motif. The deduced g-type lysozyme contained 187 residues and possessed a goose egg white lysozyme (GEWL) domain containing three conserved catalytic residues (Glu⁷¹, Asp⁸⁴, Asp⁹⁵) essential for catalytic activity. Real time quantitative PCR (qRT-PCR) revealed that the two lysozyme genes were constitutively expressed in all the examined tissues. The c-type lysozyme was most abundant in liver, while the g-type lysozyme was predominantly expressed in intestine and weakly expressed in muscle. The c-type and g-type transcripts were up-regulated in the kidney, spleen and liver in response to a challenge with Vibrio harveyi. The up-regulation of the c-type lysozyme was much stronger than that of the g-type lysozyme in kidney and spleen. The recombinant proteins of the c-type and g-type lysozymes showed lytic activities against the bacterial pathogens Vibrio harveyi and Photobacterium damselae in a dosage-dependent manner. We identified single nucleotide polymorphisms (SNPs) in the two lysozyme genes. There were significant associations of these polymorphisms with resistance to the big belly disease. These results suggest that the c- and g-type genes play an important role in resistance to bacterial pathogens in fish. The SNP markers in the two genes associated with the resistance to bacterial pathogens may facilitate the selection of Asian seabass resistant to bacterial diseases.

Three vibrio-resistance related EST-SSR markers revealed by selective genotyping in the clam Meretrix meretrix

The clam Meretrix meretrix is an important commercial bivalve distributed in the coastal areas of South and Southeast Asia. In this study, marker-trait association analyses were performed based on the stock materials of M. meretrix with different vibrio-resistance profile obtained by selective breeding. Forty-eight EST-SSR markers were screened and 27 polymorphic SSRs of them were genotyped in the clam stocks with different resistance to Vibrio parahaemolyticus (11-R and 11-S) and to Vibrio harveyi (09-R and 09-C). Allele frequency distributions of the SSRs among different stocks were compared using Pearson's Chi-square test, and three functional EST-SSR markers (MM959, MM4765 and MM8364) were found to be associated with vibrio-resistance trait. The 140-bp allele of MM959 and 128-bp allele of MM4765 had significantly higher frequencies in resistant groups (11-R and 09-R) than in susceptive/control groups (11-S and 09-C) (P < 0.01), which suggested that the clams carrying these two alleles have stronger resistance against vibrio. Clam individuals of 11-S were divided into three subgroups based on the survival time post-challenge, and the multi-dimensional scaling (MDS) analysis showed that clusters generated by genetic similarity revealed by the three SSR markers were consistent with the three subgroups distinctions. The putative functions of contig959, contig4765 and contig8364 also suggested that the three SSR-involved genes might play important roles in immunity of M. meretrix. All these results supported that EST-SSR markers MM959, MM4765 and MM8364 were associated with vibrio-resistance and would be useful for marker-assisted selection (MAS) in M. meretrix genetic breeding.

The association of SNPs in Hsp90β gene 5' flanking region with thermo tolerance traits and tissue mRNA expression in two chicken breeds

Thermo stress induces heat shock proteins (HSPs) expression and HSP90 family is one of them that has been reported to involve in cellular protection against heat stress. But whether there is any association of genetic variation in the Hsp90β gene in chicken with thermo tolerance is still unknown. Direct sequencing was used to detect possible SNPs in Hsp90β gene 5' flanking region in 3 chicken breeds (n = 663). Six mutations, among which 2 SNPs were chosen and genotypes were analyzed with PCR-RFLP method, were found in Hsp90β gene in these 3 chicken breeds. Association analysis indicated that SNP of C.-141G>A in the 5' flanking region of the Hsp90β gene in chicken had some effect on thermo tolerance traits, which may be a potential molecular marker of thermo tolerance, and the genotype GG was the thermo tolerance genotype. Hsp90β gene mRNA expression in different tissues detected by quantitative real-time PCR assay were demonstrated to be tissue dependent, implying that different tissues have distinct sensibilities to thermo stress. Besides, it was shown time specific and varieties differences. The expression of Hsp90β mRNA in Lingshan chickens in some tissues including heart, liver, brain and spleen were significantly higher or lower than that of White Recessive Rock (WRR). In this study, we presume that these mutations could be used in marker assisted selection for anti-heat stress chickens in our breeding program, and WRR were vulnerable to tropical thermo stress whereas Lingshan chickens were well adapted.

Polymorphisms of anti-lipopolysaccharide factors in the swimming crab Portunus trituberculatus and their association with resistance/susceptibility to Vibrio alginolyticus

Anti-lipopolysaccharide factor (ALF) is an important antimicrobial peptide (AMP) that can bind and neutralize major component of Gram-negative bacteria cell wall, lipopolysaccharide (LPS). Seven isoforms of anti-lipopolysaccharide factors (PtALF1-7) were previously identified from the swimming crab Portunus trituberculatus in our laboratory. Here, polymorphisms of PtALF1-7 were detected and their association with resistance/susceptibility to Vibrio alginolyticus (a main Gram-negative bacteria causing high mortality in P. trituberculatus) were investigated. We identified 127, 96, 103, 53 and 158 single nucleotide polymorphisms (SNPs) in genomic fragments of PtALF1-3, PtALF4, PtALF5, PtALF6 and PtALF7, respectively. Among them, totally sixteen SNPs were significantly associated with resistance/susceptibility to V. alginolyticus (P < 0.05). Of these sixteen SNPs, most were located in introns and noncoding exons, while two synonymous SNPs and one nonsynonymous SNP were in coding exons. Additionally, simple sequence repeats (SSRs) were only identified in introns and noncoding exons of PtALF4, PtALF5 and PtALF7. Although no significant difference of allele frequencies was found, these SSRs had different polymorphic alleles according to the repeat number between susceptible and resistant stocks. After further confirmation, polymorphisms investigated here might be applied as potential molecular markers for future selection of resistant strains to diseases caused by Gram-negative bacteria.

Significant association between SNPs in the superoxide dismutase 3, extracellular (SOD3) gene and resistance to Aeromonas hydrophila in the freshwater mussel Hyriopsis cumingii

Extracellular superoxide dismutase (SOD3) is a major antioxidant enzyme that protects organs from damage by reactive oxygen species (ROS). In this study, the SOD3 gene was identified and characterized from the freshwater mussel Hyriopsis cumingii (Hc-SOD3). The cDNA sequence consists of 763 bp, encoding a protein of 208 amino acids. The amino acid sequence possesses two CuZnSOD signature sequences, and amino acids required for binding of Cu (His-93, -95, -110 and -169) and Zn (His-110, -118, -129 and Asp-132) were conserved in Hc-SOD3. The Hc-SOD3 genomic sequence was 9165 bp in length, containing four exons and three introns. Eighteen single nucleotide polymorphisms were detected in the Hc-SOD3 gene from resistant stock (RS) and susceptible stock (SS) of H. cumingii to Aeromonas hydrophila. The genotype and allele distribution were examined in resistant and susceptible stocks. Among them, a C/G substitution at the g.7994C>G locus and G/C substitution at the g.8087G>C locus were significantly associated with resistance/susceptibility of H. cumingii to A. hydrophila, both in genotype (P = 0.017, P = 0.004 respectively) and allele frequency (P = 0.021, P = 0.006 respectively). Linkage disequilibrium analysis revealed that g.7994C>G, g.8001A>G, g.8035G>A, g.8087G>C and g.8191T>A were in linkage disequilibrium. The results suggest that the two polymorphic loci, g.7994C>G and g.8087G>C, could be potential genetic markers for future molecular selection of strains that are resistant to diseases.

Genomic sequence comparison, promoter activity, SNP detection of RIG-I gene and association with resistance/susceptibility to grass carp reovirus in grass carp (Ctenopharyngodon idella)

As an intracellular pattern recognition receptor (PRR), retinoic acid-inducible gene-I (RIG-I) is responsible for detection of nucleic acids from pathogens in infected cells and activation of type I interferon (IFN). In the present study, the 5'-flanking region, introns and single nucleotide polymorphisms (SNPs) of CiRIG-I (Ctenopharyngodon idella RIG-I) were identified and characterized. The genomic CiRIG-I was 12810 bp in length, consisted of an 1864 bp 5'-flank region whose promoter activity was confirmed, 15 exons and 14 introns. By pooled DNA sequencing, two SNPs were detected in the 5'-flanking region; 10 SNPs were discovered in introns; and one SNP was found in exons. After a challenge experiment, these SNPs were selected to analyze their association with the resistance/susceptibility of C. idella to grass carp reovirus (GCRV), using case-control study. Chi-square test was employed to assess the association. The result showed that -780 C/T, 4731 C/T, 4945 A/G, 8461 C/T, and haplotype 3428A-3432G were significantly associated with the phenotype (P<0.05). To confirm the correlation, another independent challenge experiment was performed, in which the cumulative mortality of -780 genotype CC, 4731 genotype CC and 4945 genotype AA were significantly lower than that of -780 genotype TT, 4731 genotype TT and 4945 genotype GG, respectively (P<0.05). In addition, the SNP-SNP interaction analysis revealed that there was no significant interaction among those SNPs (P>0.05). These significant SNPs and the haplotype might be potential genetic markers for the molecular selection of C. idella strains that are resistant to GCRV.

Molecular cloning, genomic structure and antimicrobial activity of PtALF7, a unique isoform of anti-lipopolysaccharide factor from the swimming crab Portunus trituberculatus

Anti-lipopolysaccharide factors (ALFs), as the potent antimicrobial peptides, are becoming predominant candidates for potential therapeutic agents of bacterial and viral diseases. In this study, a unique isoform of ALF (PtALF7) was identified from hemocytes cDNA library of the swimming crab Portunus trituberculatus. The PtALF7 cDNA contained an open reading frame (ORF) of 372 bp encoding 123 amino acids. The deduced peptide of PtALF7 shared high similarity with our previously reported PtALF1-3 but low with PtALF4-6. The PtALF7 gene consisted of three exons interrupted by two introns, and was clearly transcribed from different genomic loci compared with other PtALF isoforms. Totally 128 SNPs including 12 in coding region and 116 in noncoding region were detected in PtALF7 gene by direct sequencing of 20 samples. The mRNA expression of PtALF7 transcript was primarily observed in hemocytes followed by gill and eyestalk, but barely detectable in hepatopancreas. After challenge with Vibrio alginolyticus, a main pathogen causing high mortality in P. trituberculatus, the PtALF7 transcript in hemocytes showed a clear time-dependent response expression pattern with obvious decrease at 6 h and significant increase at 24 h. The recombinant PtALF7 protein exhibited antimicrobial activity against the test Gram-negative and Gram-positive bacteria, but did not inhibit the growth of fungus Pichia pastoris. These results together indicate a potential involvement for PtALF7 in the innate immune response of P. trituberculatus.

Association between the polymorphism of CfPGRP-S1 gene and disease susceptibility/resistance of zhikong scallop (Chlamys farreri) to Listonella anguillarum challenge

Peptidoglycan recognition protein (PGRP) is a pattern recognition receptor, playing important roles in the innate immune response against invasive pathogens. The single nucleotide polymorphism (SNP) loci in scallop PGRP gene (CfPGRP) were screened from Chlamys farreri to investigate their association with disease resistance of scallop against Listonella anguillarum. Thirteen SNP sites were identified in PGRP domain of CfPGRP, and two of them at positions 4407 and 4408 which are located in the same codon resulted in a nonsynonymous substitution. The genotype frequency of CG/CG in the resistant stock was significantly lower than that in susceptible stock (0% vs 32.4%), while that of CG/TA in the resistant stock was significantly higher than that in susceptible stock (P < 0.01). The pathogen-associated molecular patterns (PAMP) binding activity of two recombinant proteins, rCfPGRP-S1 (R) with CG variant in 4407-4408 site, rCfPGRP-S1 (Y) with TA variant in 4407-4408 site, were elucidated by examining their P/N value at 405 nm with ELISA assay. The in vitro binding activities of the two rCfPGRP-S1 variants to both lipopolysaccharide (LPS) and peptidoglycan (PGN) varied (P < 0.05) in a dose-dependent manner, and rCfPRPP-S1(Y) exhibited significantly higher affinity to PGN and LPS than that of rCfPGRP-S1(R) (P < 0.05). The growth inhibition assay was conducted to find the antibacterial activities of the two variants. Both rCfPGRP-S1(R) and rCfPGRP-S1 (Y) displayed obvious activity to suppress the growth of Escherichia coli, but there was no significant difference in suppression activity of two variants (P > 0.05). The results suggested that the polymorphism at locus 4407-4408 of CfPGRP-S1 considerably affected its PAMP binding activity, and the SNP locus 4407-4408 CG/TA was associated with disease resistance of scallop against L. anguillarum infection, which could be used as a candidate marker for future selection in zhikong scallop breeding program.

Single nucleotide polymorphisms in i-type lysozyme gene and their correlation with vibrio-resistance and growth of clam Meretrix meretrix based on the selected resistance stocks

I-type lysozyme is considered to play crucial roles in both anti-bacteria and digestion function of the bivalve, which signifies that it is related to both immunity and growth. In this study, based on the principle of case-control association analysis, using the stock materials with different vibrio-resistance profile obtained by selective breeding, single nucleotide polymorphisms (SNPs) in the DNA partial sequence of an i-type lysozyme of Meretrix meretrix (MmeLys) were discovered and examined for their association with vibrio-resistance and growth. Twenty-seven SNPs were detected and fifteen of them were genotyped in clam stocks with different resistance to Vibrio harveyi (09-C and 09-R) and to Vibrio parahaemolyticus (11-S and 11-R). Allele frequency distribution among different stocks was compared. And wet weight of clams with different genotype at each SNP locus was compared. The results indicated that SNP locus 9 was associated with V. harveyi and V. parahaemolyticus resistance and growth of M. meretrix. Loci 12 and 14 were associated with both V. parahaemolyticus-resistance and growth, and also have the potential to be related with V. harveyi-resistance of M. meretrix. Therefore these three SNPs especially locus 9 were the potential markers which may be involved in assisting resistance selective breeding. In addition, this study showed evidence that improvements in clam resistance to vibriosis could be achieved through selective breeding. All results provided encouragement for the continuation of the selective breeding program for vibrio-resistance gain in clam M. meretrix and the application of polymorphisms in MmeLys to the future marker assisted selection.

Association of CfLGBP gene polymorphism with disease susceptibility/resistance of Zhikong scallop (Chlamys farreri) to Listonella anguillarum

Lipopolysaccharide and β-1, 3-glucan binding protein (LGBP) is a pattern recognition receptor (PRR) recognizing and binding both LPS and β-1, 3-glucan, playing important roles in innate immunity. In the present study, the single nucleotide polymorphisms (SNPs) were assessed in LGBP gene from scallop Chlamys farreri (designated CfLGBP), and eight SNPs were found in its potential LPS and glucanase binding motif. The locus +7679 with the transition of G-A, which produced an amino acid substitution at codon 360 from a non polar Glycine to polar Serine, was selected to inspect their association with disease resistance/susceptibility to Listonella anguillarum. Three genotypes G/G, G/A and A/A, were revealed at locus +7679, and their frequencies were 89.7%, 7.7% and 2.6% in the resistant stock, while 63.2%, 34.2% and 2.6% in the susceptible stock, respectively. The frequency of genotypes G/G and G/A were significantly different (P < 0.05) between the two stocks. The pathogen-associated molecular patterns (PAMP) binding activity of two recombinant proteins, rCfLGBP (G) with G variant at locus +7679 and rCfLGBP (S) with A variant at locus +7679, were elucidated by ELISA assay. The binding affinities of both LPS and β-glucan binding affinity were varied in a dose-dependent manner, where the binding affinity of rCfLGBP (G) was significantly higher than that of rCfLGBP (S) (P < 0.05). The results collectively suggested that the polymorphism of +7679 G/G in CfLGBP possibly enhances the binding activity of LPS and β-glucan, and was associated to disease resistance of scallop against L. anguillarum, which could be a potential marker applied in future selection of scallop with enhanced resistance to L. anguillarum.

Identification, mRNA expression and genomic structure of TLR22 and its association with GCRV susceptibility/resistance in grass carp (Ctenopharyngodon idella)

Toll-like receptor 22 (TLR22) plays a crucial role in response to virus infection by recognizing double stranded RNA (dsRNA) in aquatic animals. In the present study, a TLR22 homologue gene was identified and characterized from grass carp (Ctenopharyngodon idella) (CiTLR22). CiTLR22 genomic sequence comprises 4754 base pairs (bp), containing one intron. The cDNA sequence consists of 3831bp, encoding a protein of 954 amino acid residues. CiTLR22 was constitutively expressed in all 15 investigated tissues, highly in gill and lowly in liver and spleen. The expression profile of CiTLR22 in spleen was rapidly and significantly up-regulated at 6h (456.13-fold, P<0.05), then rapidly recovered to normal level at 12h (P>0.05) post-injection of grass carp reovirus (GCRV). The expression levels of CiTLR22 were rapidly elevated post-poly(I:C) stimulation in dose- and time-dependent manners in CIK (C. idella kidney) cell line. After GCRV infection, CiTLR22 transcripts were inhibited at the early stage, then were up-regulated and reached a peak at 24h post-infection, latterly down-regulated in CIK cell culture. In the whole genomic sequence, six single nucleotide polymorphisms (SNPs) were detected. Five of them were sited in the coding region and all synonymous, and another located in the 5' untranslated region (UTR). The following SNP analysis revealed that 2406 C/T was just a mutation. Only 417 G/T was significantly associated with the resistance of grass carp to GCRV both in genotype (P=0.013) and allele (P=0.015). -8 A/T and 2574 C/T, 863 C/T and 1923 G/T, 863 C/T and 2574 C/T were pairwise linkage disequilibrium. None of the haplotype was associated with the resistance of grass carp to GCRV. The results indicate that CiTLR22 plays an important role in the responses to dsRNA and GCRV, and is partially inhibited by GCRV in vitro. The potential molecular marker lays foundation for the selective breeding of the GCRV-resistant grass carp.

The Gln32Lys polymorphism in HSP22 of Zhikong scallop Chlamys farreri is associated with heat tolerance

Background

Heat shock protein 22 is a member of small heat shock proteins with molecular chaperone activity. Though their multiple functions have been well characterized, there is no report about the association between the polymorphisms of HSP22 and heat tolerance.

Methodology

Three single nucleotide polymorphisms were identified in HSP22 from scallop Chlamys farreri (CfHSP22), and the +94 C-A locus was found to be nonsynonymous. Three genotypes at locus +94, A/A, A/C and C/C, were revealed by using Bi-PASA PCR analysis, and their frequencies were 19.5%, 27.6% and 52.9% in the heat resistant stock, while 9.3%, 17.4% and 73.3% in the heat susceptible stock, respectively. The frequency differences of the three genotypes were significant (P<0.05) between the two stocks. After incubating at 30°C for 84 h, the cumulative mortality of scallops with +94 C/C genotype and +94 A/C genotypes was 95% and 90%, respectively, which was significantly higher (P<0.01) than that of scallops with +94 A/A genotype (70%). The molecular chaperone activity of two His-tagged fusion proteins, rCfHSP22Q with +94 C/C genotype and rCfHSP22K with +94 A/A genotype were analyzed by testing the ability of protecting citrate synthase (CS) against thermal inactivation in vitro. After incubated with rCfHSP22Q or rCfHSP22K at 38°C for 1 h, the activity of CS lost 50% and 45%, and then recovered to 89% and 95% of the original activity following 1 h restoration at 22°C, respectively, indicating that the mutation from Gln to Lys at this site might have an impact on molecular chaperone activities of CfHSP22.

Conclusions

These results implied that the polymorphism at locus +94 of CfHSP22 was associated with heat tolerance of scallop, and the +94 A/A genotype could be a potential marker available in future selection of Zhikong scallop with heat tolerance.

A TRAF and TNF receptor-associated protein (TTRAP) in mollusk with endonuclease activity

Tumor necrosis factor (TNF) signaling pathway plays crucial roles in the regulation of various immune responses. In the present study, a TNF signaling pathway related regulatory factor, TRAF and TNF receptor-associated protein (TTRAP), was firstly identified from the mollusk Zhikong scallop Chlamys farreri (designated as CfTTRAP). The full-length cDNA of CfTTRAP was of 2326bp, containing an open reading frame (ORF) of 1008 bp encoding a polypeptide of 335 amino acids with the predicted molecular weight of 38.4 kDa. There was an Exo_endo_phos domain in CfTTRAP, and it was well conserved when compared with other TTRAPs, especially the endonuclease activity related motifs. The recombinant protein of CfTTRAP exhibited prominent endonuclease activity to digest the genome DNA from C. farreri in the presence of Mg(2+), but it could not digest genome DNA of Escherichia coli and Bacillus subtilis, indicating CfTTRAP was a new member of Mg(2+)/Mn(2+)-dependent phosphodiesterase enzymes (MDP) superfamily. The mRNA transcripts of CfTTRAP were detected in all tested tissues of scallop, including muscle, mantle, gonad, gill, kidney and hemocytes. The expression level of CfTTRAP mRNA in hemocytes varied greatly after the stimulation of LPS, PGN or β-glucan. LPS induced significant down-regulation (P<0.05) of CfTTRAP mRNA expression, while PGN or β-glucan up-regulated the expression significantly (P<0.01), indicating that this regulatory factor was involved in modulating immune responses towards different stimulus. The present results provided new evidences for the potential roles of such molecule in C. farreri, and further confirmed the existence of TTRAP modulated TNF signaling pathway in mollusk.

A primitive Toll-like receptor signaling pathway in mollusk Zhikong scallop Chlamys farreri

As a member of pattern-recognition receptors (PRRs), the Toll-like receptor (TLR) and its signaling pathway play pivotal roles in recognizing various pathogen-associated molecular patterns (PAMPs), and buildup the front-line against invading pathogens. In the present study, the sequence features and mRNA expression profiles of five key genes involved in TLR signal pathway were characterized, and their functions in the immune responses were also investigated in order to validate the TLR signaling pathway and its potential roles in the immune defense of Zhikong scallop Chlamys farreri. These five genes, including CfTLR, CfMyD88, CfTRAF6, CfIκB and CfNFκB, exhibited significant similarity with their homologues from other model organisms, and contained the typical motifs. A strong interaction between the TIR domain from CfTLR and CfMyD88 protein was revealed via ELISA assays. The mRNA transcripts of these five genes were all up-regulated after LPS stimulation, indicating that they were involved in the immune response against LPS. When CfTLR expression was inhibited by RNAi technology, the mRNA expression level of CfMyD88, CfTRAF6, CfIκB, CfNFκB and G-type lysozyme were all decreased, while those of superoxide dismutase and catalase were increased. After Listonella anguillara challenge, the apoptosis level of those CfTLR-suppressed scallops was significantly lower than that in control groups (p<0.05) at the beginning of bacteria challenge, while the cumulative mortality was significantly higher than that of control groups (p<0.05). These results collectively favored that a rather canonical MyD88-dependent TLR pathway existed in scallop and this pathway was involved in immune signaling to active the diverse downstream reaction including anti-oxidant, anti-bacteria and apoptosis.

Identification of a bacterial inhibitor against g-type lysozyme

Lysozymes are antibacterial effectors of the innate immune system in animals that hydrolyze peptidoglycan. Bacteria have evolved protective mechanisms that contribute to lysozyme tolerance such as the production of lysozyme inhibitors, but only inhibitors of chicken (c-) and invertebrate (i-) type lysozyme have been identified. We here report the discovery of a novel Escherichia coli inhibitor specific for goose (g-) type lysozymes, which we designate PliG (periplasmic lysozyme inhibitor of g-type lysozyme). Although it does not inhibit c- or i-type lysozymes, PliG shares a structural sequence motif with the previously described PliI and MliC/PliC lysozyme inhibitor families, suggesting a common ancestry and mode of action. Deletion of pliG increased the sensitivity of E. coli to g-type lysozyme. The existence of inhibitors against all major types of animal lysozyme and their contribution to lysozyme tolerance suggest that lysozyme inhibitors may play a role in bacterial interactions with animal hosts.

Three isoforms of anti-lipopolysaccharide factor identified from eyestalk cDNA library of swimming crab Portunus trituberculatus

Anti-lipopolysaccharide factors (ALFs), as the potent antimicrobial peptides, can bind and neutralize lipopolysaccharide (LPS) and exhibit broad spectrum antimicrobial activities. In this study, three isoforms of the ALF homologues (PtesALF1-3) were identified from eyestalk cDNA library of swimming crab Portunus trituberculatus. The full-length cDNA sequences of PtesALF1, 2 and 3 were 1138, 1052 and 1057 bp encoding 92, 108 and 123 amino acids, respectively. PtesALF1-3 contained two conserved cysteine residues and shared high similarity with other reported ALFs. Predicted tertiary structures of PtesALF2 and 3 containing four β-strands and three α-helix were similar to that described in Limulus polyphemus, while PtesALF1 had only one α-helix in its spatial structure. Sequence analysis revealed PtesALF1-3 were encoded by the same genomic locus and generated by alternative splicing of the pre-mRNA. Totally 89 SNPs including 18 in coding region and 71 in noncoding region were detected by direct sequencing of 30 genomic samples. The mRNA expression of PtesALF1 and PtesALF1-3 transcripts was mainly detected in haemocytes but showed different expression pattern in other tissues including hepatopancreas, gill, eyestalk and muscle. After challenge with Vibrio alginolyticus, the temporal expression level of PtesALF1-3 transcripts in haemocytes showed a clear time-dependent response expression pattern with two peaks within the experimental period of 32 h, while PtesALF1 was up-regulated only once with obvious decrease at 6 h and significant increase at 24 h. These results suggest that the PtesALF isoforms have different tissue specificity and might provide multiple protective functions against invading bacteria in P. trituberculatus.

Polymorphism of the superoxide dismutase gene family in the bay scallop (Argopecten irradians) and its association with resistance/susceptibility to Vibrio anguillarum

The superoxide dismutases (SODs) are a family of enzymes that function as the first line of antioxidant defense against highly reactive superoxide radicals. The bay scallop Argopecten irradians contains three unique superoxide dismutases: Ai-icCuZnSOD, Ai-MnSOD and Ai-ecCuZnSOD, which were characterized in our previous studies. qRT-PCR was also performed to characterize the temporal expression of SODs in the hemocytes of bay scallops injected with the bacterium Vibrio anguillarum. To characterize the SOD family in A. irradians completely, we evaluated the polymorphism in the SOD genes and investigated the association of this polymorphism with resistance/susceptibility to V. anguillarum. Fifty-nine SNPs were identified in the promoter, exon and partial intron sequences of the three SOD genes. AiECSOD contained the most SNPs, as compared to AiCuZnSOD and AiMnSOD, and the majority of these were located in the promoter. Among them, the genotypes of -1739 T-C SNP in the AiCuZnSOD promoter and alleles of the -498 A-T and -267 G-A SNPs in the AiECSOD promoter showed a significant association with resistance/susceptibility to V. angullarum (P<0.05). The only non-synonymous SNP that was identified, E1-38 C-A in Ai-ecCuZnSOD, was a dimorphism caused by a C to A transition that resulted in a Thr to Lys substitution at position 13 in the signal peptide. The Thr allele was associated with increased susceptibility to V. anguillarum (P<0.05). To confirm the presumption, another independent challenge experiment was performed, in which the cumulative mortality of Ai-icCuZnSOD Q-1739 genotype TT was significantly lower than TC (P<0.05). Ai-ecCuZnSOD Q-498 genotype AA and AT were significantly lower than TT (P<0.05), Ai-ecCuZnSOD E1-3 genotype AA was significantly higher than CA and CC (P<0.05). The results suggested that these three polymorphic loci could be potential gene markers for the future molecular selection of strains that are resistant to diseases caused by V. anguillarum.

A SNP in the HSP90AA1 gene 5' flanking region is associated with the adaptation to differential thermal conditions in the ovine species

Molecular chaperones have long been understood to be preferentially transcribed in response to multiple perturbations of the cellular homeostasis. In this study, several polymorphisms in the gene encoding the inducible form of the cytoplasmic Hsp90 (HSP90AA1) were addressed in 24 sheep breeds reared in different climatic regions of Europe, Africa, and Asia. Significant differences in the genotype frequencies for a C/G single nucleotide polymorphism (SNP) located at position -660 in the HSP90AA1 5'flanking region were found between the different breeds. Regression analyses reflected significant correlations (from 0.41 to 0.62) between the alternative genotypes of this polymorphism and several climatic and geographic variables characteristic of the regions where these breeds are reared. Real-time analysis revealed that animals bearing the CC(-660) genotype presented higher expression levels than those presenting the CG(-660) or GG(-660) in summer, but not in spring. Mutation at -660 site seems to affect HSP90AA1 transcription rates which could have important effects on the adaptation to different environmental conditions in sheep. Thus, the variability found in the genotype frequencies for the SNP at -660 in the ovine HSP90AA1 locus could be the result of the different environmental pressures occurring in the regions where these breed are maintained.

Differential transcriptomic responses of Biomphalaria glabrata (Gastropoda, Mollusca) to bacteria and metazoan parasites, Schistosoma mansoni and Echinostoma paraensei (Digenea, Platyhelminthes)

A 70-mer-oligonucleotide-based microarray (1152 features) that emphasizes stress and immune responses factors was constructed to study transcriptomic responses of the snail Biomphalaria glabrata to different immune challenges. In addition to sequences with relevant putative ID and Gene Ontology (GO) annotation, the array features non-immune factors and unknown B. glabrata ESTs for functional gene discovery. The transcription profiles of B. glabrata (3 biological replicates, each a pool of 5 snails) were recorded at 12h post-wounding, exposure to Gram negative or Gram positive bacteria (Escherichia coli and Micrococcus luteus, respectively), or infection with compatible trematode parasites (Schistosoma mansoni or Echinostoma paraensei, 20 miracidia/snail), relative to controls, using universal reference RNA. The data were subjected to Significance Analysis for Microarrays (SAM), with a false positive rate (FPR) <or=10%. Wounding yielded a modest differential expression profile (27 up/21 down) with affected features mostly dissimilar from other treatments. Partially overlapping, yet distinct expression profiles were recorded from snails challenged with E. coli (83 up/20 down) or M. luteus (120 up/42 down), mostly showing up-regulation of defense and stress-related features. Significantly altered expression of selected immune features indicates that B. glabrata detects and responds differently to compatible trematodes. Echinostoma paraensei infection was associated mostly with down-regulation of many (immune-) transcripts (42 up/68 down), whereas S. mansoni exposure yielded a preponderance of up-regulated features (140 up/23 down), with only few known immune genes affected. These observations may reflect the divergent strategies developed by trematodes during their evolution as specialized pathogens of snails to negate host defense responses. Clearly, the immune defenses of B. glabrata distinguish and respond differently to various immune challenges.