Astakine LvAST binds to the β subunit of F1-ATP synthase and likely plays a role in white shrimp Litopeneaus vannamei defense against white spot syndrome virus

Toxicological mechanism of ammonia-N on haematopoiesis and apoptosis of haemocytes in Litopenaeus vannamei

Ammonia, as an important pollutant, contributed to the reduction of immunity, disruption of physiology in animals. RNA interference (RNAi) was performed to understand the function of astakine (AST) in haematopoiesis and apoptosis in Litopenaeus vannamei under ammonia-N exposure. Shrimps were exposed to 20 mg/L ammonia-N from 0 to 48 h with injection of 20 μg AST dsRNA. Further, shrimps were exposed to 0, 2, 10 and 20 mg/L ammonia-N also from 0 to 48 h. The results showed that the total haemocytes count (THC) decreased under ammonia-N stress and the knockdown of AST resulted in a further decrease of THC, suggesting that 1) the proliferation was decreased through the reduction of AST and Hedgehog, the differentiation was interfered by Wnt4, Wnt5 and Notch, and the migration was inhibited by the decrease of VEGF; 2) oxidative stress was induced under ammonia-N stress, leading to the increase of DNA damage with the up-regulated gene expression of death receptor, mitochondrial and endoplasmic reticulum stress pathways; 3) the changes of THC resulted from the decrease of proliferation, differentiation and migration of haematopoiesis cells and the increase of apoptosis of haemocytes. This study helps to deepen our understanding of risk management in shrimp aquaculture.

Transcriptome analysis of the hepatopancreas in Penaeus vannamei under experimental infection with Enterocytozoon hepatopenaei (EHP)

Enterocytozoon hepatopenaei (EHP) is a specialized intracellular parasite that mainly resides in the hepatopancreas of shrimp, causing significant growth retardation in shrimp. In this study, Penaeus vannamei was infected with EHP through an artificial challenge experiment, and the different genes and pathways in the hepatopancreas between EHP-infected and healthy shrimp were analyzed by transcriptome sequencing. The results showed that a total of 240 significantly differentially expressed genes were obtained, including 99 up-regulated genes and 141 down-regulated genes. Immune-related genes such as Astakine, lysozyme, NACHT, LRR, and PYD domains-containing protein 3 (NLRP3), and macrophage mannose receptor 1-like (MMR) were up-regulated, and the expression levels of lipid metabolism-related genes pancreatic lipase-related protein 2 (PLRP2), lysosomal acid lipase (LIPA), and adiponectin receptor protein (AdipoR) were also increased. However, several genes were down-regulated in carbohydrate and protein metabolism, such as glyceraldehyde-3-phosphate dehydrogenase (GAPDH), trypsin-1, and delta-1-pyrroline-5-carboxylate synthase (ALDH18A1). The results suggested that EHP infection of shrimps could significantly activate the immune system, but the energy and material metabolism processes were disturbed. This study identified a substantial number of genes and pathways associated with EHP infection, providing a valuable resource for revealing the molecular mechanism of growth retardation in shrimp.

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

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

Silencing of ATP synthase β reduces phytoplasma multiplication in a leafhopper vector

The leafhopper Euscelidius variegatus is a natural vector of the chrysanthemum yellows phytoplasma (CYp) and a laboratory vector of the Flavescence dorée phytoplasma (FDp). Previous studies indicated a crucial role for insect ATP synthase α and β subunits during phytoplasma infection of the vector species. Gene silencing of ATP synthase β was obtained by injection of specific dsRNAs in E. variegatus. Here we present the long-lasting nature of such silencing, its effects on the small RNA profile, the significant reduction of the corresponding protein expression, and the impact on phytoplasma acquisition capability. The specific transcript expression was silenced at least up to 37 days post injection with an average reduction of 100 times in insects injected with dsRNAs targeting ATP synthase β (dsATP) compared with those injected with dsRNAs targeting green fluorescent protein (dsGFP), used as negative controls. Specific silencing of this gene was also confirmed at protein level at 15 days after the injection. Total sRNA reads mapping to dsATP and dsGFP sequences in analysed libraries showed in both cases a peak of 21 nt, a length consistent with the generation of dsRNA-derived siRNAs by RNAi pathway. Reads mapped exclusively to the fragment corresponding to the injected dsATPs, probably indicating the absence of a secondary machinery for siRNA synthesis. Insects injected either with dsATP or dsGFP successfully acquired CYp and FDp during feeding on infected plants. However, the average phytoplasma amount in dsATP insects was significantly lower than that measured in dsGFP specimens, indicating a probable reduction of the pathogen multiplication when ATP synthase β was silenced. The role of the insect ATP synthase β during phytoplasma infection process is discussed.

Identification of SNPs potentially related to immune responses and growth performance in Litopenaeus vannamei by RNA-seq analyses

Litopenaeus vannamei is one of the most important shrimp species for worldwide aquaculture. Despite this, little genomic information is available for this penaeid and other closely related taxonomic crustaceans. Consequently, genes, proteins and their respective polymorphisms are poorly known for these species. In this work, we used the RNA sequencing technology (RNA-seq) in L. vannamei shrimp evaluated for growth performance, and exposed to the White Spot Syndrome Virus (WSSV), in order to investigate the presence of Single Nucleotide Polymorphisms (SNPs) within genes related to innate immunity and growth, both features of great interest for aquaculture activity. We analyzed individuals with higher and lower growth rates; and infected (unhealthy) and non-infected (healthy), after exposure to WSSV. Approximately 7,000 SNPs were detected in the samples evaluated for growth, being 3,186 and 3,978 exclusive for individuals with higher and lower growth rates, respectively. In the animals exposed to WSSV we found about 16,300 unique SNPs, in which 9,338 were specific to non-infected shrimp, and 7,008 were exclusive to individuals infected with WSSV and symptomatic. In total, we describe 4,312 unigenes containing SNPs. About 60% of these unigenes returned GO blastX hits for Biological Process, Molecular Function and Cellular Component ontologies. We identified 512 KEGG unique KOs distributed among 275 pathways, elucidating the majority of metabolism roles related to high protein metabolism, growth and immunity. These polymorphisms are all located in coding regions, and certainly can be applied in further studies involving phenotype expression of complex traits, such as growth and immunity. Overall, the set of variants raised herein enriches the genomic databases available for shrimp, given that SNPs originated from nextgen are still rare for this relevant crustacean group, despite their huge potential of use in genomic selection approaches.

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.

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.

A cytokine-like factor astakine accelerates the hemocyte production in Pacific oyster Crassostrea gigas

Astakine has been reported to be a hematopoietic growth factor of prokineticin homolog firstly found in arthropods freshwater crayfish Pacifastacus leniusculus. In the present study, an astakine homologous gene was identified from Pacific oyster Crassostrea gigas (designated CgAstakine). The full length cDNA of CgAstakine encoded a polypeptide of 103 amino acids containing a prokineticin (PK) domain homologous to that in astakine from freshwater crayfish P. leniusculus. The deduced amino acid sequence of CgAstakine shared higher similarity with those of other invertebrate astakines than prokineticins from vertebrates. The mRNA of CgAstakine was highly expressed in hepatopancreas and adductor muscle of oyster, while the CgAstakine protein was mainly distributed in hepatopancreas, gill and hemocytes. The mRNA expression of CgAstakine in hemocytes was significantly increased (p < 0.01) and maintained at a high level from 3 h to 9 h after Vibrio anguillarum challenge. After the oyster hemocytes were incubated with 5 μg/mL recombinant CgAstakine protein (rCgAstakine) for 24 h in vitro, the proliferation of hemocytes was significantly increased to 1.89 fold of that in control group (p < 0.05). Moreover, the total count of oyster hemocytes was significantly upregulated (2.45 fold of that in control group, p < 0.05) at 12 h after the oysters were received an injection of rCgAstakine (0.5 μg/g). These results collectively indicated that CgAstakine could modulate the hemocytes proliferation both in vitro and in vivo, and probably involved in the hematopoietic process fighting against the invasion of foreign pathogens.

ATP synthesis is active on the cell surface of the shrimp Litopenaeus vannamei and is suppressed by WSSV infection

BACKGROUND

Over the past a few years, evidences indicate that adenosine triphosphate (ATP) is an energy source for the binding, maturation, assembly, and budding process of many enveloped viruses. Our previous studies suggest that the F1-ATP synthase beta subunit (ATPsyn β, BP53) of the shrimp Litopenaeus vannamei (L. vannamei) might serve as a potential receptor for white spot syndrome virus (WSSV)'s infection.

METHODS

BP53 was localized on the surface of shrimp hemocytes and gill epithelial cells by immunofluorescence assay and immunogold labeling technique. Cell surface ATP synthesis was demonstrated by an in vitro bioluminescent luciferase assay. Furthermore, the expression of bp53 after WSSV infection was investigated by RT-PCR test. In addition, RNAi was developed to knock down endogenous bp53.

RESULTS

BP53 is present on shrimp cell surface of hemocytes and gill epithelia. The synthesized ATP was detectable in the extracellular supernatant by using a bioluminescence assay, and the production declined post WSSV binding and infection. Knocking down endogenous bp53 resulted in a 50% mortality of L. vannamei.

CONCLUSION

These results suggested that BP53, presenting on cell surface, likely served as one of the receptors for WSSV infection in shrimp. Correspondingly, WSSV appears to disturb the host energy metabolism through interacting with host ATPsyn β during infection. This work firstly showed that host ATP production is required and consumed by the WSSV for binding and proceeds with infection process.