A trypsin-like protease with apparent dual function in early Lepeophtheirus salmonis (Krøyer) development

Comparative transcriptome reveals the potential modulation mechanisms of estradiol affecting ovarian development of female Portunus trituberculatus

Estradiol is an important sex steroid hormone that is involved in the regulation of crustacean ovarian development. However, the molecular regulatory mechanisms of estradiol on ovarian development are largely unknown. This study performed transcriptome sequencing of ovary, hepatopancreas, brain ganglion, eyestalk, and mandibular organ of crabs after estradiol treatment (0.1μg g^-1 crab weight). A total of 23, 806 genes were annotated, and 316, 1300, 669, 142, 383 genes were expressed differently in ovary, hepatopancreas, brain ganglion, eyestalk, and mandibular organ respectively. Differentially expressed gene enrichment analysis revealed several crucial pathways including protein digestion and absorption, pancreatic secretion, insect hormone biosynthesis, drug metabolism-cytochrome P450 and signal transduction pathway. Through this study, some key genes in correlation with the ovarian development and nutrition metabolism were significantly affected by estradiol, such as vitelline membrane outer layer 1-like protein, heat shock protein 70, Wnt5, JHE-like carboxylesterase 1, cytochrome P302a1, crustacean hyperglycemic hormone, neuropeptide F2, trypsin, carboxypeptidase B, pancreatic triacylglycerol lipase-like, and lipid storage droplet protein. Moreover, RT-qPCR validation demonstrated that expression of transcripts related to ovarian development (vitelline membrane outer layer 1-like protein and cytochrome P302a1) and nutrition metabolism (trypsin, glucose dehydrogenase and lipid storage droplet protein) were significantly affected by estradiol treatment. This study not only has identified relevant genes and several pathways that are involved in estradiol regulation on ovarian development of P. trituberculatus, but also provided new insight into the understanding of the molecular function mechanisms of estradiol in crustacean.

Catching the complexity of salmon-louse interactions

The study of host-parasite relationships is an integral part of the immunology of aquatic species, where the complexity of both organisms has to be overlayed with the lifecycle stages of the parasite and immunological status of the host. A deep understanding of how the parasite survives in its host and how they display molecular mechanisms to face the immune system can be applied for novel parasite control strategies. This review highlights current knowledge about salmon and sea louse, two key aquatic animals for aquaculture research worldwide. With the aim to catch the complexity of the salmon-louse interactions, molecular information gleaned through genomic studies are presented. The host recognition system and the chemosensory receptors found in sea lice reveal complex molecular components, that in turn, can be disrupted through specific molecules such as non-coding RNAs.

High level efficacy of lufenuron against sea lice (Lepeophtheirus salmonis) linked to rapid impact on moulting processes

Drug resistance in the salmon louse Lepeophtheirus salmonis is a global issue for Atlantic salmon aquaculture. Multiple resistance has been described across most available compound classes with the exception of the benzoylureas. To target this gap in effective management of L. salmonis and other species of sea lice (e.g. Caligus spp.), Elanco Animal Health is developing an in-feed treatment containing lufenuron (a benzoylurea) to be administered prior to seawater transfer of salmon smolts and to provide long-term protection of salmon against sea lice infestations. Benzoylureas disrupt chitin synthesis, formation, and deposition during all moulting events. However, the mechanism(s) of action are not yet fully understood and most research completed to date has focused on insects. We exposed the first parasitic stage of L. salmonis to 700 ppb lufenuron for three hours and observed over 90% reduction in survival to the chalimus II life stage on the host, as compared to vehicle controls. This agrees with a follow up in vivo administration study on the host, which showed >95% reduction by the chalimus I stage. Transcriptomic responses of salmon lice exposed to lufenuron included genes related to moulting, epithelial differentiation, solute transport, and general developmental processes. Global metabolite profiles also suggest that membrane stability and fluidity is impacted in treated lice. These molecular signals are likely the underpinnings of an abnormal moulting process and cuticle formation observed ultrastructurally using transmission electron microscopy. Treated nauplii-staged lice exhibited multiple abnormalities in the integument, suggesting that the coordinated assembly of the epi- and procuticle is impaired. In all cases, treatment with lufenuron had rapid impacts on L. salmonis development. We describe multiple experiments to characterize the efficacy of lufenuron on eggs, larvae, and parasitic stages of L. salmonis, and provide the most comprehensive assessment of the physiological responses of a marine arthropod to a benzoylurea chemical.

Maternal inheritance of deltamethrin resistance in the salmon louse Lepeophtheirus salmonis (Krøyer) is associated with unique mtDNA haplotypes

Parasitic infections by the salmon louse, Lepeophtheirus salmonis (Krøyer), cause huge economic damage in salmon farming in the northern hemisphere, with combined treatment costs and production losses in 2014 having been estimated at US$ 350 million for Norway (annual production 1.25 million tonnes). The control of L. salmonis relies significantly on medicinal treatments, supplemented by non-pharmacological approaches. However, efficacy losses have been reported for several delousing agents, including the pyrethroid deltamethrin. The aim of the present study was to analyse the genetic basis of deltamethrin resistance in L. salmonis. Deltamethrin median effective concentrations (EC50) were 0.28 μg L-1 in the drug susceptible L. salmonis strain IoA-00 and 40.1 μg L-1 in the pyrethroid resistant strain IoA-02. IoA-00 and IoA-02 were crossed to produce families spanning one parental and three filial generations (P0, F1-F3). In three families derived from P0 crosses between an IoA-00 sire and an IoA-02 dam, 98.8% of F2 parasites (n = 173) were resistant, i.e. remained unaffected after exposure to 2.0 μg L-1 deltamethrin. F3 parasites from these crosses showed a deltamethrin EC50 of 9.66 μg L-1. In two families of the inverse orientation at P0 (IoA-02 sire x IoA-00 dam), 16.7% of F2 parasites were resistant (n = 84), while the deltamethrin EC50 in F3 animals was 0.26 μg L-1. The results revealed a predominantly maternal inheritance of deltamethrin resistance. The 15,947-nt mitochondrial genome was sequenced and compared among six unrelated L. salmonis strains and parasites sampled from wild salmon in 2010. IoA-02 and three further deltamethrin resistant strains, established from isolates originating from different regions of Scotland, showed almost identical mitochondrial haplotypes. In contrast, the mitochondrial genome was variable among susceptible strains and L. salmonis from wild hosts. Deltamethrin caused toxicity and depletion of whole body ATP levels in IoA-00 but not IoA-02 parasites. The maternal inheritance of deltamethrin resistance and its association with mitochondrial haplotypes suggests that pyrethroid toxicity in L. salmonis may involve molecular targets encoded by mitochondrial genes.

Vitellogenin is an immunocompetent molecule for mother and offspring in fish

Our understanding of the function of vitellogenin (Vg) in reproduction has undergone a transformation over the past decade in parallel with new insights into the role of Vg in immunity. Initially, Vg was regarded as a female-specific reproductive protein, which is cleaved into yolk proteins such as phosvitin (Pv) and lipovitellin (Lv), stored in egg, providing the nutrients for developing embryos. Recently, Vg is shown to be an immune-relevant molecule involved in the defense of the host against the microbes including bacterium and virus. Furthermore, Pv and Lv, that both are proteolytically cleaved products of Vg, play a defense role in developing embryos. Importantly, yolk protein-derived small peptides also display antimicrobial activity. These data together indicate that Vg, in addition to being involved in yolk protein formation, plays a non-reproductive role via functioning as an immune-relevant molecule in both parent fishes and their offspring. It also shows that yolk proteins and their degraded peptides are novel players in maternal immunity, opening a new avenue to study the functions of reproductive proteins.

Maternally derived trypsin may have multiple functions in the early development of turbot (Scopthalmus maximus)

Trypsin is an important serine protease that is considered to be involved in digestion of protein in teleost fish. Nevertheless, studies on trypsin/trypsinogen in fish embryos are very limited. In this study, the trypsinogen of turbot (Scophthalmus maximus) (tTG) was identified and the expression patterns and activity of trypsinogen/trypsin were investigated. The results showed that the tTG mRNA was evenly distributed in the oocytes and was also expressed along the yolk periphery in early embryos. At later embryo stages and 1 days after hatching (dph), the tTG mRNA concentrated at the alimentary tract and head. Quantitative expression analysis showed that the tTG transcripts decreased after fertilization until the gastrula stage, then increased with the embryo and larvae development. This result was also confirmed by the specific activity analysis of trypsin and in-situ-hybridization (ISH). All of the results indicated that tTG in early embryo stages was maternally derived and expressed by itself after gastrula stages. Additionally, location of tTG mRNA in embryos and larvae was investigated; we considered that trypsin may have multiple functions during the embryo development process. Based on our results regarding trypsinogen in embryos and early development, we concluded that the trypsin/trypsinogen in turbot embryos was inherited from a maternal source and we suggested that trypsin in early development has multiple functions in the process of development.

Characterization of a novel RXR receptor in the salmon louse (Lepeophtheirus salmonis, Copepoda) regulating growth and female reproduction

BACKGROUND

Nuclear receptors have crucial roles in all metazoan animals as regulators of gene transcription. A wide range of studies have elucidated molecular and biological significance of nuclear receptors but there are still a large number of animals where the knowledge is very limited. In the present study we have identified an RXR type of nuclear receptor in the salmon louse (Lepeophtheirus salmonis) (i.e. LsRXR). RXR is one of the two partners of the Ecdysteroid receptor in arthropods, the receptor for the main molting hormone 20-hydroxyecdysone (E20) with a wide array of effects in arthropods.

RESULTS

Five different LsRXR transcripts were identified by RACE showing large differences in domain structure. The largest isoforms contained complete DNA binding domain (DBD) and ligand binding domain (LBD), whereas some variants had incomplete or no DBD. LsRXR is transcribed in several tissues in the salmon louse including ovary, subcuticular tissue, intestine and glands. By using Q-PCR it is evident that the LsRXR mRNA levels vary throughout the L. salmonis life cycle. We also show that the truncated LsRXR transcript comprise about 50% in all examined samples. We used RNAi to knock-down the transcription in adult reproducing female lice. This resulted in close to zero viable offspring. We also assessed the LsRXR RNAi effects using a L. salmonis microarray and saw significant effects on transcription in the female lice. Transcription of the major yolk proteins was strongly reduced by knock-down of LsRXR. Genes involved in lipid metabolism and transport were also down regulated. Furthermore, different types of growth processes were up regulated and many cuticle proteins were present in this group.

CONCLUSIONS

The present study demonstrates the significance of LsRXR in adult female L. salmonis and discusses the functional aspects in relation to other arthropods. LsRXR has a unique structure that should be elucidated in the future.

The ovarian transcriptome of the cattle tick, Rhipicephalus (Boophilus) microplus, feeding upon a bovine host infected with Babesia bovis

BACKGROUND

Cattle babesiosis is a tick-borne disease of cattle with the most severe form of the disease caused by the apicomplexan, Babesia bovis. Babesiosis is transmitted to cattle through the bite of infected cattle ticks of the genus Rhipicephalus. The most prevalent species is Rhipicephalus (Boophilus) microplus, which is distributed throughout the tropical and subtropical countries of the world. The transmission of B. bovis is transovarian and a previous study of the R. microplus ovarian proteome identified several R. microplus proteins that were differentially expressed in response to infection. Through various approaches, we studied the reaction of the R. microplus ovarian transcriptome in response to infection by B. bovis.

METHODS

A group of ticks were allowed to feed on a B. bovis-infected splenectomized calf while a second group fed on an uninfected splenectomized control calf. RNA was purified from dissected adult female ovaries of both infected and uninfected ticks and a subtracted B. bovis-infected cDNA library was synthesized, subtracting with the uninfected ovarian RNA. Four thousand ESTs were sequenced from the ovary subtracted library and annotated.

RESULTS

The subtracted library dataset assembled into 727 unique contigs and 2,161 singletons for a total of 2,888 unigenes, Microarray experiments designed to detect B. bovis-induced gene expression changes indicated at least 15 transcripts were expressed at a higher level in ovaries from ticks feeding upon the B. bovis-infected calf as compared with ovaries from ticks feeding on an uninfected calf. We did not detect any transcripts from these microarray experiments that were expressed at a lower level in the infected ovaries compared with the uninfected ovaries. Using the technique called serial analysis of gene expression, 41 ovarian transcripts from infected ticks were differentially expressed when compared with transcripts of controls.

CONCLUSION

Collectively, our experimental approaches provide the first comprehensive profile of the R. microplus ovarian transcriptome responding to infection by B. bovis. This dataset should prove useful in molecular studies of host-pathogen interactions between this tick and its apicomplexan parasite.

The Salmon Louse Lepeophtheirus salmonis (Copepoda: Caligidae) life cycle has only two Chalimus stages

Each year the salmon louse (Lepeophtheirussalmonis Krøyer, 1838) causes multi-million dollar commercial losses to the salmon farming industry world-wide, and strict lice control regimes have been put in place to reduce the release of salmon louse larvae from aquaculture facilities into the environment. For half a century, the Lepeophtheirus life cycle has been regarded as the only copepod life cycle including 8 post-nauplius instars as confirmed in four different species, including L. salmonis. Here we prove that the accepted life cycle of the salmon louse is wrong. By observations of chalimus larvae molting in incubators and by morphometric cluster analysis, we show that there are only two chalimus instars: chalimus 1 (comprising the former chalimus I and II stages which are not separated by a molt) and chalimus 2 (the former chalimus III and IV stages which are not separated by a molt). Consequently the salmon louse life cycle has only six post-nauplius instars, as in other genera of caligid sea lice and copepods in general. These findings are of fundamental importance in experimental studies as well as for interpretation of salmon louse biology and for control and management of this economically important parasite.

Characterization of proteolytic activities during intestinal regeneration of the sea cucumber, Holothuria glaberrima

Proteolysis carried out by different proteases control cellular processes during development and regeneration. Here we investigated the function of the proteasome and other proteases in the process of intestinal regeneration using as a model the sea cucumber Holothuria glaberrima. This echinoderm possesses the ability to regenerate its viscera after a process of evisceration. Enzymatic activity assays showed that intestinal extracts at different stages of regeneration possessed chymotrypsin-like activity. This activity was inhibited by i) MG132, a reversible inhibitor of chymotrypsin and peptidylglutamyl peptidase hydrolase (PGPH) activities of the proteasome, ii) E64d, a permeable inhibitor of cysteine proteases and iii) TPCK, a serine chymotrypsin inhibitor, but not by epoxomicin, an irreversible and potent inhibitor of all enzymatic activities of the proteasome. To elucidate the role which these proteases might play during intestinal regeneration, we carried out in vivo experiments injecting MG132, E64d and TPCK into regenerating animals. The results showed effects on the size of the regenerating intestine, cell proliferation and collagen degradation. These findings suggest that proteolysis by several proteases is important in the regulation of intestinal regeneration in H. glaberrima.

Gut transcriptome of replete adult female cattle ticks, Rhipicephalus (Boophilus) microplus, feeding upon a Babesia bovis-infected bovine host

As it feeds upon cattle, Rhipicephalus (Boophilus) microplus is capable of transmitting a number of pathogenic organisms, including the apicomplexan hemoparasite Babesia bovis, a causative agent of bovine babesiosis. The R. microplus female gut transcriptome was studied for two cohorts: adult females feeding on a bovine host infected with B. bovis and adult females feeding on an uninfected bovine. RNA was purified and used to generate a subtracted cDNA library from B. bovis-infected female gut, and 4,077 expressed sequence tags (ESTs) were sequenced. Gene expression was also measured by a microarray designed from the publicly available R. microplus gene index: BmiGI Version 2. We compared gene expression in the tick gut from females feeding upon an uninfected bovine to gene expression in tick gut from females feeding upon a splenectomized bovine infected with B. bovis. Thirty-three ESTs represented on the microarray were expressed at a higher level in female gut samples from the ticks feeding upon a B. bovis-infected calf compared to expression levels in female gut samples from ticks feeding on an uninfected calf. Forty-three transcripts were expressed at a lower level in the ticks feeding upon B. bovis-infected female guts compared with expression in female gut samples from ticks feeding on the uninfected calf. These array data were used as initial characterization of gene expression associated with the infection of R. microplus by B. bovis.

Characterization and expression analysis of a trypsin-like serine protease from planarian Dugesia japonica

Trypsin-like serine proteases are involved in large number of processes, especially in digestive degradation and immune responses. Here, we identify the characterization of a trypsin-like serine protease in planarian, Djtry, which interestingly has the incompletely conserved catalytic triad (K, D, and S). Phylogenetic analysis suggests that Djtry is an ancient type of trypsin-like serine proteases. The spatial and temporal expression patterns of Djtry are shown during regenerating and embryonic development by whole-mount in situ hybridization. Djtry is found to display a tissue specific expression pattern, with a predominant expression detected in whole gut region of intact and regenerating planarian. While the tissue- and stage-specific expression patterns during the embryonic development imply the roles of Djtry involve in yolk degradation and gut formation. Quantitative real-time PCR was carried out to analyze the function of this protease in vivo after planarians were stimulated to a bacterial challenge and food. The results showed that Djtry increased after a bacterial challenge and was basically stable for food. Therefore, the trypsin-like serine protease might be involved in the innate defense reactions against bacterial infection.

Observing copepods through a genomic lens

Background

Copepods outnumber every other multicellular animal group. They are critical components of the world's freshwater and marine ecosystems, sensitive indicators of local and global climate change, key ecosystem service providers, parasites and predators of economically important aquatic animals and potential vectors of waterborne disease. Copepods sustain the world fisheries that nourish and support human populations. Although genomic tools have transformed many areas of biological and biomedical research, their power to elucidate aspects of the biology, behavior and ecology of copepods has only recently begun to be exploited.

Discussion

The extraordinary biological and ecological diversity of the subclass Copepoda provides both unique advantages for addressing key problems in aquatic systems and formidable challenges for developing a focused genomics strategy. This article provides an overview of genomic studies of copepods and discusses strategies for using genomics tools to address key questions at levels extending from individuals to ecosystems. Genomics can, for instance, help to decipher patterns of genome evolution such as those that occur during transitions from free living to symbiotic and parasitic lifestyles and can assist in the identification of genetic mechanisms and accompanying physiological changes associated with adaptation to new or physiologically challenging environments. The adaptive significance of the diversity in genome size and unique mechanisms of genome reorganization during development could similarly be explored. Genome-wide and EST studies of parasitic copepods of salmon and large EST studies of selected free-living copepods have demonstrated the potential utility of modern genomics approaches for the study of copepods and have generated resources such as EST libraries, shotgun genome sequences, BAC libraries, genome maps and inbred lines that will be invaluable in assisting further efforts to provide genomics tools for copepods.

Summary

Genomics research on copepods is needed to extend our exploration and characterization of their fundamental biological traits, so that we can better understand how copepods function and interact in diverse environments. Availability of large scale genomics resources will also open doors to a wide range of systems biology type studies that view the organism as the fundamental system in which to address key questions in ecology and evolution.