Environmental Changes Drives the Transcriptome and Gene Regulation Plasticity During Sea Lice Infestation

The sea louse, Caligus rogercresseyi, is one of the main concerns in the Chilean salmon industry. The free-living copepodid stage can recognize the host and initiate the parasitic phase, where environmental factors can shape the host recognition process. This study aimed to explore the ecological influence on the transcriptome of copepodids infesting Atlantic salmon experimentally exposed to different salinity and temperature (S/T) conditions. Herein, 200 salmon were infested with 35 copepodids per fish previously acclimatized to four S/T treatments: 32 and 26 PSU; 8 and 16°C. After 48 h of infestation, the attached copepodids from each experimental group were counted and digitalized for geometric morphometric analysis. Copepodids were then collected for RNA sequencing to analyze transcriptome modulation and gene regulation. Morphological changes in copepodids were mainly associated with temperature rather than salinity conditions. The transcriptome survey revealed molecular signatures related to salinity and temperature changes, where salinity drives the gene expression of copepodids. Notably, specific genes, such as those encoding cuticle proteins and trypsin-like kinases, were regulated by all three post-transcriptional mechanisms assessed: alternative splicing, miRNA, and gene fusion. The transcriptome analysis revealed that trypsin-like kinase genes exhibited upregulation and downregulation across the various S/T conditions. In contrast, cuticle protein genes were consistently downregulated in the 32 PSU/8°C, 26 PSU/8°C, and 26 PSU/16°C groups compared to the 32 PSU/16°C control. This suggests that the three post-transcriptional mechanisms may exert a combined influence on the expression of specific genes, potentially driven by salinity and temperature environmental conditions in sea lice biology.

Transgenerational effects of water-soluble polymers on Daphnia magna at environmentally relevant concentrations: The role of multigenerational plasticity

The widespread use of water-soluble polymers (WSPs) like polyethylene glycol (PEG) and polyvinyl alcohol (PVA) across multiple industrial and household uses has recently raised concerns about their environmental persistence and potential toxicity to aquatic organisms. Despite being excluded from regulatory oversight, recent studies suggest possible ecological risks associated with sub-lethal exposures to these polymers. In this context, this study investigates the transgenerational effects of PEG and PVA on Daphnia magna, focusing on both life-history parameters and epigenetic modifications at the environmentally relevant concentration of 1 μg/L. Through continuous exposure experiments, spanning three generations (from F0 to F3), and "recovery" groups, where only the parental generation (F0) was exposed, our results reveal significant reductions in the number of newborns and reproductive parameters in the F0 generation exposed to PEG but not in subsequent generations. This suggests a multigenerational plasticity in Daphnia through a compensatory or acclimation reproductive response over time. Global cytosine methylation patterns also showed a significant initial increase in the F0 generation exposed to PEG, which decreased in later generations, indicating a possible epigenetic mechanism underlying observed reproductive effects. In contrast, PVA exhibited no significant changes in both life history parameters and methylation but showed a global methylation trend suggesting its likely epigenetic influence. These findings underscore the need for comprehensive risk assessments of WSPs, particularly their potential for inducing long-term (epigenetic) effects, influencing reproductive functions across generations and how increased plasticity may affect responses against novel other stressors.

Daphnia stress response to environmental concentrations of chloramphenicol-multi-omics approach

Commonly used medicines, when discarded or improperly disposed of, are known to contaminate freshwater ecosystems. Pharmaceuticals can be toxic and mutagenic, and can modify freshwater organisms, even at environmentally relevant concentrations. Chloramphenicol (CAP) is an antibiotic banned in Europe. However, it is still found in surface waters around the world. The aim of this study was to evaluate the impact of chloramphenicol contamination in freshwater on the model organism Daphnia magna. Specific life history parameters, proteome, and host-associated microbiome of four D. magna clones were analyzed during a three-generation exposure to CAP at environmental concentrations (32 ng L-1). In the first generation, no statistically significant CAP effect at the individual level was detected. After three generations, exposed animals were smaller at first reproduction and on average produced fewer offspring. The differences in D. magna's life history after CAP treatment were in accordance with proteome changes. D. magna's response to CAP presence indicates the high stress that the tested organisms are under, e.g., male production, upregulation of ubiquitin-conjugating enzyme E2 and calcium-binding protein, and downregulation of glutathione transferase. The CAP-exposed D. magna proteome profile confirms that CAP, being reactive oxygen species (ROS)-inducing compounds, contributes to structural changes in mitochondria. Microbiome analysis showed a significant difference in the Shannon index between control and CAP-exposed animals, the latter having a more diverse microbiome. Multilevel analyses, together with long exposure in the laboratory imitating conditions in a polluted environment, allow us to obtain a more complete picture of the impact of CAP on D. magna.

Unveiling the multilevel impact of four water-soluble polymers on Daphnia magna: From proteome to behaviour (a case study)

The ubiquitous presence of water-soluble polymers (WSPs) in freshwater environments raises concerns regarding potential threats to aquatic organisms. This study investigated, for the first time, the effects of widely used WSPs -polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), and polyethylene glycol (PEG)- using a multi-level approach in the freshwater biological model Daphnia magna. This integrated assessment employed a suite of biomarkers, evaluation of swimming behaviour, and proteomic analysis to investigate the effects of three environmentally relevant concentrations (0.001, 0.5, and 1 mg/L) of the tested WSPs from molecular to organismal levels, assessing both acute and chronic effects. Our findings reveal that exposure to different WSPs induces specific responses at each biological level, with PEG being the only WSP inducing lethal effects at 0.5 mg/L. At the physiological level, although all WSPs impacted both swimming performance and heart rate of D. magna specimens, PAA exhibited the greatest effects on the measured behavioural parameters. Furthermore, proteomic analyses demonstrated altered protein profiles following exposure to all WSPs, with PVA emerging as the most effective.

Sex-Biased Transcription Expression of Vitellogenins Reveals Fusion Gene and MicroRNA Regulation in the Sea Louse Caligus rogercresseyi

The caligid ectoparasite, Caligus rogercresseyi, is one of the main concerns in the Chilean salmon industry. The molecular mechanisms displayed by the parasite during the reproductive process represent an opportunity for developing novel control strategies. Vitellogenin is a multifunctional protein recognized as a critical player in several crustaceans' biological processes, including reproduction, embryonic development, and immune response. This study aimed to characterize the C. rogercresseyi vitellogenins, including discovering novel transcripts and regulatory mechanisms associated with microRNAs. Herein, vitellogenin genes were identified by homology analysis using the reference sea louse genome, transcriptome database, and arthropods vitellogenin-protein database. The validation of expression transcripts was conducted by RNA nanopore sequencing technology. Moreover, fusion gene profiling, miRNA target analysis, and functional validation were performed using luciferase assay. Six putative vitellogenin genes were identified in the C. rogercresseyi genome with high homology with other copepods vitellogenins. Furthermore, miR-996 showed a putative role in regulating the Cr_Vitellogenin1 gene, which is highly expressed in females. Moreover, vitellogenin-fusion genes were identified in adult stages and highly regulated in males, demonstrating sex-related expression patterns. In females, the identified fusion genes merged with several non-vitellogenin genes involved in biological processes of ribosome assembly, BMP signaling pathway, and biosynthetic processes. This study reports the genome array of vitellogenins in C. rogercresseyi for the first time, revealing the putative role of fusion genes and miRNA regulation in sea lice biology.

Identification and characterization of the Doublesex gene and its mRNA isoforms in the brine shrimp Artemia franciscana

Doublesex (DSX) proteins are members of the Doublesex/mab-3-related (DMRT) protein family and play crucial roles in sex determination and differentiation among the animal kingdom. In the present study, we identified two Doublesex (Dsx)-like mRNA isoforms in the brine shrimp Artemia franciscana (Kellogg 1906), which are generated by the combination of alternative promoters, alternative splicing and alternative polyadenylation. The two transcripts exhibited sex-biased enrichment, which we termed AfrDsxM and AfrDsxF. They share a common region which encodes an identical N-terminal DNA-binding (DM) domain. RT-qPCR analyses showed that AfrDsxM is dominantly expressed in male Artemia while AfrDsxF is specifically expressed in females. Expression levels of both isoforms increased along with the developmental stages of their respective sexes. RNA interference with dsRNA showed that the knockdown of AfrDsxM in male larvae led to the appearance of female traits including an ovary-like structure in the original male reproductive system and an elevated expression of vitellogenin. However, silencing of AfrDsxF induced no clear phenotypic change in female Artemia. These results indicated that the male AfrDSXM may act as inhibiting regulator upon the default female developmental mode in Artemia. Furthermore, electrophoretic mobility shift assay analyses revealed that the unique DM domain of AfrDSXs can specifically bind to promoter segments of potential downstream target genes like AfrVtg. These data show that AfrDSXs play crucial roles in regulating sexual development in Artemia, and further provide insight into the evolution of sex determination/differentiation in sexual organisms.

High-quality genome of Diaphanosoma dubium provides insights into molecular basis of its broad ecological adaptation

Diaphanosoma dubium Manuilova, 1964, is a widespread planktonic water flea in Asian freshwater. Although sharing similar ecological roles with species of Daphnia, studies on D. dubium and its congeners are still few and lacking a genome for the further studies. Here, we assembled a high quality and chromosome level genome of D. dubium by combining long reads sequencing and Hi-C technologies. The total length of assembled genome was 101.8 Mb, with 98.92 Mb (97.2%) anchored into 22 chromosomes. Through comparative genomic analysis, we found the genes, involved in anti-ROS, detoxification, protein digestion, germ cells regulation and protection, underwent expansion in D. dubium. These genes and their expansion helpfully explain its widespread geographical distribution and dominance in eutrophic waters. This study provides insight into the adaptive evolution of D. dubium at genomic perspectives, and the present high quality genomic resource will be a footstone for future omics studies of the species and its congeners.

Vitellogenin offsets oxidative costs of reproduction in female painted dragon lizards

Vitellogenesis ('yolking' of follicles) is a bioenergetically costly stage of reproduction requiring enlargement of the liver to produce vitellogenin (VTG) yolk precursor proteins, which are transported and deposited at the ovary. VTG may, however, serve non-nutritive anti-oxidant functions, a hypothesis supported by empirical work on aging and other life-history transitions in several taxa. We test this hypothesis in female painted dragon lizards (Ctenophorus pictus) by examining covariation in VTG with the ovarian cycle, and relative to reactive oxygen species (ROS) including baseline superoxide (bSO). Plasma VTG decreased prior to ovulation, when VTG is deposited into follicles. VTG, however, remained elevated post-ovulation when no longer necessary for yolk provisioning and was unrelated to reproductive investment. Instead, VTG was strongly and positively predicted by prior bSO. ROS, in turn, was negatively predicted by prior VTG, while simultaneously sampled VTG was a positive predictor. These findings are consistent with the hypothesis that VTG functions as an anti-oxidant to counteract oxidative stress associated with vitellogenesis. The relationship between bSO and VTG was strongest in post-ovulatory females, indicating that its function may be largely anti-oxidant at this time. In conclusion, VTG may be under selection to offset oxidative costs of reproduction in egg-producing species.

Cloning and molecular characterization of estrogen-related receptor (ERR) and vitellogenin genes in the brackish water flea Diaphanosoma celebensis exposed to bisphenol A and its structural analogues

Although it has previously been shown that bisphenol (BP) analogues may interfere with the normal hormonal regulation by acting as endocrine disrupting chemicals (EDCs), little information is available on effects of BP analogues in invertebrates, particularly on cladocerans. In the present study, we identified estrogen-related receptors (EER), vitellogenin (VTG), and VTG receptor (VtgR) from the brackish water flea Diaphanosoma celebensis, and examined the effects of BPA and the substitutes, BPF and BPS, in different sublethal concentrations. Gene expression varied with time well matched with brooding, suggesting that DcEER, DcVTG, and DcVtgR play a role in reproduction in D. celebensis. qRT-PCR analysis showed that BPA and its substitutes differently modulated mRNA expressions of DcEER, DcVTG, and DcVtgR, indicating that these compounds adversely affect the normal reproduction-related pathway. This study facilitates better understanding of the molecular mode of action of BP analogues on the reproductive system of D. celebensis.

Quantitative Proteomic Analysis to Understand the Mechanisms of Zinc Oxide Nanoparticle Toxicity to Daphnia pulex (Crustacea: Daphniidae): Comparing with Bulk Zinc Oxide and Zinc Salt

The widespread use of zinc oxide nanoparticles (ZnO NPs) has resulted in their release to the environment. There has been concern about the ecotoxicity of ZnO NPs, but little is known about their toxic mechanisms. In the present study, we conducted acute toxicity tests to show that ZnO NPs are more toxic to the freshwater crustacean Daphnia pulex compared to bulk ZnO or ZnSO₄·7H₂O. To provide an integrated and quantitative insights into the toxicity of ZnO NPs, we conducted isobaric tags for relative and absolute quantitation (iTRAQ) proteomic analysis, which detected 262, 331, and 360 differentially expressed proteins (DEPs) in D. pulex exposed to ZnO NPs, bulk ZnO, and ZnSO₄·7H₂O, respectively. Among the DEPs, 224 were shared among the three treatments. These proteins were related to energy metabolism, oxidative stress, and endoplasmic reticulum stress. The three forms of Zn all caused D. pulex to downregulate Chitinase expression, disrupt Ca²⁺ homeostasis, and reduce expression of digestive enzymes. Nevertheless, 29 proteins were expressed only in the ZnO NP treatment. In particular, histone (H3) and ribosomal proteins (L13) were obviously influenced under ZnO NP treatment. However, increased expression levels of h3 and l13 genes were not induced only in ZnO NP treatment, they were sensitive to Zn ions under the same exposure concentration. These results indicate that the three zinc substances have a similar mode of action and that released zinc ions are the main contributor to ZnO NP toxicity to D. pulex under a low concentration. Further investigation is needed to clarify whether a small proportion of DEPs or higher bioavailability cause ZnO NPs to be more toxic compared to bulk ZnO or ionic zinc.

The transcriptomic and proteomic responses of Daphnia pulex to changes in temperature and food supply comprise environment-specific and clone-specific elements

Background

Regulatory adjustments to acute and chronic temperature changes are highly important for aquatic ectotherms because temperature affects their metabolic rate as well as the already low oxygen concentration in water, which can upset their energy balance. This also applies to severe changes in food supply. Thus, we studied on a molecular level (transcriptomics and/or proteomics) the immediate responses to heat stress and starvation and the acclimation to different temperatures in two clonal isolates of the model microcrustacean Daphnia pulex from more or less stressful environments, which showed a higher (clone M) or lower (clone G) tolerance to heat and starvation.

Results

The transcriptomic responses of clone G to acute heat stress (from 20 °C to 30 °C) and temperature acclimation (10 °C, 20 °C, and 24 °C) and the proteomic responses of both clones to acute heat, starvation, and heat-and-starvation stress comprised environment-specific and clone-specific elements. Acute stress (in particular heat stress) led to an early upregulation of stress genes and proteins (e.g., molecular chaperones) and a downregulation of metabolic genes and proteins (e.g., hydrolases). The transcriptomic responses to temperature acclimation differed clearly. They also varied depending on the temperature level. Acclimation to higher temperatures comprised an upregulation of metabolic genes and, in case of 24 °C acclimation, a downregulation of genes for translational processes and collagens. The proteomic responses of the clones M and G differed at any type of stress. Clone M showed markedly stronger and less stress-specific proteomic responses than clone G, which included the consistent expression of a specific heat shock protein (HSP60) and vitellogenin (VTG-SOD).

Conclusions

The expression changes under acute stress can be interpreted as a switch from standard products of gene expression to stress-specific products. The expression changes under temperature acclimation probably served for an increase in energy intake (via digestion) and, if necessary, a decrease in energy expenditures (e.g, for translational processes). The stronger and less stress-specific proteomic responses of clone M indicate a lower degree of cell damage and an active preservation of the energy balance, which allowed adequate proteomic responses under stress, including the initiation of resting egg production (VTG-SOD expression) as an emergency reaction.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4742-6) contains supplementary material, which is available to authorized users.

Protein profiling as early detection biomarkers for TiO2 nanoparticle toxicity in Daphnia magna

The mode of action for nanoparticle (NP) toxicity in aquatic organisms is not yet fully understood. In this work, a strategy other than toxicity testing was applied to Daphnia magna exposed to TiO₂-NPs: the use of nuclear microscopy and the assessment of protein profile. D. magna is a keystone species broadly used as a model system in ecotoxicology. Titanium (Ti) was found in the D. magna digestive tract, mainly in the gut. The penetration of Ti into the epithelial region was greater at higher exposure levels and also observed in eggs in the brood pouch. The protein profile of individuals exposed to different concentrations showed that 2.8 and 5.6 mg/L TiO₂-NP concentrations induced an over-expression of the majority of proteins, in particular proteins with molecular weight of ∼120, 85 and 15 kDa, while 11.2 mg/L TiO₂-NP had an inhibitory effect on protein expression. The Matrix-assisted laser desorption ionization with tandem time of flight mass spectrometry (MALDI-TOF/TOF MS) analysis of these proteins consistently identified them as vitellogenin (Vtg)-like proteins, associated with enzymes involved in redox balance. These results indicate that Vtg-like proteins are up-regulated in D. magna exposed to TiO₂-NPs. Vitellogenesis is associated with the reproduction system, suggesting that TiO₂-NP exposure can impair reproduction by affecting this process. The precise mode of action of TiO₂-NPs is still unclear and the results from this study are a first attempt to identify specific proteins as potential markers of TiO₂-NP toxicity in D. magna, providing useful information for future research.

How cyclophosphamide at environmentally relevant concentration influences Daphnia magna life history and its proteome

The waste of commonly used medicines is known to contaminate freshwater ecosystems. Pharmaceuticals can be toxic, mutagenic, or modifying to freshwater organisms even at low concentrations if consider their permanent presence in the environment. Chemotherapeutics used to treat cancer, and in particular alkylating agents, contribute significantly to this form of pollution, the latter introducing cytotoxic and/or mutagenic lesions to the DNA and RNA of organisms which can be disruptive to their cells. The aim of the present study was to investigate the influence of the alkylating anticancer agent cyclophosphamide (CP) on Daphnia magna clones. We evaluated the life history parameters and protein profiles of this crustacean following exposure to environmentally relevant CP concentration of 10 ng L^-1. Even at this low concentration, the alkylating agent caused modification of the life history parameters and proteome profile of the Daphnia. These changes were clone-specific and involved growth rate, age at first reproduction, neonate number, and proteins related to cell cycle and redox state regulation. The disturbance caused by pharmaceuticals contaminating freshwater ecosystem is probably weaker and unlikely to be cytotoxic in character due to the high dilution of these substances in the water. However, our results indicate that prolonged exposure of organisms to these toxins may lead to modifications on the organismal and molecular levels with unpredictable significance for the entire ecosystem.

Molecular characterization and functional analyses of a diapause hormone receptor-like gene in parthenogenetic Artemia

In arthropods, mature females under certain conditions produce and release encysted gastrula embryos that enter diapause, a state of obligate dormancy. The process is presumably regulated by diapause hormone (DH) and diapause hormone receptor (DHR) that were identified in the silkworm, Bombyx mori and other insects. However, the molecular structure and function of DHR in crustaceans remains unknown. Here, a DHR-like gene from parthenogenetic Artemia (Ar-DHR) was isolated and sequenced. The cDNA sequence consists of 1410bp with a 1260-bp open reading frame encoding a protein consisting of 420 amino acid residues. The results of real-time PCR (qRT-PCR) and Western blot analysis showed that the mRNA and protein of Ar-DHR were mainly expressed at the diapause stage. Furthermore, we found that Ar-DHR was located on the cell membrane of the pre-diapause cyst but in the cytoplasm of the diapause cyst by analysis of immunofluorescence. In vivo knockdown of Ar-DHR by RNA interference (RNAi) and antiserum neutralization consistently inhibited diapause cysts formation. The results indicated that Ar-DHR plays an important role in the induction and maintenance of embryonic diapause in Artemia. Thus, our findings provide an insight into the regulation of diapause formation in Artemia and the function of Ar-DHR.

The transcription factor p8 regulates autophagy during diapause embryo formation in Artemia parthenogenetica

Autophagy is an essential homeostatic process by which cytoplasmic components, including macromolecules and organelles, are degraded by lysosome. Increasing evidence suggests that phosphorylated AMP-activated protein kinase (p-AMPK) and target of rapamycin (TOR) play key roles in the regulation of autophagy. However, the regulation of autophagy in quiescent cells remains unclear, despite the fact that autophagy is known to be critical for normal development, regeneration, and degenerative diseases. Here, crustacean Artemia parthenogenetica was used as a model system because they produced and released encysted embryos that enter a state of obligate dormancy in cell quiescence to withstand various environmental threats. We observed that autophagy was increased before diapause stage but dropped to extremely low level in diapause cysts in Artemia. Western blot analyses indicated that the regulation of autophagy was AMPK/TOR independent during diapause embryo formation. Importantly, the level of p8 (Ar-p8), a stress-inducible transcription cofactor, was elevated at the stage just before diapause and was absent in encysted embryos, indicating that Ar-p8 may regulate autophagy. The results of Ar-p8 knockdown revealed that Ar-p8 regulated autophagy during diapause formation in Artemia. Moreover, we observed that activating transcription factors 4 and 6 (ATF4 and ATF6) responded to Ar-p8-regulated autophagy, indicating that autophagy targeted endoplasmic reticulum (ER) during diapause formation in Artemia. Additionally, AMPK/TOR-independent autophagy was validated in human gastric cancer MKN45 cells overexpressing Ar-p8. The findings presented here may provide insights into the role of p8 in regulating autophagy in quiescent cells.

Expression profiles of miRNAs and involvement of miR-100 and miR-34 in regulation of cell cycle arrest in Artemia

Regulation of the cell cycle is complex but critical for proper development, reproduction and stress resistance. To survive unfavourable environmental conditions, the crustacean Artemia produces diapause embryos whose metabolism is maintained at extremely low levels. In the present study, the expression profiles of miRNAs during Artemia diapause entry and termination were characterized using high-throughput sequencing. A total of 13 unclassified miRNAs and 370 miRNAs belonging to 87 families were identified; among them, 107 were differentially expressed during diapause entry and termination. We focused on the roles of two of these miRNAs, miR-100 and miR-34, in regulating cell cycle progression; during the various stages of diapause entry, these miRNAs displayed opposing patterns of expression. A functional analysis revealed that miR-100 and miR-34 regulate the cell cycle during diapause entry by targeting polo-like kinase 1 (PLK1), leading to activation of the mitogen-activated protein kinase kinase-extracellular signal-regulated kinase-ribosomal S6 kinase 2 (MEK-ERK-RSK2) pathway and cyclin K, leading to suppression of RNA polymerase II (RNAP II) activity respectively. The findings presented in the present study provide insights into the functions of miR-100 and miR-34 and suggest that the expression profiles of miRNAs in Artemia can be used to characterize their functions in cell cycle regulation.

Transcriptional changes during Daphnia pulex development indicate that the maturation decision resembles a rate more than a threshold

Maturation is a critical developmental process, and the age and size at which it occurs have important fitness consequences. Although maturation is remarkably variable, certain mechanisms, including a minimum size or state threshold, are proposed to underlie the process across a broad diversity of taxa. Recent evidence suggests that thresholds may themselves be developmentally plastic, and in the crustacean Daphnia pulex it is unclear whether maturation follows a threshold or is a gradual process more akin to a rate. Changes in gene expression across four instars before and during maturation were compared in a cDNA microarray experiment. Developmental stage was treated statistically both as a discontinuous and as a continuous variable, to determine whether genes showed gradual or discrete changes in expression. The continuous analysis identified a greater number of genes with significant differential expression (45) than the discontinuous analysis (11). The majority of genes, including those coding for histones, factors relating to transcription and cell cycle processes, and a putative developmental hormone showed continuous increases or decreases in expression from the first to the fourth instars that were studied, suggestive of a prolonged and gradual maturation process. Three genes coding for a fused vitellogenin/superoxide dismutase showed increases in expression following the second instar and coincided with the posited maturation threshold, but even their expression increased in a continuous fashion.

Characterization of PHB1 and its role in mitochondrial maturation and yolk platelet degradation during development of Artemia embryos

BACKGROUND

To cope with harsh environments, crustaceans such as Artemia produce diapause gastrula embryos (cysts) with suppressed metabolism. Metabolism and development resume during post-diapause development, but the mechanism behind these cellular events remains largely unknown.

PRINCIPAL FINDING

Our study investigated the role of prohibitin 1 (PHB1) in metabolic reinitiation during post-diapause development. We found that PHB1 was developmentally regulated via changes in phosphorylation status and localization. Results from RNA interference experiments demonstrated PHB1 to be critical for mitochondrial maturation and yolk degradation during development. In addition, PHB1 was present in yolk platelets, and it underwent ubiquitin-mediated degradation during the proteolysis of yolk protein.

CONCLUSIONS/SIGNIFICANCE

PHB1 has an indispensable role in coordinating mitochondrial maturation and yolk platelet degradation during development in Artemia. This novel function of PHB1 provides new clues to comprehend the roles of PHB1 in metabolism and development.

Proteomic evaluation of citrate-coated silver nanoparticles toxicity in Daphnia magna

Recent decades have seen a strong increase in the promise and uses of nanotechnology. This is correlated with their growing release in the environment and there is concern that nanomaterials may endanger ecosystems. Silver nanoparticles (AgNPs) have some of the most varied applications, making their release into the environment unavoidable. In order to assess their potential toxicity in aquatic environments, the acute toxicity of citrate-coated AgNPs to Daphnia magna was measured and compared to that of AgNO3. AgNPs were found to be ten times less toxic by mass than silver ions, and most of this toxicity was removed by ultracentrifuging. At the protein level, the two forms of silver had different impacts. Both increased protein thiol content, while only AgNP increased carbonyl levels. In 2DE of samples labelled for carbonyls, no feature was significantly affected by both compounds, indicating different modes of toxicity. Identified proteins showed functional overlap between the two compounds: vitellogenins (vtg) were present in most features identified, indicating their role as a general stress sensor. In addition to vtg, hemoglobin levels were increased by the AgNP exposure while 14-3-3 protein (a regulatory protein) carbonylation levels were reduced by AgNO3. Overall, this study confirms the previously observed lower acute toxicity of AgNPs, while demonstrating that the toxicity of both forms of silver follow somewhat different biologic pathways, potentially leading to different interactions with natural compounds or pollutants in the aquatic environment.

Two p90 ribosomal S6 kinase isoforms are involved in the regulation of mitotic and meiotic arrest in Artemia

There are multiple isoforms of p90 ribosomal S6 kinase (RSK), which regulate diverse cellular functions such as cell growth, proliferation, maturation, and motility. However, the relationship between the structures and functions of RSK isoforms remains undetermined. Artemia is a useful model in which to study cell cycle arrest because these animals undergo prolonged diapauses, a state of obligate dormancy. A novel RSK isoform was identified in Artemia, which was termed Ar-Rsk2. This isoform was compared with an RSK isoform that we previously identified in Artemia, termed Ar-Rsk1. Ar-Rsk2 has an ERK-docking motif, whereas Ar-Rsk1 does not. Western blot analysis revealed that Ar-Rsk1 was activated by phosphorylation, which blocked meiosis in oocytes. Knockdown of Ar-Rsk1 reduced the level of phosphorylated cdc2 and thereby suppressed cytostatic factor activity. This indicates that Ar-Rsk1 regulates the cytostatic factor in meiosis. Expression of Ar-Rsk2 was down-regulated in Artemia cysts in which mitosis was arrested. Knockdown of Ar-Rsk2 resulted in decreased levels of cyclin D3 and phosphorylated histone H3, and the production of pseudo-diapause cysts. This indicates that Ar-Rsk2 regulates mitotic arrest. PLK and ERK RNAi showed that Ar-Rsk2, but not Ar-Rsk1, could be activated by PLK-ERK in Artemia. This is the first study to report that RSK isoforms with and without an ERK-docking motif regulate mitosis and meiosis, respectively. This study provides insight into the relationship between the structures and functions of RSK isoforms.

Vitellogenin-like protein measurement in caged Gammarus fossarum males as a biomarker of endocrine disruptor exposure: inconclusive experience

A vitellogenin (Vg) mass spectrometry-based assay was recently developed to actively biomonitor and assess the exposure of the amphipod Gammarus fossarum to endocrine-disrupting chemicals in freshwater hydrosystems. This paper focuses on the appropriate use of this biomarker, which requires good knowledge of its basal level in males and its natural variability related to intrinsic biotic and environmental abiotic factors. To obtain the lowest biomarker variability, we first studied some of these confounding factors. We observed that the spermatogenesis stage did not have an impact on the Vg level, allowing flexibility in the choice of transplanted gammarids. In the second part of the study, males were transplanted in two clean stations for 21 days, with results indicating a spatial and temporal variability of Vg levels. These Vg changes could not be correlated to environmental factors (e.g., temperature, pH and hardness of waters). Vg induction was then assessed in 21 stations having various levels of contamination. Inductions were observed for only two of the impacted stations studied. Under reference and contaminated conditions, a high interindividual variability of Vg levels was observed in caged organisms, severely limiting the sensitivity of the biomarker and its ability to detect a significant endocrine-disruptor effect. This may be explained by unidentified environmental factors that should later be determined to improved the use of Vg as a biomarker in male G. fossarum. Moreover, as discussed in this paper, recent advancements regarding the pleiotropic functions of the Vg gene in some species may complicate the application of this biomarker in males of invertebrate species.

Vitellogenin-like proteins among invertebrate species diversity: potential of proteomic mass spectrometry for biomarker development

Cost-effective methodologies along with cross-species applicability constitute key points for biomarker development in ecotoxicology. With the advent of cheaper affordable genomic techniques and high throughput sequencing, omics tools could facilitate the assessment of effects of environmental contaminants for all taxa biodiversity. We assessed the potential of absolute quantification of proteins using mass spectrometry to develop vitellogenin (Vg)-like protein assays for invertebrates. We used available sequences in public databases to rapidly identify Vg-proteotypic peptides in seven species from different main taxa of protostome invertebrates (mollusk bivalves, crustacean amphipods, branchiopods, copepods and isopods, and insect diptera). Functional validation was performed by comparing proteomic signals from reproductive female tissue samples and negative controls (male or juvenile tissues). In a second part, we demonstrate in gammarids, daphnids, drosophilids, and gastropods that the assay validated in Vg-sequenced species can be applied to Vg-unsequenced species thanks to the evolutionary conservation of Vg-proteotypic peptide motifs. Finally, we discuss the relevance of mass spectrometry for biomarker development (specific measurement, rapid development, transferability across species). Our study supplies an illustration of the promising strategy to address the challenge of biodiversity in ecotoxicology, which consists in employing omics tools from comparative and evolutionary perspectives.

Involvement of cyclin K posttranscriptional regulation in the formation of Artemia diapause cysts

Background

Artemia eggs tend to develop ovoviviparously to yield nauplius larvae in good rearing conditions; while under adverse situations, they tend to develop oviparously and encysted diapause embryos are formed instead. However, the intrinsic mechanisms regulating this process are not well understood.

Principal Finding

This study has characterized the function of cyclin K, a regulatory subunit of the positive transcription elongation factor b (P-TEFb) in the two different developmental pathways of Artemia. In the diapause-destined embryo, Western blots showed that the cyclin K protein was down-regulated as the embryo entered dormancy and reverted to relatively high levels of expression once development resumed, consistent with the fluctuations in phosphorylation of position 2 serines (Ser2) in the C-terminal domain (CTD) of the largest subunit (Rpb1) of RNA polymerase II (RNAP II). Interestingly, the cyclin K transcript levels remained constant during this process. In vitro translation data indicated that the template activity of cyclin K mRNA stored in the postdiapause cyst was repressed. In addition, in vivo knockdown of cyclin K in developing embryos by RNA interference eliminated phosphorylation of the CTD Ser2 of RNAP II and induced apoptosis by inhibiting the extracellular signal-regulated kinase (ERK) survival signaling pathway.

Conclusions/Significance

Taken together, these findings reveal a role for cyclin K in regulating RNAP II activity during diapause embryo development, which involves the post-transcriptional regulation of cyclin K. In addition, a further role was identified for cyclin K in regulating the control of cell survival during embryogenesis through ERK signaling pathways.