Habitat diversity and adaptation to environmental stress in encysted embryos of the crustaceanArtemia

Enhanced sequestration of Pb2+ and Cu2+ by Artemia cyst shell supported nano-Mg composite and the potential photocatalytic performance of carbonized exhausted-adsorbent

This study reported a new strategy for enhanced Pb2+ and Cu2+ sequestration by Artemia cyst shell (shell) supported nano-Mg from aqueous solutions and the carbonated exhausted-adsorbents sequenced potential application in photo-catalyst, which obtained two expected results. One is that the immobilization of nano-Mg onto Artemia cyst shell (shell-Mg) can greatly strengthen the adsorption effect of the neat cyst shell on Pb2+ and Cu2+. The adsorption capacities of shell-Mg for both metal ions reached to 622.01 and 313.91 mg/g, which was 10-15 and 30-50 times that of the neat shell respectively. And shell-Mg has strong selectivity, which was approximately 2-4 times that of shell. The shell-Mg can be used to retrieve Pb2+ and Cu2+ from aqueous solutions efficiently. Another is that the carbonated exhausted-adsorbents (C-shell-Mg-Pb and C-shell-Mg-Cu) showed their potential photocatalytic degradation effects on congo red under pH = 4 condition, the decolorization rate reached to 61.19% and 80.39% respectively. Reuse of exhausted adsorbents can avoid the secondary pollution caused by the regeneration, extend the utilization value of exhausted adsorbents, and provide a new viewpoint for the reuse of spent bio-nanomaterial adsorbents.

The pre- and postembryonic development of Artemia franciscana (Anostraca: Artemiidae)

Artemia franciscana is a universal live feed in aquaculture, and it has been reported as an invasive species in many Asian hypersaline ecosystems. The present observations illustrated the pre- and postembryonic development stages of the A. franciscana population confined to the Indian saltern of Kelambakkam. We observed their growth patterns during various hydration periods with specific time intervals. Results showed differences in the development stages with respect to unique identity. Interestingly, a period of hydration showed notable cellular movement toward clockwise positions in the hydrating cysts. After 10 h of hydration, blastocoel appeared, accelerating the dynamic route of nuclei movement. At the end of the invagination, the embryo burst out of the cyst, and a sequence of emerging stages was noted. With reference to light microscopic observations, a series of developmental stages were observed, and each instar was documented by developing limb buds of nauplii. Excitingly, the 10th and 11th instar stages reveal sexual differentiation between male and female individuals. Thus, the laboratory culture study clearly documented the different developmental stages with their specific characteristic features. However, further molecular study would provide a cellular basis for understanding the early development of A. franciscana.

Silver nanoparticle toxicity on Artemia parthenogenetica nauplii hatched on axenic tryptic soy agar solid medium

The use of gnobiotic brine shrimp (Artemia spp.) for ecotoxicology and bacteria-host interaction studies is common. However, requirements for axenic culture and matrix effects of seawater media can be an obstacle. Thus, we investigated the hatching ability of Artemia cysts on a novel sterile Tryptic Soy Agar (TSA) medium. Herein, we demonstrate for the first time that Artemia cysts can hatch on a solid medium without liquid, which offers practical advantages. We further optimized the culture conditions for temperature and salinity and assessed this culture system for toxicity screening of silver nanoparticles (AgNPs) across multiple biological endpoints. Results revealed that maxima hatching (90%) of embryos occurred at 28 °C and without addition of sodium chloride. When capsulated cysts were cultured on TSA solid medium Artemia were negatively impacted by AgNPs at 30-50 mgL^-1 in terms of the embryo hatching ratio (47-51%), umbrella- to nauplii-stage transformation ratio (54-57%), and a reduction in nauplii-stage growth (60-85% of normal body length). At 50-100 mgL^-1 AgNPs and higher, evidence of damage to lysosomal storage was recorded. At 500 mgL^-1 AgNPs, development of the eye was inhibited and locomotory behavior impeded. Our study reveals that this new hatching method has applications in ecotoxicology studies and provides an efficient means to control axenic requirements to produce gnotobiotic brine shrimp.

Effect of Different Culture Conditions on Gene Expression Associated With Cyst Production in Populations of Artemia franciscana

Artemia franciscana inhabits hypersaline environments in the Americas and has a well-adapted reproductive system that allows it to survive in these extreme conditions, represented by the production of diapause cysts (oviparous reproduction). This reproduction mode is controlled by numerous genes that are expressed in response to different environmental stressors, enabling this species to avoid population extinction. However, to date, the expression of these genes has not been sufficiently studied to clarify their levels in response to a combination of different environmental factors under controlled conditions. We analyzed the expression of eight genes related to oviparous reproduction (SGEG, Arp-CBP, artemin, BRCA1, p8, ArHsp21, ArHsp22, and p26) to determine their association with cyst production in two populations of A. franciscana with contrasting phenotypes, one with high (Barro Negro, BNE, Chile) and one with low (San Francisco Bay, SFB, United States) cyst production. Populations were cultured under controlled conditions of salinity (SAL, 35 and 75 ppt), photoperiod (PHO, 12L:12D and 24L:00D), iron concentration (IC, 0[Fe] and 5[Fe]), and microalgae diet (DIE; Dunaliella tertiolecta (DUN) and Tetraselmis suecica (TETRA)). Sixteen treatments were performed by combining the two conditions of each of the four factors. Data on nine reproductive parameters per female were recorded, including the percent of offspring encysted (%) (POE). The gene expression levels were analyzed by semiquantitative RT-PCR. The mean POE was significantly greater in BNE than in SFB (32.40 versus 12.74%, Mann-Whitney's test, p < 0.05). Significantly upregulated expression of seven genes in BNE (more than twofold, p < 0.05) was observed in 38.28% of the treatments (e.g., DUN-75ppt-12L:12D-5[Fe] and TETRA-35ppt-12L:12D-5[Fe]). In SFB, seven genes showed significant differential expression, but most were downregulated in 29.69% of the treatments (e.g., DUN-75ppt-12L:12D-0[Fe] and DUN-75ppt-24L:00D-0[Fe]). Multiple regression analyses indicated that in BNE, five genes (SGEG, artemin, Arp-CBP, p8, and BRCA1) and three environmental factors (DIE, SAL, and IC) were important predictor variables for the POE response variable given that all of them were included in the highest-ranking models. In SFB, only two genes (ArHsp21 and artemin) and one environmental factor (SAL) were important explanatory variables in the highest-ranking models. It was concluded that the BNE population presented a characteristic gene expression pattern that differed from that of the SFB population. This pattern might be related to the marked oviparous reproduction of the BNE population. This gene expression pattern could be useful for monitoring the reproductive mode leading to diapause in Artemia and to assist with intensive cyst production in pond systems.

Histological study of gonadal tissues of adult Artemia salina (Linnaeus 1758) and immunohistochemistry by Caspase 3 and HSP70 to detect specific apoptosis markers on gonadal tissues after exposure to TBTCl

Background:

Several types of research have been recently carried out on the biological effects of TBTs, including investigations of genitals in invertebrates in response to exposure to TBTs in marine water.

Aim:

The objective of this research was to investigate the acute effects of tributyltin chloride (TBTCl) on gonads in the adult stage of Artemia salina by use normal histology and immunohistochemistry (IHC) (Caspase 3 and HSP70) to see specific apoptosis markers.

Methods:

After exposure of A. salina to different concentrations of TBTCl (25, 50, 100, 200, and 300 ng.l⁻¹), 50 adult A. salina (25 male and 25 female) were selected randomly from each concentration to histologically study the gonads. The gonad tissue was sectioned (5 μm) and some slides were stained with hematoxylin and eosin and others were stained with IHC avidin–biotin complex, and were examined under a light microscope.

Results:

The results showed significant differences (p < 0.05) in histological lesions between different concentrations of TBTCl. The histological lesions in the testis and ovary section were undifferentiated cells, degenerating yolk globules, and follicle cells enveloping the oocyte which was then compared with control tissue, and these effects were found to be increased in females more than in males with the highest concentration of TBTCl. Immunohistochemistry (IHC) showed that positive immunostaining was observed in the testis and ovary as brownish deposits to Caspase 3 and HSP70 antibody after exposure to TBTCl, while the testis and ovary section in control tissue had no immunoreactivity to Caspase 3 and HSP70 antibody; these effects were profoundly increased with the highest concentration of TBTCl in females more than in males. Finally, the histological lesions and IHC (Caspase 3 and HSP70) revealed that the apoptosis and immune system stress of A. salina gonad tissue damage in females were more sensitive to TBTCl toxicity as compared to white males.

Conclusion:

In general, the present study aimed to observe the effects TBTCl on A. salina gonads by using histological sections and IHC (Caspase 3 and HSP70), which were evaluated for the first time and have been proven to possess an important function in apoptosis marker and immune system stress in Artemia. Finally, the specific mechanisms through which TBTCl affects A. salina Caspase 3 and HSP70 expression need further investigation.

Mechanisms of Desiccation Tolerance: Themes and Variations in Brine Shrimp, Roundworms, and Tardigrades

Water is critical for the survival of most cells and organisms. Remarkably, a small number of multicellular animals are able to survive nearly complete drying. The phenomenon of anhydrobiosis, or life without water, has been of interest to researchers for over 300 years. In this review we discuss advances in our understanding of protectants and mechanisms of desiccation tolerance that have emerged from research in three anhydrobiotic invertebrates: brine shrimp (Artemia), roundworms (nematodes), and tardigrades (water bears). Discovery of molecular protectants that allow each of these three animals to survive drying diversifies our understanding of desiccation tolerance, and convergent themes suggest mechanisms that may offer a general model for engineering desiccation tolerance in other contexts.

Characteristics, dynamics and mechanisms of actions of some major stress-induced biomacromolecules; addressing Artemia as an excellent biological model

Stress tolerance is one of the most prominent and interesting topics in biology since many macro- and micro-adaptations have evolved in resistant organisms that are worth studying. When it comes to confronting various environmental stressors, the extremophile Artemia is unrivaled in the animal kingdom. In the present review, the evolved molecular and cellular basis of stress tolerance in resistant biological systems are described, focusing on Artemia cyst as an excellent biological model. The main purpose of the review is to discuss how the structure and physicochemical characteristics of protective factors such as late embryogenesis abundant proteins (LEAPs), small heat shock proteins (sHSPs) and trehalose are related to their functions and by which mechanisms, they exert their functions. In addition, some metabolic depressors in Artemia encysted embryos are also mentioned, indirectly playing important roles in stress tolerance. Importantly, a great deal of attention is given to the LEAPs, exhibiting distinctive folding behaviors and mechanisms of actions. For instance, molecular shield function, chaperone-like activity, moonlighting property, sponging and snorkeling capabilities of the LEAPs are delineated here. Moreover, the molecular interplay between some of these factors is mentioned, leading to their synergistic effects. Interestingly, Artemia life cycle adapts to environmental conditions. Diapause is the defense mode of this life cycle, safeguarding Artemia encysted embryos against various environmental stressors. Communicated by Ramaswamy H. Sarma.

Morphological and molecular clues for recording the first appearance of Artemia franciscana () in Egypt

Artemia franciscana is a native species to the New World, and became an exotic species to most parts of the world. The Egyptian hypersaline, continental Qaroun Lake (Fayoum Governorate, Middle of Egypt) is subjected to a gradually increasing salinity rates that approximate or exceed these of seawater. Artemia populations there are known to be parthenogenetic. Yet, these populations started to exhibit abnormal morphologies. Therefore, Qaroun Lake samples of Artemia were subjected to several morphological, biometric, and molecular phylogenetic analyses for accurate species identification and phylogeographic origin approximation. These analyses revealed the existence of the alien sexual species of brine shrimp A. franciscana in Qaroun Lake. The characteristics of the subspherical frontal knob with several spines on the top, ovisac lateral triangular lobe on both sides and its projection together with the biometrics confirmed this species morphotype. DNA barcoding and other molecular analyses based on PCR-based amplification and sequencing of the barcode region of the cytochrome oxidase subunit I gene (COI) exhibited that all the collected samples belong to five haplotypes. Egyptian A. franciscana COI sequences phylogeny and pairwise distances analysis exhibited closer proximity to Latin American strains than to the Northern American ones. A. franciscana presence may be ascribed to the migratory birds present in Qaroun Lake protectorate, since no marine aquaculture activity in Qaroun Lake is known. Therefore, and for the best of our knowledge, this is the first record of the invasive A. franciscana in Egypt.

Resurrection ecology in Artemia

Resurrection ecology (RE) is a very powerful approach to address a wide range of question in ecology and evolution. This approach rests on using appropriate model systems, and only few are known to be available. In this study, we show that Artemia has multiple attractive features (short generation time, cyst bank and collections, well‐documented phylogeography, and ecology) for a good RE model. We show in detail with a case study how cysts can be recovered from sediments to document the history and dynamics of a biological invasion. We finally discuss with precise examples the many RE possibilities with this model system: adaptation to climate change, to pollution, to parasites, to invaders and evolution of reproductive systems.

Ultraviolet B radiation induces impaired lifecycle traits and modulates expression of cytochrome P450 (CYP) genes in the copepod Tigriopus japonicus

To evaluate the effects of ultraviolet B (UV-B) radiation at the developmental, reproductive, and molecular levels in aquatic invertebrates, we measured UV-B-induced acute toxicity, impairments in developmental and reproductive traits, and UV-B interaction with the entire family of cytochrome P450 (CYP) genes in the intertidal benthic copepod Tigriopus japonicus. We found a significant, dose-dependent reduction (P<0.05) in the survival of T. japonicus that began as a developmental delay and decreased fecundity. The 48h LD10 and LD50 were 1.35 and 1.84kJ/m², and the CYP inhibitor (PBO) elevated mortality, confirming the involvement of CYP genes in UV-B induced toxicity. Low-dose UV-B (1.5kJ/m²) induced developmental delays, and higher doses (6-18kJ/m²) caused reproductive impairments in ovigerous females. The significant up-regulation of CYP genes belonging to clans 2/3/MT/4/20 in T. japonicus exposed to UV-B (12kJ/m²) confirmed molecular interaction between UV-B and CYP genes. Moreover, orphan CYPs, such as CYP20A1, provide good insight on the deorphanization of invertebrate CYPs. Overall, these results demonstrate the involvement of UV-B radiation in the expression of all the CYP genes in T. japonicus and their susceptibility to UV-B radiation. This will provide a better understanding of the mechanistic effects of UV-B in copepods through the predicted AhR-mediated up-regulation of CYP genes.

The Effects of Purified Artemia Extract Proteins on Proliferation, Differentiation and Apoptosis of Human Leukemic HL-60 Cells

There has been an increment in the number of studies focused on marine bioactive materials. Many peptides and other biomaterials with anticancer potential have been extracted from various marine animals. Artemia extracts have found uses in sun-light protection cosmetics and anti-aging products. However, contents of biochemical compounds in Artemia spp. and molecular mechanisms of have not been clearly studied in leukemic cells in vitro. In this work, we isolated and purified proteins of Artemia Urmiana. Six clear fractions (A-F) observed on DEAE-cellulose chromatography were assayed for effects on cell growth, differentiation and apoptosis using the human leukemic HL-60 cell line. Cell proliferation analysis by MTT and BrdU assays indicated that did not affect cells, growth. Cells treated with crude extract and fractions A, B and C, but not E and F (up to 100 µg/mL), exhibited increase of cell growth in a dose dependent manner. Stimulatory effects of fraction D were observed at concentrations of 10 µg/ml and above. In nitro blue tetrazolium (NBT) reduction assays, treatment with 100 µg/mL of fraction E or F for 96 hr increased the fraction of differentiated cells up to 14.8 ± 3.56% and 16.5 ± 2.08% respectively. Combination of those fractions with retinoic acid had significant synergistic effects on the differentiation of cells (56.8 ± 3.7% and 67.4 ± 4.2%, p≤0.01). Annexin-V FITC staining for apoptosis and flow cytometric assays indicated induction of apoptosis by fractions E and F up to 23.8 and 31.8% of cells.

The RNA-editing deaminase ADAR is involved in stress resistance of Artemia diapause embryos

The most widespread type of RNA editing, conversion of adenosine to inosine (A→I), is catalyzed by two members of the adenosine deaminase acting on RNA (ADAR) family, ADAR1 and ADAR2. These enzymes edit transcripts for neurotransmitter receptors and ion channels during adaption to changes in the physical environment. In the primitive crustacean Artemia, when maternal adults are exposed to unfavorable conditions, they release diapause embryos to withstand harsh environments. The aim of the current study was therefore to elucidate the role of ADAR of Artemia diapause embryos in resistance to stress. Here, we identified Artemia ADAR (Ar-ADAR), which harbors a putative nuclear localization sequence (NLS) and two double-stranded RNA-binding motifs (dsRBMs) in the amino-terminal region and an adenosine deaminase (AD) domain in the carboxyl-terminal region. Western blot and immunofluorescence analysis revealed that Ar-ADAR is expressed abundantly in post-diapause embryos. Artemia (n = 200, three replicates) were tested under basal and stress conditions. We found that Ar-ADAR was significantly induced in response to the stresses of salinity and heat-shock. Furthermore, in vivo knockdown of Ar-ADAR (n = 100, three replicates) by RNA interference induced formation of pseudo-diapause embryos, which lack resistance to the stresses and exhibit high levels of apoptosis. These results indicate that Ar-ADAR contributes to resistance to stress in Artemia diapause embryos.

Mechanisms of animal diapause: recent developments from nematodes, crustaceans, insects, and fish

Life cycle delays are beneficial for opportunistic species encountering suboptimal environments. Many animals display a programmed arrest of development (diapause) at some stage(s) of their development, and the diapause state may or may not be associated with some degree of metabolic depression. In this review, we will evaluate current advancements in our understanding of the mechanisms responsible for the remarkable phenotype, as well as environmental cues that signal entry and termination of the state. The developmental stage at which diapause occurs dictates and constrains the mechanisms governing diapause. Considerable progress has been made in clarifying proximal mechanisms of metabolic arrest and the signaling pathways like insulin/Foxo that control gene expression patterns. Overlapping themes are also seen in mechanisms that control cell cycle arrest. Evidence is emerging for epigenetic contributions to diapause regulation via small RNAs in nematodes, crustaceans, insects, and fish. Knockdown of circadian clock genes in selected insect species supports the importance of clock genes in the photoperiodic response that cues diapause. A large suite of chaperone-like proteins, expressed during diapause, protects biological structures during long periods of energy-limited stasis. More information is needed to paint a complete picture of how environmental cues are coupled to the signal transduction that initiates the complex diapause phenotype, as well as molecular explanations for how the state is terminated. Excellent examples of molecular memory in post-dauer animals have been documented in Caenorhabditis elegans It is clear that a single suite of mechanisms does not regulate diapause across all species and developmental stages.

Study of model systems to test the potential function of Artemia group 1 late embryogenesis abundant (LEA) proteins

Embryos of the brine shrimp, Artemia franciscana, are genetically programmed to develop either ovoviparously or oviparously depending on environmental conditions. Shortly upon their release from the female, oviparous embryos enter diapause during which time they undergo major metabolic rate depression while simultaneously synthesize proteins that permit them to tolerate a wide range of stressful environmental events including prolonged periods of desiccation, freezing, and anoxia. Among the known stress-related proteins that accumulate in embryos entering diapause are the late embryogenesis abundant (LEA) proteins. This large group of intrinsically disordered proteins has been proposed to act as molecular shields or chaperones of macromolecules which are otherwise intolerant to harsh conditions associated with diapause. In this research, we used two model systems to study the potential function of the group 1 LEA proteins from Artemia. Expression of the Artemia group 1 gene (AfrLEA-1) in Escherichia coli inhibited growth in proportion to the number of 20-mer amino acid motifs expressed. As well, clones of E. coli, transformed with the AfrLEA-1 gene, expressed multiple bands of LEA proteins, either intrinsically or upon induction with isopropyl-β-thiogalactoside (IPTG), in a vector-specific manner. Expression of AfrLEA-1 in E. coli did not overcome the inhibitory effects of high concentrations of NaCl and KCl but modulated growth inhibition resulting from high concentrations of sorbitol in the growth medium. In contrast, expression of the AfrLEA-1 gene in Saccharomyces cerevisiae did not alter the growth kinetics or permit yeast to tolerate high concentrations of NaCl, KCl, or sorbitol. However, expression of AfrLEA-1 in yeast improved its tolerance to drying (desiccation) and freezing. Under our experimental conditions, both E. coli and S. cerevisiae appear to be potentially suitable hosts to study the function of Artemia group 1 LEA proteins under environmentally stressful conditions.

Stress tolerance during diapause and quiescence of the brine shrimp, Artemia

Oviparously developing embryos of the brine shrimp, Artemia, arrest at gastrulation and are released from females as cysts before entering diapause, a state of dormancy and stress tolerance. Diapause is terminated by an external signal, and growth resumes if conditions are permissible. However, if circumstances are unfavorable, cysts enter quiescence, a dormant stage that continues as long as adverse conditions persist. Artemia embryos in diapause and quiescence are remarkably resistant to environmental and physiological stressors, withstanding desiccation, cold, heat, oxidation, ultraviolet radiation, and years of anoxia at ambient temperature when fully hydrated. Cysts have adapted to stress in several ways; they are surrounded by a rigid cell wall impermeable to most chemical compounds and which functions as a shield against ultraviolet radiation. Artemia cysts contain large amounts of trehalose, a non-reducing sugar thought to preserve membranes and proteins during desiccation by replacing water molecules and/or contributing to vitrification. Late embryogenesis abundant proteins similar to those in seeds and other anhydrobiotic organisms are found in cysts, and they safeguard cell organelles and proteins during desiccation. Artemia cysts contain abundant amounts of p26, a small heat shock protein, and artemin, a ferritin homologue, both ATP-independent molecular chaperones important in stress tolerance. The evidence provided in this review supports the conclusion that it is the interplay of these protective elements that make Artemia one of the most stress tolerant of all metazoan organisms.

UV-B radiation-induced oxidative stress and p38 signaling pathway involvement in the benthic copepod Tigriopus japonicus

Ultraviolet B (UV-B) radiation presents an environmental hazard to aquatic organisms. To understand the molecular responses of the intertidal copepod Tigriopus japonicus to UV-B radiation, we measured the acute toxicity response to 96 h of UV-B radiation, and we also assessed the intracellular reactive oxygen species (ROS) levels, glutathione (GSH) content, and antioxidant enzyme (GST, GR, GPx, and SOD) activities after 24 h of exposure to UV-B with LD50 and half LD50 values. Also, expression patterns of p53 and hsp gene families with phosphorylation of p38 MAPK were investigated in UV-B-exposed copepods. We found that the ROS level, GSH content, and antioxidant enzyme activity levels were increased with the transcriptional upregulation of antioxidant-related genes, indicating that UV-B induces oxidative stress by generating ROS and stimulating antioxidant enzymatic activity as a defense mechanism. Additionally, we found that p53 expression was significantly increased after UV-B irradiation due to increases in the phosphorylation of the stress-responsive p38 MAPK, indicating that UV-B may be responsible for inducing DNA damage in T. japonicus. Of the hsp family genes, transcriptional levels of hsp20, hsp20.7, hsp70, and hsp90 were elevated in response to a low dose of UV-B radiation (9 kJ m(-2)), suggesting that these hsp genes may be involved in cellular protection against UV-B radiation. In this paper, we performed a pathway-oriented mechanistic analysis in response to UV-B radiation, and this analysis provides a better understanding of the effects of UV-B in the intertidal benthic copepod T. japonicus.

Artemin, a diapause-specific chaperone, contributes to the stress tolerance of Artemia franciscana cysts and influences their release from females

Females of the crustacean Artemia franciscana produce either motile nauplii or gastrula stage embryos enclosed in a shell impermeable to nonvolatile compounds and known as cysts. The encysted embryos enter diapause, a state of greatly reduced metabolism and profound stress tolerance. Artemin, a diapause-specific ferritin homolog in cysts has molecular chaperone activity in vitro. Artemin represents 7.2% of soluble protein in cysts, approximately equal to the amount of p26, a small heat shock protein. However, there is almost twice as much artemin mRNA in cysts as compared with p26 mRNA, suggesting that artemin mRNA is translated less efficiently. RNA interference employing the injection of artemin double-stranded RNA into the egg sacs of A. franciscana females substantially reduced artemin mRNA and protein in cysts. Decreasing artemin diminished desiccation and freezing tolerance of cysts, demonstrating a role for this protein in stress resistance. Knockdown of artemin increased the time required for complete discharge of a brood of cysts carried within a female from a few hours up to 4 days, an effect weakened in successive broods. Artemin, an abundant molecular chaperone, contributes to stress tolerance of A. franciscana cysts while influencing their development and/or exit from females.

Food odor, visual danger stimulus, and retrieval of an aversive memory trigger heat shock protein HSP70 expression in the olfactory lobe of the crab Chasmagnathus granulatus

Although some of the neuronal substrates that support memory process have been shown in optic ganglia, the brain areas activated by memory process are still unknown in crustaceans. Heat shock proteins (HSPs) are synthesized in the CNS not only in response to traumas but also after changes in metabolic activity triggered by the processing of different types of sensory information. Indeed, the expression of citosolic/nuclear forms of HSP70 (HSC/HSP70) has been repeatedly used as a marker for increases in neural metabolic activity in several processes, including psychophysiological stress, fear conditioning, and spatial learning in vertebrates. Previously, we have shown that, in the crab Chasmagnathus, two different environmental challenges, water deprivation and heat shock, trigger a rise in the number of glomeruli of the olfactory lobes (OLs) expressing HSC/HSP70. In this study, we initially performed a morphometric analysis and identified a total of 154 glomeruli in each OL of Chasmagnathus. Here, we found that crabs exposed to food odor stimuli also showed a significant rise in the number of olfactory glomeruli expressing HSC/HSP70. In the crab Chasmagnathus, a powerful memory paradigm based on a change in its defensive strategy against a visual danger stimulus (VDS) has been extensively studied. Remarkably, the iterative presentation of a VDS caused an increase as well. This increase was triggered in animals visually stimulated using protocols that either build up a long-term memory or generate only short-term habituation. Besides, memory reactivation was sufficient to trigger the increase in HSC/HSP70 expression in the OL. Present and previous results strongly suggest that, directly or indirectly, an increase in arousal is a sufficient condition to bring about an increase in HSC/HSP70 expression in the OL of Chasmagnathus.

Extracellular matrix peptides of Artemia cyst shell participate in protecting encysted embryos from extreme environments

Background

Many species of the brine shrimp Artemia are found in various severe environments in many parts of the world where extreme salinity, high UV radiation levels, high pH, anoxia, large temperature fluctuations, and intermittent dry conditions are often recorded. To withstand adverse environments, Artemia undergoes an oviparous developmental pathway to release cysts whereas, under favorable conditions, swimming nauplius larvae are formed directly via an ovoviviparous pathway. In the former case these cysts have an extraordinary ability to keep the embryos protected from the harsh environment for long periods. This is achieved through the protection by a complex out-wrapping cyst shell. However, the formation and function of the cyst shell is complex; the details remain largely unclear.

Principal Finding

A shell gland-specific gene (SGEG2) was cloned and identified from a suppression subtractive hybridization library. Western blot analysis showed that SGEG2 presumably requires post-translational proteolysis in order to be processed into two mature peptides (SGEG2a and 2b). The three matrix peptides (SGEG1 reported previously, 2a, and 2b) were found to distribute throughout the cyst shell. The results of gene knockdown by RNAi and subsequent resistance to environmental stresses assays indicated that these matrix peptides are required for cyst shell formation and are involved in protecting the encysted embryos from environmental stress.

Conclusions/Significance

This study revealed that extracellular matrix peptides participate in protecting embryos from extreme salinity, UV radiation, large temperature fluctuations and dry environments, thereby facilitating their survival. The cyst shell provides an excellent opportunity to link the ecological setting of an organism to the underlying physiological and biochemical processes enabling its survival. The cyst shell material has also a high potential to become an excellent new biomaterial with a high number of prospective uses due, specifically, to such biological characteristics.

The structural stability and chaperone activity of artemin, a ferritin homologue from diapause-destined Artemia embryos, depend on different cysteine residues

Diapause-destined embryos of the crustacean, Artemia franciscana, accumulate large amounts of an oligomeric, heat-stable, molecular chaperone termed artemin, a cysteine-enriched ferritin homologue. In this study, cysteines 22, 61, 166, and 172 of artemin were substituted with alanines, respectively yielding ArtC22A, ArtC61A, ArtC166A, and ArtC172A. Wild-type and modified artemins were synthesized in transformed bacteria and purified. As measured by heat-induced denaturation of citrate synthase in vitro, each substitution reduced chaperone activity, with ArtC172A the least active. Protein modeling indicated that C172 is close to a region of surface hydrophobicity, also present in ferritin, suggesting that this site contributes to chaperone activity. Only slight differences in oligomer molecular mass were apparent between artemin variants, but ArtC22A and ArtC61A displayed significantly reduced thermostability, perhaps due to the disruption of an inter-subunit disulphide bridge. In contrast, ArtC172A was thermostable, reflecting the location of C172 on the oligomer surface and that it contributes minimally to artemin stabilization. To our knowledge, this is the initial study of structure/function relationships within a ferritin homologue of importance in diapause and the first to indicate that a defined region of hydrophobicity contributes to artemin and ferritin chaperoning.

Gene expression, metabolic regulation and stress tolerance during diapause

Diapause entails molecular, physiological and morphological remodeling of living animals, culminating in a dormant state characterized by enhanced stress tolerance. Molecular mechanisms driving diapause resemble those responsible for biochemical processes in proliferating cells and include transcriptional, post-transcriptional and post-translational processes. The results are directed gene expression, differential mRNA and protein accumulation and protein modifications, including those that occur in response to changes in cellular redox potential. Biochemical pathways switch, metabolic products change and energy production is adjusted. Changes to biosynthetic activities result for example in the synthesis of molecular chaperones, late embryogenesis abundant (LEA) proteins and protective coverings, all contributing to stress tolerance. The purpose of this review is to consider regulatory and mechanistic strategies that are potentially key to metabolic control and stress tolerance during diapause, while remembering that organisms undergoing diapause are as diverse as the processes itself. Some of the parameters described have well-established roles in diapause, whereas the evidence for others is cursory.

Characterization of a group 1 late embryogenesis abundant protein in encysted embryos of the brine shrimp Artemia franciscana

Late embryogenesis abundant (LEA) proteins are hydrophilic molecules that are believed to function in desiccation and low-temperature tolerance in some plants and plant propagules, certain prokaryotes, and several animal species. The brine shrimp Artemia franciscana can produce encysted embryos (cysts) that enter diapause and are resistant to severe desiccation. This ability is based on biochemical adaptations, one of which appears to be the accumulation of the LEA protein that is the focus of this study. The studies described herein characterize a 21 kDa protein in encysted Artemia embryos as a group 1 LEA protein. The amino acid sequence of this protein and its gene have been determined and entered into the NCBI database (no. EF656614). The LEA protein consists of 182 amino acids and it is extremely hydrophilic, with glycine (23%), glutamine (17%), and glutamic acid (12.6%) being the most abundant amino acids. This protein also consists of 8 tandem repeats of a 20 amino acid sequence, which is characteristic of group 1 LEA proteins from non-animal species. The LEA protein and its gene are expressed only in encysted embryos and not in larvae or adults. Evidence is presented to show that the LEA protein functions in the prevention of drying-induced protein aggregation, which supports its functional role in desiccation tolerance. This report describes, for the first time, the purification and characterization of a group 1 LEA protein from an animal species.

Sequence and structural analysis of artemin based on ferritin: a comparative study

Artemia cysts can tolerate extreme environments, partly due to a heat-stable protein called artemin. According to previous studies, artemin shares structural similarity with ferritins. Actually, there is still no strong structural information about artemin three-dimensional (3-D) structure. In this research, the artemin encoding gene from Artemia urmiana was cloned and sequenced. A reliable 3-D model of artemin was initially built using ferritin as template and refined using Molecular Dynamic (MD) Simulation. It is interesting that the proposed model, confirmed by circular dichroism (CD), shows significant differences in secondary structure contents with ferritin. Three conserved regions (ferroxidase center, iron nucleation center and 3-fold channel) in ferritins, cooperating in iron-interaction, have been substantially changed in artemin. Analysis of C-terminal region of the model revealed its major role in preventing artemin from iron-binding due to some suitable interactions. Finally, it is concluded that significant differences between artemin and ferritin, both in conserved regions related to iron-interaction and three-dimensional structure, can justify their functional differences.

Formation of diapause cyst shell in brine shrimp, Artemia parthenogenetica, and its resistance role in environmental stresses

Artemia has attracted much attention for its ability to produce encysted embryos wrapped in a protective shell when subject to extremely harsh environmental conditions. However, what the cyst shell is synthesized from and how the formative process is performed remains, as yet, largely unknown. Over 20 oviparous specifically expressed genes were identified through screening the subtracted cDNA library enriched between oviparous and ovoviviparous Artemia ovisacs. Among them, a shell gland-specifically expressed gene (SGEG) has been found to be involved in the cyst shell formation. Lacking SGEG protein (by RNA interference) caused the cyst shell to become translucent and the chorion layer of the shell to become less compact and pultaceous and to show a marked decrease of iron composition within the shell. The RNA interference induced defective diapause cysts with a totally compromised resistibility to UV irradiation, extremely large temperature differences, osmotic pressure, dryness, and organic solvent stresses. In contrast, the natural cyst would provide adequate protection from all such factors. SGEG contains a 345-bp open reading frame, and its consequentially translated peptide consists of a 33-amino acid residue putative signal peptide and an 81-amino acid residue mature peptide. The results of Northern blotting and in situ hybridization indicate that the gene is specifically expressed in the cells of shell glands during the period of diapause cyst formation of oviparous Artemia. This investigation adds strong insight into the mechanism of cyst shell formation of Artemia and may be applicable to other areas of research in extremophile biology.

Two highly diverged New World Artemia species, A. franciscana and A. persimilis, from contrasting hypersaline habitats express a conserved stress protein complement

The brine shrimp Artemia is a well known animal extremophile adapted to survive in very harsh hypersaline environments. We compared the small stress proteins artemin and p26, and the chaperone hsc70 in encysted embryos (cysts) of the New World species, A. franciscana and A. persimilis. Cysts of the former, from San Francisco Bay, USA (SFB), were used essentially as a reference for these proteins, while both species were from locations in Chile where they occur in habitats at latitudinal extremes, the Atacama desert and Patagonia. These two species are phylogenetically distant, A. persimilis being closer to the Old World species, whilst A. franciscana is considered younger and undergoing evolutionary expansion. Using western blotting we found all three stress proteins in cysts from these five populations in substantial although variable amounts. The protein profiles revealed by Coomassie staining after electrophoresis (SDS-PAGE) were similar qualitatively, in spite of marked differences in the habitats from which these populations originated, and the long time since they diverged. We interpret these findings as further evidence for the adaptive importance of these three conserved proteins in coping with the variable, but severe stresses these encysted embryos endure.

Both heat shock and water deprivation trigger Hsp70 expression in the olfactory lobe of the crab Chasmagnathus granulatus

Heat-shock proteins (Hsp) are synthesized in the central nervous system in response to traumas but also after physical exercise and psychophysiological stress. Therefore, an increase in Hsp expression is a good marker of changes in metabolic activity. In the crab Chasmagnathus, a powerful memory paradigm has been established. Memory modulation is possible by water shortage. The brain areas activated by either training protocols and/or water-deprivation are still unknown. Hsp expression might be a marker to sensing the increase in metabolic activity in crab Chasmagnathus brain neuropils engaged in the physiological responses triggered by water deprivation and cognitive processing. Here, we observed an increase in brain Hsp of 70kDa (Hsp70) expression after a heat-shock treatment. Additionally, immunohistochemistry analysis revealed that, under basal conditions, some glomeruli of the olfactory lobes showed Hsp70 immunoreactivity in an on-off manner. Both a hot environment and water deprivation increased the number of glomeruli expressing Hsp70. This marker of neuropil's activity might turn out to be a powerful tool to test whether crustacean olfactory lobes not only process olfactory information but also integrate multimodal signals.

CONDITIONAL PRODUCTION OF A FUNCTIONAL FISH GROWTH HORMONE IN THE TRANSGENIC LINE OF NANNOCHLOROPSIS OCULATA (EUSTIGMATOPHYCEAE)(1)

Plasmid phr-YPGHc, containing the fish growth hormone (GH) cDNA driven by a heat shock protein 70A promoter and a RUBISCO SSU 2 promoter, was transferred into the protoplast of marine microalga Nannochloropsis oculata (Droop) D. J. Hibberd by electroporation. Four transgenic clones were obtained in which the transferred phr-YPGHc was integrated into the genome and existed stably at least until the 50th generation. When we treated these transgenic microalgae by heat shock, the heterologous fish GH was produced in the amount of 0.42 to 0.27 μg · mL(-1) from the 50 mL of medium. We incubated artemia with the wildtype and transgenic N. oculata for 6 h and then fed these microalgae-treated artemia to red-tilapia larvae. After feeding, the growth of larvae that were fed artemia incubated with transgenic microalgae was greater (i.e., statistically significant: P < 0.05) than that of larvae that were fed artemia incubated with nontransgenic microalgae: 316% versus 104% in weight gain, and 217% versus 146% in body length increase, respectively. Therefore, the N. oculata enables production of functional GH, and we propose that it might be an excellent bioreactor material.

Tardigrades as a potential model organism in space research

Exposure of living organisms to open space requires a high level of tolerance to desiccation, cold, and radiation. Among animals, only anhydrobiotic species can fulfill these requirements. The invertebrate phylum Tardigrada includes many anhydrobiotic species, which are adapted to survive in very dry or cold environmental conditions. As a likely by-product of the adaptations for desiccation and freezing, tardigrades also show a very high tolerance to a number of other, unnatural conditions, including exposure to ionizing radiation. This makes tardigrades an interesting candidate for experimental exposure to open space. This paper reviews the tolerances that make tardigrades suitable for astrobiological studies and the reported radiation tolerance in other anhydrobiotic animals. Several studies have shown that tardigrades can survive gamma-irradiation well above 1 kilogray, and desiccated and hydrated (active) tardigrades respond similarly to irradiation. Thus, tolerance is not restricted to the dry anhydrobiotic state, and I discuss the possible involvement of an efficient, but yet undocumented, mechanism for DNA repair. Other anhydrobiotic animals (Artemia, Polypedium), when dessicated, show a higher tolerance to gamma-irradiation than hydrated animals, possibly due to the presence of high levels of the protective disaccharide trehalose in the dry state. Tardigrades and other anhydrobiotic animals provide a unique opportunity to study the effects of space exposure on metabolically inactive but vital metazoans.

Identification of a novel DNA methyltransferase 2 from the brine shrimp, Artemia franciscana

DNA methyltransferase 2 (Dnmt2) is a dual-specificity DNA methyltransferase, which contains a weak DNA methyltransferase and novel tRNA methyltransferase activity. However, its biological function is still enigmatic. To elucidate the expression profiles of Dnmt2 in Artemia franciscana, we isolated the gene encoding a Dnmt2 from A. franciscana and named it as AfDnmt2. The cDNA of AfDnmt2 contained a 1140-bp open reading frame that encoded a putative Dnmt2 protein of 379 amino acids exhibiting 32% approximately 39% identities with other known Dnmt2 homologs. This is the first report of a DNA methyltransferase gene in Crustacean. By using semi-quantitative RT-PCR, AfDnmt2 was found to be expressed through all developmental stages and its expression increased during resumption of diapause cysts development. Southern blot analysis indicated the presence of multiple copies of AfDnmt2 genes in A. franciscana.

Protein stability in Artemia embryos during prolonged anoxia

Encysted embryos (cysts) of the brine shrimp, Artemia franciscana, are arguably the most stress-resistant of all animal life-history stages. One of their many adaptations is the ability to tolerate anoxia for periods of years, while fully hydrated and at physiological temperatures. Previous work indicated that the overall metabolism of anoxic embryos is brought to a reversible standstill, including the transduction of free energy and the turnover of macromolecules. But the issue of protein stability at the level of tertiary and quaternary structure was not examined. Here I provide evidence that the great majority of proteins do not irreversibly lose their native conformation during years of anoxia, despite the absence of detectable protein turnover. Although a modest degree of protein denaturation and aggregation occurs, that is quickly reversed by a brief post-anoxic aerobic incubation. I consider how such extraordinary stability is achieved and suggest that at least part of the answer involves massive amounts of a small heat shock protein (p26) that acts as a molecular chaperone, the function of which does not appear to require ribonucleoside di- or tri-phosphates.

Embryo stability and vulnerability in an always changing world

Contrary to the view that embryos and larvae are the most fragile stages of life, development is stable under real-world conditions. Early cleavage embryos are prepared for environmental vagaries by having high levels of cellular defenses already present in the egg before fertilization. Later in development, adaptive responses to the environment either buffer stress or produce alternative developmental phenotypes. These buffers, defenses, and alternative pathways set physiological limits for development under expected conditions; teratology occurs when embryos encounter unexpected environmental changes and when stress exceeds these limits. Of concern is that rapid anthropogenic changes to the environment are beyond the range of these protective mechanisms.

Functional characterization of artemin, a ferritin homolog synthesized in Artemia embryos during encystment and diapause

Oviparously developing embryos of the crustacean Artemia franciscana encyst and enter diapause, exhibiting a level of stress tolerance seldom seen in metazoans. The extraordinary stress resistance of encysted Artemia embryos is thought to depend in part on the regulated synthesis of artemin, a ferritin superfamily member. The objective of this study was to better understand artemin function, and to this end the protein was synthesized in Escherichia coli and purified to apparent homogeneity. Purified artemin consisted of oligomers approximately 700 kDa in molecular mass that dissociated into monomers and a small number of dimers upon SDS/PAGE. Artemin inhibited heat-induced aggregation of citrate synthase in vitro, an activity characteristic of molecular chaperones and shown here to be shared by apoferritin and ferritin. This is the first report that apoferritin/ferritin may protect cells from stress other than by iron sequestration. Stably transfected mammalian cells synthesizing artemin were more resistant to heat and H(2)O(2) than were cells transfected with vector only, actions also shared by molecular chaperones such as the small heat shock proteins. The data indicate that artemin is a structurally modified ferritin arising either from a common ancestor gene or by duplication of the ferritin gene. Divergence, including acquisition of a C-terminal peptide extension and ferroxidase center modification, eliminated iron sequestration, but chaperone activity was retained. Therefore, because artemin accumulates abundantly during development, it has the potential to protect embryos from stress during encystment and diapause without adversely affecting iron metabolism.

Comparative observations on the cyst shells of sevenArtemia strains from China

The quiescent Artemia cysts of seven geographical origins in China were examined with scanning and transmission electron microscopes. SEM observations on cysts of these Artemia strains showed that the surface topography of cyst shells could be categorized into 6 types: complete smooth surface; smooth surface with sparsely distributed glabrate humps; surface with densely arranged wart-like humps that are composed of packed minute tubercles; rugged surface, with densely arranged tubercles not piling up to form larger humps; shallow-pocked surface; and surface with numerous and densely spaced pore-like fossulae. Some of the patterns were strain specific [e.g., cysts from Ga Hai (GH) are characterized by having a surface with wart-like ornaments that are composed of packed minute tubercles, rugged surface is only found in Chengkou (CK) cysts], and apparent intrastrain variation of cyst surface topography was found in Xizang (XZ), Jingyu Hu, and Xie Chi (SIN) strains. TEM studies on the ultrastructure of cyst shells revealed an apparent divergence in the structure of outer cuticular membrane (OCM) among Artemia strains. In CK, Aqqikkol Hu (AQK), SIN, and GH strains, it is a normal, asymmetrical, and multi-layered structure similar to those described in previous works. In XZ, JYH, and Lagkor Co (LGC) strains, however, the OCM is not obviously multi-layered and the borderlines between OCM and adjacent layers seem indistinct. The present results suggest that the diversity of the surface topography of Artemia cysts may be an available tool for identifying certain Artemia strains as well as for tracking the origins of some Artemia cysts, and the hypoplastic OCM may be a characteristic of the species A. tibetiana.

Comparisons of stress proteins and soluble carbohydrate in encysted embryos of Artemia franciscana and two species of Parartemia

We compared stress proteins (p26, artemin, hsp70) and alcohol-soluble carbohydrates (ASC) in cysts of Artemia franciscana and two as yet un-named species populations of Parartemia, the brine shrimp endemic to Australia. The small stress proteins and molecular chaperones, p26 and artemin, previously thought to be restricted to Artemia, and present in very large amounts in its encysted embryos (cysts), were also detected by western blotting in Parartemia cysts, even though roughly 85-100 million years have passed since these genera diverged. We interpret this finding as further evidence for the adaptive importance of these proteins in coping with the severe stresses these encysted embryos endure. As expected, hsp70 was present in all three groups of cysts, but apparently at somewhat lower concentrations in those of Parartemia. Based on measurements of ASC we propose that the disaccharide trehalose, critical for desiccation tolerance in many animal cells, has probably also been maintained in the metabolic repertoire of Parartemia whose cysts have well developed tolerance to severe desiccation.