HSP70 from the Antarctic sea urchin Sterechinus neumayeri: molecular characterization and expression in response to heat stress

Molecular responses to ocean acidification in an Antarctic bivalve and an ascidian

Southern Ocean organisms are considered particularly vulnerable to Ocean acidification (OA), as they inhabit cold waters where calcite-aragonite saturation states are naturally low. It is also generally assumed that OA would affect calcifying animals more than non-calcifying animals. In this context, we aimed to study the impact of reduced pH on both types of species: the ascidian Cnemidocarpa verrucosa sp. A, and the bivalve Aequiyoldia eightsii, from an Antarctic fjord. We used gene expression profiling and enzyme activity to study the responses of these two Antarctic benthic species to OA. We report the results of an experiment lasting 66 days, comparing the molecular mechanisms underlying responses under two pCO2 treatments (ambient and elevated pCO2). We observed 224 up-regulated and 111 down-regulated genes (FC ≥ 2; p-value ≤ 0.05) in the ascidian. In particular, the decrease in pH caused an upregulation of genes involved in the immune system and antioxidant response. While fewer differentially expressed (DE) genes were observed in the infaunal bivalve, 34 genes were up-regulated, and 69 genes were downregulated (FC ≥ 2; p-value ≤ 0.05) in response to OA. We found downregulated genes involved in the oxidoreductase pathway (such as glucose dehydrogenase and trimethyl lysine dioxygenase), while the heat shock protein 70 was up-regulated. This work addresses the effect of OA in two common, widely distributed Antarctic species, showing striking results. Our major finding highlights the impact of OA on the non-calcifying species, a result that differ from the general trend, which describes a higher impact on calcifying species. This calls for discussion of potential effects on non-calcifying species, such as ascidians, a diverse and abundant group that form extended three-dimensional clusters in shallow waters and shelf areas in the Southern Ocean.

A genome-wide screening of the 70 kDa heat shock protein (HSP70) genes in the rotifer Brachionus plicatilis sensu stricto with a characterization of two heat-inducible HSP70 genes

The 70 kDa heat shock proteins (HSP70s) and the constitutive members of the HSP70 family (heat shock cognates; HSC70s) play essential roles in various biological processes. The number of hsp70/hsc70 in the database is rapidly increasing because of their importance and the automatic annotation of newly sequenced genomes. However, accumulating evidence indicates that neither hsp70 nor hsc70 forms a monophyletic gene family, raising the need to reconsider the annotation strategy based on the traditional concept of the inducible HSP70 and constitutive HSC70s. The main aim of this study is to establish a systematic scheme to annotate hsp70-like genes taking the latest phylogenetic insights into account. We cloned two hsp70s from the rotifer Brachionus plicatilis sensu stricto (s.s.), an emerging model in evolutionary genetics, and conducted a genome-wide screening of B. plicatilis s.s. hsp70s using the two sequences as queries. A total of 15 hsp70-like genes were found, and 7 of them encoded distant members of the HSP70 family, the function of which largely remains unknown. Eight canonical hsp70s were annotated according to a recently proposed nomenclature based on the molecular evolution: e.g., HSP70cA1/B1 for the cytosolic lineage, HSP70er1 for the endoplasmic reticulum lineage, and HSP70m1 for the mitochondrial lineage. The two cloned hsp70s, HSP70cB1 and HSP70cB2, ubiquitously increased their mRNA levels up to 7.5 times after heat treatment as assessed by semi-quantitative PCR, real-time PCR, and in situ hybridization. This systematic screening incorporating a reasonable update to the annotation strategy would provide a useful example for future HSP70 studies, especially those in non-traditional model organisms.

Can heat shock protein 70 (HSP70) serve as biomarkers in Antarctica for future ocean acidification, warming and salinity stress?

The Antarctic Peninsula is one of the fastest-warming places on Earth. Elevated sea water temperatures cause glacier and sea ice melting. When icebergs melt into the ocean, it “freshens” the saltwater around them, reducing its salinity. The oceans absorb excess anthropogenic carbon dioxide (CO2) causing decline in ocean pH, a process known as ocean acidification. Many marine organisms are specifically affected by ocean warming, freshening and acidification. Due to the sensitivity of Antarctica to global warming, using biomarkers is the best way for scientists to predict more accurately future climate change and provide useful information or ecological risk assessments. The 70-kilodalton (kDa) heat shock protein (HSP70) chaperones have been used as biomarkers of stress in temperate and tropical environments. The induction of the HSP70 genes (Hsp70) that alter intracellular proteins in living organisms is a signal triggered by environmental temperature changes. Induction of Hsp70 has been observed both in eukaryotes and in prokaryotes as response to environmental stressors including increased and decreased temperature, salinity, pH and the combined effects of changes in temperature, acidification and salinity stress. Generally, HSP70s play critical roles in numerous complex processes of metabolism; their synthesis can usually be increased or decreased during stressful conditions. However, there is a question as to whether HSP70s may serve as excellent biomarkers in the Antarctic considering the long residence time of Antarctic organisms in a cold polar environment which appears to have greatly modified the response of heat responding transcriptional systems. This review provides insight into the vital roles of HSP70 that make them ideal candidates as biomarkers for identifying resistance and resilience in response to abiotic stressors associated with climate change, which are the effects of ocean warming, freshening and acidification in Antarctic organisms.

Variable heat shock response in Antarctic biofouling serpulid worms

The classical heat shock response (HSR) with up-regulation of hsp70 in response to warming is often absent in Antarctic marine species. Whilst in Antarctic fish, this is due to a mutation in the gene promoter region resulting in permanent constitutive expression of the inducible form of hsp70; there are further questions as to whether evolution to life below 0 °C has resulted in a generalised alteration to the HSR in Antarctic marine invertebrates. However, the number of species investigated to date is limited. In the first evaluation of the HSR in two spirorbid polychaetes Romanchella perrieri and Protolaeospira stalagmia, we show highly variable results of HSR induction depending on warming regimes. These animals were subjected to in situ warming (+ 1 °C and + 2 °C above ambient conditions) using heated settlement panels for 18 months, and then the HSR was tested in R. perrieri using acute and chronic temperature elevation trials. The classic HSR was not induced in response to acute thermal challenge in this species (2 h at 15 °C) and significant down-regulation of hsp90 occurred during chronic warming at 4 °C for 30 days. Analysis of heat shock protein (HSP) genes in a transcriptome study of P. stalagmia, which had been warmed in situ for 18 months, showed up-regulation of HSP70 and HSP90 family members, thus further emphasising the complexity of the response in Antarctic marine species. It is increasingly apparent that the Antarctic HSR has evolved in a species-specific manner to life in the cold.

Characterization of Inducible HSP70 Genes in an Antarctic Yeast, Glaciozyma antarctica PI12, in Response to Thermal Stress

The induction of highly conserved heat shock protein 70 (HSP70) is often related to a cellular response due to harmful stress or adverse life conditions. In this study, we determined the expression of Hsp70 genes in the Antarctic yeast, Glaciozyma antarctica, under different several thermal treatments for several exposure periods. The main aims of the present study were (1) to determine if stress-induced Hsp70 could be used to monitor the exposure of the yeast species G. antarctica to various types of thermal stress; (2) to analyze the structures of the G. antarctica HSP70 proteins using comparative modeling; and (3) to evaluate the relationship between the function and structure of HSP70 in G. antarctica. In this study, we managed to amplify and clone 2 Hsp70 genes from G. antarctica named GaHsp70-1 and GaHsp70-2. The cells of G. antarctica expressed significantly inducible Hsp70 genes after the heat and cold shock treatments. Interestingly, GaHsp70-1 showed 2–6-fold higher expression than GaHsp70-2 after the heat and cold exposure. ATP hydrolysis analysis on both G. antarctica HSP70s proved that these psychrophilic chaperones can perform activities in a wide range of temperatures, such as at 37, 25, 15, and 4 °C. The 3D structures of both HSP70s revealed several interesting findings, such as the substitution of a β-sheet to loop in the N-terminal ATPase binding domain and some modest residue substitutions, which gave the proteins the flexibility to function at low temperatures and retain their functional activity at ambient temperatures. In conclusion, both analyzed HSP70s played important roles in the physiological adaptation of G. antarctica.

The macronuclear genome of the Antarctic psychrophilic marine ciliate Euplotes focardii reveals new insights on molecular cold adaptation

The macronuclear (MAC) genomes of ciliates belonging to the genus Euplotes species are comprised of numerous small DNA molecules, nanochromosomes, each typically encoding a single gene. These genomes are responsible for all gene expression during vegetative cell growth. Here, we report the analysis of the MAC genome from the Antarctic psychrophile Euplotes focardii. Nanochromosomes containing bacterial sequences were not found, suggesting that phenomena of horizontal gene transfer did not occur recently, even though this ciliate species has a substantial associated bacterial consortium. As in other euplotid species, E. focardii MAC genes are characterized by a high frequency of translational frameshifting. Furthermore, in order to characterize differences that may be consequent to cold adaptation and defense to oxidative stress, the main constraints of the Antarctic marine microorganisms, we compared E. focardii MAC genome with those available from mesophilic Euplotes species. We focussed mainly on the comparison of tubulin, antioxidant enzymes and heat shock protein (HSP) 70 families, molecules which possess peculiar characteristic correlated with cold adaptation in E. focardii. We found that α-tubulin genes and those encoding SODs and CATs antioxidant enzymes are more numerous than in the mesophilic Euplotes species. Furthermore, the phylogenetic trees showed that these molecules are divergent in the Antarctic species. In contrast, there are fewer hsp70 genes in E. focardii compared to mesophilic Euplotes and these genes do not respond to thermal stress but only to oxidative stress. Our results suggest that molecular adaptation to cold and oxidative stress in the Antarctic environment may not only be due to particular amino acid substitutions but also due to duplication and divergence of paralogous genes.

Molecular mechanisms underlying responses of the Antarctic coral Malacobelemnon daytoni to ocean acidification

Benthic organisms of the Southern Ocean are particularly vulnerable to ocean acidification (OA), as they inhabit cold waters where calcite-aragonite saturation states are naturally low. OA most strongly affects animals with calcium carbonate skeletons or shells, such as corals and mollusks. We exposed the abundant cold-water coral Malacobelemnon daytoni from an Antarctic fjord to low pH seawater (LpH) (7.68 ± 0.17) to test its physiological responses to OA, at the level of gene expression (RT-PCR) and enzyme activity. Corals were exposed in short- (3 days) and long-term (54 days) experiments to two pCO₂ conditions (ambient and elevated pCO₂ equaling RCP 8.5, IPCC 2019, approximately 372.53 and 956.78 μatm, respectively). Of the eleven genes studied through RT-PCR, six were significantly upregulated compared with control in the short-term in the LpH condition, including the antioxidant enzyme superoxide dismutase (SOD), Heat Shock Protein 70 (HSP70), Toll-like receptor (TLR), galaxin and ferritin. After long-term exposure to low pH conditions, RT-PCR analysis showed seven genes were upregulated. These include the mannose-binding C-Lectin and HSP90. Also, the expression of TLR and galaxin, among others, continued to be upregulated after long-term exposure to LpH. Expression of carbonic anhydrase (CA), a key enzyme involved in calcification, was also significantly upregulated after long-term exposure. Our results indicated that, after two months, M. daytoni is not acclimatized to this experimental LpH condition. Gene expression profiles revealed molecular impacts that were not evident at the enzyme activity level. Consequently, understanding the molecular mechanisms behind the physiological processes in the response of a coral to LpH is critical to understanding the ability of polar species to cope with future environmental changes. Approaches integrating molecular tools into Antarctic ecological and/or conservation research make an essential contribution given the current ongoing OA processes.

Application of a biological multilevel response approach in the copepod Acartia tonsa for toxicity testing of three oil Water Accommodated Fractions

Copepods play a critical role in the marine food webs, being a food source for marine organisms. In this study, we investigated the toxic effects of Water Accommodated Fractions (WAFs) from three types of oil: Naphthenic North Sea crude oil (NNS), Intermediate Fuel Oil (IFO 180) and a commercial Marine Gas Oil (MGO). The WAFs were prepared at 10 °C and 30 PSU (practical salinity unit), and tested on the marine copepod Acartia tonsa at different endpoints and at different levels of biological organization. We determined the median lethal concentrations after 96 h (LC50) and reproduction capabilities were calculated in adult females following seven days of exposure to sublethal WAF doses. The total lipid content was measured in reproductive females using Nile red lipophilic dye after 96 h of WAF exposure. We also measured the transcription levels of genes involved in antioxidant response and xenobiotic biotransformation after short exposure for 48 h. High doses (7% WAF) of MGO affected survival, percentage of fecund females, egg hatching success, and total lipid content. The IFO 180 WAF affected, at medium (20%) and high (40%) doses, the number of fecund females, mortality and produced significant effects on gene expression levels. In conclusion, toxicity assays showed that the WAFs prepared from refined oils were more toxic than crude oil WAF to Acartia tonsa.

Prospecting Biomarkers for Diagnostic and Therapeutic Approaches in Pythiosis

Pythiosis, whose etiological agent is the oomycete Pythium insidiosum, is a life-threatening disease that occurs mainly in tropical and subtropical countries, affecting several animal species. It is frequently found in horses in Brazil and humans in Thailand. The disease is difficult to diagnose because the pathogen's hyphae are often misdiagnosed as mucoromycete fungi in histological sections. Additionally, there is no specific antigen to use for rapid diagnosis, the availability of which could improve the prognosis in different animal species. In this scenario, we investigated which P. insidiosum antigens are recognized by circulating antibodies in horses and humans with pythiosis from Brazil and Thailand, respectively, using 2D immunoblotting followed by mass spectrometry for the identification of antigens. We identified 23 protein spots, 14 recognized by pooled serum from horses and humans. Seven antigens were commonly recognized by both species, such as the heat-shock cognate 70 KDa protein, the heat-shock 70 KDa protein, glucan 1,3-beta-glucosidase, fructose-bisphosphate aldolase, serine/threonine-protein phosphatase, aconitate hydratase, and 14-3-3 protein epsilon. These results demonstrate that there are common antigens recognized by the immune responses of horses and humans, and these antigens may be studied as biomarkers for improving diagnosis and treatment.

Antioxidant and immune response of the sea urchin Paracentrotus lividus to different re-suspension patterns of highly polluted marine sediments

Marine pollution due to disused industrial activities is a major threat to ecosystems and human health, for example through the effects of re-suspension of toxic substances that are present in contaminated sediments. Here, we examined the effects of different re-suspension patterns of polluted sediments from the site of national interest Bagnoli-Coroglio, on the immune system of the sea urchin Paracentrotus lividus. An indoor experiment was set up exposing sea urchins for 34 days to such sediments and evaluating the effects of two patterns of water turbulence, mimicking natural storms at sea. One group of animals experienced an "aggregated" pattern of turbulence, consisting in two events, each lasting 2 days, separated by only 3 calm days, while a second group experienced two events of turbulence separated by 17 calm days (spaced pattern). At different times from the beginning of the experiment, coelomic fluid was collected from the animals and immune cells were examined for cell count and morphology, oxidative stress variables, and expression of genes involved in metal detoxification, stress response and inflammation. Our results highlighted that the aggregated pattern of turbulence was more noxious for sea urchins. Indeed, their immune system was altered, over the exposure time, as indicated by the increase of red amoebocytes number. Moreover, despite of an increase of the antioxidant power, animals from this group displayed a very significant ROS over-production at the end of the experiment. Conversely, animals in the spaced condition activated a different immune response, mainly having phagocytes as actors, and were able to partially recover from the received stress at the end of the experiment. No changes in the expression of genes related to antioxidant and anti-inflammatory responses were observed in both groups. By contrast, a down-regulation of various metallothioneins (4, 6, 7 and 8) in the group subjected to aggregated pattern was observed, while metallothionein 8 was up-regulated in the animals from the group exposed to the spaced pattern of turbulence. This work provides the first evidence of how sea urchins can respond to different re-suspension patterns of polluted sediments by modulating their immune system functions. The present data are relevant in relation to the possible environmental restoration of the study site, whose priorities include the assessment of the effects of marine pollution on local organisms, among which P. lividus represents a key benthic species.

Combined stress of ocean acidification and warming influence survival and drives differential gene expression patterns in the Antarctic pteropod, Limacina helicina antarctica

The ecologically important thecosome pteropods in the Limacina spp. complex have recently been the focus of studies examining the impacts global change factors - e.g., ocean acidification (OA) and ocean warming (OW) - on their performance and physiology. This focus is driven by conservation concerns where the health of pteropod populations is threatened by the high susceptibility of their shells to dissolution in low aragonite saturation states associated with OA and how coupling of these stressors may push pteropods past the limits of physiological plasticity. In this manipulation experiment, we describe changes in the transcriptome of the Antarctic pteropod, Limacina helicina antarctica, to these combined stressors. The conditions used in the laboratory treatments met or exceeded those projected for the Southern Ocean by the year 2100. We made two general observations regarding the outcome of the data: (1) Temperature was more influential than pH in terms of changing patterns of gene expression, and (2) these Antarctic pteropods appeared to have a significant degree of transcriptomic plasticity to respond to acute abiotic stress in the laboratory. In general, differential gene expression was observed amongst the treatments; here, for example, transcripts associated with maintaining protein structure and cell proliferation were up-regulated. To disentangle the effects of OA and OW, we used a weighted gene co-expression network analysis to explore patterns of change in the transcriptome. This approach identified gene networks associated with OW that were enriched for transcripts proposed to be involved in increasing membrane fluidity at warmer temperatures. Together these data provide evidence that L.h.antarctica has a limited capacity to acclimate to the combined conditions of OA and OW used in this study. This reduced scope of acclimation argues for continued study of how adaptation to polar aquatic environments may limit the plasticity of present-day populations in responding to future environmental change.

Ocean warming and acidification pose synergistic limits to the thermal niche of an economically important echinoderm

To make robust projectios of the impacts of climate change, it is critical to understand how abiotic factors may interact to constrain the distribution and productivity of marine flora and fauna. We evaluated the effects of projected end of the century ocean acidification (OA) and warming (OW) on the thermal tolerance of an important living marine resource, the sea urchin Loxechinus albus, a benthic shallow water coastal herbivore inhabiting part of the Pacific coast of South America. After exposing young juveniles for a 1-month period to contrasting pCO₂ (~500 and 1400 μatm) and temperature (~15 °C and 20 °C) levels, critical thermal maximum (CTmax) and minimum (CTmin) as well as thermal tolerance polygons were assessed based on self-righting success as an end point. Transcription of heat shock protein 70 (HSP70), a chaperone protecting cellular proteins from environmental stress, was also measured. Exposure to elevated pCO₂ significantly reduced thermal tolerance by increasing CTmin at both experimental temperatures and decreasing CTmax at 20 °C. There was also a strong synergistic effect of OA × OW on HSP70 transcription levels which were 75 times higher than in control conditions. If this species is unable to adapt to elevated pCO₂ in the future, the reduction in thermal tolerance and HSP response suggests that near-future warming and OA will disrupt their performance and reduce their distribution with ecological and economic consequences. Given the wider latitudinal range (6 to 56°S) and environmental tolerance of L. albus compared to other members of this region's benthic invertebrate community, OW and OA may cause substantial changes to the coastal fauna along this geographical range.

Effects of elevated temperature on gonadal functions, cellular apoptosis, and oxidative stress in Atlantic sea urchin Arbacia punculata

Increasing seawater temperature affects growth, reproduction and development in marine organisms. In this study, we examined the effects of elevated temperatures on reproductive functions, heat shock protein 70 (HSP70) and nitrotyrosine protein (NTP, an indicator of reactive nitrogen species) expressions, protein carbonyl (PC, an indicator of oxidative stress) contents, cellular apoptosis, and coelomic fluid (CF) conditions in Atlantic sea urchin. Sea urchins were housed in six aquaria with control (24 °C) and elevated temperatures (28 °C and 32 °C) for a 7-day period. After exposure, sea urchins exhibited decreased percentages of gametes (eggs/sperm), as well as increased HSP70 and NTP expressions in eggs and spermatogenic cells, increased gonadal apoptosis, and decreased CF pH compared to controls. PC contents were also significantly increased in gonadal tissues at higher temperatures. These results suggest that elevated temperature acidifies CF, increases oxidative stress and gonadal apoptosis, and results in impairment of reproductive functions in sea urchins.

Molecular characterization, tissue-specific expression, and RNA knockdown of the putative heat shock cognate 70 protein from Rhipicephalus haemaphysaloides

Heat shock cognate 70-kDa protein (RH-Hsc70) was identified from a cDNA library synthesized from the sialotranscriptomes of unfed and fed Rhipicephalus haemaphysaloides. The RH-Hsc70 open reading frame is 1950 bp long and encodes a protein that is 649 amino acids in length, with a predicted molecular weight of 71.1 kDa and a theoretical pI of 5.43. RH-Hsc70 exhibits 98% amino acid identity with Hsc70 in Haemaphysalis flava and 83% identity with Hsc70 in arthropods and mammals. RH-Hsc70 was mainly expressed in nymphs and adult ticks, not in larvae. Real-time quantitative PCR analysis indicated that RH-Hsc70 mRNA expression was induced by blood feeding in adult ticks. In addition, RH-Hsc70 gene expression was higher in the ovaries of fed adult ticks than that in the midguts, salivary glands, and fat bodies of unfed or fed adult ticks. RH-Hsc70 gene knockdown inhibited tick blood feeding, significantly decreased tick engorgement rate, and increased tick death rate. These data illustrate the importance of RH-Hsc70 in tick blood feeding and aging, which makes it a promising candidate for the development of anti-tick vaccines.