Transcriptome analysis reveals fluid shear stress (FSS) and atherosclerosis pathway as a candidate molecular mechanism of short-term low salinity stress tolerance in abalone.

BACKGROUND: Transcriptome sequencing is an effective tool to reveal the essential genes and pathways underlying countless biotic and abiotic stress adaptation mechanisms. Although severely challenged by diverse environmental conditions, the Pacific abalone Haliotis discus hannai remains a high-value aquaculture mollusk and a Chinese predominantly cultured abalone species. Salinity is one of such environmental factors whose fluctuation could significantly affect the abalone's cellular and molecular immune responses and result in high mortality and reduced growth rate during prolonged exposure. Meanwhile, hybrids have shown superiority in tolerating diverse environmental stresses over their purebred counterparts and have gained admiration in the Chinese abalone aquaculture industry. The objective of this study was to investigate the molecular and cellular mechanisms of low salinity adaptation in abalone. Therefore, this study used transcriptome analysis of the gill tissues and flow cytometric analysis of hemolymph of H. discus hannai (DD) and interspecific hybrid H. discus hannai ♀ x H. fulgens ♂ (DF) during low salinity exposure. Also, the survival and growth rate of the species under various salinities were assessed. RESULTS: The transcriptome data revealed that the differentially expressed genes (DEGs) were significantly enriched on the fluid shear stress and atherosclerosis (FSS) pathway. Meanwhile, the expression profiles of some essential genes involved in this pathway suggest that abalone significantly up-regulated calmodulin-4 (CaM-4) and heat-shock protein90 (HSP90), and significantly down-regulated tumor necrosis factor (TNF), bone morphogenetic protein-4 (BMP-4), and nuclear factor kappa B (NF-kB). Also, the hybrid DF showed significantly higher and sustained expression of CaM and HSP90, significantly higher phagocytosis, significantly lower hemocyte mortality, and significantly higher survival at low salinity, suggesting a more active molecular and hemocyte-mediated immune response and a more efficient capacity to tolerate low salinity than DD. CONCLUSIONS: Our study argues that the abalone CaM gene might be necessary to maintain ion equilibrium while HSP90 can offset the adverse changes caused by low salinity, thereby preventing damage to gill epithelial cells (ECs). The data reveal a potential molecular mechanism by which abalone responds to low salinity and confirms that hybridization could be a method for breeding more stress-resilient aquatic species.

Divergent Carry-Over Effects of Hypoxia during the Early Development of Abalone.

After being exposed to environmental stimuli during early developmental stages, some organisms may gain or weaken physiological regulating abilities, which would have long-lasting effects on their performance. Environmental hypoxia events can have significant effects on marine organisms, but for breeding programs and other practical applications, it is important to further explore the long-term physiological effects of early hypoxia exposure in economically significant species. In this study, the Pacific abalone Haliotis discus hannai was exposed to moderate hypoxia (∼4 mg/L) from zygote to trochophora, and the assessments of hypoxia tolerance were conducted on the grow-out stage. The results revealed that juvenile abalones exposed to hypoxia at the early development stages were more hypoxia-tolerant but with slower weight growth, a phenomenon called the trade-off between growth and survival. These phenotypic effects driven by the hypoxia exposure were explained by strong selection of genes involved in signal transduction, autophagy, apoptosis, and hormone regulation. Moreover, long non-coding RNA regulation plays an important role modulating carry-over effects by controlling DNA replication and repair, signal transduction, myocardial activity, and hormone regulation. This study revealed that the ability to create favorable phenotypic differentiation through genetic selection and/or epigenetic regulation is important for the survival and development of aquatic animals in the face of rapidly changing environmental conditions.

Transcriptome analysis reveals the molecular mechanisms of heterosis on thermal resistance in hybrid abalone.

BACKGROUND: Heterosis has been exploited for decades in different animals and crops due to it resulting in dramatic increases in yield and adaptability. Hybridization is a classical breeding method that can effectively improve the genetic characteristics of organisms through heterosis. Abalone has become an increasingly economically important aquaculture resource with high commercial value. However, due to changing climate, abalone is now facing serious threats of high temperature in summer. Interspecific hybrid abalone (Haliotis gigantea ♀ × H. discus hannai ♂, SD) has been cultured at large scale in southern China and has been shown high survival rates under heat stress in summer. Therefore, SD has become a good model material for heterosis research, but the molecular basis of heterosis remains elusive. RESULTS: Heterosis in thermal tolerance of SD was verified through Arrhenius break temperatures (ABT) of cardiac performance in this study. Then RNA-Sequencing was conducted to obtain gene expression patterns and alternative splicing events at control temperature (20 °C) and heat stress temperature (30 °C). A total of 356 (317 genes), 476 (435genes), and 876 (726 genes) significantly diverged alternative splicing events were identified in H. discus hannai (DD), H. gigantea (SS), and SD in response to heat stress, respectively. In the heat stress groups, 93.37% (20,512 of 21,969) of the expressed genes showed non-additive expression patterns, and over-dominance expression patterns of genes account for the highest proportion (40.15%). KEGG pathway enrichment analysis showed that the overlapping genes among common DEGs and NAGs were significantly enriched in protein processing in the endoplasmic reticulum, mitophagy, and NF-κB signaling pathway. In addition, we found that among these overlap genes, 39 genes had undergone alternative splicing events in SD. These pathways and genes may play an important role in the thermal resistance of hybrid abalone. CONCLUSION: More alternative splicing events and non-additive expressed genes were detected in hybrid under heat stress and this may contribute to its thermal heterosis. These results might provide clues as to how hybrid abalone has a better physiological regulation ability than its parents under heat stress, to increase our understanding of heterosis in abalone.

Preliminary analysis of pathways and their implications during salinity stress in abalone.

Transcriptome sequencing has offered immense opportunities to study non-model organisms. Abalone is an important marine mollusk that encounters harsh environmental conditions in its natural habitat and under aquaculture conditions; hence, research that increases molecular information to understand abalone physiology and stress response is noteworthy. Accordingly, the study used transcriptome sequencing of the gill tissues of abalone exposed to low salinity stress. The aim is to explore some enriched pathways during salinity stress and the crosstalk and functions of the genes involved in the candidate biological processes for future further analysis of their expression patterns. The data suggest that abalone genes such as YAP/TAZ, Myc, Nkd, and Axin (involved in the Hippo signaling pathway) and PI3K/Akt, SHC, and RTK (involved in the Ras signaling pathways) might mediate growth and development. Thus, deregulation of the Hippo and Ras pathways by salinity stress could be a possible mechanism by which unfavorable salinities influence growth in abalone. Furthermore, PEPCK, GYS, and PLC genes (mediating the Glucagon signaling pathway) might be necessary for glucose homeostasis, reproduction, and abalone meat sensory qualities; hence, a need to investigate how they might be influenced by environmental stress. Genes such as MYD88, IRAK1/4, JNK, AP-1, and TRAF6 (mediating the MAPK signaling pathway) could be useful in understanding abalone's innate immune response to environmental stresses. Finally, the aminoacyl-tRNA biosynthesis pathway hints at the mechanism by which new raw materials for protein biosynthesis are mobilized for physiological processes and how abalone might respond to this process during salinity stress. Low salinity clearly regulated genes in these pathways in a time-dependent manner, as hinted by the heat maps. In the future, qRT-PCR verification and in-depth study of the various genes and proteins discussed would provide enormous molecular information resources for the abalone biology.

New genes helped acorn barnacles adapt to a sessile lifestyle.

Barnacles are the only sessile lineages among crustaceans, and their sessile life begins with the settlement of swimming larvae (cyprids) and the formation of protective shells. These processes are crucial for adaptation to a sessile lifestyle, but the underlying molecular mechanisms remain poorly understood. While investigating these mechanisms in the acorn barnacle, Amphibalanus amphitrite, we discovered a new gene, bcs-6, which is involved in the energy metabolism of cyprid settlement and originated from a transposon by acquiring the promoter and cis-regulatory element. Unlike mollusks, the barnacle shell comprises alternate layers of chitin and calcite and requires another new gene, bsf, which generates silk-like fibers that efficiently bind chitin and aggregate calcite in the aquatic environment. Our findings highlight the importance of exploring new genes in unique adaptative scenarios, and the results will provide important insights into gene origin and material development.

Advanced inorganic nanomaterials for high-performance electrochromic applications.

Electrochromic materials and devices with the capability of dynamic optical regulation have attracted considerable attention recently and have shown a variety of potential applications including energy-efficient smart windows, multicolor displays, atuto-diming mirrors, military camouflage, and adaptive thermal management due to the advantages of active control, wide wavelength modulation, and low energy consumption. However, its development still experiences a number of issues such as long response time and inadequate durability. Nanostructuring has demonstrated that it is an effective strategy to improve the electrochromic performance of the materials due to the increased reaction active sites and the reduced ion diffusion distance. Various advanced inorganic nanomaterials with high electrochromic performance have been developed recently, significantly contributing to the development of electrochromic applications. In this review, we systematically introduce and discuss the recent advances in advanced inorganic nanomaterials including zero-, one-, and two-dimensional materials for high-performance electrochromic applications. Finally, we outline the current major challenges and our perspectives for the future development of nanostructured electrochromic materials and applications.

Potential involvement of the microbiota-gut-brain axis in the neurotoxicity of triphenyl phosphate (TPhP) in the marine medaka (Oryzias melastigma) larvae.

Triphenyl phosphate (TPhP), a prevalent pollutant in the aquatic environment, has been reported to induce neurotoxicity (e.g., a suppression in locomotor activity) in fish larvae, posing a great threat to fish populations. However, the underlying mechanism was not fully revealed. In this study, the Oryzias melastigma larvae (21 dph) were exposed to waterborne TPhP (20 and 100 µg/L) for 7 days and a decreased locomotor activity was found. After exposure, the brain transcriptome and communities of gut microbiota were investigated to explore the potential mechanism underlying the suppressed locomotor activity by TPhP. The results showed that 1160 genes in the brain were dysregulated by TPhP, of which 24 genes were identified as being highly associated with the neural function and development (including nerve regeneration, neuronal growth and differentiation, brain ion homeostasis, production of neurotransmitters and etc), suggesting a general impairment in the central nervous system. Meanwhile, TPhP caused disorders in the gut microbiota. The relative abundance of Gammaproteobacteria and Alphaproteobacteria, which can influence the brain functions of host via the microbiota-gut-brain axis, were significantly altered by TPhP. Furthermore, the Redundancy analysis (RDA) revealed positive correlations between the intestinal genera Ruegeria, Roseivivax and Nautella and the dysregulated brain genes by TPhP. These results suggest that TPhP might impair the central nervous system of the O. melastigma larvae not only directly but also through the microbiota-gut-axis (indirectly), contributing to the suppressed locomotor activity. These findings enrich our mechanistic understanding of the toxicity of TPhP in fish larvae and shed preliminary light on the involvement of microbiota-gut-brain axis in the neurotoxicity of environmental pollutants.

Genomic selection applications can improve the environmental performance of aquatics: A case study on the heat tolerance of abalone.

Aquaculture is one of the world's fastest-growing and most traded food industries, but it is under the threat of climate-related risks represented by global warming, marine heatwave (MHW) events, ocean acidification, and deoxygenation. For the sustainable development of aquaculture, selective breeding may be a viable method to obtain aquatic economic species with greater tolerance to environmental stressors. In this study, we estimated the heritability of heat tolerance trait of Pacific abalone Haliotis discus hannai, performed genome-wide association studies (GWAS) analysis for heat tolerance to detect single nucleotide polymorphisms (SNPs) and candidate genes, and assessed the potential of genomic selection (GS) in the breeding of abalone industry. A total of 1120 individuals were phenotyped for their heat tolerance and genotyped with 64,788 quality-controlled SNPs. The heritability of heat tolerance was moderate (0.35-0.42) and the predictive accuracy estimated using BayesB (0.55 ± 0.05) was higher than that using GBLUP (0.40 ± 0.01). A total of 11 genome-wide significant SNPs and 2 suggestive SNPs were associated with heat tolerance of abalone, and 13 candidate genes were identified, including got2,znfx1,l(2)efl, and lrp5. Based on GWAS results, the prediction accuracy using the top 5K SNPs was higher than that using randomly selected SNPs and higher than that using all SNPs. These results suggest that GS is an efficient approach for improving the heat tolerance of abalone and pave the way for abalone selecting breeding programs in rapidly changing oceans.

Exploring the Intestinal Microbiota and Metabolome Profiles Associated With Feed Efficiency in Pacific Abalone (Haliotis discus hannai).

Feed efficiency (FE) is critical to the economic and environmental benefits of aquaculture. Both the intestines and intestinal microbiota play a key role in energy acquisition and influence FE. In the current research, intestinal microbiota, metabolome, and key digestive enzyme activities were compared between abalones with high [Residual feed intake (RFI) = -0.029] and low FE (RFI = 0.022). The FE of group A were significantly higher than these of group B. There were significant differences in intestinal microbiota structures between high- and low-FE groups, while higher microbiota diversity was observed in the high-FE group. Differences in FE were also strongly correlated to variations in intestinal digestive enzyme activity that may be caused by Pseudoalteromonas and Cobetia. In addition, Saprospira, Rhodanobacteraceae, Llumatobacteraceae, and Gaiellales may potentially be utilized as biomarkers to distinguish high- from low-FE abalones. Significantly different microorganisms (uncultured beta proteobacterium, BD1_7_clade, and Lautropia) were found to be highly correlated to significantly different metabolites [DL-methionine sulfoxide Arg-Gln, L-pyroglutamic acid, dopamine, tyramine, phosphatidyl cholines (PC) (16:0/16:0), and indoleacetic acid] in the high- and low-FE groups, and intestinal trypsin activity also significantly differed between the two groups. We propose that interactions occur among intestinal microbiota, intestinal metabolites, and enzyme activity, which improve abalone FE by enhancing amino acid metabolism, immune response, and signal transduction pathways. The present study not only elucidates mechanisms of variations in abalone FE, but it also provides important basic knowledge for improving abalone FE by modulating intestinal microbiota.

Genomic insights into the adaptation and evolution of the nautilus, an ancient but evolving "living fossil".

The nautilus, commonly known as a "living fossil," is endangered and may be at risk of extinction. The lack of genomic information hinders a thorough understanding of its biology and evolution, which can shed light on the conservation of this endangered species. Here, we report the first high-quality chromosome-level genome assembly of Nautilus pompilius. The assembled genome size comprised 785.15 Mb. Comparative genomic analyses indicated that transposable elements (TEs) and large-scale genome reorganizations may have driven lineage-specific evolution in the cephalopods. Remarkably, evolving conserved genes and recent TE insertion activities were identified in N. pompilius, and we speculate that these findings reflect the strong adaptability and long-term survival of the nautilus. We also identified gene families that are potentially responsible for specific adaptation and evolution events. Our study provides unprecedented insights into the specialized biology and evolution of N. pompilius, and the results serve as an important resource for future conservation genomics of the nautilus and closely related species.

Comparative Transcriptome and DNA Methylation Analysis of Phenotypic Plasticity in the Pacific Abalone (Haliotis discus hannai).

Phenotypic plasticity is an adaptive mechanism used by organisms to cope with environmental fluctuations. Pacific abalone (Haliotis discus hannai) are large-scale farmed in the temperate area of northern China and in the warmer waters of southern China. RNA-seq and comparative transcriptomic analysis here were performed to determine if the northern and southern populations have evolved divergent plasticity and if functional differences are associated with protein synthesis and growth-related biological progress. The DNA methylation (5mC) landscape of H. discus hannai from the two populations using whole genomic bisulfite sequencing (WGBS), exhibited different epigenetic patterns. The southern population had significant genomic hypo-methylation that may have resulted from long-term acclimation to heat stress. Combining 790 differentially expressed genes (DEGs) and 7635 differentially methylated genes (DMGs), we found that methylation within the gene body might be important in predicting abalone gene expression. Genes related to growth, development, transduction, and apoptosis may be regulated by methylation and could explain the phenotypic divergence of H. discus hannai. Our findings not only emphasize the significant roles of adaptive plasticity in the acclimation of H. discus hannai to high temperatures but also provide a new understanding of the epigenetic mechanism underlying the phenotypic plasticity in adaptation to climate change for marine organisms.

Distinct metabolic shifts occur during the transition between normoxia and hypoxia in the hybrid and its maternal abalone.

Due to anthropogenic activities that have increased global climate change and nutrient discharges, severe hypoxic events have frequently occurred in coastal waters in recent years. Relying on coastal waters, the aquaculture area has suffered ecological and economic losses caused by hypoxia, especially in summer. In this study, to investigate the stress resistance of the Pacific abalone Haliotis discus hannai (DD) and the hybrid H. discus hannai ♀ × H. fulgens ♂ (DF), a combination of physiological, biochemical, and metabolomic methods were used to compare the metabolic responses of these two abalones to acute hypoxia (~0.5 mg O2/L, 12 h) and reoxygenation (~6.6 mg O2/L, 10-20 h). Hemolymph characteristics and aerobic/anaerobic respiratory capacity changed significantly under hypoxia or reoxygenation conditions, and they were regulated in different trends in two abalones. The contents of hepatopancreas glycogen in two abalones reached the trough after 10 h recovery, implying that short-term hypoxia leads to a long-lasting (several hours) imprint on the energy storage of abalone. In response to dissolved oxygen fluctuation, metabolic profiles of two abalones changed in distinct ways both in the hypoxia group or the reoxygenation group. The conversion of carbohydrate metabolism and amino acid metabolism indicated that hypoxia prompts abalone to change the way of energy metabolism, which may also reflect the difference in the energy utilization of DD and DF abalones. In addition, 3 metabolites (L-glutamate, 2-hydroxy-butanoic acid, and 2-methyl-3-hydroxybutyric acid) as potential biomarkers for hypoxia and reoxygenation response in abalone were determined by operating characteristic analysis (ROC). Overall, this study provides information towards understanding the damage caused by frequent hypoxic events and implies the metabolic shifts that occur under hypoxia and reoxygenation conditions in DD and DF abalones.

Publisher Correction: Evolutionary transcriptomics of metazoan biphasic life cycle supports a single intercalation origin of metazoan larvae.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Evolutionary transcriptomics of metazoan biphasic life cycle supports a single intercalation origin of metazoan larvae.

The transient larva-bearing biphasic life cycle is the hallmark of many metazoan phyla, but how metazoan larvae originated remains a major enigma in animal evolution. There are two hypotheses for larval origin. The 'larva-first' hypothesis suggests that the first metazoans were similar to extant larvae, with later evolution of the adult-added biphasic life cycle; the 'adult-first' hypothesis suggests that the first metazoans were adult forms, with the biphasic life cycle arising later via larval intercalation. Here, we investigate the evolutionary origin of primary larvae by conducting ontogenetic transcriptome profiling for Mollusca-the largest marine phylum characterized by a trochophore larval stage and highly variable adult forms. We reveal that trochophore larvae exhibit rapid transcriptome evolution with extraordinary incorporation of novel genes (potentially contributing to adult shell evolution), and that cell signalling/communication genes (for example, caveolin and innexin) are probably crucial for larval evolution. Transcriptome age analysis of eight metazoan species reveals the wide presence of young larval transcriptomes in both trochozoans and other major metazoan lineages, therefore arguing against the prevailing larva-first hypothesis. Our findings support an adult-first evolutionary scenario with a single metazoan larval intercalation, and suggest that the first appearance of proto-larva probably occurred after the divergence of direct-developing Ctenophora from a metazoan ancestor.

Hemolymph and transcriptome analysis to understand innate immune responses to hypoxia in Pacific abalone.

Hypoxia was thought to inhibit immune responses, causing severe mortality to marine organisms. The Pacific abalone, Haliotis discus hannai, is the most widely cultured abalone species in China, but suffering from "summer mortality" in which hypoxia has been one of the main reasons. The effect of hypoxia exposure on immune responses in H. discus hannai was investigated, including cellular immune response using flow cytometry and transcriptome profiles. The influence of hypoxia treatment on the total hemocyte count (THC) of H. discus hannai was rather limited but the hemocyte survival rate of abalone increased during 48 h exposure. There was an initial rise in the production of phagocytes and reactive oxygen species (ROS) shortly (3 h) after hypoxic stimulation, but finally decreased after 48 h. This indicates that hypoxia inhibited redox activity of abalone. RNA-seq studies of gill tissues also revealed immune response mechanism in abalone after 24 h of hypoxia. Totally 954 differentially expressed genes (DEGs) were detected under different degrees of deoxygenation. Though oxidation-reduction turbulence was a result of both up- and down-regulated DEGs, cell death/apoptosis induction resulted from up-regulated DEGs, whilst DNA metabolic and immunity suppression resulted from down-regulated DEGs. In summary, our data provides evidence that deoxygenation greatly affects abalone immunity, probably making it more vulnerable. The present study also lays the foundation for further research in hypoxia-associated conditions in abalone aquaculture.

The enzyme-like catalytic hydrogen abstraction reaction mechanisms of cyclic hydrocarbons with magnesium-diluted Fe-MOF-74.

Enzymatic heme and non-heme Fe(iv)-O species usually play an important role in hydrogen abstraction of biocatalytic reactions, yet duplicating the reactivity in biomimicry remains a great challenge. Based on Xiao et al.'s experimental work [Nat. Chem., 2014, 6(7), 590], we theoretically found that in the presence of the oxidant N2O, the enzyme-like metal organic framework, i.e., magnesium-diluted Fe-MOF-74 [Fe/(Mg)-MOF-74] can activate the C-H bonds of 1,4-cyclohexadiene (CHD) into benzene with a two-step hydrogen abstraction mechanism based on the density functional theory (DFT) level. It is shown that the first transition state about the cleavage of the N-O bond of N2O to form the Fe(iv)-O species is the rate-determining step with activation enthalpy of 19.4 kcal mol-1 and the complete reaction is exothermic by 62.8 kcal mol-1 on quintet rather than on triplet PES. In addition, we proposed a rebound mechanism of cyclic cyclohexane (CHA) hydroxylation to cyclohexanol which has not been studied experimentally. Note that the activation enthalpies on the first hydrogen abstraction for both cyclic CHD and cyclohexane are just 8.1 and 3.5 kcal mol-1, respectively, which are less than that of 13.9 kcal mol-1 for chained ethane. Most importantly, for the hydrogen abstraction of methane catalyzed by M/(Mg)-MOF-74 (M = Cu, Ni, Fe, and Co), we found that the activation enthalpies versus the C-H bond length of methane of TSs, NPA charge of the reacting oxyl atom have linear relationships with different slopes, i.e., shorter C-H bond and less absolute value of NPA charge of oxyl atom are associated with lower activation enthalpy; while for the activation of methane, ethane, propane and CHD catalyzed by Fe/(Mg)-MOF-74, there also exists positive correlations between activation enthalpies, bond dissociation energies (BDEs) and C-H bond lengths in TSs, respectively. We hope the present theoretical study may provide the guideline to predict the performance of MOFs in C-H bond activation reactions.

Expression profiling of lncRNAs and mRNAs reveals regulation of muscle growth in the Pacific abalone, Haliotis discus hannai.

Long non-coding RNAs (lncRNAs) are known to play a major role in the epigenetic regulation of muscle development. Unfortunately there is little understanding of the mechanisms with which they regulate muscle growth in abalone. Therefore, we used RNA-seq to study the muscle transcriptomes of six Haliotis discus hannai specimens: three large (L_HD group) and three small (S_HD group). We identified 2463 lncRNAs in abalone muscle belonging to two subtypes: 160 anti-sense lncRNAs and 2303 intergenic lncRNAs (lincRNAs). In the L_HD group, we identified 204 significantly differentially expressed lncRNAs (55 upregulated and 149 downregulated), and 2268 significantly differentially expressed mRNAs (994 upregulated and 1274 downregulated), as compared to the S_HD group. The bioinformatics analysis indicated that lncRNAs were relate to cell growth, regulation of growth, MAPK signaling pathway, TGF-ß signaling pathway, PI3K-Akt and insulin signaling pathway, which involved in regulating muscle growth. These findings contribute to understanding the possible regulatory mechanisms of muscle growth in Pacific abalone.

Different Transcriptomic Responses to Thermal Stress in Heat-Tolerant and Heat-Sensitive Pacific Abalones Indicated by Cardiac Performance.

The Pacific abalone Haliotis discus hannai is one of the most economically important mollusks in China. Even though it has been farmed in southern China for almost 20 years, summer mortality remains the most challengeable problem for Pacific abalone aquaculture recently. Here, we determined the different heat tolerance ability for five selective lines of H. discus hannai by measuring the cardiac performance and Arrhenius breakpoint temperature (ABT). The Red line (RL) and Yangxia line (YL) were determined as the most heat-sensitive and most heat-tolerant line, respectively. Heart rates for RL were significantly lower than those of the YL at the same temperature (p < 0.05). The differentially expressed genes (DEGs), which were enriched in several pathways including cardiac muscle contraction, glutathione metabolism and oxidative phosphorylation, were identified between RL and YL at control temperature (20°C) and heat stress temperature (28.5°C, the ABT of the RL) by RNA-seq method. In the RL, 3370 DEGs were identified between the control and the heat-stress temperature, while only 1351 DEGs were identified in YL between these two temperature tests. Most of these DEGs were enriched in the pathways such as protein processing in endoplasmic reticulum, nucleotide binding and oligomerization domain (NOD) like receptor signaling, and ubiquitin mediated proteolysis. Notably, the most heat-tolerant line YL used an effective heat-protection strategy based on moderate transcriptional changes and regulation on the expression of key genes.

Transcriptome analysis of the key role of GAT2 gene in the hyper-accumulation of copper in the oyster Crassostrea angulata.

One paradigm of oysters as the hyper-accumulators of many toxic metals is the inter-individual variation of metals, but the molecular mechanisms remain very elusive. A comprehensive analysis of the transcriptome of Crassostrea angulata was conducted to reveal the relationship between gene expression and differential Cu body burden in oysters. Gene ontology analysis for the differentially expressed genes showed that the neurotransmitter transporter might affect the oyster behavior, which in turn led to difference in Cu accumulation. The ATP-binding cassette transporters superfamily played an important role in the maintenance of cell Cu homeostasis, vitellogenin and apolipophorin transport, and elimination of excess Cu. Gill and mantle Cu concentrations were significantly reduced after silencing the GABA transporter 2 (GAT2) gene, but increased after the injection of GABA receptor antagonists, suggesting that the function of GABA transporter 2 gene was strongly related to Cu accumulation. These findings demonstrated that GABA transporter can control the action of transmitter GABA in the nervous system, thereby affecting the Cu accumulation in the gills and mantles.