Potential role for microRNA in facilitating physiological adaptation to hypoxia in the Pacific whiteleg shrimp Litopenaeus vannamei

Impact of hypoxia on glucose metabolism and hypoxia signaling pathways in juvenile horseshoe crabs Tachypleus tridentatus

Marine hypoxia poses a significant challenge in the contemporary marine environment. The horseshoe crab, an ancient benthic marine organism, is confronted with the potential threat of species extinction due to hypoxia, making it an ideal candidate for studying hypoxia tolerance mechanisms. In this experiment, juvenile Tachypleus tridentatus were subjected to a 21-day trial at DO:2 mg/L (hypoxia) and DO:6 mg/L conditions. The experimental timeline included a 14-day exposure phase followed by a 7-day recovery period. Sampling occurred on days 0, 7, 14, and 21, where the period from day 14 to day 21 corresponds to seven days of recuperation. Several enzymatic activities of important proteins throughout this investigation were evaluated, such as succinate dehydrogenase (SDH), phosphofructokinase (PFK), hexokinase (HK), lactate dehydrogenase (LDH), and pyruvate kinase (PK). Concurrently, the relative expression of hexokinase-1 (HK), hypoxia-inducible factor 1-alpha inhibitor (FIH), and hypoxia-inducible factor 1-alpha (HIF-1α), pyruvate dehydrogenase phosphatase (PDH), succinate dehydrogenase assembly factor 4 (SDH), and Glucose-6-phosphatase (G6Pase) were also investigated. These analyses aimed to elucidate alterations in the hypoxia signaling pathway and respiratory energy metabolism. It is revealed that juvenile T. tridentatus initiated the HIF pathway under hypoxic conditions, resulting in an upregulation of HIF-1α and FIH-1 gene expression, which in turn, influenced a shift in metabolic patterns. Particularly, the activity of glycolysis-related enzymes was promoted significantly, including PK, HK, PKF, LDH, and the related HK gene. In contrast, enzymes linked to aerobic respiration, PDH, and SDH, as well as the related PDH and SDH genes, displayed down-regulation, signifying a transition from aerobic to anaerobic metabolism. Additionally, the activity of gluconeogenesis-related enzymes such as PK and G6Pase gene expression were significantly elevated, indicating the activation of gluconeogenesis and glycogenolysis pathways. Consequently, juvenile T. tridentatus demonstrated an adaptive response to hypoxic conditions, marked by changes in respiratory energy metabolism modes and the activation of hypoxia signaling pathways.

miR-2765 involved in ammonia nitrogen stress via negative regulation of autophagy in shrimp

MicroRNA (miRNA) is a highly conserved non-coding tiny endogenous RNA molecule that regulates various cellular functions by inhibiting mRNA translation or promoting the degradation of proteins. In this study, we identified a specific miRNA (designed as Pva-miR-2765) from Penaeus vannamei, which widely distributed in different tissues of shrimp, with the highest concentration found in the intestine. Through fluorescence in situ hybridization (FISH), we observed that Pva-miR-2765 is primarily located in the cytoplasm. Interestingly, we found that the expression of Pva-miR-2765 significantly decreased in hemocytes, hepatopancreas and gill under ammonia nitrogen stress. Furthermore, when Pva-miR-2765 was silenced, the autophagy level in shrimp significantly increased. Additionally, Pva-miR-2765 was found to promote pathological damage in the hepatopancreas of shrimp. Subsequently, correlation analysis revealed a negative relationship between the expression of Pva-miR-2765 and PvTBC1D7. To confirm this interaction, we conducted a dual luciferase reporter gene assay, which demonstrated that Pva-miR-2765 inhibit the expression of PvTBC1D7 by interacting with its 3'UTR. And the expression level of PvTBC1D7 in shrimp decreased significantly under ammonia nitrogen stress in Pva-miR-2765 overexpressed. Our findings suggest that Pva-miR-2765 can reduce autophagy in P. vannamei by inhibiting the regulation of PvTBC1D7, thereby participating in the oxidative stress of shrimp caused by ammonia nitrogen stress.

The Multifaceted Effects of Short-Term Acute Hypoxia Stress: Insights into the Tolerance Mechanism of Propsilocerus akamusi (Diptera: Chironomidae)

Plenty of freshwater species, especially macroinvertebrates that are essential to the provision of numerous ecosystem functions, encounter higher mortality due to acute hypoxia. However, within the family Chironomidae, a wide range of tolerance to hypoxia/anoxia is displayed. Propsilocerus akamusi depends on this great tolerance to become a dominant species in eutrophic lakes. To further understand how P. akamusi responds to acute hypoxic stress, we used multi-omics analysis in combination with histomorphological characteristics and physiological indicators. Thus, we set up two groups-a control group (DO 8.4 mg/L) and a hypoxic group (DO 0.39 mg/L)-to evaluate enzyme activity and the transcriptome, metabolome, and histomorphological characteristics. With blue-black chromatin, cell tightness, cell membrane invagination, and the production of apoptotic vesicles, tissue cells displayed typical apoptotic features in the hypoxic group. Although lactate dehydrogenase (LDH), alcohol dehydrogenase (ADH), catalase (CAT), and Na+/K+ -ATPase (NKA) activities were dramatically enhanced under hypoxic stress, glycogen content, and superoxide dismutase (SOD) activities were significantly reduced compared to the control group. The combined analysis of the transcriptome and metabolome, which further demonstrated, in addition to carbohydrates, including glycogen, the involvement of energy metabolism pathways, including fatty acid, protein, trehalose, and glyoxylate cycles, provided additional support for the aforementioned findings. Lactate is the end product of glycogen degradation, and HIF-1 plays an important role in promoting glycogenolysis in acute hypoxic conditions. However, we discovered that the ethanol tested under hypoxic stress likely originates from the symbiodinium of P. akamusi. These results imply that some parameters related to energy metabolism, antioxidant enzyme activities, and histomorphological features may be used as biomarkers of eutrophic lakes in Chironomus riparius larvae. The study also provides a scientific reference for assessing toxicity and favoring policies to reduce their impact on the environment.

Hypoxia in aquatic invertebrates: Occurrence and phenotypic and molecular responses

Global deoxygenation in aquatic systems is an increasing environmental problem, and substantial oxygen loss has been reported. Aquatic animals have been continuously exposed to hypoxic environments, so-called "dead zones," in which severe die-offs among organisms are driven by low-oxygen events. Multiple studies of hypoxia exposure have focused on in vivo endpoints, metabolism, oxidative stress, and immune responses in aquatic invertebrates such as molluscs, crustaceans, echinoderms, and cnidarians. They have shown that acute and chronic exposure to hypoxia induces significant decreases in locomotion, respiration, feeding, growth, and reproduction rates. Also, several studies have examined the molecular responses of aquatic invertebrates, such as anaerobic metabolism, reactive oxygen species induction, increased antioxidant enzymes, immune response mechanisms, regulation of hypoxia-inducible factor 1-alpha (HIF-1α) genes, and differently expressed hemoglobin/hemocyanin. The genetic basis of those molecular responses involves HIF-1α pathway genes, which are highly expressed in hypoxic conditions. However, the identification of HIF-1α-related genes and understanding of their applications in some aquatic invertebrates remain inadequate. Also, some species of crustaceans, rotifers, sponges, and ctenophores that lack HIF-1α are thought to have alternative defense mechanisms to cope with hypoxia, but those factors are still unclear. This review covers the formation of hypoxia in aquatic environments and the various adverse effects of hypoxia on aquatic invertebrates. The limitations of current hypoxia research and genetic information about the HIF-1α pathway are also discussed. Finally, this paper explains the underlying processes of the hypoxia response and presents an integrated program for research about the molecular mechanisms of hypoxic stresses in aquatic invertebrates.

Sex matters: Gamete-specific contribution of microRNA following parental exposure to hypoxia in zebrafish

Oxygen availability varies among aquatic environments, and oxygen concentration has been demonstrated to drive behavioral, metabolic, and genetic adaptations in numerous aquatic species. MicroRNAs (miRNAs) are epigenetic modulators that act at the interface of the environment and the transcriptome and are known to drive plastic responses following environmental stressors. An area of miRNA that has remained underexplored is the sex specific action of miRNAs following hypoxia exposure and its effects as gene expression regulator in fishes. This study aimed to identify differences in mRNA and miRNA expression in the F1 generation of zebrafish (Danio rerio) at 1 hpf after either F0 parental male or female were exposed to 2 weeks of continuous (45 %) hypoxia. In general, F1 embryos at 1 hpf demonstrated differences in mRNA and miRNAs expression related to the stressor and to the specific sex of the F0 that was exposed to hypoxia. Bioinformatic pathway analysis of predicted miRNA:mRNA relationships indicated responses in known hypoxia signaling and mitochondrial bioenergetic pathways. This research demonstrates the importance of examining the specific male and female contributions to phenotypic variation in subsequent generations and provides evidence that there is both maternal and paternal contribution of miRNA through eggs and sperm.

Dynamic N6-methyladenosine RNA methylation landscapes reveal epi-transcriptomic modulation induced by ammonia nitrogen exposure in the Pacific whiteleg shrimp Litopenaeus vannamei

Despite the versatility of RNA m⁶A methylation in regulating various biological processes, its involvement in the physiological response to ammonia nitrogen toxicity in decapod crustaceans like shrimp remains enigmatic. Here, we provided the first characterization of dynamic RNA m⁶A methylation landscapes induced by toxic ammonia exposure in the Pacific whiteleg shrimp Litopenaeus vannamei. The global m⁶A methylation level showed significant decrease following ammonia exposure, and most of the m⁶A methyltransferases and m⁶A binding proteins were significantly repressed. Distinct from many well-studied model organisms, m⁶A methylated peaks in the transcriptome of L. vannamei were enriched not only near the termination codon and in the 3' untranslated region (UTR), but also around the start codon and in the 5' UTR. Upon ammonia exposure, 11,430 m⁶A peaks corresponding to 6113 genes were hypo-methylated, and 5660 m⁶A peaks from 3912 genes were hyper-methylated. The differentially methylated genes showing significant changes in expression were over-represented by genes associated with metabolism, cellular immune defense and apoptotic signaling pathways. Notably, the m⁶A-modified ammonia-responsive genes encompassed a subset of genes related to glutamine synthesis, purine conversion and urea production, implying that m⁶A methylation may modulate shrimp ammonia stress responses partly through these ammonia metabolic processes.

Hypoxia stress induces complicated miRNA responses in the gill of Chinese mitten crab (Eriocheir sinensis)

Hypoxia caused by global climate change and human activities has become a growing concern eliciting serious damages to aquatic animals. microRNAs (miRNAs) as non-coding regulatory RNAs exert vital effects on hypoxia responses. Chinese mitten crab (Eriocheir sinensis) with the habitat on the sediment surface or the pond bottom is susceptible to oxygen deficiency. However, whether miRNAs are involved in the response of the crabs to hypoxia stress remains enigmas. In this study, we conducted the whole transcriptome-based miRNA-mRNA integrated analysis of Chinese mitten crab gill under hypoxic condition for 3 h and 24 h We found that the acute hypoxia induces complex miRNA responses with the extensive influences on their target genes that engaged in various bio-processes, especially those associated with immunity, metabolism and endocrine. The impact of hypoxia on crab miRNAs is severer, as the exposure lasts longer. In response to the dissolved oxygen fluctuation, the HIF-1 signaling is activated by miRNAs to cope with the hypoxia stress through strategies including balancing inflammatory and autophagy involved in immunity, changing metabolism to reducing energy consumption, and enhancing oxygen-carrying and delivering capacities. The miRNAs and their corresponding target genes engaged in hypoxia response were intertwined into an intricate network. Moreover, the top hub molecular, miR-998-y and miR-275-z, discovered from the network might serve as biomarkers for hypoxia response in crabs. Our study provides the first systemic miRNA profile of Chinese mitten crab induced by hypoxia stress, and the identified miRNAs and the interactive network add new insights into the mechanism of hypoxia response in crabs.

Analysis of differentially expressed proteins after EHP-infection and characterization of caspase 3 protein in the whiteleg shrimp (Litopenaeus vannamei)

Whiteleg shrimp (Litopenaeus vannamei) is the most important species of shrimp farmed worldwide in terms of its economic value. Enterocytozoon hepatopenaei (EHP) infects the hepatopancreas, resulting in the hepatopancreatic microsporidiosis (HPM) of the host, which causes slow growth of the shrimp and poses a threat to the farming industry. In this study, differentially expressed proteins (DEPs) between EHP-infected and uninfected shrimp were investigated through proteomics sequencing. A total of 9908 peptides and 2092 proteins were identified. A total of 69 DEPs were identified in the hepatopancreas (HP), of which, 28 were upregulated and 41 were downregulated. Our results showed that the differences among the level of multiple proteins involved in the apoptosis were significant after the EHP infection, which indicated that the apoptosis pathway was activated in whiteleg shrimp. In addition, expression leve of caspase 3 gene were identified related to the EHP infection. Furthermore, predictions of spatial structure, analysis of phylogeny and chromosome-level linearity of the caspase 3 protein were performed as well. In conclusion, a relatively complete proteomic data set of hepatopancreas tissues in whiteleg shrimp were established in this study. Findings about genes involved in the apoptosis here will provide a further understanding of the molecular mechanism of EHP infection in the internal immunity of whiteleg shrimp.

Non-coding RNAs targeting NF-κB pathways in aquatic animals: A review

Nuclear factor-kappa B (NF-κB) pathways have a close relationship with many diseases, especially in terms of the regulation of inflammation and the immune response. Non-coding RNAs (ncRNAs) are a heterogeneous subset of endogenous RNAs that directly affect cellular function in the absence of proteins or peptide products; these include microRNAs (miRNAs), long noncoding RNAs (lncRNAs), circular RNAs (circRNAs), etc. Studies on the roles of ncRNAs in targeting the NF-κB pathways in aquatic animals are scarce. A few research studies have confirmed detailed regulatory mechanisms among ncRNAs and the NF-κB pathways in aquatic animals. This comprehensive review is presented concerning ncRNAs targeting the NF-κB pathway in aquatic animals and provides new insights into NF-κB pathways regulatory mechanisms of aquatic animals. The review discusses new possibilities for developing non-coding-RNA-based antiviral applications in fisheries.

Integrative analysis of the miRNA-mRNA regulation network in hemocytes of Penaeus vannamei following Vibrio alginolyticus infection

Penaeus vannamei is an important cultured shrimp that has high commercial value in the worldwide. However, the industry suffers heavy economic losses each year due to disease outbreaks caused by pathogenic bacteria. In the present study, after Vibrio alginolyticus infection, DNA damage in the hemocytes of the shrimp markedly increased, and autophagy and apoptosis increased significantly. Subsequently, hemocytes were sampled from the control and infected shrimp and sequenced for mRNA and microRNA (miRNA) 24 h after V. alginolyticus infection to better understand the response mechanism to bacterial infection in P. vannamei. We identified 1,874 and 263 differentially expressed mRNAs (DEGs) and miRNAs (DEMs) respectively, and predicted that 997 DEGs were targeted by DEMs. These DEGs were involved in the regulation of multiple signalling pathways, such as Toll and IMD signalling, TGF-beta signalling, MAPK signalling, and cell apoptosis, during Vibrio alginolyticus infection of the shrimp. We identified numerous mRNA-miRNA interactions, which provide insight into the defense mechanism that occur during the antimicrobial process of P. vannamei.

miR-10c Facilitates White Spot Syndrome Virus Infection by Targeting Toll3 in Litopenaeus vannemei

Toll-like receptors (TLRs) are canonical cell membrane receptors functioning to recognize pathogens and transduce signals to activate immune responses. It has been known that Toll3 in Pacific white shrimp Litopenaeus vannamei (LvToll3) plays a critical role in antiviral immunity by inducing the transcription of interferon regulatory factor (IRF), which mediates a signaling axis that is similar to the interferon system of vertebrates. However, the regulatory mechanism of the Toll3-IRF signaling is still unclear. In this study, a novel microRNA (miRNA) of miR-10 family, temporarily named as miR-10c, was identified from L. vannamei. miR-10c may play a nonnegligible regulatory role in shrimp immune responses since it was constitutively expressed in all detected tissues and transcriptionally induced by immune stimulation. Functional analysis validated that miR-10c could target LvToll3 to inhibit its expression, through which miR-10c blocked the nuclear translocation of IRF and facilitated white spot syndrome virus (WSSV) infection. To our knowledge, the present study revealed the first report of a Toll targeted by miRNA in crustaceans and provided a solid evidence base for supporting the role of LvToll3 in antiviral defense by activating IRF signaling in L. vannamei. Identification of the miR-10c/Toll3/IRF regulatory axis in shrimp provides new insights into the participation of miRNA in the regulation of immune responses and contributes to in-depth understanding of the mechanisms of Toll-induced immune responses in L. vannamei.

Pva-miR-252 participates in ammonia nitrogen-induced oxidative stress by modulating autophagy in Penaeus vannamei

MicroRNAs (miRNAs) are critical post-transcriptional regulators, which play a crucial role in resistance to adverse environmental stress by regulating autophagy. However, the mechanism of miRNA involved in the autophagy regulation of shrimp under ammonia nitrogen stress is still limited. In the present study, ammonia nitrogen could induce hepatopancreas injury and oxidative stress of P. vannamei, and significantly increase the content of ROS in hemocytes by flow cytometry. Simultaneously, it is accompanied by autophagy occurred in the hemocytes and hepatopancreas. Furthermore, the qRT-PCR analysis revealed that the expression of pva-miR-252 in P. vannamei decreased significantly after ammonia nitrogen stress, and pva-miR-252 negatively regulated PvPI3K by binding to 3'UTR of PvPI3K by double-luciferase assay. Pva-miR-252 overexpression could significantly increase the level of autophagy, and restore the autophagy inhibition caused by Chloroquine in vitro , whereas silencing of pva-miR-252 resulted in the opposite effect. More importantly, overexpression of pva-miR-252 could enhance the activity of antioxidant enzymes and reduced the production of ROS of shrimp under ammonia nitrogen stress. In conclusion, pva-miR-252 could positively regulate autophagy through PvPI3K and improve the antioxidant enzyme activity of P. vannamei under ammonia nitrogen stress, and our study provides a novel theoretical molecular mechanism for further understanding the shrimp cope with a high ammonia nitrogen environment.

Identification and expression analysis of cobia (Rachycentron canadum) liver-related miRNAs under hypoxia stress

At present, due to the influence of global warming, seasonal change, diurnal variation, and eutrophication of the water body, hypoxia has become one of the major factors limiting the stable development of cobia (Rachycentron canadum) culture. In this study, the miRNAs involved in hypoxia stress were screened, and the target genes of miRNAs were annotated and analyzed. The results showed that a total of 184 conservative microRNA (miRNA) and 121 newly predicted miRNA were obtained by sequencing the liver of control (C) and hypoxic (dissolved oxygen, DO (2.64 ± 0.25) mg/L; 3 h) (S) groups. The pathways involved in energy metabolism included starch and sucrose metabolism (ko00500), glycosaminoglycan degradation (ko00531), and galactose metabolism (ko00052). The results indicate that the body maintains physiological activities by regulating some important pathways at the transcriptional level under hypoxia stress, such as the conversion of aerobic metabolism and anaerobic metabolism, the reduction of energy consumption, and the promotion of red blood cell proliferation to maintain the homeostasis of the body.

Identification of microRNAs in Silver Carp (Hypophthalmichthys molitrix) Response to Hypoxia Stress

Simple Summary

Hypoxia stress is one of the main problems in silver carp (Hypophthalmichthys molitrix) culture. Severe hypoxia stress can lead to damage and even death of silver carp. Therefore, it is very important to explore how silver carp adapt to and respond to hypoxia stress. MicroRNAs play an important role in a series of important life activities in organisms. In this study, the differentiallyexpressed miRNAs were screened from a mixed pool of liver, brain, heart and gill of silver carp under different levels of hypoxia stress by high-throughput sequencing. Our findings provided new insights to further study the miRNA regulatory mechanism and molecular characteristics of anoxic response in silver carp.

Abstract

Hypoxia is one of the serious stresses in fish culture, which can lead to physical and morphological changes, and cause injury and even death to fish. Silver carp (Hypophthalmichthys molitrix) is an important economic fish and widely distributed in China. MicroRNA is a kind of endogenous non-coding single-stranded small RNA, which is involved in cell development, and immune response and gene expression regulation. In this study, silver carp were kept in the closed containers for hypoxia treatment by spontaneous oxygen consumption. The samples of heart, brain, liver and gill were collected, and the total RNAs extracted separately from the four tissues were mixed in equal amounts according to the concentration. Afterwards, the RNA pool was constructed for high-throughput sequencing, and based on the small RNA sequencing, the differentially expressed microRNAs were identified. Furthermore, their target gene prediction and enrichment analyses were carried out. The results showed that a total of 229 known miRNAs and 391 putative novel miRNAs were identified, which provided valuable resources for further study on the regulatory mechanism of miRNAs in silver carp under hypoxia stress. The authors verified 16 differentially expressed miRNAs by qRT-PCR, and the results were consistent with small RNA sequencing (sRNA-seq). The predicted target genes number of differentially expressed miRNAs was 25,146. GO and KEGG functional enrichment analysis showed that these target genes were mainly involved in the adaption of hypoxia stress in silver carp through biological regulation, catalytic activity and apoptosis. This study provides references for further study of interaction between miRNAs and target genes, and the basic data for the response mechanism under hypoxia stress in silver carp.

MicroRNA-mediated stress response in bivalve species

Bivalve mollusks are important aquatic organisms, which are used for biological monitoring because of their abundance, ubiquitous nature, and abilities to adapt to different environments. MicroRNAs (miRNAs) are small noncoding RNAs, which typically silence the expression of target genes; however, certain miRNAs directly or indirectly upregulate their target genes. They are rapidly modulated and play an essential role in shaping the response of organisms to stresses. Based on the regulatory function and rapid alteration of miRNAs, they could act as biomarkers for biotic and abiotic stress, including environmental stresses and contaminations. Moreover, mollusk, particularly hemocytes, rapidly respond to environmental changes, such as pollution, salinity changes, and desiccation, which makes them an attractive model for this purpose. Thus, bivalve mollusks could be considered a good animal model to examine a system's response to different environmental conditions and stressors. miRNAs have been reported to adjust the adaptation and physiological functions of bivalves during endogenous and environmental stressors. In this review, we aimed to discuss the potential mechanisms underlying the response of bivalves to stressors and how miRNAs orchestrate this process; however, if necessary, other organisms' response is included to explain specific processes.

MicroRNA-210 regulates placental adaptation to maternal hypoxic stress during pregnancy†

MicroRNA (miR)-210 is a well-known hypoxia-inducible small RNA. Increasing in vitro evidence demonstrates its involvement in regulating multiple behaviors of placental trophoblasts. However, direct in vivo evidence remains lacking. In the present study, we generated a miR-210-deficient mouse strain using CRISPR/Cas9 technology, in which miR-210 expression was markedly deficient in various tissues. Little influence on fertility rate and litter size was observed after the deletion of miR-210 in mice. Continuous exposure of pregnant mice to hypoxia (10.5% O2) from E6.5 to E10.5 or to E18.5 led to reduction in fetal weight, and such fetal weight loss was markedly worsened in miR-210-knockout dams. Analysis of the placental structure demonstrated the reduced expansion of placental spongiotrophoblast layer and hampered development of labyrinth fetal blood vessels in knockout mice compared to the wild-type controls upon hypoxia stimulation. The findings indicate that miR-210 participates in regulating placental adaptation to hypoxic stress during pregnancy.

Identification and Profiling of MicroRNAs During Embryogenesis in the Red Claw Crayfish Cherax quadricarinatus

MicroRNAs (miRNAs) are endogenous small non-coding RNAs that constitute a broad layer of gene regulation at both transcriptional and post-transcriptional levels from prokaryotes to eukaryotes. In embryonic development, they regulate the complex gene expression associated with the complexity of embryogenesis. There is little information about miRNAs in the red claw crayfish (Cherax quadricarinatus), an important commercial species and a potential biological model. In the present study, miRNAs and their target genes were identified during three embryonic developmental stages of C. quadricarinatus. Nineteen known miRNAs and 331 novel ones belonging to 50 miRNA families were obtained. A total of 113 differentially expressed miRNAs were identified, and 2,575 target genes were predicted, of which 1,257 were annotated. Additionally, 63 target genes of 9 miRNAs in C. quadricarinatus were found to be related to embryonic development. For example, miR-10 and its target genes may regulate the nervous system development and body segmentation and miR-2788 may regulate cell proliferation to impact embryonic development. Moreover, miR-28 (target gene tutl), miR-50 (target gene fbx5), and miR-1260b (target gene sif) may co-regulate eye development of embryonic C. quadricarinatus. These miRNAs together with their target genes constitute a network for regulating the development of tissues and organs in the embryo of C. quadricarinatus. Our results lay a foundation for further study on the fundamental molecular and developmental mechanism of crustacean embryogenesis.

MicroRNA-124 regulates lactate transportation in the muscle of largemouth bass (micropterus salmoides) under hypoxia by targeting MCT1

Carbohydrate metabolism switches from aerobic to anaerobic (glycolysis) to supply energy in response to acute hypoxic stress. Acute hypoxic stress with dissolved oxygen (DO) levels of 1.2 ± 0.1 mg/L for 24 h and 12 h re-oxygenation was used to investigate the response of the anaerobic glycolytic pathway in Micropterus salmoides muscle. The results showed that the glucose concentration was significantly lower in muscle, while the lactic acid and pyruvic acid concentrations tended to increase during hypoxic stress. No significant difference was observed in muscle glycogen, and ATP content fluctuated significantly. The activities of gluconeogenesis-related enzymes were slightly elevated, such as phosphoenolpyruvate carboxykinase (PEPCK). The activities of the glycolytic enzymes increased after the induction of hypoxia, such as hexokinase (HK), pyruvate kinase (PK), and lactate dehydrogenase (LDH). Curiously, phosphofructokinase (PFK) activity was significantly down-regulated within 4 h during hypoxia, although these effects were transient, and most indices returned to control levels after 12 h of re-oxygenation. Upregulated hif-1α, ampkα, hk, glut1, and ldh mRNA expression suggested that carbohydrate metabolism was reprogrammed under hypoxia. Lactate transport was regulated by miR-124-5p according to quantitative polymerase chain reaction and dual luciferase reporter assays. Our findings provide new insight into the molecular regulatory mechanism of hypoxia in Micropterus salmoides muscle.

Expression of lactate dehydrogenase is induced during hypoxia via HIF-1 in the mud crab Scylla paramamosain

Lactate dehydrogenase (LDH) is a key enzyme involved in anaerobic metabolism in most organisms. In the present study, we determined the structure and function of LDH sequence in Scylla paramamosain (SpLDH) by gene cloning, expression and RNA interference techniques in order to explore the genetic characteristics of LDH and its relationship with HIF-1 during hypoxia. The full-length cDNA was 1453 bp with an open reading frame (ORF) of 996 bp, and encoded a polypeptide of 332 amino acids. Homology analysis showed that the SpLDH gene is highly similar to arthropods. The SpLDH transcript increased after hypoxia in all tested tissues. The silencing of HIF-1 blocked the increase in LDH mRNA and activity, which were induced by hypoxia in gill and muscle tissues. Our results indicated that SpLDH expression was regulated transcriptionally by HIF-1.