Expression of Tshb and Tshr in the ricefield eel Monopterus albus: Potential paracrine/autocrine roles in gonads.

Thyroid stimulating hormone (TSH), a glycoprotein synthesized and secreted from thyrotrophs of the pituitary gland, is composed of a glycoprotein hormone common alpha subunit (CGA) and a specific beta subunit (TSHB). The major biological function of TSH is to stimulate thyroidal follicles to synthesize and secrete thyroid hormones through activating its cognate receptor, the thyroid stimulating hormone receptor (TSHR). In the present study, polyclonal antisera against ricefield eel Tshb and Tshr were generated respectively, and the expression of Tshb and Tshr was examined at mRNA and protein levels. RT-PCR analysis showed that tshb mRNA was expressed mainly in the pituitary as well as in some extrapituitary tissues including the ovary and testis. Tshr mRNA was also expressed in a tissue-specific manner, with transcripts detected in tissues including the kidney, ovary, and testis. The immunoreactive Tshb signals in the pituitary were shown to be localized to the inner areas of adenohypophysis which are close to the neurohypophysis of adult ricefield eels. Tshb-immunoreatvie cells in the pituitary of ricefield eel larvae were firstly observed at hatching. The expression of immunoreactive Tshb and Cga was also detected in ricefield eel ovary and testis together with Tshr. In the ovary, immunoreactive Tshb, Cga, and Tshr were observed in oocytes and granulosa cells. In the testis, immunoreactive Tshb was mainly observed in Sertoli cells while immunoreactive Cga and Tshr were detected in germ cells as well as somatic cells. Results of the present study suggest that Tsh may be synthesized both in the ovary and testis locally, which may play paracrine and/or autocrine roles in gonadal development in ricefield eels.

Effects of dietary melatonin supplementation on growth performance and intestinal health of rice field eel (Monopterus albus).

The objective was to assess the impact of melatonin supplementation on the growth performance and intestinal health of rice field eel, Monopterus albus. Three hundred and sixty fish (28.46 ± 0.24 g) were fed five diets supplemented with melatonin of 0, 30, 60, 120, and 240 mg/kg for 70 days. The study found that the variables FBW, WGR, SGR, and FCR exhibited a statistically significant quadratic relationship (P < 0.05) with the dietary melatonin concentrations, and the highest FBW, WGR and SGR as well as lowest FCR were observed in the 120 mg/kg melatonin group, digestive enzymes activities (such as amylase, trypsin, and lipase) also had significant quadratic relationship (P < 0.05), and the highest intestinal villus height and goblet cells were found in the 120 mg/kg diet (P < 0.01), melatonin in diets significantly increased SOD and CAT activities in serum, up-regulated the expression of anti-inflammatory factors (IL-10) and tight junction protein (ZO-1), and down-regulated the expression of pro-inflammatory factors (IL-1ß, IL-8, IL-15, and TNF-α) in the gut, dietary melatonin improved the intestinal microflora compositions, in the group that supplementation a dosage of 120 mg/kg, there was a noticeable rise in the abundance of Firmicutes and the ratio of Firmicutes/Bacteroidota, compared with control group (P < 0.1). Conclusively, dietary supplementation of melatonin promoted growth performance, enhanced intestinal immune capacity and serum antioxidant level, and improved intestinal morphology properties and intestinal flora composition in M. albus. In conclusion, based on quadratic broken-line regression analysis of WGR and FCR, the optimal concentration of melatonin to be supplied is predicted to be 146-148 mg/kg.

Biochemical, Histological, and Transcriptomic Analyses Reveal Underlying Differences in Flesh Quality between Wild and Farmed Ricefield Eel (Monopterus albus).

The present study aimed to systematically investigate the underlying differences in flesh quality between wild and farmed Monopterus albus. Fifteen healthy M. albus per group with an average body weight of 45 g were sampled to analyze muscle parameters by biochemical indicators, histomorphology, and molecular biology. Compared with the wild fish, the farmed M. albus in flesh had lower crude protein, collagen, lysine, histidine, total amino acids, SFA, n-3 PUFA contents, and n-3/n-6 ratio (p < 0.05), and higher moisture, crude lipid, crude ash, MUFA, n-6PUFA, and total PUFA contents (p < 0.05). The thawing loss, drip loss, steaming loss, and boiling loss in the farmed group were significantly higher, and hardness, springiness, cohesiveness, gumminess, chewiness, and resilience were significantly lower than those in the wild group (p < 0.05). In addition, higher muscle fiber density and lower muscle fiber diameter were observed in wild M. albus (p < 0.05). In muscle transcriptome profiling, differentially expressed genes and enriched pathways are primarily associated with muscle development, protein synthesis, catabolism, lipid metabolism, and immunity. To the best of our knowledge, this is the first investigation that compares the flesh quality between wild and farmed M. albus in terms of biochemistry, histology, and molecular biology levels. Overall, wild M. albus had a higher nutritional value and texture quality than farmed M. albus.

Comparative studies on the intestinal health of wild and cultured ricefield eel (Monopterus albus).

Fish intestinal health under intensive aquaculture mode plays an important role in growth, development, and immune function. The present study was aimed to systematically investigate the differences of intestinal health between wild and cultured Monopterus albus by biochemical parameters, histomorphology, and molecular biology. A total of 15 healthy M. albus per group, with an average body weight of 45 g, were sampled to analyze intestinal health parameters. Compared with wild fish, the cultured M. albus in the foregut had lower trypsin, lipase, SOD, CAT, T-AOC, and GSH-Px activities (P < 0.05) and higher amylase activity and MDA content (P < 0.05). The villus circumference and goblet cells in the cultured group were significantly lower than those in the wild group (P < 0.05). In addition, the cultured fish showed lower relative expression levels of occludin, zo-1, zo-2, claudin-12, claudin-15, mucin5, mucin15, lysozyme, complement 3, il-10, tgf-ß1, tgf-ß2, and tgf-ß3 (P < 0.05) and higher il-1ß, il-6, il-8, tnf-a, and ifnγ mRNA expressions than those of wild fish (P < 0.05). In terms of gut microbiota, the cultured group at the phylum level displayed higher percentages of Chlamydiae and Spirochaetes and lower percentages of Firmicutes, Bacteroidetes, Actinobacteria, Cyanobacteria, and Verrucomicrobia compared to the wild group (P < 0.05). At the genus level, higher abundances of Pseudomonadaceae_Pseudomonas and Spironema and lower abundances of Lactococcus and Cetobacterium were observed in the cultured group than in the wild group (P < 0.05). To our knowledge, this is the first investigation of the intestinal health status between wild and cultured M. albus in terms of biochemistry, histology, and molecular biology levels. Overall, the present study showed significant differences in intestinal health between wild and cultured M. albus and the main manifestations that wild M. albus had higher intestinal digestion, antioxidant capacity, and intestinal barrier functions than cultured M. albus. These results would provide theoretical basis for the subsequent upgrading of healthy aquaculture technology and nutrient regulation of intestinal health of cultured M. albus.

Diversification of Toll-like receptor 1 in swamp eel (Monopterus albus).

Toll-like receptor 1 (TLR1) is a pattern recognition receptor that plays critical roles in triggering immune activation via detecting bacterial lipoproteins and lipopeptides. In this study, the genetic characteristic of TLR1 was studied for an important aquaculture fish, swamp eel Monopterus albus. The eel has been seriously threatened by infectious diseases. However, a low level of genetic heterogeneity in the fish that has resulted from a demographic bottleneck presents further challenges in breeding for disease resistance. A comparison with the homologue of closely related species M. javanensis revealed that amino acid replacement (nonsynonymous) but not silent (synonymous) differences have accumulated nonrandomly over the coding sequences of the receptors at the early stage of their phylogenetic split. The combined results from comparative analyses of nonsynonymous-to-synonymous polymorphisms showed that the receptor has undergone significant diversification in M. albus driven by adaptive selection likely after the genetic bottleneck. Some of the changes reported here have taken place in the structures mediating heterodimerization with co-receptor TLR2, ligand recognition, and/or formation of active signaling complex with adaptor, which highlighted key structural elements and strategies of TLR1 in arms race against exogenous challenges. The findings of this study will add to the knowledge base of genetic engineering and breeding for disease resistance in the eel.

Protein expression patterns and metal metabolites in a protogynous hermaphrodite fish, the ricefield eel (Monopterus albus).

BACKGROUND: The ricefield eel Monopterus albus undergoes a natural sex change from female to male during its life cycle, and previous studies have shown the potential mechanisms of this transition at the transcriptional and protein levels. However, the changes in protein levels have not been fully explored, especially in the intersexual stage. RESULTS: In the present study, the protein expression patterns in the gonadal tissues from five different periods, the ovary (OV), early intersexual stage gonad (IE), middle intersexual stage gonad (IM), late intersexual stage gonad (IL), and testis (TE), were determined by untargeted proteomics sequencing. A total of 5125 proteins and 394 differentially expressed proteins (DEPs) were detected in the gonadal tissues. Of the 394 DEPs, there were 136 between the OV and IE groups, 20 between the IM and IE groups, 179 between the IL and IM groups, and 59 between the TE and IL groups. Three candidate proteins, insulin-like growth factor 2 mRNA-binding protein 3 isoform X1 (Igf2bp3), triosephosphate isomerase (Tpi), and Cu-Zn superoxide dismutase isoform X1 [(Cu-Zn) Sod1], were validated by western blotting to verify the reliability of the data. Furthermore, metal metabolite-related proteins were enriched in the IL vs. IM groups and TE vs. IL groups, which had close relationships with sex change, including Cu2+-, Ca2+-, Zn2+- and Fe2+/Fe3+-related proteins. Analysis of the combined transcriptome data revealed consistent protein/mRNA expression trends for two metal metabolite-related proteins/genes [LOC109953912 and calcium Binding Protein 39 Like (cab39l)]. Notably, we detected significantly higher levels of Cu2+ during the sex change process, suggesting that Cu2+ is a male-related metal metabolite that may have an important function in male reproductive development. CONCLUSIONS: In summary, we analyzed the protein profiles of ricefield eel gonadal tissues in five sexual stages (OV, IE, IM, IL, and TE) and verified the plausibility of the data. After preforming the functional enrichment of metal metabolite-related DEPs, we detected the contents of the metal metabolites Zn2+, Cu2+, Ca2+, and Fe2+/Fe3+ at these five stages and screened for (Cu-Zn) Sod1 and Mmp-9 as possible key proteins in the sex reversal process.

Effects on growth performance and immunity of Monopterus albus after high temperature stress.

To investigate the impact of the effect of high temperature stimulation on Monopterus albus larvae after a certain period of time, five experimental groups were established at different temperatures. Then, the M. albus under high temperature stress was fed at 30°C for 70 days. After that, the growth index of the M. albus was counted and analyzed. In terms of growth index, high temperature stress had significant effects on FCR, FBW, WGR, and SGR of M. albus (p < 0.05). The SR increased after being stimulated by temperature (p < 0.1). The study revealed that liver cells of M. albus were harmed by elevated temperatures of 36°C and 38°C. In the experimental group, the activities of digestive enzymes changed in the same trend, reaching the highest point in the 32°C group and then decreasing, and the AMS activity in the 38°C group was significantly different from that in the 30°C group (p < 0.05). The activities of antioxidase in liver reached the highest at 34°C, which was significantly different from those at 30°C (p < 0.05). In addition, the expression levels of TLR1, C3, TNF-α, and other genes increased in the experimental group, reaching the highest point at 34°C, and the expression level of the IL-1ß gene reached the highest point at 32°C, which was significantly different from that at 30°C (p < 0.05). However, the expression level of the IRAK3 gene decreased in the experimental group and reached its lowest point at 34°C (p < 0.05). The expression level of the HSP90α gene increased with the highest temperature stimulus and reached its highest point at 38°C (p < 0.05). In the α diversity index of intestinal microorganisms in the experimental group, the observed species, Shannon, and Chao1 indexes in the 34°C group were the highest (p < 0.05), and ß diversity analysis revealed that the intestinal microbial community in the experimental group was separated after high temperature stimulation. At the phylum level, the three dominant flora are Proteus, Firmicutes, and Bacteroides. Bacteroides and Macrococcus abundance increased at the genus level, but Vibrio and Aeromonas abundance decreased. To sum up, appropriate high-temperature stress can enhance the immunity and adaptability of M. albus. These results show that the high temperature stimulation of 32°C-34°C is beneficial to the industrial culture of M. albus.

Community development in the production of concentrated flourhigh in amino acids made from a combination of eel and tempe / Desarrollo comunitario en la producción de harina concentrada rica en aminoácidos a partir de una combinación de anguila y tempe

Introduction and Objectives: To date, there are no known supplement products made from a combination of eel and tempe. The development of concentrate from eels in combination with tempe (ETF) aims to create supplements containing the essential amino acid L-arginine, which has many proven health benefits. Methods: The community empowerment was held from June to July 2023 at Cangkringan, Sleman, Yogyakarta. The main agendas consisted of ETF training production and the cooking creation of ETF-based food. Aside from that, there were several secondary agendas such as food halal socialization, accessories design training, patchwork utilization training, computer and Microsoft Office training, English language education, public speaking class, Al-Qur’an and miscellaneous education for children, community service, mutual cinema, and competitions for the community. Results: The community development program in the production of high-amino acid concentrated ETF flour has succeeded in achieving the three main objectives of the program, namely functional product innovation, empowerment of micro, small, and medium enterprises and local communities, as well as increasing demand for local commodities, showing the importance of collaboration between the government, community, and private sector in supporting the development of local products that are economically and health-beneficial and can be used as examples to share similar initiatives in other areas.(AU)

Three-dimensional computed tomography reconstruction diagnosed digestive tract perforation and acute peritonitis caused by Monopterus albus: A case report.

BACKGROUND: Few reports have described living foreign bodies in the human body. The current manuscript demonstrates that computed tomography (CT) is an effective tool for accurate preoperative evaluation of living foreign bodies in clinic. The three-dimensional (3D) reconstruction technology could clearly display anatomical structures, lesions and adjacent organs, improving diagnostic accuracy and guiding the surgical decision-making process. CASE SUMMARY: Herein we describe a 68-year-old man diagnosed with digestive tract perforation and acute peritonitis caused by a foreign body of Monopterus albus. The patient presented to the emergency department with complaints of dull abdominal pain, profuse sweating and a pale complexion during work. A Monopterus albus had entered the patient's body through the anus two hours ago. During hospitalization, the 3D reconstruction technology revealed a perforation of the middle rectum complicated with acute peritonitis and showed a clear and complete Monopterus albus bone morphology in the abdominal and pelvic cavities, with the Monopterus albus biting the mesentery. Laparoscopic examination detected a large (diameter of about 1.5 cm) perforation in the mid-rectum. It could be seen that a Monopterus albus had completely entered the abdominal cavity and had tightly bitten the mesentery of the small intestine. During the operation, the dead Monopterus albus was taken out. CONCLUSION: The current manuscript demonstrates that CT is an effective tool for accurate preoperative evaluation of living foreign bodies in clinic.

Regulatory mechanism of LncRNAs in gonadal differentiation of hermaphroditic fish, Monopterus albus.

BACKGROUND: Monopterus albus is a hermaphroditic fish with sex reversal from ovaries to testes via the ovotestes in the process of gonadal development, but the molecular mechanism of the sex reversal was unknown. METHODS: We produced transcriptomes containing mRNAs and lncRNAs in the crucial stages of the gonad, including the ovary, ovotestis and testis. The expression of the crucial lncRNAs and their target genes was detected using qRT‒PCR and in situ hybridization. The methylation level and activity of the lncRNA promoter were analysed by applying bisulfite sequencing PCR and dual-luciferase reporter assays, respectively. RESULTS: This effort revealed that gonadal development was a dynamic expression change. Regulatory networks of lncRNAs and their target genes were constructed through integrated analysis of lncRNA and mRNA data. The expression and DNA methylation of the lncRNAs MSTRG.38036 and MSTRG.12998 and their target genes Psmß8 and Ptk2ß were detected in developing gonads and sex reversal gonads. The results showed that lncRNAs and their target genes exhibited consistent expression profiles and that the DNA methylation levels were negatively regulated lncRNA expression. Furthermore, we found that Ptk2ß probably regulates cyp19a1 expression via the Ptk2ß/EGFR/STAT3 pathway to reprogram sex differentiation. CONCLUSIONS: This study provides novel insight from lncRNA to explore the potential molecular mechanism by which DNA methylation regulates lncRNA expression to facilitate target gene transcription to reprogram sex differentiation in M. albus, which will also enrich the sex differentiation mechanism of teleosts.

Monopterus albus is a hermaphroditic fish that undergoes sex reversal from female to male via intersex during the process of the gonadal differentiation which was an ideal model for epigenetic modification research. After laying eggs, the female M.albus reversal to the intersex. So that the female have a shorter stage and smaller body size which cause low egg production. In the present study, we produced the transcriptomes which contain mRNA and lncRNA in the crucial stage of the gonad including ovary, ovotestis and testis. This effort reveals that gonadal development was a dynamic expression changes. Regulatory networks of lncRNAs and its target genes were constructed though integrated analysis of lncRNA and mRNA data. We found DNA methylation was negatively associated with lncRNA (MSTRG.38036 and MSTRG.12998) expression in developing gonads. Additionally, 17α-methyltestosterone inhibit the expression of lncRNA and increase methylation. Furthermore, we found that Ptk2ß probably regulates cyp19a1 expression via the Ptk2ß/EGFR/STAT3 pathway to reprogram sex differentiation. The present study on the gonadal differentiation of M. albus provides novel insights from lncRNA to explore potential molecular mechanism. In the future, function of the lncRNA will be further studied and the gene editing technology will be applied to cultivate the female with high fecundity to improve the yield of fish fry.

Disruption of intestinal structure, tight junction complex, immune response and microbiota after chronic exposure to copper in swamp eel (Monopterus albus).

As an essential micronutrient, copper is crucial in aquatic organisms' growth and development. Numerous studies have consistently reported that excessive intake of copper can have harmful effects on organisms. However, there are limited studies on the impact of copper on the intestine of the swamp eel (Monopterus albus). This study aimed to investigate the changes of intestinal histopathology, tight junction complex, immune response, and microbiota in swamp eel treated with 0 mg/L Cu2+, 0.05 mg/L Cu2+, and 0.10 mg/L Cu2+ for 56 d. Intestinal histopathology showed major changes such as the increased number of erythrocytes and goblet cells in the lamina propria, and separation of the lamina propria. The expression of genes involved in tight junction complex (ZO-1, Claudin-3, Claudin-12 and Claudin-15) was significantly changed. In addition, copper exposure significantly increased the mRNA levels of TLR3, TLR7, TLR8, NF-κB, I-κB, TNF-α and IL-8, especially in 0.10 mg/L Cu2+ group. In contrast, the relative expression level of anti-inflammatory cytokine TGF-ß was significantly decreased after exposure to copper. Analysis of the intestinal microbiome showed the intestinal microbiota of swamp eels in the control and copper exposure groups were dominated by Firmicutes and Proteobacteria at the phylum level. Notably, copper exposure changed the diversity of the intestinal microbiota and decreased the relative abundance of Firmicutes and Proteobacteria in the intestine of swamp eel. Collectively, this study demonstrates that chronic copper exposure induces intestinal pathologic changes and inflammatory response, disrupts the intestinal microbial diversity and microbiota composition, and decreases intestinal barrier function in swamp eel, which enhances our understanding of copper-induced intestinal toxicity in fish.

Neuropeptide B (NPB) and NPB receptor 2b (NPBWR2b) in the ricefield eel Monopterus albus: expression and potential involvement in the regulation of gonadotropins.

The neuropeptide B/W signaling system is composed of neuropeptide B (NPB), neuropeptide W (NPW), and two cognate receptors, NPBWR1 and NPBWR2, which are involved in diverse physiological processes, including the central regulation of neuroendocrine axes in vertebrates. The components of this signaling system are not well conserved during vertebrate evolution, implicating its functional diversity. The present study characterized the ricefield eel neuropeptide B/W system, generated a specific antiserum against the neuropeptide B/W receptor, and examined the potential roles of the system in the regulation of adenohypophysial functions. The ricefield eel genome contains npba, npbb, and npbwr2b but lacks the npw, npbwr1, and npbwr2a genes. The loss of npw and npbwr1 probably occurred at the base of ray-finned fish radiation and that of npbwr2a species specifically in ray-finned fish. Npba and npbb genes are produced through whole-genome duplication (WGD) in ray-finned fish. The ricefield eel npba was expressed in the brain and some peripheral tissues, while npbb was predominantly expressed in the brain. The ricefield eel npbwr2b was also expressed in the brain and in some peripheral tissues, such as the pituitary, gonad, heart, and eye. Immunoreactive Npbwr2b was shown to be localized to Lh and Fsh cells but not to Gh or Prl cells in the pituitary of ricefield eels. Npba upregulated the expression of fshb and cga but not lhb mRNA in pituitary fragments of ricefield eels cultured in vitro. The results of the present study suggest that the NPB system of ricefield eels may be involved in the neuroendocrine regulation of reproduction.

Integrated transcriptome and metabolome analysis reveals a possible mechanism for the regulation of lipid metabolism via vitamin A in rice field eel (Monopterus albus).

To understand the effects of vitamin A on lipid deposition in rice field eels, integrated liver transcriptome and metabolome were conducted and the changes in the genes and metabolites were assessed. Three groups of rice field eel were fed with 0, 200, and 16,000 IU/kg vitamin A supplementations in their diets for 70 days. The total lipid content in the whole body of the rice field eels was significantly increased with the vitamin A supplementations (p < 0.05). Comparative transcriptome analysis revealed 14 pathways and 46 differentially expressed genes involved in lipid metabolism. Sphingolipid metabolism, glycerolipid metabolism, primary bile acid biosynthesis and steroid hormone biosynthesis were significantly enriched pathways. In these pathways, three differential genes phospholipid phosphatase 1a (PLPP1a), phospholipid phosphatase 2b (PLPP2b), cytochrome P450 21a2 (CYP21a2) were consistent with the change trend of lipid content, and the other three differential genes aldo-keto reductase family 1 member D1 (AKR1D1), uridine diphosphate glucuronic acid transferase 1a1 (UGT1a1), cytochrome P450 1a (CYP1a) were opposite. Metabolomic analysis revealed that primary bile acid biosynthesis, sphingolipid metabolism, steroid hormone biosynthesis and biosynthesis of unsaturated fatty acids were all critical for rice field eel metabolic changes in response to vitamin A. Six important differential metabolites (eicosapentaenoic acid, sphinganine, 11-beta-hydroxyprogesterone, hydroxyeicosatetraenoic acid, cholic acid, and glycochenodeoxycholate) were identified and have provided new insights into how vitamin A regulates lipid deposition. Integrated transcriptome and metabolome analyses revealed that primary bile acid biosynthesis was the only remarkably enriched pathway in both the transcriptome and metabolome while that sphingosine was the main metabolite. Based on the above results, we have concluded that vitamin A promotes lipid deposition in the rice field eel through the primary bile acid synthesis pathway, and lipid deposits are widely stored in cell membranes, mainly in the form of sphingosine. These results will provide reference data to help improve our understanding of how vitamin A regulates lipid metabolism.

FoxH1 Represses the Promoter Activity of cyp19a1a in the Ricefield Eel (Monopterus albus).

Forkhead box H1 (FoxH1) is a sexually dimorphic gene in Oreochromis niloticus, Oplegnathus fasciatus, and Acanthopagrus latus, indicating that it is essential for gonadal development. In the present study, the molecular characteristics and potential function of FoxH1 and the activation of the cyp19a1a promoter in vitro were evaluated in Monopterus albus. The levels of foxh1 in the ovaries were three times higher than those in the testes and were regulated by gonadotropins (Follicle-Stimulating Hormone and Human Chorionic Gonadotropin). FoxH1 colocalized with Cyp19a1a in the oocytes and granulosa cells of middle and late vitellogenic follicles. In addition, three FoxH1 binding sites were identified in the proximal promoter of cyp19a1a, namely, FH1 (-871/-860), FH2 (-535/-524), and FH3 (-218/-207). FoxH1 overexpression significantly attenuated the activity of the cyp19a1a promoter in CHO cells, and FH1/2 mutation increased promoter activity. Taken together, these results suggest that FoxH1 may act as an important regulator in the ovarian development of M. albus by repressing cyp19a1a promoter activity, which provides a foundation for the study of FoxH1 function in bony fish reproductive processes.

Insights into the mechanism of growth and fat deposition by feeding different levels of lipid provided by transcriptome analysis of swamp eel (Monopterus albus, Zuiew 1793) liver.

Lipid is an important source of energy in fish feeds, and the appropriate fat content can improve the efficiency of protein utilization. However, excessive lipid content in the feed can lead to abnormal fat deposition in fish, which has a negative effect on the growth of fish. Therefore, the effects of feed lipid levels on swamp eel were studied. Essential functional genes were screened using transcriptomics. We divided 840 fish into seven groups (four replicates). A mixture of fish and soybean oils (1:4), 0%, 2%, 4%, 6%, 8%, 10%, and 12% was added to the basic feed were named groups one to seven (L1-L7), respectively. Isonitrogenous diets were fed swamp eel for 10 weeks. Growth performance, visceral index, nutritional components, and biochemical indexes were measured and analyzed. Livers of the 0%, 6%, and 12% groups were subjected to transcriptome sequencing analysis. The results of our study showed that: the suitable lipid level for the growth of swamp eel was 7.03%; the crude fat content of whole fish, liver, intestine, muscle, and skin increased with the increase of lipid level, with some significant difference, and excess fat was deposited in skin tissue; triglyceride, total cholesterol, and free fatty acid contents increased with the increase of feed lipid level. High-density lipoprotein levels in the L3 and L4 groups were higher than in the other groups. Blood glucose concentrations in the L5, L6, and L7 groups increased; the liver tissue structure was damaged when the lipid level was too high. two-hundred-and-twenty-eight differentially expressed genes were found. Several critical pathways regulating glucose metabolism and energy balance (e.g., glycerolipid metabolism, glycolysis synthesis, degradation of ketone bodies, and Janus Kinase/Signal Transducer and Activator of Transcription signaling pathway) were enriched in swamp eel compared with the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Suitable lipid levels (7.03%) can promote the growth of swamp eel, and excessive lipid levels can cause elevated blood lipids and lead to liver cell damage. Regulatory mechanisms may involve multiple metabolic pathways for glucose and lipid metabolism in eels. This study provides new insights to explain the mechanism of fat deposition due to high levels of lipid and provides a basis for the production of efficient and environmentally friendly feed for swamp eel.

Polystyrene nanospheres-induced hepatotoxicity in swamp eel (Monopterus albus): From biochemical, pathological and transcriptomic perspectives.

As ubiquitous emerging pollutants, microplastics (MPs) in aquatic environments have aroused critical global concerns. Despite the occurrence and characteristics of MPs in freshwater agroecosystems well-described by our previous study, their ecotoxicological implications in Monopterus albus remains unfathomed. Herein, we dissected toxic effects and mechanisms of PS-NPs exposure against M. albus hepatic tissues at concentrations of 0.5 (L), 5 (M), 10 (H) mg/L for 28 days using physiochemical measurements, histopathological analysis and transcriptomic sequencing. Results showed that upon PS-NPs treatments, levels of ROS, MDA, 8-OHdG and MFO activity were significantly enhanced relative to the control (C) group, while SP content and T-AOC activity were dramatically suppressed, suggesting ROS burst, lipid peroxidation and DNA damage may occur in liver tissues. This oxidative damage further triggered impaired hepatic function and histopathology, disordered lipid metabolism and hepatocyte apoptosis, as reflected by significantly diminished activities of GPT, GOT, ACP, AKP and LDH, paralleled with augmented levels of TG, TC and HSI as well as Cytc and Caspase-3,8,9 activities. Noticeably, concentration-dependent rises of apoptotic rate, vacuolar degeneration and lipid deposition were manifest in TUNEL, H&E and ORO staining. In addition, a total of 375/475/981 up-regulated as well as 260/611/1422 down-regulated DEGs in C vs L, C vs M and C vs H categories were identified based on RNA-seq, respectively. These DEGs were significantly annotated and enriched into GO terms (membrane, cytoplasm, response to stimuli, oxidation-reduction process) as well as KEGG pathways (ether lipid metabolism, apoptosis, chemical carcinogenesis-reactive oxygen species, non-alcoholic fatty liver disease). Moreover, signaling cascades Keap1-Nrf2, p53 and PPAR were either substantially initiated or dysregulated to orchestrate PS-NPs hepatotoxicity featuring oxidative damage, hepatocyte apoptosis and lipid steatosis. Collectively, this study not only expounded on toxicological mechanisms whereby PS-MPs exerted deleterious effects on M. albus, but also pointed to ecological risks of PS-MPs-induced hepatoxicity and lipid steatosis in this commercially-important species.

Dietary polystyrene nanoplastics exposure alters hepatic glycolipid metabolism, triggering inflammatory responses and apoptosis in Monopterus albus.

Microplastics and nanoplastics (MPs and NPs) are abundant, persistent, and widespread environmental pollutants that are of increasing concern as they pose a serious threat to ecosystems and aquatic species. Identifying the ecological effects of NPs pollution requires understanding the effects of changing nanoplastics concentrations in aquatic organisms. Monopterus albus were orally fed three different concentrations of 100 nm polystyrene nanoplastics (PS-NPs): 0.05 %, 0.5 %, and 1 % of the feed for 28 days. Nanoplastics significantly activated the PPAR signaling pathway, Acyl-CoA oxidase 1 (ACOX1), carnitine palmitoyltransferase 1a (CPT1A), angiopoietin-like 4 (ANGPTL4), and phosphoenolpyruvate carboxykinase (PCK) at the mRNA level, resulting in disturbed lipid metabolism. Glutathione peroxidase (GSH-px) activity, catalase (CAT) activity, and malondialdehyde (MDA) were significantly elevated in the high nanoplastics-feeding exposure group, leading to oxidative stress in the liver. Overexpression of the cytokines genes Interleukin 1 (IL1B) and Interleukin-8 (IL8), Tumor necrosis factor alpha (TNF-α), activation of MAPK signaling pathway, and increased gene expression of c-Jun amino-terminal kinases (JNK) and p38 indicate that exposure to NPs may lead to hepatopancreas apoptosis through oxidative stress and inflammation. In summary, dietary PS-NPs exposure alters hepatic glycolipid metabolism, triggering inflammatory responses and apoptosis in M. albus. The results of this study provide valuable ecotoxicological data for a better understanding of the biological fate and effects of nanoplastics in M. albus.

Effects of metamifop on ammonia production and metabolism of Monopterus albus.

The use of herbicides is believed to have an impact on the metabolism, physiology and biochemistry of fish. In this study, we studied the effects of metamifop on the production and metabolism of Monopterus. albus living in the water. According to the semi-lethal concentration of metamifop for 96 h, four MET concentration groups (0.2-, 0.4-, 0.6- and 0.8 mg L-1) were set up for 96 h exposure test. The ammonia discharge rate decreased, hemolymph ammonia content increased significantly, and hemolymph urea nitrogen content decreased at all time periods of metamifop exposure. In liver, the protein content decreased, the neutral protease content increased significantly (p < 0.01), amino acid content increased, and ATP content increased significantly (p < 0.01). In brain, the protein content increased, the activity of acid protease, neutral protease and alkaline protease all decreased, amino acid content decreased significantly (p < 0.01), and the content of ATP decreased. Glutamic-pyruvic transaminase (GPT) activity did not change in liver but decreased in brain. Glutamine synthetase (GS) activity decreased in liver and increased in brain. Glutaminase (GLS) activity decreased in liver and increased in brain. In conclusion, the liver and brain tissues of M. albus react differently to MET exposure. The liver mainly synthesizes energy through hydrolyzed protein, while the brain mainly synthesizes protein. Amino acids produced by protein hydrolysis cannot be converted to alanine for storage, and the degraded amino acids lead to the elevation of endogenous ammonia. MET inhibits the removal of ammonia from M. albus. Only liver tissue can detoxify the eel by converting ammonia into glutamine. Brain should have to tolerate high levels of endogenous ammonia.

Stimulator of interferon genes from Asian swamp eel (MaSTING) is involved in host defense against bacterial infection.

Stimulator of interferon genes (STING) is an endoplasmic reticulum (ER)-associated protein that plays critical roles in innate immunity and pathogenesis of various diseases. To date, teleost STING against viral stimulation has been identified, whereas STING signaling events in fish against bacteria are not well understood. In the present study, the open reading frame (ORF) of STING from Asian swamp eel (Monopterus albus) was cloned (named MaSTING) and its roles in bacterial infection were investigated. Amino acid sequence alignment and phylogenetic analysis revealed that MaSTING had conserved structures with mammalian STING and shared the closest relationship with mandarin fish STING. Subcellular localization analysis showed that MaSTING distributed in the whole cytoplasm and mainly co-localized with ER. Expression pattern analysis found that MaSTING was constitutively expressed in all the examined tissues with the highest expression in the liver and spleen. Post stimulation with bacteria and various PAMPs, the expression of MaSTING was induced at indicated time points in the immune-related organs and isolated peripheral blood leucocytes. Furthermore, the mechanism underlying MaSTING against bacterial infection was further studied. The qPCR analysis showed that MaSTING overexpression promoted 2'3'-cGAMP induced the expression of IFN-1, ISG15, Viperin, Mx, IL-1ß and TNF-α. Western blotting assay suggested that MaSTING significantly enhanced the phosphorylation of TANK-binding kinase 1 (TBK1) and p65. MaSTING also significantly increased the luciferase activity of IFN-1 and NF-κB promoters. Taken together, MaSTING is involved in host defense against bacterial infection by inducing the inflammatory response.

Transcription factors Dmrt1a, Foxl2, and Nr5a1a potentially interact to regulate cyp19a1a transcription in ovarian follicles of ricefield eel (Monopterus albus).

Aromatase (encoded by Cyp19a1) in the ovarian follicular cells catalyzes the production of estradiol from testosterone, which plays important roles in the ovarian development of vertebrates. In the present study, the interaction of Dmrt1, Foxl2, and Nr5a1a on the regulation of cyp19a1a transcription in ovarian follicles was examined in a teleost, the ricefield eel Monopterus albus. The expression of dmrt1a, foxl2, and nr5a1a was detected in ovarian follicular cells together with cyp19a1a at the mRNA and/or protein levels. Sequence analysis identified one conserved Foxo binding site in the proximal promoter region of ricefield eel cyp19a1a. Transient transfection assay showed that Foxl2 may bind to the conserved Foxo site to activate cyp19a1a transcription and act synergistically with Nr5a1a. Mutation of either the conserved Nr5a1 site or Foxo site abolished or significantly decreased the synergistic effects of Nr5a1a and Foxl2 on cyp19a1a transcription. The sequence between Region III and I-box of Nr5a1a was critical to this synergistic effect. Dmrt1a modulated the Foxl2- and Nr5a1a-induced activation of cyp19a1a transcription and their synergistic effects in a biphasic manner, with inhibitory roles observed at lower doses (10-50 ng) but release of the inhibition or even potentiating effects observed at higher doses (100-200 ng). Collectively, data of the present study suggest that the interaction of Dmrt1a, Foxl2, and Nr5a1a in the ovarian follicular cells may facilitate the adequate expression of cyp19a1a and the production of estradiol, and contribute to the development and maturation of ovarian follicles in ricefield eels and other vertebrates as well.