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The full-length cDNAs of amh and dax1 in the hermaphrodite, rice-field eel (Monopterus albus), were cloned and characterized in this study. Multiple sequence alignment revealed Dax1 was well conserved among vertebrates, whereas Amh had a low degree of similarity between different vertebrates. Their expression profiles in gonads during the course of sex inversion and tissues were investigated. The tissue distribution indicated amh was expressed mostly in gonads and was scarcely detectable in other tissues, whereas the expression of dax1 was widespread among the different tissues, especially liver and gonads. amh was scarcely detectable in ovaries whereas it was abundantly expressed in both ovotestis and testis. By contrast, dax1 was highly expressed in ovaries, especially in ♀IV (ovaries in IV stage), but it was decreased significantly in ♀/♂I (ovotestis in I stage). Its expression was increased again in ♀/♂III (ovotestis in III stage), and then decreased to a low level in testis. These significant different expression patterns of amh and dax1 suggest the increase of amh expression and the decline of dax1 expression are important for the activation of testis development, and the high level of amh and a low level of dax1 expression are necessary for maintenance of testis function. [ABSTRACT FROM AUTHOR]

Background: The ricefield eel is a protogynous hermaphroditic Synbranchiform species that changes sex naturally from female to male, which offers an interesting model for studying gonadal (particularly ovarian) differentiation in vertebrates. In the present study, transcriptome sequencing of the gonad of ricefield eel larvae was performed to explore the molecular mechanisms underlying the ovarian differentiation and development., Results: A total of 301,267,988 clean reads were generated from cDNA libraries of gonadal tissues of ricefield eel larvae at 6, 9, 12, and 20 days post hatching (dph), which contained undifferentiated gonads, differentiating ovaries, ovaries with oogonia, and ovaries with meiotic oocytes, respectively. De-novo assembly of all the clean reads generated a total of 265,896 unigenes with a mean size of 720 bp and a N50 of 1107 bp. RT-qPCR analysis of the developmental expression of 13 gonadal development-related functional genes indicated that RNA-seq data are reliable. Transcriptome data suggest that high expression of female development-related genes and low expression of male development-related genes in the early gonads of ricefield eel larvae participate in the cascade of sex differentiation leading to the final female phenotype. The contrasting expression patterns of genes involved in retinoid acid (RA) synthesis and degradation might result in peak production of RA at 12 dph in the gonad of ricefield eel larvae, and induce molecular events responsible for the initiation of meiosis before the meiotic signs could be observed at 20 dph. In addition, only stra6 but not stra8 could be identified in gonadal transcriptome data of ricefield eel larvae, and the expression pattern of stra6 paralleled those of genes involved in RA synthesis, suggesting that stra6 may be a downstream target of RA and play a role in RA metabolism and/or meiotic initiation in the gonad of ricefield eel larvae., Conclusions: The present study depicted the first large-scale RNA sequencing of the gonad of ricefield eel larvae, and identified many important functional genes, GO terms and KEGG pathways involved in gonadal development and germ cell meiosis. Results of the present study will facilitate future study on the ovarian differentiation of ricefield eels and other teleosts as well.

Monopterus albus or locally known as Asian swamp eel has been reputed since ancient time to have an aphrodisiac property. However, there is no scientific evidence to prove this claim. Therefore, the present study was conducted to evaluate aphrodisiac effect of M. albus extract along with its acute toxicity. Two types of extractions were used; aqueous and lipid. Three doses of each M. albus extract, respectively; 50, 100, 200 mg/kg were administered (i.p.) to male mice for mounting behaviour test. Sildenafil citrate or Viagra® (5 mg/kg) being positive control while the negative control group received saline solution. The mounting behaviour test was carried out one hour after the administration of respective dose. The mice treated with aqueous and lipid extract of M. albus at all doses exhibited mounting behaviour. All three doses of lipid extracts and higher dose (200 mg/kg) of aqueous extract administered displayed significant difference (p<0.05) from the negative control. Despite this, only the lipid extract of 50 mg/kg showed significant difference (p<0.05) with positive control. This signifies that aqueous and lipid extracts especially in dose 200 mg/kg have a substantial effect of aphrodisiac property. In addition, lipid extract also devoid of any adverse effects of toxicity. The findings from this study provide scientific evidence that lipid extract of M. albus could be used as an alternative medication of natural product for promoting sexual activity in men. [ABSTRACT FROM AUTHOR]

Na+:K+:2Cl- cotransporter 1 (NKCC1) has been implicated in mediating ischemia-, trauma- or ammonia-induced astrocyte swelling/brain edema in mammals. This study aimed to determine the effects of ammonia or terrestrial exposure on ammonia concentrations in the plasma and brain, and the mRNA expression and protein abundance of nkcc/Nkcc in the brain, of the swamp eel Monopterus albus. Ammonia exposure led to a greater increase in the ammonia concentration in the brain of M. albus than terrestrial exposure. The brain ammonia concentration of M. albus reached 4.5 µmol g-1 and 2.7 µmol g-1 after 6 days of exposure to 50 mmol l-1 NH4Cl and terrestrial conditions, respectively. The full cDNA coding sequence of nkcc1b from M. albus brain comprised 3276 bp and coded for 1092 amino acids with an estimated molecular mass of 119.6 kDa. A molecular characterization indicated that it could be activated through phosphorylation and/or glycosylation by osmotic and/or oxidative stresses. Ammonia exposure for 1 day or 6 days led to significant decreases in the nkcc1b mRNA expression and Nkcc1b protein abundance in the brain of M. albus. In comparison, a significant decrease in nkcc1b mRNA expression was observed in the brain of M. albus only after 6 days of terrestrial exposure, but both 1 day and 6 days of terrestrial exposure resulted in significant decreases in the protein abundance of Nkcc1b. These results are novel because it has been established in mammals that ammonia up-regulates NKCC1 expression in astrocytes and NKCC1 plays an important role in ammonia-induced astrocyte swelling and brain edema. By contrast, our results indicate for the first time that M. albus is able to down-regulate the mRNA and protein expression of nkcc1b/Nkcc1b in the brain when confronted with ammonia toxicity, which could be one of the contributing factors to its extraordinarily high brain ammonia tolerance. [ABSTRACT FROM AUTHOR]

The present study was performed to determine the infection status of swamp eels with Gnathostoma sp. larvae in Myanmar. We purchased total 37 Asian swamp eels, Monopterus albus, from a local market in Yangon in June and December 2013 and 2014. All collected eels were transferred with ice to our laboratory and each of them was examined by the artificial digestion technique. A total of 401 larval gnathostomes (1-96 larvae/eel) were detected in 33 (89.2%) swamp eels. Most of the larvae (n=383; 95.5%) were found in the muscle. The remaining 18 larvae were detected in the viscera. The advanced third-stage larvae (AdL3) were 2.3-4.4 mm long and 0.25-0.425 mm wide. The characteristic head bulb (0.093 × 0.221 mm in average size) with 4 rows of hooklets, muscular long esophagus (1.025 mm), and 2 pairs of cervical sacs (0.574 mm) were observed by light microscopy. The average number of hooklets in the 1st, 2nd, 3rd, and 4th rows was 41, 45, 48, and 51, respectively. As scanning electron microscopic findings, the characteristic 4-5 rows of hooklets on the head bulb, a cervical papilla, tegumental spines regularly arranged in the transverse striations, and an anus were well observed. Based on these morphological characters, they were identified as the AdL3 of Gnathostoma spinigerum. By the present study, it has been confirmed for the first time that Asian swamp eels, M. albus, from Yangon, Myanmar are heavily infected with G. spinigerum larvae.

The Asian swamp eel (Monopterus albus) is one of the most economically important freshwater fish in East Asia, but data on the immune genes of M. albus are scarce compared to other commercially important fish. A better understanding of the eel's immune responses may help in developing strategies for disease management, potentially improving yields and mitigating losses. In mammals, interferon regulatory factors (IRFs) play a vital role in both the innate and adaptive immune system; though among teleosts IRF4 and IRF10 have seldom been studied. In this study, we characterized IRF4 and IRF10 from M. albus (maIRF4 and maIRF10) and found that maIRF4 cDNA consists of 1 716 nucleotides encoding a 451 amino acid (aa) protein, while maIRF10 consists of 1 744 nucleotides including an open reading frame (ORF) of 1 236 nt encoding 411 aa. The maIRF10 gene was constitutively expressed at high levels in a variety of tissues, while maIRF4 showed a very limited expression pattern. Expression of maIRF4 and maIRF10 in head kidney, and spleen tissues was significantly up-regulated from 12 h to 48 h post-stimulation with polyinosinic: polycytidylic acid (poly I:C), lipopolysaccharide (LPS) and a common pathogenic bacteria Aeromonas hydrophila. These results suggest that IRF4 and IRF10 play roles in immune responses to both viral and bacterial infections in M. albus.

The swamp eel, Monopterus albus, is an obligatory air-breathing teleost which can undergo long period of emersion, has high environmental and tissue ammonia tolerance, and can survive in brackish water. We obtained a cDNA sequence of glutamate dehydrogenase (gdh), which consisted of a 133-bp 5' UTR, a complete coding sequence region spanning 1629 bp and a 3' UTR of approximately 717 bp, from the liver, intestine, and brain of M. albus. The translated Gdh amino acid sequence had 542 residues, and it formed a monophyletic clade with Bostrychus sinensis Gdh1a, Tetraodon nigroviridis Gdh1a, Chaenocephalus aceratus Gdh1a, Salmo salar Gdh1a1 and Gdh1a2, and O. mykiss Gdh1a. One day of exposure to terrestrial conditions or 75 mmol l(-1) NH(4)Cl, but not to water at salinity 20, resulted in a significant increase in mRNA expression of gdh1a and Gdh amination activity in the liver of M. albus. However, exposure to brackish water, but not to terrestrial conditions or 75 mmol l(-1) NH(4)Cl, led to a significant increase in the mRNA expression of gdh1a and Gdh amination activity in the intestine. By contrast, all the three experimental conditions had no significant effects on the mRNA expression of gdh1a in the brain of M. albus, despite a significant decrease in the Gdh amination activity in the brain of fish exposed to 75 mmol l(-1) NH(4)Cl for 6 days. Our results indicate for the first time that the mRNA expression of gdh1a was differentially up-regulated in the liver and intestine of M. albus in response to ammonia toxicity and salinity stress, respectively. The increases in mRNA expression of gdh1a and Gdh amination activity would probably lead to an increase in glutamate production in support of increased glutamine synthesis for the purpose of ammonia detoxification or cell volume regulation under these two different environmental conditions.