Cloning, characterization and cadmium inducibility of metallothionein in the testes of the mudskipper Boleophthalmus pectinirostris.

Metallothioneins (MTs) are cysteine-rich, low molecular weight, and heavy metal-binding protein molecules. MT participates in metallic homeostasis and detoxification in living animals due to its abundant cysteine. In order to investigate the functions of MT during spermiogenesis in the mudskipper (Boleophthalmus pectinirostris), we identified the MT complete which contains: an 83bp 5' untranslated region, a 110bp 3' untranslated region, and a 183bp open reading frame. The protein alignment between MT sequences of other species shows a high similarity and a strong identity in cysteine residues vital for the metal-binding affinity of MT. The localizations of MT were mainly in the cytoplasm of germinal cells, indicating a role in spermatogenesis and testis protection. After the cadmium (Cd) exposure, the testis presents abnormal morphology and MT mRNA expression, both of which indicate a sensitive response of testis MT to Cd. Therefore, we suggest that MTs play an important role in spermatogenesis and testes protection against Cd toxicity in B. pectinirostris.

Molecular cloning, characterization and expression analysis of metallothionein in the liver of the teleost Acrossocheilus fasciatus exposed to cadmium chloride.

Metallothionein (MT) has a characteristic molecular structure with a cysteine-rich content. This unique structure provides metal-binding and redox capabilities and promoting metal homeostasis and detoxification in living animals. In order to evaluate the effects of cadmium (Cd) on hepatic MT expression in the liver of Acrossocheilus fasciatus, we obtained the complete cDNA of the A. fasciatus liver MT for the first time. The MT cDNA contains a 605-bp sequence, which codes for 60 amino acids. Protein alignment showed that the similarity between MT protein sequences of A. fasciatus and those of other vertebrates (especially teleosts) was very high and a cysteine residue structure was also conserved. MT was detected in the liver, kidney, gill, testis, muscle, spleen, heart and brain tissues of A. fasciatus by tissue-specific expression analysis. After Cd exposure, Cd/hemoglobin saturation assay, immunohistochemistry and reverse-transcription quantitative PCR (RT-qPCR) were used to describe MT expression in liver tissue. These techniques indicate a sensitive response by liver MT to Cd exposure. The results suggest that A. fasciatus MT may play an important role in the detoxification processes in the liver, and also would be a useful biomarker for monitoring metal pollution in aquatic environments. In addition, A. fasciatus could be regarded as one candidate for a model species for bony fishes in ecotoxicology.

The complete mitochondrial genome of giant stone loach Triplophysa siluroides (Cypriniformes: Balitoridae).

In this study, the complete mitogenome sequence of balitorid fish, giant stone loach Triplophysa siluroides, which collected from the Yellow River, China has been sequenced by the long polymerase chain reaction method. The mitogenome, consisting of 16,574 base pairs (bp), had typical vertebrate mitochondrial gene arrangement, including 13 protein coding genes, 22 transfer RNAs, 2 ribosomal RNA genes and a noncoding control region (CR). CR of 918 bp length is located between tRNA(Pro) and tRNA(Phe). The overall base composition of Triplophysa siluroides is 28.8% for A, 28.7% for T, 25.0% for C, and 17.5% for G, with a slight AT bias of 57.5%. The complete mitochondrial genome may provide rather informative data for reconstructing and addressing new molecular perspectives for balitorid phylogenies.

The complete mitochondrial genome of Chinese rod gugeon Abbottina rivularis (Cypriniformes, Cyprinidae).

In this study, the complete mitogenome sequence of the Chinese rod gugeon, Abbottina rivularis (Basilewsky, 1855) has been amplified. The mitogenome, consisting of 16,608 base pairs (bp), had the typical vertebrate mitochondrial gene arrangement, including 13 protein-coding genes, 22 transfer RNAs, 2 ribosomal RNAs genes and a noncoding control region (CR). CR of 929 bp length is located between tRNA(Pro) and tRNA(Phe). The overall base composition of A. rivularis is 29.9% for A, 27.2% for C, 25.7% for T and 17.3% for G, with higher AT content of 55.6%. The complete mitogenome may provide rather essential and important DNA molecular data for further phylogenetic analysis for not only congeneric species but also higher different taxa of Cyprinid fishes.

The complete mitochondrial genome of small sliver gugeon Squalidus gracilis (Teleostei, Cyprinidae).

In this study, the complete mitogenome sequence of small silver gugeon Squalidus gracilis has been amplified. The mitogenome, consisting of 16,605 base pairs (bp), had the typical vertebrate mitochondrial gene arrangement, including 13 protein-coding genes, 22 transfer RNAs, 2 ribosomal RNAs genes and a non-coding control region (CR). CR of 928 bp length is located between tRNA(Pro) and tRNA(Phe). The overall base composition of S. gracilis is 29.8% for A, 27.6% for C, 25.7% for T and 16.9% for G, with higher AT content of 55.5%. The complete mitogenome may provide rather essential and important DNA molecular data for further phylogenetic analysis for not only congeneric species but also higher different taxa of Cyprinid fishes.

The complete mitochondrial genome of altai osman Oreoleuciscus humilis Warpachowski (Cypriniformes, Cyprinidae).

The complete mitochondrial genome of altai osman Oreoleuciscus humilis Warpachowski collected from Mongolia has been amplified and sequenced in this study. The complete mitochondrial genome is 16,606 base pairs (bp) in total length, had the typical vertebrate mitochondrial gene arrangement, including 13 protein-coding genes, 2 rRNAs, 22 tRNAs, 1 control region (CR) and 1 light-strand replication origin (OL). The overall base composition of Oreoleuciscus humilis is 27.6% for A, 26.4% for T, 27.2% for C, 18.8% for G, with higher AT content 54.0%. This study will be rather beneficial for understanding the phylogenetic approach of Oreoleuciscus species and other related genera of cyprinid fishes.

Glutathione peroxidase 1 expression, malondialdehyde levels and histological alterations in the liver of Acrossocheilus fasciatus exposed to cadmium chloride.

Cadmium (Cd) is known as a widespread pollutant in aquatic environment. The accumulation of reactive oxygen species (ROS) is attributed to Cd exposure, which may affect the growth, development and physiological metabolism of aquatic organisms. In response to these unfavorable damages, antioxidant systems have been developed to protect against oxidative stress. In this study, we investigated the expression pattern of glutathione peroxidase 1 genes (GPx-1a and GPx-1b) in the liver of Acrossocheilus fasciatus after Cd administration. Total RNA extraction, reverse-transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) were performed in order to clone the A. fasciatus GPx-1a and GPx-1b full-length cDNA sequences and partial fragment of ß-actin cDNA from the liver for the first time. Tissue-specific expression analysis proved that GPx-1 genes were widely expressed in the liver, kidney, gill, testis, muscle, spleen, heart and brain. The changes of GPx-1 mRNA and malondialdehyde (MDA) levels in the liver treated with Cd were measured. In addition, the acute toxic effects of Cd on the microstructure of the liver were studied using light microscopy. These results suggest that GPx-1, MDA and liver histology which represent molecular, biochemical and histological levels, can be used as potential biomarkers to monitor Cd pollution. The overall findings also highlight the potential use of those three bio-indicators combined together as a multi-level tool (molecular, biochemical and histological levels) when monitoring Cd contamination and other possible exogenetic pollutants in aquatic environment.