[Seasonal Difference in Water Quality Between Lake and Inflow/Outflow Rivers of Lake Taihu, China].

The seasonal and spatial variation of external nutrient loading from rivers and their impact on lake water quality were analyzed in Lake Taihu, China, using the monthly monitoring data from 16 major inflow/outflow rivers and 32 observation sites in the lake. The results showed:① The average monthly values of total nitrogen (TN), dissolved total nitrogen (DTN), total phosphorus (TP), and dissolved total phosphorus (DTP) in rivers were all higher than the corresponding areas in the lake. Significant positive correlations were found between nutrient concentrations in the inflow rivers and the corresponding areas in the lake, indicating the pronounced impact of external loading on lake water. ② Remarkable seasonal variations of nutrient concentration were found both in the rivers and in the lake. The highest TN and TP concentrations in inflow rivers were 4.82 mg·L-1 (March) and 0.218 mg·L-1 (December), while the highest TN and TP concentrations in the lake were 4.13 mg·L-1 and 0.255 mg·L-1 in July. ③ Extreme rainfall events could decrease the nutrient concentration in the rivers in the short-term, but finally would increase the external loading of nutrients, and indicated disadvantages for the restoration of Lake Taihu. Our study concluded that inflow pollution showed an obvious "shaping effect" on the seasonal and spatial distribution of water quality indicators in large and shallow lakes. Additionally, the self-purification ability of lakes, wind-induced accumulation and migration of algae, as well as the sediment resuspension under the prevailing winds in different seasons, all have vital effects on nutrient concentrations and their spatial-temporal variations.

[Insertion efficiency of Tgf2 transposon in the genome of Megalo-brama amblycephala].

To study insertion efficiency of goldfish Tgf2 transposon in the genome of Megalobrama amblycephala, we built Tgf2-Mlyz2-RFP donor plasmid with goldfish Tgf2 transposon left and right arms, and then co-injected with goldfish Tgf2 transposase mRNA into the 1-2 cell stage fertilized eggs of M. amblycephala. In 30 d- and 180 d-stage larval, RFP fluorescence can be observed in back and side muscle of the fish. The rate of RFP fluorescence expression was 48.1%. In adult fish, PCR results demonstrated that integration efficiency of goldfish Tgf2 transposition system was 31.5% in M. am-blycephala genome. RT-PCR analysis showed that RFP RNAs were highly transcribed among all the 12 tissues in three transgenic fishes, while it could be highly detected only in muscle, skin, and kidney in another two individuals. Our results suggested that RFP expression in tissues vaied among different M. amblycephala. By means of the inverse PCR, the copy numbers of Tgf2 transposon were at least 2 in transgenic M. amblycephala. The average copy number of each fish was about 5. Over 50% of flanking sequences at the insertion site have homologous sequence in other vertebrate species. Our data suggest that goldfish Tgf2 transposon can efficiently mediate gene insertion in M. amblycephala, which could been used in transgene and gene trap in M. amblycephala.

Goldfish transposase Tgf2 presumably from recent horizontal transfer is active.

Hobo/Activator/Tam3 (hAT) superfamily transposons occur in plants and animals and play a role in genomic evolution. Certain hAT transposons are active and have been developed as incisive genetic tools. Active vertebrate elements are rarely discovered; however, Tgf2 transposon was recently discovered in goldfish (Carassius auratus). Here, we found that the endogenous Tgf2 element can transpose in goldfish genome. Seven different goldfish mRNA transcripts, encoding three lengths of Tgf2 transposase, were identified. Tgf2 transposase mRNA was detected in goldfish embryos, mainly in epithelial cells; levels were high in ovaries and mature eggs and in all adult tissues tested. Endogenous Tgf2 transposase mRNA is active in mature eggs and can mediate high rates of transposition (>30%) when injected with donor plasmids harboring a Tgf2 cis-element. When donor plasmid was coinjected with capped Tgf2 transposase mRNA, the insertion rate reached >90% at 1 yr. Nonautonomous copies of the Tgf2 transposon with large-fragment deletions and low levels of point mutations were also detected in common goldfish. Phylogenetic analysis indicates the taxonomic distribution of Tgf2 in goldfish is not due to vertical inheritance. We propose that the goldfish Tgf2 transposon originated by recent horizontal transfer and maintains a highly native activity.

HIF-1alpha and -2alpha genes in a hypoxia-sensitive teleost species Megalobrama amblycephala: cDNA cloning, expression and different responses to hypoxia.

Transcriptional responses to hypoxia are primarily mediated by hypoxia-inducible factor (HIF) alpha subunits, i.e. HIF-1alpha, -2alpha and -3alpha. In fish, the molecular constructions, expression characteristics and hypoxic regulation of HIF-alpha subunits are still not well known. In this study, we identified the HIF-1alpha and HIF-2alpha full-length cDNAs in a hypoxia-sensitive fish species Wuchang bream, Megalobrama amblycephala. The whole length of HIF-1alpha cDNA was 3,815bp, consisting of an open reading frame (ORF) encoding 774 amino acid (aa) residues. The HIF-2alpha cDNA totaled 3,121-bp including an 835-aa ORF. The Wuchang bream HIF-1alpha and HIF-2alpha subunits were structurally similar in the DNA-binding and dimerization domains, but differed in the transactivation domain. In adult fish, both HIF-1alpha and HIF-2alpha mRNAs were detected in different tissues under normoxic conditions. HIF-1alpha mRNA was highly expressed in the liver, gill and testis, whereas HIF-2alpha mRNA was abundantly expressed in most of the Wuchang bream tissues. Both HIF-1alpha and HIF-2alpha mRNAs were detected in all stages of embryogenesis and expressed in a ubiquitous pattern. In contrast to HIF-1alpha, the mRNA levels of HIF-2alpha fluctuated in different stages, with higher expression in the zygote, 8-, 28-, 48- and 52-hr post fertilization (hpf) embryos. During hypoxic treatment, the mRNA levels of HIF-2alpha were significantly (p<0.01) up-regulated to 910% in the liver and 320% in the kidney, whereas no significant changes of HIF-1alpha mRNA were observed in the corresponding tissues. These results suggest that the Wuchang bream HIF-1alpha and -2alpha would be involved in different physiological functions under normoxia and hypoxia situations.