Molecular characterization, transcriptional activity and nutritional regulation of peroxisome proliferator activated receptor gamma in Nile tilapia (Oreochromis niloticus).

Peroxisome proliferator activated receptor gamma (PPARγ) is a master regulator in lipid metabolism and widely exists in vertebrates. However, the molecular structure and transcriptional activity of PPARγ in fish are still unclear. This study cloned PPARγ from Nile tilapia (Oreochromis niloticus) referred as NtPPARγ and transfected the NtPPARγ plasmids into HEK-293 cells to explore its mechanism of transcriptional regulation in fish. The expression of NtPPARγ was compared in fed and fasted fish. Two transcripts of NtPPARγ varied at the 5'-untranslated region and the DNA binding domain was highly conserved. Thirty-nine amino acid residues in the ligand binding domain in Nile tilapia were different from those in human. Two transcripts showed different expression profiles in 11 tissues, but both were highly expressed in liver, intestine and kidney. The transcriptional activity assay showed that NtPPARγ collaborates with retinoid X-receptor α (NtRXRα) to regulate the expression of Nile tilapia fatty acid binding protein 4 (FABP4), the compartment of which have been identified as the target gene of PPARγ in human. In the fish fasting trial, the mRNA expression of NtPPARγ1 and NtPPARγ2 in intestine and liver at 3h post-feeding (HPF) was lower than those at 8 HPF, 24 HPF and in fish fasted for 36h, but was relatively stable in kidney among different feeding treatments. In conclusion, the DNA binding domain in PPARγ was highly conserved, while the ligand binding domain was moderately conserved. In Nile tilapia, the PPARγ collaborates with RXRα to perform transcriptional regulation of FABP4 at least in vitro. The plasmid system established in this study along with a cell line from Nile tilapia will be useful tools for the further functional study of PPARγ in fish.

Oxygen consumption and ammonia excretion of black carp (Mylopharyngdon piceus Richardson) and allogynogenetic crucian carp (Carassius auratus gibelio female x Cyprinus carpio male) fed different carbohydrate diets.

Oxygen consumption and ammonia excretion of black carp (Mylopharyngdon piceus Richardson) (4.6±0.3 g) and allogynogenetic crucian carp (Carassius auratus gibelio ♀×Cyprinus carpio ♂) (5.7±0.5 g) were examined when fish fed two types of carbohydrate (dextrin and glucose) at two levels (20 and 40%) each. The diets were isonitrogenous (40% dry matter) and isocaloric at 18.5 kJ g(−1) (dry matter) by adjusting the oil content to 10.1 and 1.5%, respectively. In black carp, the interactions between the carbohydrate type and level were found in oxygen consumption at 3 and 6 h and in ammonia excretion at 6 h after feeding. At 20% carbohydrate, no significant difference was observed between dextrin and glucose in oxygen consumption. However, at 40% carbohydrate, oxygen consumption in fish fed glucose was significantly higher than that in fish fed dextrin at 3 and 6 h after feeding. Within the dextrin diets, no significant differences in both oxygen consumption and ammonia excretion were detected between the two carbohydrate levels. Within the glucose diets, however, fish fed 40% glucose showed significantly higher oxygen consumption than those fed 20% glucose at 3 and 6 h after feeding. Ammonia excretion in black carp fed 40% glucose was higher than that in black carp fed 40% dextrin at 6 h and also found higher than those in the other three treatments at 24 h after feeding. The postprandial oxygen consumption and the ammonia excretion in crucian carp fed 40% glucose were the highest, but no significant differences were observed. Our data indicate that the escalation of glucose to 40% in a fish diet results in high oxygen consumption and ammonia excretion in black carp, suggesting that the efficiency of glucose as an energy source for this fish is compromised by the high metabolic expenditure after feeding. Crucian carp, on the other hand, have a better ability to cope with dietary carbohydrates.

Gene discovery from an ovary cDNA library of oriental river prawn Macrobrachium nipponense by ESTs annotation.

The oriental river prawn, Macrobrachium nipponense, is an important crustacean species in aquaculture. However, early gonad maturity is a ubiquitous problem which devalues the product quality. While husbandry and nutritional management have achieved little success in tackling this issue, a molecular approach may discover the genes involved in reproduction and development, which will provide the basic knowledge on reproductive control. In this study, a high-quality cDNA library of prawn was constructed from the ovary tissue. A total of 3294 successful sequencing reactions yielded 3256 expressed sequence tags (ESTs) longer than 100 bp. The cluster and assembly analyses yielded 1514 unique sequences including 414 contigs and 1168 singletons. About 719 (47.49%) unique sequences were identified as orthologs of genes from other organisms. By sequence comparability analysis, 28 important genes including cathepsin B, chromobox protein, Cdc2, cyclin B, DEAD box protein and ADF/cofilin protein were expressed. These genes may be involved in reproductive and developmental functions in prawn. Peritrophin consisting of cortical rods was also found in this species. The identification of these EST sequences in M. nipponense would improve our understanding on the genes that regulate reproduction and development in prawn species. This study also lays the groundwork for development of molecular markers related to ovary development in other prawn species.