Molecular characterization and dietary regulation of aminopeptidase N (APN) in the grass carp (Ctenopharyngodon idella).

Aminopeptidase N (APN) is a member of the peptidase M1 family and plays an important role in protein digestion. In the present study, an APN gene was cloned from the intestine of Ctenopharyngodon idellus. The full-length cDNA sequence of APN encodes an 892-amino-acid peptide that includes one helix trans-membrane region. Phylogenetic analysis showed that the APN sequence clustered with Danio rerio as its closest neighbor, sharing a sequence similarity of 81.5%. APN mRNA was differentially expressed in different tissues, with a gradient expression from high to low in the tissues of the fore-intestine, hind-intestine, liver, mid-intestine, kidney, muscle, spleen and heart. APN expression in grass carp had a circadian pattern, showing time-dependent higher expression between 06:00 and 18:00 and lower expression between 18:00 and 06:00. In addition, the protein levels and resource in the diet-regulated APN expression suggested that low crude protein (CP) level and fish meal stimulated APN gene expression. Furthermore, the mRNA expression of APN in the intestine was significantly suppressed by high concentrations of glutamine and glutamine dipeptides, respectively. This study may provide valuable knowledge on the regulation of APN expression in teleost, which has potential applications for improving fish dietary formulations.

Complete mitochodrial genome of Bangana decora (Cypriniformes, Cyprinidae).

The complete mitochondrial genome of Bangana decora was determined in this study. The gene composition, arrangement and transcriptional orientation in B. decora mitogenome were identical to most vertebrates. The complete mitogenome of B. decora was 16,607 bp in size with 13 protein-coding genes, 22 tRNA genes and a control region. Two start codon patterns and three stop codon patterns were found in protein-coding genes. Only the tRNA-Ser2 could not fold into a typical clover-leaf secondary structure due to the absence of the dihydrouridine arm. Sequence alignment results suggest that the complete mitogenome of B. decora is an efficient tool to study molecular phylogenetics, biogeography and adaptive evolution of this lineage.