Cloning, tissue expression, and nutritional regulation of the alpha-amylase gene in the herbivorous marine teleost Siganus canaliculatus

摘要

Alpha-amylase (alpha-amylase) is a carbohydrase that plays a major role in carbohydrate metabolism. However, little is known about its molecular and biochemical characterisation in herbivorous marine teleosts. In the present study, an alpha-amylase gene was cloned and its tissue expression was determined in rabbitfish Siganus canaliculatus, a crucial cultured herbivorous marine teleost in China. The nutritional regulation of the gene, including its mRNA expression and enzymatic activity, was also investigated. The full length of its (DNA was 1903 bp, containing a 1539 bp open reading frame encoding a polypepticle of 512 amino acids, which possessed all the characteristic features of the alpha-amylase family. Its mRNA expression was detected in hepatopancreas, anterior intestine, middle intestine and posterior intestine, but not in other parts of the alimentary system. Four dietary groups of rabbitfish were each fed one of the following: raw fish (RF), formulated diet (FD), seaweed Enteromorpha prolifra (EP), or seaweed Gracilaria lemaneiformis (GL). After 8 weeks of feeding, the expression level of alpha-amylase mRNA in hepatopancreas, anterior intestine, middle intestine and posterior intestine showed no significant differences among the four dietary groups, whereas the alpha-amylase activity in the RF group was significantly lower than that in the other dietary groups (P 0.001), and significantly higher in the mid and posterior intestine of fish fed CL than those in fish fed with EP (P 0.01). These findings suggest that the nutritional regulation of alpha-amylase synthesis in rabbitfish may occur at the posttranscriptional level. This study is the first characterisation of the alpha-amylase gene from a herbivorous marine culture teleost.