Threonine influences the absorption capacity and brush-border enzyme gene expression in the intestine of juvenile blunt snout bream (Megalobrama amblycephala)

Blunt snout bream (Megalobrama amblycephala) is one of the major aquaculture species in China with extremely high economic value. In the last decade, its production in China has been rapidly increased and reached approximately 0.7 million tons in 2012. It is also introduced to North America (northern Canada to southern Mexico), Africa and Eurasia. Recently, many studies have been reported regarding nutrient requirement of blunt snout bream. This study is part of our previous studies that investigated the effects of threonine on the growth, feed utilization, digestive capacity, immune function, and gene expressions of digestive enzymes, signaling molecules related to protein synthesis, immune and cytokines in blunt snout bream. Animal growth depends on the nutrient digestion and absorption, which is governed by the activities of enzymes including brush-border enzymes. In fish species the activities of brush-border enzymes appear to be strongly correlated with the composition of diet. Among indispensible amino acids, threonine has been proved to be an indispensible amino acid for optimal growth of fish, and it is extracted in greater proportion by the small intestine in animals, suggesting that threonine is involved in intestinal functionality and maintenance. However, there is no report regarding the effects of threonine on the activities of brush-border enzymes in blunt snout bream. To date, there is no report regarding the relationship between dietary threonine and the gene expressions of brush-border enzymes in fish. Indeed, this study was conducted to test the following hypothesis: firstly, an adequate level of threonine may play an important role in absorptive function by enhancing the activities of brush-border enzymes in blunt snout bream; secondly, threonine may regulate the brush-border enzyme gene expressions in the intestinal segments of blunt snout bream, which may explain further the role of threonine in absorptive function of this fish species.