Generation of transgenic mice producing fungal xylanase in the saliva as a model for improving feed digestibility

The cell wall of animal feed grains contain a high proportion of xylan. Monogastric farm animals lack xylan-hydrolyzing enzymes in their gastro-intestinal tract. The indigestible dietary xylan impairs normal digestive function of single-stomached livestock by preventing efficient breakdown and assimilation of feed nutrients. The digestive capability of simple-stomached animals could be improved by providing them with a foreign xylanase gene for secretion of the enzyme into their digestive tract. In this study, we produced transgenic mice carrying an Aspergillus niger xylanse gene controlled by a salivary glandspecific regulatory element. The fungal xylanase is expressed specifically in the submandibular gland and secreted in the saliva of transgenic mice. The xylanase concentration in the saliva of transgenic mice reached 0.29 ± 0.03 U/ml. Digestibility of nutrients tends to increase in transgenic mice, although it does not differ significantly from that in wild-type controls. To our knowledge, this is the first demonstration of the production of fungal xylanase in the saliva of simple-stomached animals. Results from the present study encourage further investigation of employing transgenic technology to enhance the digestive capability of monogastric agriculture animals by introducing enzyme able to degrade dietary xylan into the digestive tract.