<b>Study on the Osmotic Response and Function of </b><b><i>Myo</i></b><b>-inositol Oxygenase in euryhaline fish Nile tilapia (</b><b><i>Oreochromis niloticus</i></b><b>)</b>

To understand the role of <i>myo</i>-inositol oxygenase (<i>miox</i>) in the osmotic regulation of Nile tilapia, its expression was analyzed in various tissues. The results showed that the expression of <i>miox</i> gene was highest in the kidney, followed by the liver, and was significantly upregulated in the kidney and liver under 1 h hyperosmotic stress. The relative luminescence efficiency of the <i>miox</i> gene transcription starting site (-4617 bp to +312 bp) under hyperosmotic stress was measured. Two fragments (-1640/-1619 and -620/-599) could induce the luminescence activity. Moreover, the -1640/-1619 and -620/-599 responded to hyperosmotic stress and high glucose stimulation by base mutation, suggesting that osmotic and carbohydrate response elements may exist in this region. Finally, the salinity tolerance of Nile tilapia was significantly reduced after the knocking down of <i>miox </i>gene. The accumulation of<i> myo</i>-inositol was affected and the expression of enzymes in glucose metabolism was significantly reduced after the <i>miox</i> gene was knocked down. Furthermore, hyperosmotic stress can cause oxidative stress, and MIOX may help maintain the cell redox balance under hyperosmotic stress. In summary, MIOX is essential in osmotic regulation to enhance the salinity tolerance of Nile tilapia by affecting <i>myo</i>-inositol accumulation, glucose metabolism and antioxidant performance.