Rhythmic expressions of biological clocks and metabolic genes in marine medaka ( Oryzias melastigma )

Abstract

Many researchers found that there is a close connection between biological rhythm and metabolism in mammals and humans. But, it is uncertain whether there is a central and peripheral clock system in fish or not, and it is also uncertain whether there is a relationship between them. This article used the model fish, marine medaka (Oryzias melastigma) as the experimental object, and built a complete test with 2 factors and 2 levels, the photoperiod factor with Light (L): Dark (D) = 16:8 and 12:12 and the factor of feeding time with 1 h after light and 1 h before dark, to verify the existence of the clock system and explore the relationship between biological rhythm and metabolism. The results showed that: In treatment 1# with L:D = 16:8 and 1 h after light, two clock genes of Bmal1 and Per1, among the tested 6 clock genes, had obvious rhythmic expression in the brain and in the liver, and 2 metabolic genes of Elovl5 and Lpl also had obvious rhythmic oscillations in the liver. In treatment 2# with L:D = 12:12 and 1 h after light, 3 clock genes (Bmal1, Per1 and Per2) had obvious rhythmic expression in the brain and in the liver, and 5 metabolic genes (Elovl5, Lpl, Fadsd2, Tryp, Pck) also presented rhythmic oscillations in the liver. Both treatments had the same photoperiod, the treatment with feeding at 1 h before dark still had several clock genes in the brain that were rhythmical, but neither clock gene nor metabolic gene in the liver exhibited obvious rhythmic oscillations. This study showed that there were biological rhythms in marine medaka, and there was a close relationship between the biological rhythm and the lipid metabolism. According to the set 2 factors, it is found that the photoperiod could mainly affect the central clock system, and the feeding time could mainly affect the rhythmic expression of the peripheral clock and metabolic genes. The conclusion will provide a scientific and efficient breeding strategy for marine medaka.