CIRCADIAN RHYTHMICITY OF CLOCK GENES IN LIVER AND HEART OF MANDARIN FISH (SINIPERCA CHUATSI)

Clock genes are the molecular core of circadian rhythm of vertebrates. In the present study, we investigated the expression of clock genes which contained Arntl1, Clock, Cry1a, Cry3, Cry-dash, Npas2, Npas4, Nr1d1, Nr1d2, Per1, Per3, Rora and Tim in liver and heart of Mandarin fish (Siniperca chuatsi) under the 12h-light and 12h-dark (LD) cycle condition. Melatonin and cortisol levels were also investigated under the same condition. Livers, hearts and plasma of Mandarin fish were collected at ZT0(06:00), ZT3(09:00), ZT6(12:00), ZT9(15:00), ZT12(18:00), ZT15(21:00), ZT18(24:00), ZT21(03:00, 2nd day), ZT24(06:00, 2nd day) (Zone time, ZT) with three fishes at each time point. The total mRNA was extracted from each sample, the semi-quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to determine the temporal changes in mRNA levels. Blood plasma melatonin and cortisol were quantified by competitive ELISA. The data were analyzed both by the One-Way ANOVA (SPSS 17.0) and the cosine function (Matlab 7.0) to investigate the circadian rhythm of these genes. The result indicated that: Cry-dash, Npas4, Nr1d1, Per1 and Tim displayed daily rhythmic expression in the liver. Except for Cry-dash, the expression of the other genes decreased during the light phase and increased in the dark phase. In addition, there were two rhythmic characters of the 9 genes which contained Arntl1, Clock, Cry1a, Npas2, Nr1d1, Nr1d2, Per3, Rora and Tim in the heart of Mandarin fish: 3 genes including Arntl1, Clock and Nr1d2 were reduced at light but increased at dark phase and the mRNA levels of the others sustained low in ZT0 (06:00)-ZT15 (21:00), while increased significantly in ZT15 (21:00)-ZT18 (24:00) and then decreased in ZT18 (24:00)-ZT21 (03:00). Plasma melatonin levels showed a biphasic diurnal pattern, with higher concentrations during the dark phase than the light phase, its lowest level was observed at ZT15 (21:00). Changes in the serum cortisol levels exhibited circadian pattern over a 24h period that the peak detected at ZT18 (24:00) and the trough detected at ZT15 (21:00). In summary, most of the clock genes were expressed in a circadian manner in liver and heart of Mandarin fish (Siniperca chuatsi), with differences in phase and amplitude.