Light and feeding entrainment of the molecular circadian clock in a marine teleost (Sparus aurata)

Abstract

Daily light and feeding cycles act as powerful synchronizers of circadian rhythmicity. Ultimately, these external cues entrain the expression of clock genes, which generate daily rhythmic behavioral and physiological responses in vertebrates. In the present study, we investigated clock genes in a marine teleost (gilthead sea bream). Partial cDNA sequences of key elements from both positive (Bmal1, Clock) and negative (Per2, Cry1) regulatory loops were cloned before studying how feeding time affects the daily rhythms of locomotor activity and clock gene expression in the central (brain) and peripheral (liver) oscillators. To this end, all fish were kept under a light-dark (LD) cycle and were divided into three experimental groups, depending on the time of their daily meal: mid-light (ML), mid-darkness (MD), or at random (RD) times. Finally, the existence of circadian control on gene expression was investigated in the absence of external cues (DD + RD). The behavioral results showed that seabream fed at ML or RD displayed a diurnal activity pattern (>91% of activity during the day), whereas fish fed at MD were nocturnal (89% of activity during the night). Moreover, seabream subjected to regular feeding cycles (ML and MD groups) showed food-anticipatory activity (FAA). Regardless of the mealtime, the daily rhythm of clock gene expression in the brain peaked close to the light-dark transition in the case of Bmal1 and Clock, and at the beginning of the light phase in the case of Per2 and Cry1, showing the existence of phase delay between the positive and negative elements of the molecular clock. In the liver, however, the acrophases of the daily rhythms differed depending on the feeding regime: the maximum expression of Bmal1 and Clock in the ML and RD groups was in antiphase to the expression pattern observed in the fish fed at MD. Under constant conditions (DD + RD), Per2 and Cry1 showed circadian rhythmicity in the brain, whereas Bmal1, Clock, and Per2 did in the liver. Our results indicate that the seabream clock gene expression is endogenously controlled and in liver it is strongly entrained by food signals, rather than by the LD cycle, and that scheduled feeding can shift the phase of the daily rhythm of clock gene expression in a peripheral organ (liver) without changing the phase of these rhythms in a central oscillator (brain), suggesting uncoupling of the light-entrainable oscillator (LEO) from the food-entrainable oscillator (FEO). These findings provide the basis and new tools for improving our knowledge of the circadian system and entraining pathways of this fish species, which is of great interest for the Mediterranean aquaculture

Daily Rhythms in Expression of Genes of Hepatic Lipid Metabolism in Atlantic Salmon (Salmo salar L.)

“…In contrast to previous studies on teleost liver [28], [29], [37], [38], Clock , Per1 and Per2 did not display oscillatory patterns in a 24 h cycle, however, the results for Clock and Per2 are consistent with those previously obtained in the brain of Atlantic salmon [26]. While in the teleost brain light dark cycle is considered to be the primary zeitgeber [39], hepatic clocks appear to demonstrate a greater variety in entrainment pathways [32].…”

“…In the present study the expression of four core clock genes, Bmal1, Clock, Per 1 and Per 2 was characterised, with Bmal1 the only one to display a significant daily profile of expression. Such expression was previously observed in zebrafish and gilthead sea bream ( Sparus aurata ) liver [28], [29] and the salmonid brain [22], [30]. In addition to its role in the control of daily rhythm, BMAL 1 has been suggested to contribute to lipid metabolism control and adipogenesis in mammals [31].…”

The liver of goldfish as a component of the circadian system: Integrating a network of signals

“…The presence of clock genes in a variety of tissues from different species supports the existence of an extended net of oscillators in teleost central and peripheral locations. Clock genes have been found in zebrafish (Vatine et al, 2011), and in a variety of tissues in other fish, including the retina, brain, pituitary, liver, skin, gut and gonads (Cavallari et al, 2011;Davie et al, 2009;Martín-Robles et al, 2011;Mazurais et al, 2000;Sánchez et al, 2010;Velarde et al, 2009;Vera et al, 2013).…”

Ghrelin induces clock gene expression in the liver of goldfish in vitro via protein kinase C and protein kinase A pathways

“…In mammals, the oscillators of the circadian system respond to feeding inputs with different sensitivities, the liver being one of the most sensitive peripheral oscillators in these vertebrates (Albrecht, 2012;Damiola et al, 2000;Reddy et al, 2007;Schibler et al, 2015;Schmutz et al, 2012;Sujino et al, 2012). In teleosts, the liver is highly sensitive to the feeding/fasting cycle and food-related signals (Costa et al, 2016;del Pozo et al, 2012;Feliciano et al, 2011;López-Olmeda et al, 2010;Vera et al, 2013;Sánchez-Bretaño et al, 2015b). Some studies suggest that the liver in fish may be acting as an oscillator that is synchronized by photoperiod and feeding schedule (del Pozo et al, 2012;Feliciano et al, 2011;López-Olmeda et al, 2010;Martín-Robles et al, 2011;Sánchez-Bretaño et al, 2015a,b;Tinoco et al, 2014;Vera et al, 2013).…”

“…In teleosts, the liver is highly sensitive to the feeding/fasting cycle and food-related signals (Costa et al, 2016;del Pozo et al, 2012;Feliciano et al, 2011;López-Olmeda et al, 2010;Vera et al, 2013;Sánchez-Bretaño et al, 2015b). Some studies suggest that the liver in fish may be acting as an oscillator that is synchronized by photoperiod and feeding schedule (del Pozo et al, 2012;Feliciano et al, 2011;López-Olmeda et al, 2010;Martín-Robles et al, 2011;Sánchez-Bretaño et al, 2015a,b;Tinoco et al, 2014;Vera et al, 2013).…”