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

Interplay between the endocrine and circadian systems in fishes

“…Daily rhythms in clock genes (an essential property of endogenous clocks) have now been reported in a variety of tissues across several fish species, including the retina, pineal gland, brain, pituitary gland, liver, gut, gonads and head kidney (Park et al 2007, Davie et al 2009, Velarde et al 2009, Huang et al 2010, Cavallari et al 2011, Patiño et al 2011, Vera et al 2013, Sánchez-Bretaño et al 2015b,c, Costa et al 2016; Fig. 1).…”

“…The main loop is stabilised by an auxiliary loop that includes the retinoic acid-related orphan receptor (Ror) and Rev-erb transcription factors, which act through a Ror response element (RORE) site to regulate bmal1 transcription (Guillaumond et al 2005, Albrecht 2012, Schibler et al 2015. The functioning of this molecular mechanism is comparable in mammals and teleosts, with the involvement of homologous genes, although several copies of these genes have been reported in fishes (Vatine et al 2011, Sánchez-Bretaño et al 2015b). …”

“…This classification is presented in a functional way, without involving anatomical structures, as the same tissue could be acting as a clock that is entrained by the LD cycles, the feeding-fasting cycles and perhaps other zeitgebers. The dependence of clock gene expression rhythms in the central and peripheral tissues on LD cycles has been demonstrated in a number of teleost species, including zebrafish , Atlantic salmon (Salmo salar; Huang et al 2010), rainbow trout (Oncorhynchus mykiss; Patiño et al 2011), goldfish , Sánchez-Bretaño et al 2015b, sea bream (Sparus aurata; Vera et al 2013) or Nile tilapia (Oreochromis niloticus; Costa et al 2016).…”

“…However, when the LD cycle is present, the rhythms exhibit greater amplitudes, suggesting that both environmental signals work together in sustaining the molecular clockwork, at least in the liver , Sánchez-Bretaño et al 2015b. When both zeitgebers (LD and feeding-fasting cycles) are present, the brain oscillators appear to be driven by the LD cycle, whereas the clock gene oscillations in the liver are more dependent on feeding schedule (zebrafish: López-Olmeda et al 2010;sea bream: Vera et al 2013).…”

Hypothalamic Integration of Metabolic, Endocrine, and Circadian Signals in Fish: Involvement in the Control of Food Intake

“…Neuronal feeding-synchronized clocks are suggested to reside in ventromedial and dorsomedial hypothalamus (Acosta-Galvan et al, 2011), or even in extrahypothalamic brain areas including nucleus accumbens and amygdala in mammals. The search and identification of feeding entrained clocks is a topical subject in fish, and both, peripheral (Nisembaum et al, 2012; Sánchez-Bretaño et al, 2015a) and brain (Feliciano et al, 2011; Vera et al, 2013; Sánchez-Bretaño et al, 2015b) are possible targets. This complex variety of locations of oscillators requires a functional organization among them to generate coordinated responses, and recent data suggest that nutritional cues may act as time givers (Dattolo et al, 2016).…”