Circadian Clock Genes of Goldfish, Carassius auratus: cDNA Cloning and Rhythmic Expression of Period and Cryptochrome Transcripts in Retina, Liver, and Gut

Abstract

Clock genes are known to be the molecular core of biological clocks of vertebrates. They are expressed not only in those tissues considered central pacemakers, but also in peripheral tissues. In the present study, partial cDNAs for six of the principal clock genes (Period 1-3 and Cryptochrome 1-3) were cloned from a teleost fish, the goldfish (Carassius auratus). These genes showed high homology (approximately 90%) with the respective cDNAs of zebrafish (Danio rerio), the only other teleost from which clock genes have been cloned. The daily expression pattern of each gene in retina, gut and liver of goldfish was investigated using quantitative RT-PCR and cosinor analysis. All clock genes analyzed in the retina showed circadian rhythmicity; however, only Per 2-3 and Cry 2-3 were rhythmic in goldfish liver and gut. The amplitude and phase of the expression in liver and gut were different from those found in goldfish retina. Such differences suggest that other cues, such as feeding time, may contribute to the entrainment of oscillators in goldfish liver and gut. Our results support the use of goldfish as a teleost model to investigate the location and functioning of the circadian oscillators.

Circadian rhythms in Mexican blind cavefish Astyanax mexicanus in the lab and in the field

“…In this study, we have explored, under both laboratory and field conditions, how the circadian clock has evolved in this species. In the laboratory, surface fish show a robust circadian oscillation in per1 gene expression, as has been previously reported for zebrafish and other teleost species 20,31,32,34,42 . A high-amplitude per1 rhythm is also apparent in surface fish under natural conditions.…”

“…S1). Per1 represents a key element of the core clock mechanism and, in most teleosts studied to date, shows high-amplitude circadian oscillations 20,31,32 . Per1 is therefore an excellent marker of clock function.…”

Interplay between the endocrine and circadian systems in fishes

“…In these tissues, the transcripts of the positive elements of the core clock (bmal1 and clock1) peak during the photophase, whereas the transcripts of the negative elements (per and cry) increase at the end of the scotophase, as seen in the zebrafish model (Cahill 2002, Vatine et al 2011. One exception to this pattern is the per2 gene, which is directly induced by light in zebrafish (Vatine et al 2009) and likely other teleosts (Velarde et al 2009, Patiño et al 2011). …”

“…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).…”

In vitro and ex vivo models indicate that the molecular clock in fast skeletal muscle of Atlantic cod is not autonomous

“…The discovery of peripheral oscillators had posed the intriguing hypothesis that the regulation of circadian rhythmicity could be autonomous in cells or tissues. Clock genes in fish are not only expressed in the pineal gland, the probable central clock in teleosts, but they are also found in other peripheral tissues [4][5][6][7][8].…”