Cloning, tissue expression pattern and daily rhythms of Period1, Period2, and Clock transcripts in the flatfish Senegalese sole, Solea senegalensis

Abstract

An extensive network of endogenous oscillators governs vertebrate circadian rhythmicity. At the molecular level, they are composed of a set of clock genes that participate in transcriptional-translational feedback loops to control their own expression and that of downstream output genes. These clocks are synchronized with the environment, although entrainment by external periodic cues remains little explored in fish. In this work, partial cDNA sequences of clock genes representing both positive (Clock) and negative (Period1, Period2) elements of the molecular feedback loops were obtained from the nocturnal flatfish Senegalese sole, a relevant species for aquaculture and chronobiology. All of the above genes exhibited high identities with their respective teleost clock genes, and Per-Arnt-Sim or basic helix-loop-helix binding domains were recognized in their primary structure. They showed a widespread distribution through the animal body and some of them displayed daily mRNA rhythms in central (retina, optic tectum, diencephalon, and cerebellum) and peripheral (liver) tissues. These rhythms were most robust in retina and liver, exhibiting marked Period1 and Clock daily oscillations in transcript levels as revealed by ANOVA and cosinor analysis. Interestingly, expression profiles were inverted in retina and optic tectum compared to liver. Such differences suggest the existence of tissue-dependent zeitgebers for clock gene expression in this species (i.e., light for retina and optic tectum and feeding time for liver). This study provides novel insight into the location of the molecular clocks (central vs. peripheral) and their different phasing and synchronization pathways, which contributes to better understand the teleost circadian systems and its plasticity.

Daily Rhythmicity of Clock Gene Transcripts in Atlantic Cod Fast Skeletal Muscle

“…The dark-biased expression of the 3 period genes was in agreement with the expression of other teleost orthologs in central and peripheral tissues such as in goldfish ( Carassius auratus ) [29], European sea bass [10] and zebrafish [19], [38]. On the other hand, this circadian preference is not similar to what has been observed in central and peripheral clocks of Senegalese sole [11]. In the established circadian feedback loop model, the proteins translated by per and cry genes interact to inhibit the transcriptional activation arm [1].…”

“…The molecular components of the clock system in a number of aquaculture fish species, such as in European sea bass ( Dicentrarchus labrax ) [10], Senegalese sole ( Solea senegalensis ) [11], rainbow trout ( Oncorhynchus mykiss ) [12] and Atlantic salmon ( Salmo salar ) [13], have also been studied to a limited extent. he Somalian cavefish ( Phreatichthys andruzzii ) provided significant new insights into the evolution and entrainment of circadian clocks.…”

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.…”

Daily rhythmicity of clock gene transcript levels in fast and slow muscle fibers from Chinese perch (Siniperca chuatsi)

“…Silico structural analysis of the deduced amino acid sequences indicated that clock and per1 proteins contain the conserved PAS and bHLH domains [24]. These two domains are required for the circadian clock functions and are highly conserved in different species during evolution [25].…”