Sammendrag
Circadian rhythmicity is a phenomenon that regulates the timing of almost all biological processes. In teleosts, the pineal gland is believed to be the central clock of this time-keeping system. In recent years, a number of circadian genes have been identified in other tissues revealing the presence of possible peripheral circadian systems. The Atlantic cod is an interesting species to study circadian rhythms in fish, since light manipulation is known to influence biological processes such as growth and maturation. However, the molecular components of the cod circadian system have not been identified to date. This study aims to clone the molecular components of the circadian system in Atlantic cod fast muscle and characterize their expressional oscillation in a 24-hour cycle. Twenty one circadian genes were identified, namely bmal1a, bmal1b, bmal2a, bmal2b, clock, per1, per2a, per2b, cry1a, cry1b, cry1c, cry2, cry3, npas1, npas2, nr1d1a, nr1d1b, nr1d2, phllp1, rora and tim. These genes were expressed in fast muscle, except npas1, phllp1 and rora. Circadian genes such as bmal2b, cry1b, cry3, per2a, per2b and phllp2 were maternally-transferred while the other clock genes appeared only at the later stages of embryogenesis. The ubiquitous expression of several clock genes examined indicates the presence of additional peripheral clocks in other cod tissues . Expression profiles revealed the circadian oscillation of some clocks genes, including bmal1a, bmal2a, per1, nr1d1, cry1c, naps2 and tim. Putative regulation of some muscle-related genes by circadian genes was also observed. The identified genes established the molecular components of the circadian system of Atlantic cod and revealed the possible presence of a functional clock system in the fast muscle. These results will contribute to our understanding of muscle growth regulation by light in Atlantic cod.
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