Moonlight controls lunar-phase-dependency and regular oscillation of clock gene expressions in a lunar-synchronized spawner fish, Goldlined spinefoot

<jats:title>Abstract</jats:title><jats:p>Goldlined spinefoot, <jats:italic>Siganus guttatus</jats:italic>, inhabits tropical and subtropical waters and synchronizes its spawning around the first quarter moon likely using an hourglass-like lunar timer. In previous studies, we have found that clock genes (<jats:italic>Cryptochrome3</jats:italic> and <jats:italic>Period1</jats:italic>) could play the role of state variable in the diencephalon when determining the lunar phase for spawning. Here, we identified three <jats:italic>Cry</jats:italic>, two <jats:italic>Per</jats:italic>, two <jats:italic>Clock</jats:italic>, and two <jats:italic>Bmal</jats:italic> genes in <jats:italic>S. guttatus</jats:italic> and investigated their expression patterns in the diencephalon and pituitary gland. We further evaluated the effect on their expression patterns by daily interruptions of moonlight stimuli for 1 lunar cycle beginning at the new moon. It significantly modified the expression patterns in many of the examined clock(-related) genes including <jats:italic>Cry3</jats:italic> in the diencephalon and/or pituitary gland. Acute interruptions of moonlight around the waxing gibbous moon upregulated nocturnal expressions of <jats:italic>Cry1b</jats:italic> and <jats:italic>Cry2</jats:italic> in the diencephalon and pituitary gland, respectively, but did not affect expression levels of the other clock genes. These results highlighted the importance of repetitive moonlight illumination for stable or lunar-phase-specific daily expression of clock genes in the next lunar cycle that may be important for the lunar-phase-synchronized spawning on the next first quarter moon.</jats:p>