Temporal signals such as light and temperature cycles profoundly modulate animal physiology and behaviour. Via endogenous timing mechanisms which are regulated by these signals, organisms can anticipate cyclic environmental changes and thereby enhance their fitness. The pineal gland in fish, through the secretion of melatonin, appears to play a critical role in the circadian system, most likely acting as an element of the circadian clock system. An important output of this circadian clock is the locomotor activity circadian rhythm which is adapted to the photoperiod and thus determines whether animals are diurnal or nocturnal. By using a genetically modified zebrafish strain known as Tg (Xla.Eef1a1:Cau.asip1)iim04, which expresses a higher level of the agouti signalling protein 1 (Asip1), an endogenous antagonist of the melanocortin system, we observed a complete disruption of locomotor activity patterns, which correlates with the ablation of the melatonin daily rhythm. Consistent with this, in vitro experiments also demonstrated that Asip1 inhibits melatonin secretion from the zebrafish pineal gland, most likely through the melanocortin receptors expressed in this gland. Asip1 overexpression also disrupted the expression of core clock genes, including per1a and clock1a, thus blunting circadian oscillation. Collectively, these results implicate the melanocortin system as playing an important role in modulating pineal physiology and, therefore, circadian organisation in zebrafish.

中文翻译：

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斑马鱼中刺鼠信号蛋白（asip1）过度表达揭示黑皮质素系统在运动活动节律和褪黑激素分泌中的作用

光和温度循环等时间信号深刻地调节动物的生理和行为。通过受这些信号调节的内源性计时机制，生物体可以预测周期性的环境变化，从而增强其适应性。鱼类的松果体通过分泌褪黑激素，似乎在昼夜节律系统中发挥着关键作用，很可能是生物钟系统的一个组成部分。该生物钟的一个重要输出是运动活动昼夜节律，它适应光周期，从而决定动物是昼行性还是夜行性。通过使用称为 Tg ( Xla . Eef1a1 : Cau.asip1 )iim04 的转基因斑马鱼品系，该品系表达更高水平的刺鼠信号蛋白 1 (Asip1)（一种黑皮质素系统的内源性拮抗剂），我们观察到运动活动模式，与褪黑激素每日节律的消融相关。与此一致的是，体外实验也表明 Asip1 抑制斑马鱼松果体分泌褪黑激素，很可能是通过该腺体中表达的黑皮质素受体来抑制。Asip1 过度表达还会破坏核心时钟基因的表达，包括per1a和Clock1a，从而减弱昼夜节律振荡。总的来说，这些结果表明黑皮质素系统在调节松果体生理学以及斑马鱼的昼夜节律组织中发挥着重要作用。