Lunar Phase-Dependent Expression of Cryptochrome and a Photoperiodic Mechanism for Lunar Phase-Recognition in a Reef Fish, Goldlined Spinefoot

Lunar cycle-associated physiology has been found in a wide variety of organisms. Recent study has revealed that mRNA levels of Cryptochrome (Cry), one of the circadian clock genes, were significantly higher on a full moon night than on a new moon night in coral, implying the involvement of a photoreception system in the lunar-synchronized spawning. To better establish the generalities surrounding such a mechanism and explore the underlying molecular mechanism, we focused on the relationship between lunar phase, Cry gene expression, and the spawning behavior in a lunar-synchronized spawner, the goldlined spinefoot (Siganus guttatus), and we identified two kinds of Cry genes in this animal. Their mRNA levels showed lunar cycle-dependent expression in the medial part of the brain (mesencephalon and diencephalon) peaking at the first quarter moon. Since this lunar phase coincided with the reproductive phase of the goldlined spinefoot, Cry gene expression was considered a state variable in the lunar phase recognition system. Based on the expression profiles of SgCrys together with the moonlight's pattern of timing and duration during its nightly lunar cycle, we have further speculated on a model of lunar phase recognition for reproductive control in the goldlined spinefoot, which integrates both moonlight and circadian signals in a manner similar to photoperiodic response.现已在多种生物中发现与月周期相关的生理现象。近期一项研究显示，在珊瑚体内，作为昼夜节律时钟基因之一的隐花色素（Cryptochrome, Cry）的mRNA水平在满月之夜显著高于新月之夜，这暗示光感受系统参与了月同步产卵过程。为更好地明确此类机制的普遍规律并探究其潜在分子机制，本研究以月同步产卵生物褐篮子鱼（Siganus guttatus，goldlined spinefoot）为研究对象，聚焦月相、Cry基因表达与产卵行为之间的关联，并在该物种中鉴定出两种Cry基因。它们的mRNA在脑内侧区域（中脑（mesencephalon）与间脑（diencephalon））呈现出随月周期波动的表达模式，并在上弦月时达到表达峰值。由于该月相恰好与褐篮子鱼的繁殖期相吻合，因此Cry基因表达被视为月相识别系统中的状态变量。基于SgCrys的表达谱，以及月夜中月光的时序与持续时间模式，本研究进一步推测出褐篮子鱼生殖调控相关的月相识别模型，该模型以类似光周期响应的方式整合了月光信号与昼夜节律信号。