Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, North Carolina, United States of America.
PLoS One. 2011 May 6;6(5):e19755. doi: 10.1371/journal.pone.0019755.
Natural light cycles synchronize behavioral and physiological cycles over varying time periods in both plants and animals. Many scleractinian corals exhibit diel cycles of polyp expansion and contraction entrained by diel sunlight patterns, and monthly cycles of spawning or planulation that correspond to lunar moonlight cycles. The molecular mechanisms for regulating such cycles are poorly understood. In this study, we identified four molecular clock genes (cry1, cry2, clock and cycle) in the scleractinian coral, Favia fragum, and investigated patterns of gene expression hypothesized to be involved in the corals' diel polyp behavior and lunar reproductive cycles. Using quantitative PCR, we measured fluctuations in expression of these clock genes over both diel and monthly spawning timeframes. Additionally, we assayed gene expression and polyp expansion-contraction behavior in experimental corals in normal light:dark (control) or constant dark treatments. Well-defined and reproducible diel patterns in cry1, cry2, and clock expression were observed in both field-collected and the experimental colonies maintained under control light:dark conditions, but no pattern was observed for cycle. Colonies in the control light:dark treatment also displayed diel rhythms of tentacle expansion and contraction. Experimental colonies in the constant dark treatment lost diel patterns in cry1, cry2, and clock expression and displayed a diminished and less synchronous pattern of tentacle expansion and contraction. We observed no pattern in cry1, cry2, clock, or cycle expression correlated with monthly spawning events suggesting these genes are not involved in the entrainment of reproductive cycles to lunar light cycles in F. fragum. Our results suggest a molecular clock mechanism, potentially similar to that in described in fruit flies, exists within F. fragum.
自然光周期在植物和动物中不同时间范围内同步行为和生理周期。许多珊瑚表现出昼夜节律的息肉扩张和收缩受昼夜阳光模式的控制，并且每月产卵或计划的周期与月球月光周期相对应。调节这些周期的分子机制知之甚少。在这项研究中，我们在石珊瑚 Favia fragum 中鉴定了四个分子钟基因（cry1、cry2、clock 和 cycle），并研究了假设参与珊瑚昼夜息肉行为和月球生殖周期的基因表达模式。使用定量 PCR，我们测量了这些生物钟基因在昼夜和每月产卵时间框架内的表达波动。此外，我们在正常光照：黑暗（对照）或恒定黑暗处理下的实验珊瑚中检测了基因表达和息肉扩张 - 收缩行为。在野外采集和在对照光照：黑暗条件下维持的实验群体中观察到 cry1、cry2 和 clock 表达的明确且可重复的昼夜模式，但未观察到 cycle 的模式。对照光照：黑暗处理的群体也显示出触须扩张和收缩的昼夜节律。在恒定黑暗处理的实验群体中，cry1、cry2 和 clock 的表达失去了昼夜模式，并且触须扩张和收缩的模式减弱且不同步。我们没有观察到与每月产卵事件相关的 cry1、cry2、clock 或 cycle 表达模式，这表明这些基因不参与 F. fragum 生殖周期与月球光周期的同步。我们的结果表明，在 F. fragum 中存在类似于在果蝇中描述的分子钟机制。
