Falcón Jack, Besseau Laurence, Fuentès Michael, Sauzet Sandrine, Magnanou Elodie, Boeuf Gilles
Université Pierre et Marie Curie-Paris6, Laboratoire Aragó, Banyuls-sur-Mer, France.
Ann N Y Acad Sci. 2009 Apr;1163:101-11. doi: 10.1111/j.1749-6632.2009.04435.x.
In most species daily rhythms are synchronized by the photoperiodic cycle. They are generated by the circadian system, which is made of a pacemaker, an entrainment pathway to this clock, and one or more output signals. In vertebrates, melatonin produced by the pineal organ is one of these outputs. The production of this time-keeping hormone is high at night and low during the day. Despite the fact that this is a well-preserved pattern, the pathways through which the photoperiodic information controls the rhythm have been profoundly modified from early vertebrates to mammals. The photoperiodic control is direct in fish and frogs and indirect in mammals. In the former, full circadian systems are found in photoreceptor cells of the pineal organ, retina, and possibly brain, thus forming a network where melatonin could be a hormonal synchronizer. In the latter, the three elements of a circadian system are scattered: the photoreceptive units are in the eyes, the clocks are in the suprachiasmatic nuclei of the hypothalamus, and the melatonin-producing units are in the pineal cells. Intermediate situations are observed in sauropsids. Differences are also seen at the level of the arylalkylamine N-acetyltransferase (AANAT), the enzyme responsible for the daily variations in melatonin production. In contrast to tetrapods, teleost fish AANATs are duplicated and display tissue-specific expression; also, pineal AANAT is special--it responds to temperature in a species-specific manner, which reflects the fish ecophysiological preferences. This review summarizes anatomical, structural, and molecular aspects of the evolution of the melatonin-producing system in vertebrates.
在大多数物种中，日常节律由光周期循环同步。它们由昼夜节律系统产生，该系统由一个起搏器、一条通向这个生物钟的同步途径以及一个或多个输出信号组成。在脊椎动物中，松果体产生的褪黑素就是这些输出信号之一。这种计时激素的分泌在夜间较高，白天较低。尽管这是一种保存完好的模式，但从早期脊椎动物到哺乳动物，光周期信息控制节律的途径已经发生了深刻的变化。光周期控制在鱼类和青蛙中是直接的，在哺乳动物中是间接的。在前者中，完整的昼夜节律系统存在于松果体、视网膜以及可能的大脑的光感受器细胞中，从而形成一个网络，其中褪黑素可能是一种激素同步器。在后者中，昼夜节律系统的三个组成部分是分散的：光感受单元在眼睛中，生物钟在下丘脑的视交叉上核中，产生褪黑素的单元在松果体细胞中。在蜥形纲动物中观察到中间情况。在负责褪黑素分泌每日变化的芳基烷基胺N-乙酰基转移酶（AANAT）水平上也存在差异。与四足动物不同，硬骨鱼的AANAT基因是重复的，并表现出组织特异性表达；此外，松果体AANAT很特殊——它以物种特异性的方式对温度作出反应，这反映了鱼类的生态生理偏好。这篇综述总结了脊椎动物褪黑素分泌系统进化的解剖学、结构和分子方面的内容。
