Departamento de Bioloxía Funcional e Ciencias da Saúde, Facultade de Bioloxía, Universidade de Vigo, Vigo, Pontevedra, Spain.
Chronobiol Int. 2011 May;28(5):381-9. doi: 10.3109/07420528.2011.566398.
Living organisms show daily rhythms in physiology, behavior, and gene expression, which are due to the presence of endogenous clocks that synchronize biological processes to the 24-h light/dark cycle. In metazoans, generation of circadian rhythmicity is a consequence of specialized tissues known as "master clocks," having different locations among species. A few studies have described clock-gene expression in fish neural tissues, but none of them assessed clock-gene expression in different discrete regions. The present study was designed to explore the presence/absence of circadian clock-gene expression in the rainbow trout (Oncorhynchus mykiss) retina and hypothalamus. Juvenile fish were acclimated to a 12:12 light (L)-dark (D) cycle. Then, retina and hypothalamus were collected from animals kept under LD conditions or constant darkness (DD) for 24 h. Real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) assays were performed to quantify expression of the core circadian genes Clock1a, Bmal1, and Per1 as representative members of the circadian oscillator. All clock genes analyzed in the retina and hypothalamus showed circadian fluctuations. However, gene expression peaked in the rainbow trout hypothalamus with a 3-h (Clock1a and Bmal1) or 6-h (Per1) delay relative to that observed in the retina, the latter showing highest expression levels at zeitgeber times 9 (ZT9) for Clock1a and Bmal1, and at ZT21 for Per1. When exposed to DD, the rhythmic gene expression pattern was maintained for all genes in the rainbow trout retina, but only for Clock1a and Per1 in the hypothalamus. Bmal1 failed to cycle under DD, suggesting that hypothalamic clock function might depend on either several clock-gene isoforms or regulation from external inputs. Overall, these data indicate that representative molecular members of the core circadian clock are present in both the retina and hypothalamus of rainbow trout.
生物体在生理、行为和基因表达方面表现出昼夜节律，这是由于内源性时钟的存在，使生物过程与 24 小时的光/暗循环同步。在后生动物中，昼夜节律的产生是专门组织的结果，这些组织被称为“主钟”，在不同物种中有不同的位置。一些研究描述了鱼类神经组织中时钟基因的表达，但没有一项研究评估了不同离散区域中时钟基因的表达。本研究旨在探讨虹鳟（Oncorhynchus mykiss）视网膜和下丘脑是否存在/不存在昼夜节律时钟基因表达。将幼鱼适应于 12:12 光照（L）-黑暗（D）循环。然后，将动物保持在 LD 条件或连续黑暗（DD）下 24 小时后收集视网膜和下丘脑。进行实时定量逆转录聚合酶链反应（RT-PCR）测定，以定量测定核心生物钟基因 Clock1a、Bmal1 和 Per1 的表达，作为生物钟振荡器的代表性成员。在视网膜和下丘脑分析的所有时钟基因均显示出昼夜波动。然而，与在视网膜中观察到的相比，虹鳟下丘脑的基因表达在 3 小时（Clock1a 和 Bmal1）或 6 小时（Per1）时达到峰值，后者在 zeitgeber 时间 9（ZT9）时表现出最高的表达水平 Clock1a 和 Bmal1，而 Per1 则在 ZT21 时。当暴露于 DD 时，所有基因在虹鳟视网膜中的节律基因表达模式均得以维持，但在 Hypothalamus 中仅 Clock1a 和 Per1 得以维持。Bmal1 在 DD 下无法循环，这表明下丘脑时钟功能可能依赖于几个时钟基因同工型或来自外部输入的调节。总体而言，这些数据表明，代表性的核心生物钟分子成员存在于虹鳟的视网膜和下丘脑。
