Department of Biological Sciences, University of Bergen, Bergen, Norway.
Department of Informatics, University of Bergen, Bergen, Norway.
PLoS One. 2024 Nov 15;19(11):e0312911. doi: 10.1371/journal.pone.0312911. eCollection 2024.
An organism's biological processes are adapted to and driven by rhythmicity in the natural environment and periodicity of light is one of the most influential factors. In a developing organism, the onset of circadian rhythmicity might indicate the time point of functional necessity for aligning processes to the environment. Here, the circadian clock mechanism has been studied in the developing brain of Atlantic salmon (Salmo salar), by comparing the endogenous feeding alevin, independent on the environment for nutritional supply, to the exogenous feeding fry, dependent on the light period for detecting and catching prey. The results showed that while only a few clock genes were cyclic in the yolk sac alevins, many of the clock genes and genes of the circadian rhythm pathway cycled significantly in the feeding fry. Few genes were differentially expressed between time points in the circadian sampling series during the yolk sac stage, but several hundred genes were found differentially expressed in the first feeding stage. Genes important for cell cycle progression were cyclic or differentially expressed between time points after exogenous feeding, indicating a clock-controlled cell cycle at this stage. The expression of important genes in the melatonin synthesis were also cyclic in the feeding fry with an acrophase in the transition between light and dark or in darkness. Analyzing the impact of exogenous feeding on the developing brain supported a shift from utilization of proteins and lipids in the yolk to utilization and allocation of dietary energy and nutrients. Taken together, the life history transition related to onset of exogenous feeding is linked to the establishment of a persistent circadian rhythmicity in the salmon brain, which needs to be synchronized to light-dark cycles to enable the fry to search and capture feed.
生物体的生物过程适应于自然环境的节律性，并受光的周期性影响，其中光周期是最具影响力的因素之一。在发育中的生物体中，昼夜节律的开始可能表明将过程与环境对齐的功能必要性的时间点。在这里，通过比较内源摄食的幼鱼（依赖环境获取营养）和外源摄食的鱼苗（依赖光周期来探测和捕食猎物），研究了大西洋鲑（Salmo salar）发育中的大脑中的昼夜节律机制。结果表明，虽然在卵黄囊幼鱼中只有少数时钟基因呈周期性，但许多时钟基因和昼夜节律途径的基因在摄食的鱼苗中显著呈周期性。在卵黄囊阶段的昼夜节律采样系列中，很少有基因在时间点之间存在差异表达，但在第一个摄食阶段发现了数百个基因存在差异表达。与外源摄食后时间点相关的细胞周期进展的重要基因呈周期性或差异表达，表明在此阶段存在时钟控制的细胞周期。在摄食的鱼苗中，参与褪黑素合成的重要基因的表达也呈周期性，相位在光暗转换或黑暗中。分析外源摄食对发育中大脑的影响表明，从卵黄中利用蛋白质和脂质的模式转变为利用和分配膳食能量和营养物质的模式。总之，与外源摄食开始相关的生活史过渡与鲑鱼大脑中持久昼夜节律的建立有关，这需要与光暗周期同步，以使鱼苗能够搜索和捕捉食物。
