Data_Sheet_1_Effects of Short-Term Fasting on mRNA Expression of Ghrelin and the Peptide Transporters PepT1 and 2 in Atlantic Salmon (Salmo salar).docx

Food intake is a vital process that supplies necessary energy and essential nutrients to the body. Information regarding luminal composition in the gastrointestinal tract (GIT) collected through mechanical and nutrient sensing mechanisms are generally conveyed, in both mammals and fish, to the hypothalamic neurocircuits. In this context, ghrelin, the only known hormone with an orexigenic action, and the intestinal peptide transporters 1 and 2, involved in absorption of dietary di- and tripeptides, exert important and also integrated roles for the nutrient uptake. Together, both are potentially involved in signaling pathways that control food intake originating from different segments of the GIT. However, little is known about the role of different paralogs and their response to fasting. Therefore, after 3 weeks of acclimatization, 12 Atlantic salmon (Salmo salar) post-smolt were fasted for 4 days to explore the gastrointestinal response in comparison with fed control (n = 12). The analysis covered morphometric (weight, length, condition factor, and wet content/weight fish %), molecular (gene expression variations), and correlation analyses. Such short-term fasting is a common and recommended practice used prior to any handling in commercial culture of the species. There were no statistical differences in length and weight but a significant lower condition factor in the fasted group. Transcriptional analysis along the gastrointestinal segments revealed a tendency of downregulation for both paralogous genes slc15a1a and slc15a1b and with significant lowered levels in the pyloric ceca for slc15a1a and in the pyloric ceca and midgut for slc15a1b. No differences were found for slc15a2a and slc15a2b (except a higher expression of the fasted group in the anterior midgut), supporting different roles for slc15 paralogs. This represents the first report on the effects of fasting on slc15a2 expressed in GIT in teleosts. Transcriptional analysis of ghrelin splicing variants (ghrl-1 and ghrl-2) showed no difference between treatments. However, correlation analysis showed that the mRNA expression for all genes (restricted to segment with the highest levels) were affected by the residual luminal content. Overall, the results show minimal effects of 4 days of induced fasting in Atlantic salmon, suggesting that more time is needed to initiate a large GIT response.

食物摄入是一种至关重要的生理过程，它为身体提供必要的能量和必需的营养素。通过机械和营养感应机制收集到的关于胃肠道（GIT）腔内成分的信息，在哺乳动物和鱼类中，通常传递至下丘脑神经回路。在此背景下，生长激素释放激素（ghrelin），作为唯一已知具有食欲促进作用（orexigenic action）的激素，以及参与膳食二肽和三肽吸收的肠肽转运蛋白1和2，在营养摄取过程中发挥着重要且综合的作用。二者共同参与调控来自胃肠道不同部位的信号通路，以控制食物摄入。然而，关于不同同源异构体及其对禁食的反应所知甚少。因此，在适应环境3周后，对12尾大西洋鲑（Salmo salar）的幼鱼进行为期4天的禁食，以探究其与饱食对照组（n = 12）相比的胃肠道反应。分析涵盖了形态计量学（体重、长度、体型指数和含水量/体重比）、分子生物学（基因表达变异）和相关性分析。这种短期禁食是商业养殖中在处理该物种之前的一种常见且推荐的实践。在长度和体重上没有发现统计学差异，但在禁食组中体型指数显著降低。对胃肠道各段的转录分析显示，同源异构基因slc15a1a和slc15a1b的表达呈现下调趋势，且在幽门盲肠中slc15a1a和幽门盲肠及中肠中slc15a1b的表达水平显著降低。slc15a2a和slc15a2b（除禁食组在前肠中表达量较高外）没有发现差异，这支持了slc15同源异构体在不同作用中的角色。这代表了首次报道禁食对硬骨鱼类胃肠道中slc15a2表达的影响。生长激素释放激素（ghrelin）剪接变体（ghrl-1和ghrl-2）的转录分析显示，在处理间没有差异。然而，相关性分析表明，所有基因的mRNA表达（限于表达水平最高的部位）均受到残余腔内成分的影响。总体而言，结果表明，4天的诱导禁食对大西洋鲑的影响微乎其微，这表明需要更多的时间才能引发较大的胃肠道反应。