Data_Sheet_1_Low Temperature Effect on the Endocrine and Circadian Systems of Adult Danio rerio.docx

The control of the biological rhythms begins with the activation of photo- and thermosensitive cells located in various organs of the fish such as brain, eye, and skin, but a central clock is still to be identified in teleosts. Thermal changes are stressors which increase cortisol and affect the rhythm of other hormones such as melatonin and growth hormone (GH), in both endo- and ectothermic organisms. Our aim was to investigate how temperature (23°C for 6 days) lower than the optimal (28°C) modulates expression of several gene pathways including growth hormone (gh1) and its receptors (ghra, ghrb), insulin-like growth factor1 (igf1a, igf1b) and its receptors (igf1ra, igf1rb), cortisol and its receptor (gr), the limiting enzyme of melatonin synthesis (arylalkylamine N-acetyltransferase, aanat) and melatonin receptors (mtnr1aa, mtnr1bb), as well as their relationship with clock genes in Danio rerio in early light and early dark phases of the day. Lower temperature reduced the expression of the hormone gene gh1, and of the related receptors ghra, ghrb, igf1ra, and igf1rb. Cortisol levels were higher at the lower temperature, with a decrease of its receptor (gr) transcripts in the liver. Interestingly, we found higher levels of aanat transcripts in the brain at 23°C. Overall, lower temperature downregulated the transcription of hormone related genes and clock genes. The results suggest a strong correlation of temperature challenge with the clock molecular mechanism and the endocrine systems analyzed, especially the growth hormone and melatonin axes, in D. rerio tissues.

生物节律的调控始于硬骨鱼（teleosts）脑、眼睛、皮肤等多种器官内感光与热敏细胞的激活，但该类生物的中枢生物钟仍有待探明。温度变化属于应激源，在恒温动物与变温动物体内均可升高皮质醇水平，并影响褪黑素、生长激素（growth hormone, GH）等其他激素的分泌节律。本研究旨在探究相较于最适温度（28°C）更低的温度（23°C，持续6天）对多条基因通路表达的调控作用，涵盖生长激素基因（gh1）及其受体基因（ghra、ghrb）、胰岛素样生长因子1（insulin-like growth factor1, igf1a、igf1b）及其受体基因（igf1ra、igf1rb）、皮质醇及其受体基因（gr）、褪黑素合成限速酶芳基烷基胺N-乙酰基转移酶（arylalkylamine N-acetyltransferase, aanat）以及褪黑素受体基因（mtnr1aa、mtnr1bb），同时分析该温度调控效应与斑马鱼（Danio rerio）在一日清晨光照期与清晨黑暗期的生物钟基因之间的关联。低温条件下，激素基因gh1及其相关受体基因ghra、ghrb、igf1ra与igf1rb的表达水平均出现下调。低温环境中皮质醇水平升高，同时肝脏内该激素受体（gr）的转录本表达量下降。值得注意的是，本研究在23°C条件下检测到大脑内aanat转录本的表达水平升高。整体而言，低温可下调激素相关基因与生物钟基因的转录水平。本研究结果表明，斑马鱼组织中温度胁迫与生物钟分子机制及所分析的内分泌系统（尤其是生长激素轴与褪黑素轴）之间存在显著相关性。