Gene-specific primers used for quantitative PCR.

Gravity is one of the most constant environmental factors across Earth’s evolution and all organisms are adapted to it. Consequently, spatial exploration has captured the interest in studying the biological changes that physiological alterations are caused by gravity. In the last two decades, epigenetics has explained how environmental cues can alter gene functions in organisms. Although many studies addressed gravity, the underlying biological and molecular mechanisms that occur in altered gravity for those epigenetics-related mechanisms, are mostly inexistent. The present study addressed the effects of hypergravity on development, behavior, gene expression, and most importantly, on the epigenetic changes in a worldwide animal model, the zebrafish (Danio rerio). To perform hypergravity experiments, a custom-centrifuge simulating the large diameter centrifuge (100 rpm ~ 3 g) was designed and zebrafish embryos were exposed during 5 days post fertilization (dpf). Results showed a significant decrease in survival at 2 dpf but no significance in the hatching rate. Physiological and morphological alterations including fish position, movement frequency, and swimming behavior showed significant changes due to hypergravity. Epigenetic studies showed significant hypermethylation of the genome of the zebrafish larvae subjected to 5 days of hypergravity. Downregulation of the gene expression of three epigenetic-related genes (dnmt1, dnmt3, and tet1), although not significant, was further observed. Taken altogether, gravity alterations affected biological responses including epigenetics in fish, providing a valuable roadmap of the putative hazards of living beyond Earth.

重力是地球演化过程中最恒定的环境因子之一，所有生物均已适应其作用。因此，空间探索领域引发了学界对研究重力诱导生理变化所关联的生物学改变的浓厚兴趣。近二十年来，表观遗传学（epigenetics）已经阐明了环境信号如何调控生物体的基因功能。尽管已有诸多研究围绕重力展开，但针对重力改变下表观遗传相关机制的底层生物学与分子机制，目前仍几乎空白。本研究以全球通用的模式动物斑马鱼（Danio rerio）为对象，探究了超重力（hypergravity）对其发育、行为、基因表达的影响，尤为关键的是，探究了超重力诱导的表观遗传变化。为开展超重力实验，本研究定制了一款可模拟大直径离心机（large diameter centrifuge，100转/分钟~3g）的装置，并将斑马鱼胚胎在受精后5天（dpf）期间持续暴露于该环境中。实验结果显示，在受精后2天（dpf）时，斑马鱼的存活率出现显著下降，但孵化率无显著变化。超重力暴露还引发了斑马鱼的多项生理与形态学改变，包括鱼体姿态、运动频率及游泳行为均出现显著变化。表观遗传学分析显示，经过5天超重力暴露的斑马鱼幼鱼，其基因组出现显著的高甲基化现象。此外，本研究还观察到3个表观遗传相关基因（dnmt1、dnmt3及tet1）的表达出现下调趋势，尽管该趋势未达到统计学显著性水平。综合来看，重力改变会影响鱼类包括表观遗传在内的多种生物学响应，本研究为探究地球外生存的潜在风险提供了极具价值的参考框架。