In deep space exploration, quick and simple assessment of the radiation injury and the risks of individuals in the early stage of radiation is a great challenge for the traditional radiation do⁃simeters. Circulating microRNA ( miRNA) has good specificity and stability, and can positively re⁃spond to changes of the environment. So, screening miRNAs signatures in blood is of great signifi⁃cance for developing noninvasive dosimeters. In this study, kunming mice were whole⁃body exposed to X rays and serum was collected after 24 hours. Expression levels of 21 candidate circulating miR⁃NAs were detected by miRNA PCR array. It was found that many kinds of circulating miRNAs re⁃sponded to radiation, among which miR⁃21 had a bigger change. Then, the dose⁃dependent and time⁃dependent effects of miR⁃21 after exposure to X rays, carbon ions and iron ions radiation were validated. Moreover, the background expression level of miR⁃21 in different mice was detected. The results showed that the expression level of miR⁃21 was up⁃regulated with a significant dose⁃depend⁃ent after exposure to different kinds of radiation, especially responded to low dose radiation. Its ex⁃pression level kept in a stable threshold value within 6~72 hours. The background expression level of miR⁃21 had no significance in the same or different age mice. All the above results demonstrate that miR⁃21 has the potential to assess the radiation injury as a dosimeter.%深空探测中如何在辐射暴露早期用快速、简便的方法进行辐射损伤及风险评估问题，对传统的辐射剂量计提出巨大的挑战。循环血microRNA（ miRNA）具有很好的特异性和稳定性，且积极响应外界环境变化，因此，筛选循环血中辐射敏感的miRNA，对开发基于血液的微创生物辐射标志物具有较大的研究意义和应用价值。本文利用X射线对昆明小鼠进行全身照射，24小时后取血，利用miRNA PCR array的方法检测了21种候选miRNA的表达谱水平，发现多种miRNA对辐射有响应，其中miR⁃21具有较大的变化幅度。利用实时定量PCR分别验证了miR⁃21在不同射线（ X射线、碳离子束、铁离子束）条件下的剂量效应和时间效应。检测了miR⁃21在相同和不同鼠龄小鼠个体间的本底表达水平。结果表明，miR⁃21在不同类型射线照射下表达水平都有升高的趋势，特别是对低剂量辐射也具有显著的响应，具有较强的剂量效应关系。在6～72小时内，其表达水平维持在一个稳定的阈值内。 miR⁃21在相同和不同鼠龄小鼠个体间的本底表达水平不具有差异性，在血清样本的保存及RNA的提取过程中具有较强的稳定性。以上特征说明miR⁃21具有作为生物辐射剂量计并应用于辐射损伤检测的潜力。
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