Department of Biology, West Virginia University, 53 Campus Drive, Morgantown, WV 26506, USA.
Forensic Sci Int. 2013 Jun 10;229(1-3):163.e1-6. doi: 10.1016/j.forsciint.2013.03.035. Epub 2013 May 4.
The accurate determination of time since death, or postmortem interval (PMI), can be critical in the investigation of suspicious deaths. Knowing when a suspicious death occurred can limit the number of potential suspects to those without a viable alibi for the time of the crime. The forensic techniques currently employed to determine PMI: pathology, entomology, and anthropology, are accurate over different time periods following death. A large gap in time exists between the capabilities of forensic entomology and traditional anthropology, leaving a period in which PMI is difficult to estimate. In this study, time-dependent differences in RNA decay rates were examined to extend the time frame over which early PMI estimates can be made. Comparing the decay rates of a large, labile segment of β-actin RNA and a smaller, more stable, non-overlapping segment of the same RNA from tooth pulp, we were able to estimate PMI values of pigs buried within a shallow grave for up to 84 days. This compares favorably to an estimate of PMI using insect data. Full skeletonization and loss of insect activity was observed by day 28 of our study. In addition to differences in RNA decay rates, morphological changes were observed in the pulp as it aged postmortem. To provide a quantitative measure of progressive color changes, analysis of digital photographs of each tooth's pulp were used to construct a simple colorimetric assay. This assay was then used to cluster ages of pulp samples by color. The two assays, used in combination with one another, can create a more precise estimate of PMI. The potential advantages of this molecular means of estimating PMI include extending the time frame for such estimates, is applicable to samples collected worldwide (no specialized knowledge of local insect fauna is required), is relatively fast, and inexpensive.
准确判断死亡时间，即死后间隔时间（PMI），在可疑死亡案件的调查中至关重要。了解可疑死亡发生的时间，可以将潜在嫌疑人的范围缩小到那些在犯罪时间没有可行不在场证明的人。目前用于确定 PMI 的法医技术：病理学、昆虫学和人类学，在死亡后不同时间段都具有准确性。法医昆虫学和传统人类学之间存在着很大的时间差距，使得 PMI 难以估计的时间段很长。在这项研究中，研究了 RNA 降解率随时间的差异，以扩展可以进行早期 PMI 估计的时间框架。比较牙齿牙髓中 β-肌动蛋白 RNA 较大的、不稳定的片段和相同 RNA 较小的、更稳定的、不重叠的片段的降解率，我们能够估计埋在浅坟中的猪的 PMI 值长达 84 天。这与使用昆虫数据估计 PMI 的结果相当。在我们的研究中，第 28 天就观察到了完全骨骼化和昆虫活动的丧失。除了 RNA 降解率的差异外，还观察到牙髓在死后随着时间的推移发生形态变化。为了提供对渐进性颜色变化的定量测量，对每个牙齿牙髓的数字照片进行了分析，以构建简单的比色测定法。然后，该测定法用于根据颜色对牙髓样本的年龄进行聚类。这两种检测方法相互结合，可以更精确地估计 PMI。这种估计 PMI 的分子方法的潜在优势包括延长了进行此类估计的时间框架，适用于全球范围内采集的样本（不需要了解当地昆虫区系的专门知识），相对较快且成本低廉。
