Biology Department, Science Museum of Minnesota, Saint Paul, MN, United States of America.
Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D.C., United States of America.
PLoS One. 2020 Sep 18;15(9):e0238783. doi: 10.1371/journal.pone.0238783. eCollection 2020.
Diffusible iodine-based contrast-enhanced computed tomography (diceCT) techniques allow visualization of soft tissues of fluid-preserved specimens in three dimensions without dissection or histology. Two popular diceCT stains, iodine-potassium iodide (I2KI) dissolved in water and elemental iodine (I2) dissolved in 100% ethanol (EtOH), yield striking results. Despite the widespread use of these stains in clinical and biological fields, the molecular mechanisms that result in color change and radiopacity attributed to iodine staining are poorly understood. Requests to apply these stains to anatomical specimens preserved in natural history museums are increasing, yet curators have little information about the potential for degradation of treated specimens. To assess the molecular effects of iodine staining on typical museum specimens, we compared the two popular stains and two relatively unexplored stains (I2KI in 70% EtOH, I2 in 70% EtOH). House sparrows (Passer domesticus) were collected and preserved under uniform conditions following standard museum protocols, and each was then subjected to one of the stains. Results show that the three ethanol-based stains worked equally well (producing fully stained, life-like, publication quality scans) but in different timeframes (five, six, or eight weeks). The specimen in I2KI in water became degraded in physical condition, including developing flexible, demineralized bones. The ethanol-based methods also resulted in some demineralization but less than the water-based stain. The pH of the water-based stain was notably acidic compared to the water used as solvent in the stain. Our molecular analyses indicate that whereas none of the stains resulted in unacceptable levels of protein degradation, the bones of a specimen stained with I2KI in water demineralized throughout the staining process. We conclude that staining with I2KI or elemental I2 in 70% EtOH can yield high-quality soft-tissue visualization in a timeframe that is similar to that of better-known iodine-based stains, with lower risk of negative impacts on specimen condition.
弥散碘基对比增强计算机断层扫描（diceCT）技术允许在不解剖或组织学的情况下，以三维方式观察保存在液体中的软组织。两种流行的 diceCT 染色剂，即溶于水的碘-碘化钾（I2KI）和溶于 100%乙醇（EtOH）的元素碘（I2），都能产生惊人的效果。尽管这些染色剂在临床和生物学领域得到了广泛应用，但导致碘染色产生颜色变化和放射不透性的分子机制还知之甚少。越来越多的人要求将这些染色剂应用于自然历史博物馆保存的解剖标本，但馆长们对处理过的标本可能发生降解的情况知之甚少。为了评估碘染色对典型博物馆标本的分子影响，我们比较了两种流行的染色剂和两种相对未探索的染色剂（溶于 70%EtOH 的 I2KI 和溶于 70%EtOH 的 I2）。我们按照标准博物馆协议收集并保存了家麻雀（Passer domesticus），然后将每只麻雀分别用一种染色剂进行处理。结果表明，三种基于乙醇的染色剂效果相同（产生完全染色、栩栩如生、可发表质量的扫描图像），但所需时间不同（五周、六周或八周）。溶于水的 I2KI 染色剂的标本在物理条件下发生了降解，包括骨骼变得柔韧、脱矿。乙醇基方法也导致了一些脱矿，但比水基染色剂少。水基染色剂的 pH 值明显低于作为溶剂的水。我们的分子分析表明，虽然所有染色剂都没有导致不可接受的蛋白质降解水平，但用 I2KI 水基染色剂染色的标本的骨骼在整个染色过程中都脱矿了。我们得出的结论是，用溶于 70%EtOH 的 I2KI 或元素 I2 进行染色可以在与更知名的碘基染色剂相似的时间框架内获得高质量的软组织可视化效果，对标本状况的负面影响风险较低。
