Temporal rate of post-mortem DNA degradation in archived samples: Evidence from liver and muscle tissues

Best field practices for post-mortem tissue harvesting for optimal DNA preservation is a curatorial concern of any Genetic Resource Collection. To establish time parameters for when to collect biological samples in the field, we collected five individuals of Sigmodon hispidus and harvested liver and muscle tissues. Each tissue type was sectioned into 15 subsamples, and each was preserved in liquid nitrogen at different time intervals following death of the individual. Each tissue sample was preserved at 2, 4, 8, 16 and 32 minutes after death, 1, 2, 4, 8 and 16 hours after death, and 1, 2, 4, 8 and 16 days post-mortem. DNA was extracted with a Kingfisher Cell and Tissue DNA kit. A DNA fragment analysis was performed with method DNF-464- 0500 High Sensitivity Large Fragment 50kb (Advanced Analytical Technologies). As expected, DNA degradation was dependent on time post-mortem prior to preservation. Results indicated that DNA fragmentation was a steady and continuous process that was affected significantly by individual sample differences. DNA fragments of ≥10,000 base pair in length were present in muscle tissues across all time intervals, whereas liver tissue possessed ≥ 10,000 base pair length segments only until 8 to16 hours after death of the organism. DNA molecular mass distribution showed that muscle samples retained 80% of total DNA until 2 days post-mortem, whereas liver retains the same percentage until 32 minutes after death. Therefore, we conclude that muscle tissue is best suited for long-term archiving.