Witwer teamed up with colleagues to check the results with a similar experiment of their own. They bought soy-based smoothies at a grocery store and tested their microRNA content, then fed the smoothies to macaques and took samples of the animals' blood.
Knowing that the concentrations of any plant microRNAs in the blood would be too low to measure directly, they used a common technique called polymerase chain reaction (PCR) to bring up the concentration of the genetic material. PCR is designed so that only certain fragments of genetic material in a sample the ones researchers choose to target will be copied. Zhang's studies had also used PCR to look for plant microRNAs.
Just as Zhang had, the Johns Hopkins team found what appeared to be the targeted plant microRNAs in the macaques' blood. But when they ran the experiment several times, they got highly variable results: Sometimes the microRNAs were present in low concentrations, and sometimes not at all. In addition, the samples from before the macaques drank the smoothies were just as likely to have the microRNAs as were the post-smoothie samples a result that just didn't make sense if the source of the microRNAs was the plant material in the drinks.
To Witwer, the results indicated that what he was seeing was not the targeted plant microRNAs, but fragments of the macaques' own genetic material that were similar enough to the targeted segments that the PCR copied them at low levels.
To test this, the team used a new technique in which PCR takes place in tiny aerosolized droplets rather than in a test tube. The advantage, Witwer says, is that by effectively running tens or hundreds of thousands of reactions at the same time, researchers can see whether the outcomes of those reactions are consistent in other words, whether the results are meaningful or just a fluke. In this case, the results were all over the pla
|Contact: Shawna Williams|
Johns Hopkins Medicine