Rare success
The researchers spent time to ensure that the enzymes they had, the methylation changes as expected, and that development started as usual. Their general finding is that the enzymes have changed the methylation state for around 500 bases on either side of the intended site, and did this fairly consistent. But there are seven different printing places that must be changed, each arranging several in the neighborhood. So although the changes were consistent, they were not always thorough enough to lead to the expected changes in all nearby genes.
This limited efficiency appeared in the speed of survival. Starting with more than 250 reprogrammed embryos that DNA wore of two men, they finished with sixteen pregnancies, but only four who died at birth, and three living; Based on other experiments, most of the rest died during the second half of the embryonic development. Of the three living, one was almost 40 percent larger than the typical puppy, which suggests problems that regulate growth – it died the day after birth.
All three living births were male, although the figures are small enough that it is impossible to say whether that is important or not.
The researchers suggest various possible reasons for low efficiency. One of them is simple that, although the chance of at least one of the sites is well reprogrammed is high, the reprogramming of all seven is considerably more challenging. There is also the risk of off-target effects, where the adjustment takes place at locations with comparable sequences such as the intended sequences. They also admit that there may be other important printed regions that we have simply not yet identified.
That sorting would be necessary if we want to use this approach as a tool, which can potentially be useful as a way to breed mice that influence mutations that influence the viability of women or fertility. But this work has already been useful, even in its inefficient state, because it serves as a fairly definitive validation of our ideas about the function of print in embryonic development, as well as the critical role that methylation plays in this process. If we were not largely right about both, the efficiency of this approach would not be low – it would be zero.
PNAS, 2025. DOI: 10.1073/PNAS.2425307122 (About Dois).
