Enlarge / Top row: individual steps in the reaction process. Bottom row: cartoon diagram of the top, showing the position of each DNA and RNA strand. (credit: Hiraizumi, et. al.)

While CRISPR is probably the most prominent gene-editing technology, there are others, some developed before and since. And people have been developing CRISPR variants to perform more specialized functions, like altering specific bases. In all of these cases, researchers are trying to balance a number of competing factors: convenience, flexibility, specificity and precision for the editing, low error rates, and so on.

So, having additional options for editing can be a good thing, enabling new ways of balancing those different needs. On Wednesday, a pair of papers in Nature describe a DNA-based parasite that moves itself around bacterial genomes through a mechanism that hasn't been previously described. It's nowhere near ready for use in humans, but it may have some distinctive features that make it worth further development.

Going mobile

Mobile genetic elements, commonly called transposons, are quite common in many species—they make up nearly half the sequences in the human genome, for example. They are indeed mobile, showing up in new locations throughout the genome, sometimes by cutting themselves out and hopping to new locations, other times by sending a copy out to a new place in the genome. For any of this to work, they need to have an enzyme that cuts DNA and specifically recognizes the right transposon sequence to insert into the cut.

Enlarge (credit: DrAfter123)

The development of gene editing tools, which enable the specific targeting and correction of mutations, hold the promise of allowing us to correct those mutations that cause genetic diseases. However, the technology has been around for a while now—two researchers were critical to its development in 2020—and there have been only a few cases where gene editing has been used to target diseases.

One of the reasons for that is the challenge of targeting specific cells in a living organism. Many genetic diseases affect only a specific cell type, such as red blood cells in sickle-cell anemia, or specific tissue. Ideally, to limit potential side effects, we'd like to ensure that enough of the editing takes place in the affected tissue to have an impact, while minimizing editing elsewhere to limit side effects. But our ability to do so has been limited. Plus, a lot of the cells affected by genetic diseases are mature and have stopped dividing. So, we either need to repeat the gene editing treatments indefinitely or find a way to target the stem cell population that produces the mature cells.

On Thursday, a US-based research team said that they've done gene editing experiments that targeted a high-profile genetic disease: cystic fibrosis. Their technique largely targets the tissue most affected by the disease (the lung), and occurs in the stem cell populations that produce mature lung cells, ensuring that the effect is stable.