Picture a book of instructions inside every cell: that's DNA. Some pages are always open, others are closed, and still others open up when the cell needs to do something. With age, the book starts to fall open too much, and the cell loses track of what it's supposed to do. For a long time, scientists couldn't see those open pages, because a microscope doesn't show how accessible DNA is to proteins.
The new method works like this: a special enzyme, the Tn5 transposase, is delivered into the cell, and it can insert itself only into open stretches of DNA. A glowing label is attached to the enzyme, so under the microscope the open pages flash as bright dots. This approach used to work poorly on fixed cells, because the enzyme couldn't make its way into the dense nucleus. The scientists fine-tuned the conditions the way a cook fine-tunes cooking time, and now the signal comes through clearly.
Now we can quickly test how different drugs or rejuvenation procedures affect DNA packaging. If a way can be found to close the extra pages, this method will show whether the cells have been made young again.
ATAC-see uses the same Tn5 transposase as ATAC-seq, but with a fluorescent tag: the enzyme literally "highlights" open regions of DNA, making them visible under a microscope.
The idea of visualizing the epigenetic state of cells echoes the film "Gattaca," where a genetic passport determines a person's fate. Here the chromatin landscape becomes a visible marker of age and potential reversibility.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.