We receive one set of chromosomes from our mother and one from our father. That is why most genes are represented by two copies, and a cell can use them differently. Imagine two books with identical text: one lies open at the needed page, while the other stands on a shelf with its covers tightly shut. The content is the same, but access to it differs.
It is precisely such differences that FIRE helps to reveal—a computational tool for analyzing DNA packaging. A study by a team that included scientists from the University of Washington and the University of Utah was published in the journal Cell. The work shows how DNA sequence and persistent cellular states together take part in controlling genes.
Inside the cell, DNA is wrapped around proteins and forms chromatin. Its packaging affects how easily regulatory proteins can reach a particular region. FIRE helps to identify accessible regions that are highly likely to be involved in controlling genes. An open region serves as an important clue: contact with the molecular machinery of regulation is possible here. The activity of a neighboring gene, however, requires separate verification.
The foundation is the Fiber-seq technology: a special enzyme marks accessible regions of DNA, after which sequencing reads long molecules. Differences in their sequence make it possible to distinguish the two chromosomal copies. FIRE adds machine learning that assesses the likely regulatory role of the marked regions.
A particularly interesting result concerns regions where the two copies differed in chromatin accessibility. In approximately 40% of such cases, the DNA sequence directly in the region under study was identical. The same text turned out to be packaged differently. This figure refers to the identified differences between copies; its significance for genome regulation as a whole remains to be determined.
Further analysis showed that certain chromatin states persist through cell division. The authors describe them as somatic epimutations—stable changes in epigenetic state. Here inheritance occurs within a cell lineage: daughter cells retain the features of the parent cell. The transmission of such changes from parents to children is a separate research question.
The researchers demonstrated the practical value of the approach using a DNA variant associated with the risk of celiac disease. It is located in a regulatory region next to an immune gene. A laboratory replacement of a single DNA letter changed the accessibility of this region. In this way, the scientists were able to single out, from among many neighboring variants, the one that actually affects the chromatin state. Its precise significance for the functioning of immune cells requires further study.
For medicine, such tools are important above all as a way to understand disease mechanisms more precisely and to choose targets for future interventions. Moving from this knowledge to treatment will require separate studies of efficacy and safety.
Epigenetic regulation has been known for a long time. FIRE makes it possible to examine it in greater detail by distinguishing the two copies of the genome. That is where the beauty of the result lies: identical letters allow for a different reading, and the history of a cell can persist in the way its DNA is packaged.
