Twenty thousand genes, twenty thousand proteins. This has long been the model taught in every biology textbook. A team at Harvard Medical School has just shown that this paradigm, traceable to Francis Crick, omits a whole dimension of what our cells actually manufacture.
Instructions from two distinct genes, sometimes located on different chromosomes, can fuse to form a chimeric messenger RNA, which then gives rise to a hybrid protein that no one anticipated. This finding was published in early September 2026 in Nature by the teams led by the researcher Peter Jackson.
- Two distinct genes fuse to produce functional hybrid proteins without genetic mutation.
- More than 30,000 chimeric messenger RNAs have been identified in mammalian cells.
- The physical proximity of chromosomes triggers this genetic fusion during the immune response.
The mechanism: when chromosomes draw near
The old dogma holds that a gene corresponds to a single protein. Researchers have observed that instructions from different genes, even on separate chromosomes, can intertwine to create chimeric messenger RNAs that produce functional proteins unknown until now. The cell does not simply read each gene in isolation: under certain conditions, it can stitch together fragments from different regions of the genome.
The trigger identified is physical. The team found that healthy chromosomes can fold against one another in mouse cells during the immune response, bringing together genes that are normally far apart. Once this proximity is established, the transcriptional machinery takes over. The nearby genes generate a chimera RNA, which borrows portions from each gene and manufactures a hybrid protein composed of the two.
No mutation. No DNA break.
The phenomenon is not an ordinary genetic accident like a chromosomal translocation typically linked to cancers. Here, everything happens at the RNA level, on otherwise normal chromosomes. This distinction makes the discovery striking: the body quietly produces these molecular objects, without any genetic abnormality being involved.
A library of 30,000 unknown molecules
To map the scope of the phenomenon, the team employed a technique known as direct RNA sequencing, which is more sensitive than conventional methods for spotting these unexpected junctions. With this technology, the researchers assembled a list of more than 30,000 chimeric messenger RNAs observed at least once in mammalian cells, what Jackson calls the “dark genome” library.
Thirty thousand. A staggering figure when compared to the 20,000 genes catalogued in the human genome: it means there could be more chimera combinations than there are genes themselves.
Of this total, scientists were able to determine how nearly 400 of these molecules are regulated by inflammatory signals, with some conserved between humans and mice. This cross-species conservation is a strong clue: it suggests the phenomenon is not mere molecular background noise, but a mechanism shaped by evolution because it serves a purpose.
To verify that one of these chimera proteins really had a biological function, the team studied a specific case in mice. The researchers focused on a fusion combining the genes for GSDMD and TMEM106A, two players previously studied separately in the context of the immune response. The resulting hybrid protein actively modulates the animal’s immune responses, demonstrating that these assemblies are not simply laboratory artefacts.
What it changes about the gene’s image
The implication is straightforward. “Nobody knows these exist,” one author of the study notes regarding these proteins. For decades, the scientific community assumed the catalog of human messenger RNAs was fixed.
“We thought we had the map of all the mRNAs produced in the body, and now we realize that was only the first page,” summarizes Jackson. He adds that all these other possible combinations can emerge. The finding deserves serious consideration: it means large swaths of the proteome remain to be explored, even in healthy individuals.
The result does not erase the gene as we know it, but it seriously complicates how we read it. A gene is no longer a closed unit that always yields the same protein: under certain physiological conditions, it can become a fragment of a sentence that combines with a fragment from somewhere else. The cell thus possesses a vocabulary far richer than what is catalogued by genes alone.
Research avenues, not yet a treatment
The authors remain cautious about medical exploitation of their discovery. The team continues to explore the molecular signals behind the formation of these RNAs, why the two partial sequences connect at the same point, why chimera proteins adopt particular shapes, and what triggers the bringing together of specific genes; the precise mechanism remains to be fully described.
The stated ambition goes beyond pure curiosity. The researchers say they are especially eager to evaluate various chimera molecules for potential medical applications, seeking in particular those that could be involved in currently incurable diseases. Jackson’s lab is currently examining several of these chimeric RNAs in the contexts of cancer, inflammatory diseases, and neurodegenerative disorders.
Nothing guarantees, at this stage, that any one of these candidates will become a drug. The gap between spotting an interesting molecule in the lab and turning it into a therapy for humans typically spans years, sometimes decades. But the map of life has grown by a previously unknown continent, and for now, no one knows exactly what it contains.
Sources: abcam.com | frontiersin.org
