For decades, scientists treated most of our DNA like junk mail—interesting to have around, but not doing much. A new discovery from Toronto's Hospital for Sick Children just changed that assumption.
Researchers have identified a stretch of non-coding DNA that acts as a master control for cell size. It's a long non-coding RNA called CISTR-ACT, and it directly tells cells whether to grow larger or stay small. The finding matters because cell size isn't trivial—get it wrong, and you're looking at cancer, anemia, developmental disorders, and a host of other conditions.
"Our study shows that long non-coding RNAs and the non-coding regions of the genome can drive important biological processes, including cell size regulation," said Dr. Philipp Maass, Senior Scientist at SickKids. The non-coding genome makes up about 98% of human DNA, so this discovery suggests there's a lot more functional machinery hiding in what we've long dismissed as filler.
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Start Your News DetoxHow CISTR-ACT works
The team used CRISPR gene-editing tools combined with computational biology to trace CISTR-ACT's influence. What they found was elegant: the RNA guides a protein called FOSL2, which then binds to and activates genes involved in cell growth and structure. When researchers removed CISTR-ACT in their preclinical models, cells grew larger. When they added more, cells shrank. "CISTR-ACT and FOSL2 control cell size much like a magnet," explained Dr. Katerina Kiriakopulos, the lead author. "When the magnet is removed, the cells grow, and when you put the magnet in, cells shrink."
The effect held across multiple cell types and even across different species, suggesting this isn't a quirk of one cell line but a fundamental biological mechanism that's been conserved through evolution.
What makes this particularly exciting for medical research is that CISTR-ACT operates at both the DNA and RNA levels—meaning there are multiple ways to influence it. "This opens new directions for potentially translating these findings into precision therapies," Maass noted. Rather than a single pathway to target, researchers now know there are multiple entry points for intervention.
The work, published in Nature Communications, involved collaboration across SickKids' genetics, brain imaging, and computational biology teams, funded by Canada's national research agencies. It's the kind of foundational discovery that doesn't immediately become a treatment, but it does rewrite what we thought we knew about how our cells regulate themselves. And that rewiring of understanding is often where breakthroughs begin.
