Knowing when you’re going to die is a fact best left unexplored. But for better or for worse, scientists have discovered a part of human cells that is tightly linked to the aging process, and it may very well be able to tell us how long a cell will live. By extension, as the researchers write in a new Cell Biology review, it might also tell us how long the person who owns those cells might live.

While previous research on cell lifespan largely centers around the telomeres at the ends of DNA strands, the paper, published Thursday, focuses on a tiny part of the cell called a nucleolus. Think back to high school biology: In the center of every cell is a nucleus, which is where all the instructions for cell function live in the form of DNA. Zoom in even closer, and there’s a “nucleus” in the center of the nucleus called a nucleolus, which is where the cell’s protein-making machines — the ribosomes — are made. And, as Max Planck Institute for Biology of Ageing director Adam Antebi, Ph.D. and postdoctoral fellow Varnesh Tiku, Ph.D. write, the size of the nucleolus tells us a lot about how long a cell will live.

nucleolus
The nucleolus lives in the center of the nucleus, which is the heart of the cell. 

Through their review of studies on yeast, mice, worms, and humans, they found that the size of the nucleolus can determine the rate that a cell ages. In general, they write, organisms with smaller nucleoli tend to live longer than those with bigger ones. They’re not entirely sure why, though studies on longevity have suggested that the NCL-1 gene — a gene that’s linked to nucleolus regulation — plays a role. In experiments on life-extending conditions, like dietary restriction and reduced insulin signaling, longer-lived organisms have higher NCL-1 activity and smaller nucleoli.

Smaller, it seems, is better — though the researchers don’t understand why yet. They do know that people with diseases that cause accelerated aging, like cancer or progeria, tend to have bigger nucleoli and more ribosomes. As Antebi said in an interview with The New York Times on Sunday, it may be that smaller nucleoli are generally better coordinated and make better use of their resources than bigger, more unwieldy ones.

To understand how we can use nucleolus size to help us predict how long a cell or organism will live, we’ll first have to figure out the exact nature of the relationship. Scientists can’t say for sure yet whether the link is cause-and-effect: It’d be most useful to us if it is, because that would mean the relationship can be disrupted in order to slow aging.

That, of course, is the goal at the heart of longevity research. Scientists want to know how to predict how long you’ll live so they can figure out ways to change it. But the question for individuals will always remain: Do you really want to know?