A worm a millimeter long eats labeled atoms, and then the dance begins. Every carbon and nitrogen atom that enters the body takes its place in the cells: it becomes part of proteins, fats, DNA. The scientists labeled the worm's food with the stable isotopes ¹³C and ¹⁵N, then switched it back to ordinary food and began tracking how quickly the labeled atoms leave the tissues. In this way, for the first time, it became possible to see biomass turnover at all levels at once: from individual organelles to whole organs.
Calorie restriction is known to extend life in many organisms. But what exactly happens to the body's matter during this process remained a mystery for a long time. Some data said that protein turnover slows down, while others showed that cells more actively digest themselves. The new method settled the dispute: it produced a map showing where and at what rate turnover speeds up and where it stays the same.
Mitochondria, the cells' power stations, behaved especially interestingly. They renewed faster than the tissue as a whole, and dietary restriction affected them in the same way as it did the tissue. But the main discovery concerns their interaction: neighboring mitochondria are more similar in isotopic composition than distant ones. Over time, this similarity spread over a distance of up to nine micrometers. This means that mitochondria do not live on their own but constantly exchange contents, like dancers who come together and move apart but always keep the rhythm.
Previously, such a dance could not be seen: conventional biochemical methods averaged data across the whole tissue and lost the details. Now it is clear that dietary restriction does not simply accelerate the overall turnover of substances but selectively rearranges carbon and nitrogen renewal in different tissues. It is like an orchestra where the conductor does not make everyone play louder but changes the parts of individual instruments.
Thus the worm's metabolic dance reveals its steps. Labeled atoms, like glowing dots on a dance floor, show where the matter of life is moving. And now that the dance is visible, we can learn to direct it.
The worm's cuticle, composed mainly of collagen, after labeling showed a ¹⁵N/¹⁴N ratio of about 15,000, which is thousands of times higher than the natural level and demonstrates almost complete saturation with isotopes.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.