For the first time, an internal clock has been found inside a living human cell.

We know cells dramatically change their shape and size during a lifetime. But this is the first time the changes have been seen over short time periods.

The research, published today in the Proceedings of the National Academy of Sciences (PNAS), opens up the possibility for us to learn about how and when diseases start.

“Previously, a precise point of a cell in its life cycle could only be determined by studying dead cells,” said Alexandra Zidovska, senior author of paper, from New York University.

“However, with this discovery, which shows that the nucleus exhibits rapid fluctuations that decrease during the life cycle of the cell, we can enhance our knowledge of both healthy and diseased human cells.”

The researchers studied the nucleus of the living cells, and saw a part of it, known as the nuclear envelope, flickering over a period of a few seconds. This has not been possible before due to limitations in measurement, but a new fluorescent microscope meant it was possible.

During the lifetime of the cell, the amount the cell changes in shape during these ‘flickers’ also gets smaller. This means measuring the fluctuations can give away the age of the cell.

“This process can serve as an internal clock of the cell, telling you at what stage in the cell cycle the cell is,” said Zidovska.

“We know that structural and functional errors of the nuclear envelope lead to a large number of developmental and inherited disorders, such as cardiomyopathy, muscular dystrophy, and cancer,” she said. “Illuminating the mechanics of nuclear shape fluctuations might contribute to efforts to understand the nuclear envelope in health and disease.”