Baker's yeast knows how to cheat time. Its sex cells are born with a full supply of divisions, even if the parent cell has already aged. But how the cell clears out accumulated damage remained a mystery for a long time: measuring the age of hundreds of cells by hand was too labor-intensive.
Now scientists have built a tiny platform with traps in which hundreds of cells divide simultaneously, while a camera films them every 15 minutes. The result was a census of lives: cells from young and old parents lived equally long. This made it possible for the first time to directly compare how sexual reproduction resets age.
The answer was found by switching off the genes responsible for cleanup in yeast. When two proteins that recognize the damaged membrane network inside the cell (the endoplasmic reticulum) were removed, cells from old parents lived shorter than those from young ones. And when the cleanup of other cell parts (mitochondria) was switched off, rejuvenation was unaffected. So the key 'old furniture' is the endoplasmic reticulum.
Now it is clear: if this membrane network is not cleaned during the creation of sex cells, age will be passed on to the offspring. The discovery shifts the focus: instead of mitochondria, which were long considered the main culprits of aging, it turns to the endoplasmic reticulum. And the tiny platform will help search for other ways in which cells erase age.
A yeast gamete is 4 times smaller than the mother cell, yet after rejuvenation it can produce just as many descendants as a young cell. And the protein Pma2, which the authors used as a gamete marker, remains on the gamete surface for several generations after germination but never gets into daughter cells.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.