Carl Zimmer in The New York Times:
None of us was made from scratch. Every human being develops from the fusion of two cells, an egg and a sperm, that are the descendants of other cells. The lineage of cells that joins one generation to the next — called the germline — is, in a sense, immortal. Biologists have puzzled over the resilience of the germline for 130 years, but the phenomenon is still deeply mysterious. Over time, a cell’s proteins become deformed and clump together. When cells divide, they pass that damage to their descendants. Over millions of years, the germline ought to become too devastated to produce healthy new life. “You take humans — they age two, three or four decades, and then they have a baby that’s brand new,” said K. Adam Bohnert, a postdoctoral researcher at Calico Life Sciences in South San Francisco, Calif. “There’s some interesting biology there we just don’t understand.” On Thursday in the journal Nature, Dr. Bohnert and Cynthia Kenyon, vice president for aging research at Calico, reported the discovery of one way in which the germline stays young.
Right before an egg is fertilized, it is swept clean of deformed proteins in a dramatic burst of housecleaning. The researchers discovered this process by studying a tiny worm called Caenorhabditis elegans. The worm has been a favorite of biologists for 50 years because its inner workings are much the same as our own. C. elegans relies on many of the same genes that we do to control the division of cells, for example, and to program faulty cells to commit suicide. In 1993, Dr. Kenyon discovered that a gene called daf-2 greatly influenced the life span of these worms. Shutting down the gene more than doubled the worm’s lifetime from 18 days to 42 days. That finding, which Dr. Kenyon made while a professor at the University of California, San Francisco, led to the discovery of an entire network of genes involved in repairing cells, allowing animals to live longer. Humans depend on similar genes to repair our cells, too. “Cynthia really pioneered the field of aging and rejuvenation using C. elegans,” said Irina M. Conboy, a biologist at the University of California, Berkeley.