Clones' Cells Look Rejuvenated

Cells from cloned calves seem younger than those from their conventionally conceived peers. The finding, reported in the 28 April issue of Science, suggests that cloning somehow resets the molecular clock of mature cells. It's not clear whether the clones will live longer than normal, but it does lessen the worry that clones derived from adult cells would age prematurely.

Three years ago, when Dolly the sheep was cloned, many scientists asked a question that sounds almost metaphysical: Are her cells older than she is? Dolly was cloned from an adult sheep's cell, and so her cells could have hallmarks of age that would be characteristic of an animal as old as the combined life-spans of Dolly plus her cell donor. Indeed, a 1998 finding suggested that Dolly's telomeres, the "caps" on the ends of her chromosomes, are shorter than normal--and telomeres shrink with age.

To test the theory of old cells in extremis, physician Robert Lanza of Advanced Cell Technology in Worcester, Massachusetts, and his colleagues cloned calves by using very old cells. They started with cells from a fetal calf and allowed them to replicate in the lab for several months, until near death. The cells showed characteristics of aged cells, including large size, accumulated debris, and shortened telomeres.

The researchers then transferred nuclei from nearly 1900 of the cultured cells into egg cells whose nuclei had been removed, eventually producing six calves. Five to 10 months after birth, the animals' telomeres were significantly longer than the telomeres of normal cattle the same age. In some cases, the telomeres were even longer than those of normal newborns.

It's not yet clear why the findings differ so dramatically from those in Dolly's cells. But cell biologist Leonard Guarente of the Massachusetts Institute of Technology says the evidence does suggest that being cloned was able to "restore a youthful state" to the donor cell's nucleus. Scientists will have to wait a while to find out whether cells that live longer in a test tube will translate into longer lived animals: Cows can live about 20 years.

--GRETCHEN VOGEL