A recent study from Japan may help to answer the question of whether cloned mammals age prematurely.1 Analysis of telomere lengths in Dolly, the cloned sheep, suggested that she might be aging more rapidly than controls.2 Dolly was cloned using a technique known as somatic nuclear transfer in which an adult donor cell is implanted into an enucleated oocyte. It appears that Dolly inherited her mother's shortened telomeres and that the telomeres may have been further shortened during the brief in vitro culture of the cells. This suggests that shortened telomeres may not be restored by the nuclear transfer method and raises the question of whether normal animals can be cloned from an aged animal.
To determine how cellular aging might affect aging of cloned animals, the Japanese group took cells from the ear of a 17-year-old bull and grew them in culture for different periods of time. It was expected that cells from short-term culture would be better for cloning than those from longer-term culture. Surprisingly, the developmental competence of embryos derived from cells of long-term culture was actually better than that of cells from short-term culture. These findings suggest that reprogramming may alter the life span of cells and that the age of the donor animal may not relate to the cell's ability to grow and divide in vitro. Currently, the telomeres from the cloned calves, the donor cells and the donor bull are being analyzed, and the health of the young calves is being monitored to determine their biological ages.
- PNAS. 2000. 97:990-995.
- Nature. 1999. 399:316-317.