Remember Dolly the sheep? The female Finn-Dorset sheep made headlines around the world when she became the first mammal to be cloned from adult cells in 1996. Dolly was cloned by removing the nucleus of a sheep mammary gland cell, which was then inserted into an undeveloped egg cell, shocked with electricity, and finally squirted into the womb of a surrogate mother sheep. True story.
Dolly, despite having a remarkable birth, lived an otherwise unremarkable life before being euthanized due to osteoarthritis and a lung infection in 2003. Luckily for clone watchers, Dolly is back in the news this week, thanks to a long-term study of her cloned siblings that was published in Nature. Just days after the 20th anniversary of Dolly’s cloning, researchers announced that all of the thirteen sheep monitored in this study are doing fine, including Dolly’s four “siblings:” Daisy, Debbie, Denise and Diana.
The sheep aren’t exactly Dolly’s true siblings, but were cloned from the same mammary gland tissue sample that Dolly was. Researchers examined the thirteen cloned sheep, took samples of various fluids and tissues from each animal, and checked major health indicators. The study found that almost all the animals are in excellent health, with a few suffering from mild arthritis:
This study represents the first detailed and comprehensive assessment of age-related, non-communicable diseases in adult cloned offspring of large animals. Working with sheep, four of which were cloned from the cell line that gave rise to Dolly, we undertook assessments of metabolic, cardiovascular and musculoskeletal health. Importantly, despite their advanced age (7–9 years), none of the clones showed any clinical signs of disease, being euglycaemic, insulin sensitive and normotensive.
Researchers are still awaiting data on the animals’ telomeres, which could provide insights into how cloned DNA ages. Still, this study is significant because it not only suggests Dolly’s health problems had nothing to do with her being a clone, but also in that it shows cloned animals can be just as healthy as their sexually-produced counterparts:
From the current series of assessments we conclude that there are no long-term detrimental health effects of cloning by SCNT [(somatic-cell nuclear transfer)] for a long-lived species such as the sheep. This conclusion is consistent with less detailed longevity studies in cattle, and suggests that the ageing process in surviving clones of large animal species is not accelerated.
Cloning is still nowhere near as efficient as sexual reproduction and often results in non-viable embryos. While many animals have been successfully cloned, no human being has been cloned to date; human embryos have been successfully created from cloned cells, however, but destroyed when still in blastula form. While there have been many dubious claims over the years that a successful human clone has been created, no concrete proof has yet surfaced.