Dolly siblings’ ninth birthday is boost for cloning
Four identical sibling sheep roaming in field have aged normally and restored faith in process
THE ninth birthday of four sheep who spend their days largely minding their own business in a quiet Nottinghamshire field might seem an unusual cause for celebration.
But because they are related to the most famous sheep in history, the anniversary is being hailed as a scientific milestone. Dolly, the first mammal to be successfully world in 1996.
But Dolly’s subsequent ill health, premature ageing and her death after six and a half years raised doubts about the safety of the process that created her.
Yesterday, however, Dolly’s genetic “siblings” – Debbie, Denise, Diana and Daisy – were declared fit and well for their age, indicating that large cloned animals age normally.
The clean bill of health restores confidence in the process of reprogramming mammalian cells, according to biologists, and has positive implications for fields of human healthcare, such as stem cell therapies.
The four sheep, nicknamed the Nottingham Dollies, were cloned from the same line of cells as Dolly and are part of a flock of 13 being monitored by scientists at the University of Nottingham.
The animals underwent detailed musculoskeletal investigations, assessments of glucose tolerance, insulin sensitivity and blood pressure.
The also compared X-rays and MRI scans of the clones with images taken from healthy control animals.
Prof Kevin Sinclair, who led the research, said: “One of the concerns in the early days was that cloned offspring were ageing prematurely and Dolly was diagnosed with osteoarthritis at the age of around five, so clearly this was a relevant area to investigate.
“We found that our clones, considering their age, were at the time of our research, healthy.
“This shows that there are cells that can undergo complete reprogramming and be completely normal.
“So whether you’re aiming for stem cells, or whether you’re aiming for cloned offspring, there is a target you can aim for, and that target is normality.”
The method used to create Dolly and her siblings, called somatic cell nuclear transfer (SCNT), involves transferring an adult cell nucleus containing an animal’s signature DNA to an unfertilised donor egg whose own nucleus has been removed. Electrical stimulus causes the egg to start dividing and form an embryo that is genetically identical to the donor of the adult cell.
In 1996, Dolly was the only lamb to survive to adulthood from 277 attempts by Professor Sir Ian Wilmut at the Roslin Institute in Edinburgh.
The Nottingham flock came about as a result of studies to improve the efficiency of SCNT.
Part of the cloning process involved reprogramming cells so that they became blank slates with limitless potential, which helped advance work in stem cell science following Dolly’s birth.