Dolly the Sheep: A Success Story?

I was recently walking around the National Museum of Scotland and came across the lamb rotisserie  counter that is the Dolly the Sheep display and very quickly I realized how little I knew about Dolly. My view of this experiment prior to my visit was that of Dolly being an almost Frankenstein’s Monster creature, created sick and ill and never meant for this world. However the story of Dolly seems to be far more complicated than that of any fiction.

For those of you who may have missed that we magically cloned an animal, here is a short introduction.

Dolly was a female sheep born in 1996 through a process known as somatic cell nuclear transfer. They (the people in white lab coats) then took somatic cells from a sheep and starved these cells of nutrients. While also taking some reproductive cells, that-is egg cells, from a different sheep. They removed the genetic material from the egg and after some magical electrical zapping they force the membrane of the somatic cell to break open and its information to pass into the now ’empty’ egg. More magical zapping follows to ensure this cell would later form into an embryo and finally this stew of scientific wizardry is ready for the oven.

And ding! Dolly was born.

Now Dolly was the first ever clone  created from an adult cell, and one of the few sheep I know with three mothers. She was born without any complications and even went on to produce six lambs. At first it seemed she was one of the greatest scientific achievements of our age. Unfortunately however, Dolly developed a severe case of arthritis and lung disease at a very young age and passed away at the age of six. Maybe then she wasn’t so healthy?

You can see where in my mind the fact and fiction meld. She was a clone and to die so young, perhaps these were linked?

However the lung cancer she had (Jaagsiekte) was fairly common and there appears to be no direct link between this disease and the fact she was a clone. Although this cancer is typically found in older sheep. So what went wrong?

A paper released in 1999 in the journal Nature suggests one answer. It appears some cloned animals, which may include Dolly, have shorter telomeres. Obviously. Those darn telomeres.

Telomeres are the ends of each strand of DNA  and are integral to how cells age. Telomeres shorten over an animals lifespan, so the shorter the telomere the older the animal, at least this is the case for non-cloned animals. It appears then that since Dolly’s parent, from whom she got her genetic material, was six when the sample was taken, then Dolly may have been genetically six when she was born. Obviously this means Dolly was more susceptible to diseases, such as as Jaagsiekte, that effect older sheep.

A Family of Clones

However new research, again in Nature, suggests this  theory may be false and that instead cloned animals age at the normal ageing rate. How do we know this? Dolly’s family of little clones of course.

Since Dolly passed away four sheep have been cloned from the same mammary gland cells used to clone Dolly, their names; Debbie, Denise, Dianna and Daisy. As well as nine more being cloned from foetal skin cells.

So how have these sheep grown up? Just fine it seems. They appeared to be just as healthy as sheep that were not cloned. They do not suffer from any of the issues Dolly had and so it appears Dolly was the victim of bad luck and an odd lifestyle. The disease being bad luck and her osteoarthritis being the result of an indoor lifestyle.

A Success?

Yes.

The scientists successfully cloned a typically healthy sheep. Since this event there have been many new attempts to clone other animals such as horses, pigs and bulls.

Although far from perfect, cloning perhaps offers a last resort solution to saving an excessive number of animals on the brink of extinction. And with nuclear somatic transfer no longer a commonly used method and cloning becoming a far safer and easier practice, who knows what they could clone next?

References:

Burgstaller, J., Schinogl, P., Dinnyes, A., Müller, M. and Steinborn, R. (2007). Mitochondrial DNA heteroplasmy in ovine fetuses and sheep cloned by somatic cell nuclear transfer. BMC Developmental Biology, 7(1), p.141.

Sample, I. (2016). Dolly’s clones ageing no differently to naturally-conceived sheep, study finds. [online] the Guardian. Available at: https://www.theguardian.com/science/2016/jul/26/dollys-clones-ageing-no-differently-to-naturally-conceived-sheep-study-finds [Accessed 22 Nov. 2016].

Sinclair, K., Corr, S., Gutierrez, C., Fisher, P., Lee, J., Rathbone, A., Choi, I., Campbell, K. and Gardner, D. (2016). Healthy ageing of cloned sheep. Nature Communications, 7, p.12359.