Cloning to resurrect
(March 13rd 2009) For the first time, an extinct animal has been cloned from frozen tissue by scientists in Spain. Although this cloned wild mountain goat died shortly after birth, Bettina Dupont asks: Are we on the way to some kind of Jurassic Park?
Scientists in Spain recently managed for the first time to clone an extinct animal using frozen tissue. The last Pyrenean ibex, a form of wild mountain goat, was found dead in January 2000 in northern Spain with her skull crushed. After the death of the 13-year-old female named "Celia" the Pyrenean ibex was declared extinct. Jose Folch and colleagues from the Centre of Food Technology and Research of Aragon, in Zaragoza, used nuclei from Celia's cryopreserved skin and tranferred them into enucleated eggs from domestic goats. This technique is called somatic cell nuclear transfer. The resulting embryos were implanted into goats as surrogate mothers.
Unfortunately, the only offspring died within minutes of birth due to breathing problems. But, even if the cloned female ibex had survived, she would have been in the unusual position of being the only individual of her species with no potential breeding partners.
Last year, Teruhiko Wakayama and colleagues published the generation of healthy mouse clones from mice frozen for 16 years without any cryoprotection. The Japanese scientists first generated embryonic stem cell lines using brain nuclei of frozen mice. Subsequently, they transferred nuclei of the stem cells into enucleated, unfertilised eggs. After transfer into surrogate mothers, several healty cloned mice were born.
These findings have raised hopes that extinct animal species could be resurrected from frozen samples without the need for live cells. Will we soon observe the first cloned mammoths in the zoo? Or even dodos and dinosaurs?
So far, attempts to resurrect extinct species from samples collected in nature are fraught with difficulties. The sample DNA is degraded to various degrees and additionally contaminated by bacterial, fungal and other DNA. In samples frozen in permafrost, DNA and cellular membranes are damaged by ice crystals.
Last year, a US and Russian team of scientists reported the nearly complete sequencing of the woolly mammoth genome using DNA from hair shafts. This sparked hopes that it might be possible to synthesise the mammoth genome for cloning. However, there are many obstacles down the road: mammoth chromosomes have to be reconstituted, the short supply of elephant eggs has to be overcome and the regulation of embryonic development has to be understood. Cloning extinct animals by nuclear transfer is particularly difficult, because the egg donor and the surrogate mother are of a species different from the nucleus donor.
Over the next 30 years, a quarter of the world's mammals face extinction.
Several projects around the world are already collecting samples of endangered animals. The Nottingham based Frozen Ark Project saves DNA, viable cells and gametes from endangered species. The organisers point out that they will not only preserve material of the cute and cuddly, warm and furry, but also of the less appealing damp and slimy - because of their importance for the ecosystem.
Considering the progress in cloning technology in the last decades, the phrase "dead as a dodo" might soon be outdated for an increasing number of species. Though perhaps it would be better not try the dinosaur species, Velociraptor and Tyrannosaurus rex!
