14 August 2005

Cloning Becomes Common

Making genetic copies of adult animals -- cloning -- has become almost routine. Recent Korean success cloning a dog, one of the most difficult species reproductively, shows that technical hurdles are behind us. (Picture from Seoul National University/Reuters)

I am talking about using genetic material from an adult animal to make a "clone" with the same nuclear genetics. The method used is called "nuclear transfer". Other methods, such as taking cells from early-stage embryos, or splitting embryos, also produce "clones". Embryo splitting is what happens to give rise to identical twins. But clones produced by these methods aren't included in the list below. Since you start with an embryo, the product of sexual fertilization, you aren't copying the genetics of any adult organism. Embryo splitting has been practiced for many years in agriculture and research.

Animals Cloned

SpeciesFirst ClonedLabComments
Carp1963Chinese Academy of Sciences Institute of OceanologyFirst animal cloned by nuclear transfer
Frog1966Oxford U.Demonstration of nuclear transfer technique
Sheep1996Roslin Institute, ScotlandFirst mammal cloned from adult cell
Cow1998Ishikawa Pref. Livestock Research Centre, JapanAgricultural productivity
Mouse1998U. Hawai'iDisease models for research
Goat1999Genzyme Transgenics, Tufts U., Louisiana State U.From 40-day-old embryo; for therapeutic protein production
Pig2000PPL Therapeutics, ScotlandObjective to produce organs for transplant (with some pig genes knocked out)
Cat2001Texas A. & M. U.
Guar2001Advanced Cell Technology, MassachusettsEndangered species
Deer2003Texas A. & M. U.
Mule2003U. Idaho
Rat2003INRA, France, and Chinese Acad. of Sci.Research models
Horse2003Laboratory of Reproductive Technology, Cremona, Italy
Rabbit2003INRA, France
Drosophila (fruit fly)2004Dalhousie U., Halifax, CanadaResearch tools
Dog2005Seoul Nat. U.For disease models for medical research

Types of "Cloning"

Of course plants can be regenerated from adult cells routinely. Nobody seems to get excited about cloning plants (except some botanists). Did you ever notice that there is no Nobel prize for botany? Botanists have to be given the prize in physiology or medicine (Barbara McClintock) or the peace prize (Norman Borlaug). Sigh.

In cloning by nuclear transfer the nuclear genome of the cloned offspring matches that of the donor, but the cytoplasmic genome (mitochondrial genes) does not. Thus the clone is not as biologically identical to the donor as two twins are to each other. Eventually we will probably develop methods that enable the regeneration of an adult cell perhaps a stem cell, into an embryo, and thus another adult, without nuclear transfer.

There are many, many cloned cell lines. The first, the HeLa line, dates from 1951. It is a culture of cervical cancer cells from a patient named Henrietta Lacks, and continues to be used in research. Since then thousands of cell lines have been created for many research and industrial production purposes.

In 2004 South Korean researchers cloned human embryos and from them developed a human human stem cell line. These stem cells may be useful for research, but this in not the same as cloning an organism to produce a genetic "twin". The same researchers got a lot more press for their dog clone, but the therapeutic cell line cloning work is much more revolutionary and has significant potential to lead to useful therapies for many diseases and conditions. (Image source Seoul National University)

Further Reading

Guardian gallery of pictures of clones

History of nuclear transfer cloning

Excellent discussion of cloning, stems cells, and cell lines for therapy

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