DOLLY the sheep may soon be joined by a herd of cloned cows. Researchers
in Denmark and Australia are adapting the technique pioneered by a team at the
Roslin Institute in Edinburgh to clone cattle. More controversially, the Danish
team is using genetic material from dead cows鈥攚hich points to the
disturbing possibility of applying the technology to dead humans.
Ian Wilmut and his colleagues at Roslin caused a sensation last week when
they unveiled Dolly to the world (This Week, 1 March, p 4). Dolly鈥檚 DNA came
from a live udder cell that had been taken from a six-year-old ewe and then
frozen.
Henrik Callesen and his colleagues in the Viborg laboratories of Denmark鈥檚
National Institute of Animal Science and a team led by Alan Trounson of Monash
University in Clayton, Victoria, are now trying to clone cows with DNA extracted
from the cells of cattle. 鈥淥ur donor cows had been dead around half an hour when
we collected the cells,鈥� says Peter Holm, one of the researchers at Viborg.
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The Danish researchers take two types of cells from the freshly slaughtered
animals. First, they extract immature, unfertilised eggs called oocytes, which
are then emptied of their DNA. Next they take adult cells from the cows鈥�
ovaries. These 鈥渄onor鈥� cells provide all the genetic material for the cloned
cow.
The final step in the lab is to fuse the donor cell with the empty oocyte by
exposing them to an electric current while they are touching. After about a
week, the fused cell grows into an early-stage embryo called a blastocyst. The
researchers鈥� next step is to implant the blastocyst into the womb of a foster
mother. 鈥淭he culture system we use is more or less the same as Roslin鈥檚,鈥� says
Holm.
The Danish work began two months ago. So far, the researchers have only got
as far as culturing fused cells. 鈥淲e鈥檙e working totally in the laboratory, and
as soon as we get proper blastocysts, we will transfer them into cows,鈥� says
Holm.
The Australian group鈥檚 technique is similar, although the donor DNA used by
Trounson comes from fibroblast cells taken from fetuses or cells from the
ovaries of live cows. His team has also yet to achieve a pregnancy using cloned
cells. Trounson believes that at least a dozen labs around the world are
experimenting with the cloning technique.
The possibility that cloning technology could be used to recreate dead people
attracted banner headlines in British newspapers last week. But Trounson
dismisses such speculation. 鈥淚t鈥檚 good for scaring people,鈥� he says . 鈥淚 don鈥檛
hear any scientists talking about it. No one wants to go down that line.鈥�
Ron James, the managing director of PPL Therapeutics, the company based in
Edinburgh whose researchers shared the credit for creating Dolly, stresses the
technical obstacles. 鈥淭he DNA must be intact,鈥� he says. 鈥淚f an animal鈥檚 dead,
the DNA will rapidly decompose. You can鈥檛 just put it in the fridge and clone it
later. It needs much more care and attention, and the cells must be in perfect
肠辞苍诲颈迟颈辞苍.鈥�
Trounson argues that alarm over the potential human applications of cloning
is obscuring the real medical benefits of the technology. Once cows can be
cloned, it will be possible to mass-produce cattle that have been genetically
engineered to produce drugs such as interferon in their milk. 鈥淐ows will be a
factory for pharmaceuticals,鈥� says Trounson. 鈥淚t will be possible to make drugs
much more cheaply.鈥�