www.checkbiotech.org ; www.raupp.info ; www.czu.cz

Four years after Dolly's death, scientists are still amazed she was ever
born. That's because the decade since the announcement of Dolly's birth has
brought cloning researchers few triumphs and many frustrations. They may
have learned a little more about the events that allow an egg to reprogramme
the nucleus of an adult cell to produce a new organism. But these advances
haven't led to big improvements in the cloning process, or yielded huge
commercial payoffs, February 2007 by Erika Check.

In many ways, scientists are still fumbling in the dark, says Robert
Lanza, vice-president for research and development at Advanced Cell
Technology in Worcester, Massachusetts. "When Dolly was born, we thought
that in a few years we would understand the magic in the egg that allows it
to reprogramme a cell's DNA," Lanza says. "But cloning is still essentially
a black box."

Frogs were cloned as early as 1952, but mammals proved too problematic until
scientists at the Roslin Institute in Edinburgh cloned two sheep ? Megan and
Morag ? from embryonic cells in 1995. But it was the group's creation of
Dolly, cloned from an adult udder cell, that finally overturned the idea
that in mammals, developed cells could not reverse their fate.

After Dolly, scientists thought they would soon be able to clone many other
mammals. Some envisaged an industry of cloning applications, from the
production of medicines in live bioreactors ? cloned, genetically modified
livestock ? to the creation of herds of cloned food animals.

Scientists have made some progress towards potential applications. For
instance, they have cloned transgenic pigs that might one day be used as
organ donors, transgenic cows and goats that produce proteins that some
humans lack ? they have even cloned pets. But the low efficiency of the
cloning process has stymied industrial development, and most companies set
up to commercialize cloning have shut down.

Only 2?5% of cloned animal embryos grow into healthy offspring. This is
slightly better than a decade ago ? Dolly was the only lamb born from 277
cloned embryos ? but it is still far below the efficiency demanded by
industry.

There are several reasons why it has been difficult to figure out how
cloning works. Early development is slightly different in every species, so
cloning a new species is an arduous, trial-and-error process that requires
scientists to use thousands of eggs. But eggs aren't always easy to obtain,
especially for monkeys and humans, and no clones of either have been born.
And even if eggs are available, some of scientists' traditional model
species, such as mice, have proved extremely problematic.

Yet some see a way ahead. Many of the abnormalities that doom cloned embryos
are due to faulty epigenetics ? a set of controls that silences or activates
genes by chemically modifying the DNA or by binding it to certain proteins.
Epigenetic processes guide young cells with limitless potential into
restricted adult fates, by shutting down certain genes. During cloning, an
adult nucleus is transplanted into an egg, which must then erase the adult
genome's epigenetic marks, so it can re-express every gene necessary to
build a new animal.

But requiring an egg to do this reprogramming on its own bypasses other
natural mechanisms that normally help reset a cell's epigenetic programme.
Perhaps it's not surprising that the egg doesn't always do a perfect job,
says Ian Wilmut, Dolly's creator and director of the Scottish Center for
Regenerative Medicine at the University of Edinburgh. "When you think about
what we're asking the egg to do for us, in a way, I think we should still be
surprised that cloning works at all," Wilmut says.

Rudolf Jaenisch, a biologist at the Massachusetts Institute of Technology's
Whitehead Institute for Biomedical Research, is among those trying to
decipher these epigenetic glitches. If they can understand what goes wrong
with the reprogramming, they may be able to fix it ? or, better yet,
initiate the process themselves by adding chemicals or proteins to adult
cell nuclei. This would allow scientists to bypass the need for eggs
altogether.

The field is moving in this direction, trying to find ways to reprogramme
cells without using eggs. Last summer, for instance, Shinya Yamanaka and
Kazutoshi Takahashi from Kyoto University in Japan used a cocktail of
proteins to turn adult mouse cells into more flexible cells that behave a
lot like stem cells (K. Takahashi and S. Yamanaka Cell 126, 663?676; 2006).

This molecular approach solves the efficiency problem and avoids society's
ethical qualms about cloning (see page 800). "For many of us, that is the
holy grail, and nuclear transplantation is an intermediate stage," says Alan
Colman, chief executive of Singapore-based company ES Cell International and
former research director at PPL Therapeutics, which contributed to the Dolly
paper.

Egg-free approaches may also enable what many see as the most promising
potential application of cloning: the creation of human embryonic stem
cells, or cells made from them, that could be used to treat human disease.

Many scientists see human embryonic stem cells as having the most potential
for the next decade, especially if scientists learn to reprogramme cells
without using eggs.

"I think in ten years, people will learn how to convert one cell type to
another, without nuclear transfer, without eggs, in a Petri dish," says
Jaenisch. "Once we learn all the rules, maybe one day it will be possible."

[www.nature.com]