Egg’s missing proteins thwart primate cloning

Don’t go ordering your clone just yet. A new study indicates that it’s almost impossible to clone a person by using the same techniques that work in mice and other nonprimates.

Although scientists can now routinely clone mice, sheep, cattle, and many other animals, they’ve struggled to clone monkeys and other primates (SN: 10/20/01, p. 251: Dolly Was Lucky). One research group has reported cloning a monkey, but neither those scientists nor others have replicated that success (SN: 3/8/97, p. 142). Moreover, researchers seeking to use cloning to produce human embryos as a source for multipurpose stem cells have failed in all their attempts so far.

In the April 11 Science, Calvin Simerly of the University of Pittsburgh School of Medicine and his colleagues describe more than 700 futile attempts to clone rhesus monkeys. They found that in the few monkey embryos that began to grow after eggs were put through the cloning procedure, cells contained abnormal amounts of chromosomes and eventually stopped dividing.

The investigators traced this problem to aberrant spindles, the meshwork of proteins that a dividing cell uses to partition chromosomes into two new cells. When scientists remove the DNA from an unfertilized primate egg, an initial step in cloning, they also apparently strip the egg of certain proteins that enable spindles to function properly. In other animals, these spindle proteins aren’t as tightly bound to the egg’s DNA and remain in the egg after the DNA is removed.

Simerly and his colleagues are already investigating new cloning techniques that might bypass the roadblock they’ve discovered. In theory, for example, a researcher could replenish the egg’s missing spindle proteins.


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