Tetley is no ordinary mouse. And it's not just because he's a clone. Tetley is special because he was created using a new technology that researchers say has produced the most efficient results to date for cloning mice. He is also the first mouse clone whose genetic material was modified in the laboratory before cloning. The technology used to create Tetley, say researchers, will have a major impact on improving the efficiency of cloning in general.

In the February issue of Nature Genetics, researchers, led by Dr. Rudolf Jaenisch at the Whitehead Institute for Biomedical Research, report that they have successfully used embryonic stem cells to clone mice with the highest efficiency to date. Their study comparing clones generated by two different donor strains suggests that the genetic make up of donor cells plays a key role in determining the viability of clones.

In addition, the scientists show for the first time that it is possible to modify the genetic material in embryonic cells before using these cells to clone new animals. The scientists inserted a gene derived from the tetracycline (tet) receptor into an embryonic stem cell and then transplanted the modified genome into an egg cell whose genetic material had been removed. The result was Tetley: a transgenic clone who now carries the tet gene. The new technology will improve cloning efficiency by providing researchers the genetic tools needed to understand why so few clones survive to term and grow into healthy adults.

"Our technology will help scientists tackle one of the major challenges of mammalian cloningthe low numbers of viable clones," says Dr. Jaenisch. "Most clones die during gestation or soon after birth, and there are many possible reasons for this, including genetic make up of the donor, the cell-cycle stage of the donor cell, loss of genetic information, or the inability of the egg cell to reprogram the donor cell nucleus."

Assessing the impact of these factors
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Contact: Seema Kumar
kumar@wi.mit.edu
617-258-6153
Whitehead Institute for Biomedical Research
30-Jan-2000