In the February issue of Nature Genetics, Whitehead Institute and University of Hawaii researchers led by Professor of Biology and Whitehead member Rudolf Jaenisch reported 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 makeup 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 them to clone new animals. 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. Most clones die during gestation or soon after birth, and there are many possible reasons for this, including genetic makeup 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.
Somatic cells have a limited lifespan, and they are difficult to manipulate genetically.
As a result, they make poor tools for studying the genetic basis of cloning efficiency. The technology of cloning using embryonic stem cells removes that obstacle, allowing researchers to study the various parameters that affect cloning efficiency, said Professor Jaenisch. Embryonic stem cells normally direct the development of an entire animal. They can grow indefinitely in culture and can also be genetically manipulated to carry extra genes or knockout genes under study. Thus they provide researchers the perfect genetic tool to study cloning.