New Haven, Conn. -- A collaborative projectbetween American and Chinese researchers developed a way to study thefunction of genes in mice and man by using a moveable genetic elementfrom moths, according to a report in the journal Cell.
"We know how many genes are in the mammalian genome, but thatdoes not tell us how they carry out their jobs," said senior authorTian Xu, Professor and Vice Chair of Genetics at Yale University Schoolof Medicine and a Howard Hughes Medical Institute Investigator. "Wehave found a way to systematically inactivate genes in the mouse genomeso we can understand the functions of these genes."
After sequencing the human and mouse genomes, many scientists haveshifted their attention to determining the function of all of thosegenes. The strategy is to mutate each gene, to observe theconsequences, and investigate the molecular mechanisms. In the past twodecades, only a small percentage of the genes shared by mice and humanshave been analyzed in detail.
Genetic elements, called transposons, move from place to placein the DNA and allow material to be inserted or relocated. Bacteriaswap antibiotic-resistance genes with transposons. Scientists havetailored this natural gene shuffling technique to insert genes and tomutate genes in fruit flies and simple organisms to learn the functionof individual genes.
Transposons have proved to be valuable genetic tools for manyorganisms, but not for vertebrates and mammals. General application inmouse genetics was limited as they travel at low frequencies to limitedlocations, and had little capacity to carry DNA fragments.It tookXu'steam six years to develop an efficient tool for genetic manipulationsin vertebrates and mammals.
Xu and his colleagues at Fudan University in Shanghai, China finallychose a transposon called piggyBac that was originally identified inthe cabbage looper moth. They discovered that it was stable andversatile in mouse and human cell lines , providing a new way togenetically manipulate mammalian cells. It also worked in mice evenwhen it carried a couple of extra genes.
Xu's team made it easier to see the genes piggyBac associates with byadding a red fluorescent protein and an enzyme that changes the coatcolor of a white mouse to grey or black. The genes carried by thetransposons have been stably inherited and expressed through fivegenerations.
"The transposon acts as a genetic beacon, so researchers caneasily track its location without having to sequence the entiregenome," said Xu. In their experiments, piggyBac incorporated into manychromosomes in human and mouse cells. PiggyBac can be removed from amouse lineage by breeding with another mouse that has the enzyme toexcise the transposon.
This technique is a powerful new tool for generating transgenic animalsfor vertebrates and mammals, and a potential new vehicle for human genetherapy.Although piggyBac inserts itself randomly into the DNA, it mostoften locates in genes, making it useful for mutating genes and thus,revealing gene functions.
"This work represents another major step forward from Tian'slaboratory. It teaches us how transposons work in mammalian systems,while providing a tool for the systematic study of gene functionthroughout the human and mouse genomes."
In three months, the two graduate students who worked on the projectgenerated mice mutating 75 different genes. Xu, Min Han, an HHMIinvestigator at the University of Colorado, Boulder, and Yuan Zhuang ofDuke University, and their colleagues at Fudan University are in theprocess of scaling up piggyBac for the Mouse Functional Genome Project,which is aiming to mutate the majority of mouse genes at astate-of-the-art research facility in China to systematicallyunderstand the functions of the mammalian genes.
Xu expects the technique to be particularly useful for identifyinggenes and drug targets for diseases such as cancers and diabetes.
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