By David N. Leff
The three scientists who created knockout mice ¿ the boon of biotech research ¿ received the Lasker Foundation¿s annual rewards for Basic Medical Research at a luncheon ceremony in New York Friday. They were honored, their citations read, for ¿development of a powerful technology for manipulating the mouse genome with exquisite precision, which allows the creation of animal models of human disease.¿
The three honorees are Mario Capecchi from the University of Utah in Salt Lake City; Martin Evans at Cardiff University in Wales, UK; and Oliver Smithies at the University of North Carolina at Chapel Hill.
Since 1945, when Albert and Mary Lasker launched their foundation, 63 Basic Medical Research award recipients have gone on to receive Nobel prizes in physiology or medicine. For 10 straight years ¿ 1979 to 1989 ¿ scientists who had previously received the Lasker Award soon garnered Nobels.
Molecular geneticist Joseph L. Goldstein, himself a Nobel laureate in medicine (1985), chairs the international jury of researchers that chooses Lasker awardees. In conferring the Lasker ¿Oscars,¿ ¿ statuettes of the Winged Victory of Samothrace, symbol of mankind¿s victory over disability, disease and death ¿ together with honoraria of $17,000, Goldstein explained the significance of this year¿s honors to some 300 attendees at the event:
¿Advances in biology and medicine often depend on the development of new technologies. The basic award,¿ he continued, ¿honors three individuals who developed a technology, based on mouse embryonic stem cells, that allows the creation of designer strains of mice in which virtually any gene can be disabled, or knocked out.¿ Using this KO technology, researchers have now produced animal models for hundreds of human diseases ¿ from atherosclerosis to Alzheimer¿s. These new laboratory models enable academic scientists to test new ideas, and the pharmaceutical industry to test new drugs, in ways that were not hitherto possible. Knockout mice also are providing the first clues to fundamental biological questions, such as how the brain develops in the embryo and how the immune system defends the body against invaders.¿
The first of some 300 Lasker awards went in 1946 to American biochemist Carl Ferdinand Cori, who with his wife developed the Cori Cycle of carbohydrate metabolism. In 1947 he won a Nobel prize.
Since biotechnology came of age in the 1960s, an increasing titer of Lasker awards have gone to biotechies. Watson, Crick and Wilkins shared the Lasker in 1960, and Nobels in ¿62.
Besides the basic medical research category, a separate Lasker Award honors clinical medical research. This year¿s recipient is Robert G. Edwards at the University of Cambridge, UK, for the development of in vitro fertilization. ¿This technological advance,¿ Goldstein pointed out, ¿has revolutionized the treatment of human fertility. It has resulted in close to 1 million children for couples who were considered infertile. The first test-tube baby, conceived in 1978, laid the groundwork for numerous refinements and innovations in reproductive health, and it also paved the way for human embryonic stem cell research, providing the platform for the promising advances that are being heralded today.¿
A final Lasker category is the award for public service in support of medical research and the health sciences, presented to William H. Foege of Emory University in Atlanta. Its selection committee is chaired by Daniel Koshland Jr., who said, ¿Foege helped to unravel the mysteries of toxic shock syndrome and Reyes syndrome, issued early warnings about AIDS, and played a pivotal role in eradicating smallpox and preventing river blindness. As director of the Centers for Disease Control from 1977 to 1983,¿ Koshland went on, ¿Foege was guided by a humanitarian vision that all people ¿ regardless of economic status, nationality or age ¿ should live long and healthy lives.¿
Evans Goes For Embryonic Gold
In the early 1980s, molecular embryologist Martin Evans zeroed in on the reproductive time period when he thought embryonic stem cells (ESCs) existed in the early mouse embryo.
He harvested the embryos, grew them in culture dishes and picked out cells that closely resembled ESCs. These cells formed teratocarcinomas when injected into mice and possessed all the features that identified them as long-sought embryonic stem cells. In principle, their DNA could be manipulated to create any mutation of interest ¿ i.e., knock out any gene of interest.
Capecchi Hits On Homologous Recombination
Meanwhile, molecular biologist Mario Capecchi was trying to target genes by homologous recombination ¿ ¿homologous¿ because the incoming DNA sequences line up with their twin target sequences in the chromosome, and ¿recombination¿ because both molecules break and rejoin with each other. He showed in 1982 that mammalian cells contain efficient enzymatic machinery to effect this recombination between newly added DNA molecules injected into the cell and the matching chromosomal sequence.
In 1988, Capecchi contrived a strategy to enrich for cells that have incorporated DNA in which the homologous targeting event had occurred. It also eliminated those that allowed it to integrate at random sites, making it possible to replace virtually any gene of interest, and construct designer mice.
Smithies Finds Cell Needle In 4,400-Cell Haystack
Molecular pathologist Oliver Smithies devised a sensitive method to find cells in which gene integration occurred at a chosen location. He aimed to detect such rare cells among the many more in which the gene occurred at random sites. The winning cell would contain a single piece of DNA that carried unique features of both the input gene and the resident one.
He sequentially divided a population of 4,400 cells into ever-smaller pools, tracking the ones that contained DNA fragments with diagnostic features of both the donor and recipient molecules. In 1985, he announced discovery of a cell that carried the critical combination of DNA sequences on a single molecule.
¿What we¿ve done,¿ Smithies told BioWorld Today in 1996, ¿is demonstrate the usefulness of combining transgenesis technology with homologous recombination. This allows one reproducibly to make transgenic animals in a chosen place on the genome. In other words, any time you make a transgenic mouse by this method, all of them will be the same. Whereas by the standard technique, they are all essentially different.¿
Today, more than 4,000 genetically engineered mice owe their existence to the technology developed by Capecchi, Evans and Smithies.