13 YEARS OF MANIPULATING THE MOUSE GENOME - A PERSONAL HISTORY

In 1974, Dr. Ralph Brinster published a paper describing the consequen ces of injecting embryonal carcinoma cells, the predecessors of embryo nic stem cells, into mouse blastocysts. Despite their early promise, e mbryonal carcinoma cells would not efficiently populate the germ line of mice, A decade later Elizabeth Robertson and I described the effici ent generation of germline chimaeras from cultured embryonic stem cell s and shortly afterwards the genetic manipulation of the mouse germlin e using ES cells. Our demonstration of the potency of Embryonic Stem c ells gave birth to a new era in manipulative mouse genetics, one in wh ich endogenous genes can now be mutated at will using gene targeting o f retroviral mutagenesis. This review focuses on the development and t esting of concepts and techniques during the thirteen years after we k new germline modification of endogenous genes in the mouse would be po ssible. This period is one in which more and more sophisticated tools for manipulating the mouse germline were developed and implemented. In this review I have taken the rare opportunity to reveal some of my th ought processes, frustrations, successes and failures as we moved thro ugh this exciting period of rapid technological change. As I look forw ard to the next thirteen years, I feel that this will be an equally ex citing period for manipulative genetics as we struggle to formulate co ncepts and design experiments that enable us to understand gene functi on in an era when the sequence of all genes will be known.