Genetically engineered "knockout" mice, developed at MUSC, are the first of their kind in South Carolina and provide a new avenue for understanding the roles of genes in normal and diseased conditions.

A Hollings Cancer Center laboratory team announced recently the establishment of several procedures (gene-, stem cell-, and embryo-manipulation) necessary for the generation of laboratory mice whose chromosomes carry the substitution of specific genes. This laboratory team constitutes the Gene Targeting, Knockout Mouse Facility, which is a University Research Resource Facility and includes Tina Cooper, Specialist II, Yong Gong, M.D., and Demetri Spyropoulos, Ph.D., facility director and assistant professor in the Center for Molecular and Structural Biology.

Inappropriate activity of certain key genes, termed "oncogenes," in the human body cause various forms of cancer. By replacing a specific mouse oncogene with a defective or "knockout" version of that same gene, biomedical investigators have a ready animal model to study the role of that gene in maintaining a normal condition. In converse, knockout mice for tumor-suppresser genes, genes that prevent tumor progression, additionally provide animal models on which to test new therapies and observe the development of cancer. To further understand the function of a specific oncogene, Dennis K. Watson, Ph.D., professor in the Center for Molecular and Structural Biology, in collaboration with Spyropoulos used the facility to generate one such oncogene knockout mouse.

Virtually a one-to-one correspondence exists between the genes of man and mouse. But subtle differences often exist in each corresponding gene and in their coordinated patterns of activity. Hence, the differences between man and mouse. Although genetic disorders may manifest their effects in different tissues in man and mouse, the underlying genetic controls tend to be similar. Mutations, or genetic errors, are responsible for an estimated three to four thousand hereditary diseases in man.

MUSC already has transgenic mouse facilities, headed by James Norris, Ph.D., and Alexander Awgulewitsch, Ph.D., with the capability of randomly adding into the chromosomes of laboratory mice repeated copies of genetic information, including newly designed genes. Such transgenic technology is used, for example, to generate a mouse that overproduces an oncogene product in an animal model to observe cancer progression and test new therapies. With the establishment of the "knockout" mouse technology, MUSC investigators now have at their disposal two complementary systems to further their genetic studies.

"This is more than just a knockout system," Spyropoulos said. "Using the procedures established, the investigator can have a mouse in which all or part of a gene or genetic element is deleted, changed, or even replaced by that of another gene. This precise molecular dissection can be applied to modifications ranging in size from an entire collection of genes on a chromosome all the way down to a single DNA nucleotide base pair of the three billion that make up all of the cell's chromosomes."

In cases where the knocked-out gene causes too profound a disorder for mouse survival, the system can be applied to make animal embryos formed entirely from the knockout stem-cell and observe how embryo development fails. Just such a study is currently underway to assist a Pasteur Institute laboratory group in Paris, France.