University of Hawaii scientists, together with colleagues in Japan, have developed a new method for producing transgenic mammals. The method - Honolulu transgenesis - uses sperm to deliver genetic information (DNA) from one organism into the egg of another. The egg can then divide so that every cell in the new individual contains the introduced DNA. The experiments demonstrated the new method using DNA for jellyfish green fluorescent protein to make green mice, and are reported in the May 14 issue of the journal, Science.
The team, whose members made headlines last summer with Honolulu cloning, reported success in producing transgenic mice by injecting eggs in a method called intracytoplasmic sperm injection. About one in five offspring resulting from the new procedure contain the introduced DNA.
The production of transgenic animals isn't new; transgenic mice were first produced in 1974, and the prevailing method of producing them by injection of DNA into the pronucleus of a one-cell embryo was first described in 1980. The pronucleus microinjection method is the most commonly used. It works well in mice, but is difficult in mammals such as cows and pigs, in which the pronucleus is difficult to locate within the cell, says Tony Perry, an assistant professor in the UH Manoa John A. Burns School of Medicine and corresponding author on the Science paper. "The great thing about this new method is that it is very straight forward," Perry says. "It may prove to be more efficient."
In Honolulu transgenesis, mouse sperm are fozen, freeze-dried, or treated with a chemical to disrupt their coat. The sperm are mixed with DNA (the researchers used from a jellyfish, but it could, in principle, be any DNA). Sperm and the DNA are then injected into oocytes. Developing embryos are transferred into a foster mother. The introduced DNA contains a gene that directs production of a protein that glows green under long-wave ultraviolet light, so the scientists could easily see that the jellyfish 'green gene' DNA was incorporated into the mouse genome if the mouse appeared green when illuminated by ultraviolet light.
The 'green gene' is just a marker to indicate that the technique works, says Perry. "We hope and believe that the technique will be useful in medical research and in development of xenotransplant donors," he says. Possible applications could include using the mouse as a model for studying the function of human genes. Also, more organs could be available for human transplant if pig genomes could be modified so that the corresponding pig organs wouldn't trigger a crtical immune rejection in patients who receive them.
Collaborators on the project include Teruhiko Wakayama, Ryuzo Yanagimachi, Hidefumi Kishikawa and Tsuyoshi Kasai of the University of Hawaii; Masaru Okabe of the Genome Information Research Center, Osaka University; and Yutaka Toyoda of the Research Center for Protozoan Molecular Immunology, Obihiro University of Agriculture and Veterinary Medicine.