A comparative study on the integration of exogenous DNA into mouse, rat, rabbit, and pig genomes

Transgenic mammals, from small laboratory rodents to domestic animals, have been successfully produced to date, but their production efficiency within or across species has been variable. This is probably due to the differenc es in the type of injected DNA and/ or technical procedures employed in eac h laboratory, as well as the reproductive characteristics of the species. H ere we report the direct comparison of the efficiencies of producing transg enic mice, rats, rabbits and pigs by one technician using a fusion gene com posed of the bovine alphaS(1)-casein promoter and human growth hormone (hGH ) gene. Before the fusion gene was injected into the zygotes, high magnitud e centrifugation to visualize the pronuclei was necessary for all of the pi g zygotes and one-third of the rabbit zygotes, but not for mouse and rat zy gotes. Post-injection survival of the mouse zygotes (67.1 %) was lower than those of the rat, rabbit and pig zygotes (89.6 to 100%). The volume change of the pronucleus following DNA injection was the lowest in mice (50% incr ease), moderate in rabbits (148% increase), and the most prominent in rats (238% increase). The data from only I pig zygote indicated a 22% increase i n the pronucleus volume by DNA injection. The PCR analyses of the tail DNA of new born offspring indicated that 0.8% (4/ 493), 4.8% (22/463), 0.8% (3/ 367) and 0.9% (2/221) of the injected eggs in mice, rats, rabbits and pigs, respectively, developed into transgenic offspring. Some of the founder ani mals in all four species expressed the transgene in the mammary gland which was confirmed in AGH mRNA by RT-PCR and/or hGH peptide in Witch's milk wit h ELISA. These results suggest that the maximum volume of DNA solution inje ctable into the pronucleus is a possible factor explaining the species diff erences in the production of transgenic animals.