Sperm-mediated gene transfer in mice

Sperm-mediated DNA transfer to offspring has the potential to markedly simplify the generation of transgenic animals, but the efficiency in mice has been controversial. To determine the basis of the variability of the procedure in mice, we undertook a large, collaborative study of sperm-mediated DNA transfer to mouse eggs in well-established laboratory conditions for in vitro fertilization and offspring development following embryo transfer. Sperm were incubated with plasmid DNA during the capacitation period and then added to freshly ovulated mouse oocytes for fertilization; cleaved embryos were then transferred to the oviducts of pseudopregnant recipients for gestation. From a total of 75 experiments, 13 produced 130 transgenic offspring, amounting to 7.4% of total fetuses. In five experiments, more than 85% of offspring were transgenic, but the factors leading to this high success rate were not discovered. Clustering of such a low frequency event could account for the disparate reports of transgenic success with sperm-mediated DNA transfer to mouse offspring. Discovering the factors important to success would not only allow this simplified approach to become an important tool in the generation of transgenic mice, but could also lead to important insights into natural protective mechanisms against sperm-mediated transfer of foreign DNA.