Plasmid pMLP10 gp50.5 (gD) (Eloit et al., 1990) provided the sequence to integrate. The construct has been injected into the male pronucleus of one-cell mouse embryos (CBA/C5B1). A total of 1,567 microinjected embryos were transferred into the oviduct of pseudopregnant females (Hogan et al., 1986). PCR revealed that 3 out of 10 mice were born with an integrated construct; among them, 2 mice have integrated the construct in their gonads because 20 out of 107 (18.7%) of their offspring were also transgenic. This low percentage could be explained by germline mosaicism and/or differential mortality between transgenic and non-transgenic embryos.