50. Rederivation of Infected Mice by Embryo Transfer Technique

Masanori Okamoto

Keywords: embryo transfer, germfree mice, infected mice, rederivation

This introduces a reproductive biotechnology, mainly an embryo manipulation technique, for the purposes of strain maintenance, transport, rederivation of infected mice, etc. in management laboratory mice. We developed a strain maintenance system using the embryo cryopreservation method on inbred mice which were produced in our facilities, which includes rederivation of HVJ (hemagglutinating virus of Japan) infected mice and production of germfree mice using an embryo transfer technique.

This study was undertaken to determine whether HVJ infected mice at inoculation were rederived by the embryo transfer technique. The embryos were collected from donor mice, all HVJ positive, and were transferred to the uteri of pseudopregnant recipients that were HVJ-free SPF mice. All the recipients and live young obtained after transferred were negative to testing by HVJ antibody. These results indicate that the embryo transfer technique is useful for rederivation of HVJ infected mice. Besides, conventionally, in preparing germfree (GF) mice, the uterus is removed from animals immediately before delivery; the fetus is taken out, and nursed by a GF foster mother. With this technique, it is difficult to determine the optimum time to remove the uterus. The resuscitation rate of offspring can be reduced if natural delivery occurs earlier than expected or if surgical delivery is too early. Furthermore, foster nursing requires skill. To increase the efficiency of GF mouse production, we examined the embryo transfer technique. The embryos were collected from conventional donor mice in a clean bench, and were transferred to the uteri of pseudopregnant recipients, which were GF mice reared in a flexible vinyl isolator. All the recipients and live young delivered after transfer were negative when examined for sterility. The results indicated that GF mice could be produced by embryo transfer, in addition to the conventional techniques of hysterectomy and cesarotomy. Furthermore, we developed new aseptic techniques for producing vasectomized sterile males from GF mice and for manipulating embryos. These methods of producing GF and clean mice by the embryo transfer technique, in combination with reproductive biotechnology such as techniques for storing frozen embryos, should be useful for strain maintenance, transportation of mice, and in vitro fertilization.