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Profiles of the genomic DNA of 104 strains of T. equigenitalis isolated from brood mares with contagious equine metritis in Hokkaido during the breeding seasons from 1980 to 1993, as well as those of five strains (SS28, EQ56, EQ59, EQ70 and HH139) previously isolated in Japan were examined after restriction digestion and crossed-field gel electrophoresis. These profiles were essentially identical to each other and the various isolates and strains appeared to have a common genotype, designated 'genotype J', with respect to two restriction enzymes, ApaI and NotI. These results suggest a common source for all these isolates obtained over the course of more than 10 years in Japan.

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Vitrification is a technique for cryopreserving cells without crystallization due to elevation of the viscosity during the cooling process. We have developed a rapid and convenient mean of cryopreserving mouse preimplantation embryos by vitrification using a solution (hereafter named DPS) consisting of 2.75 M dimethylsulfoxide, 2.75 M propylene glycol and 1.0 M sucrose. In vitro fertilized pronucleate stage eggs were used because a large number of stage-matched eggs can be obtained at once. Only successfully fertilized eggs were collected and vitrified in DPS. After warming, two DNA constructs were injected into a total of 257 cryopreserved eggs, of which 175 (68%) survived the injection and were transferred into six recipients. All recipients became pregnant and gave birth to a total of 20 pups. When these DNA constructs were concomitantly injected into fresh eggs, 18% of eggs that were transferred developed into live pups, which was the same as the 18% figure for the cryopreserved eggs. With respect to transgenesis, 40% of the pups (8/20) developed from vitrified eggs were transgenic. In terms of the injected eggs that had been transferred, 4.5% of the 213 fresh eggs and 3.1% of the 112 vitrified eggs developed into transgenic mice. These results indicate that the efficiency of production of transgenic mice from vitrified eggs is comparable to that from fresh eggs.