Embryo manipulation and gene transfer in domestic animals

Effects of superovulation, culture and microinjection on development of rabbit embryos in vitro

Factors influencing the developmental potential of cultured rabbit zygotes and their ability to incorporate and integrate the WAP-hPC (human protein C) gene were investigated. Rabbit zygotes (n = 1053) were recovered from both superovulated and nontreated New Zealand White females. The hormonal treatment of rabbit donors resulted in a doubling of the number of recovered ova per donor when compared with the nontreated group (18 vs 9 ova). However, the quality of recovered zygotes (presence of both pronuclei) was significantly better in the nontreated group (99 vs 88%, Experiment 1). The effect of various culture media on the development of rabbit zygotes in vitro was evaluated after incubation under CO2-free conditions (Experiment 2). In serum-free, growth factor-supplemented medium (BSEITS, DME/F12, 1.5% BSA, EGF, insulin, transferrin and sodium selenite) the percentage of morula/blastocyst stage embryos was significantly higher (88%) than in DME/FCS, (DME/F12, 10% fetal calf serum, 59%) or the control group (DME/F12, 1.5% BSA, 25%). In Experiment 3, zygotes were microinjected with the WAP-hPC gene and were examined after 72 h of culture. Zygote cleavage and the percentage of morula/blastocyst stage intact embryos were higher (79 and 58%, respectively) than in microinjected embryos (31.0 and 21.5%, respectively). Summarized data of the PCR assay of microinjected zygotes demonstrated positive signals for the integration of the WAP-hPC gene in 6.6% (34 of 515) of all the microinjected zygotes.

The efficiency of production, centrifugation, microinjection and transfer of one- and two-cell bovine ova in a gene transfer program

Forty crossbred beef heifers were superovulated with 2000 IU pregnant mare serum gonadotropin (PMSG) and mated twice by natural service during estrus. Ovulations were counted and ova were recovered during mid-ventral laparotomy between 44 and 54 h after the onset of estrus. The overall donor ovulation rate (M+/-SEM) was 15.2+/-1.3. There was a positive association between ovulation rate and the number of ova recovered (P<0.001), and between ovulation rate and the incidence of ova advanced beyond the two-cell stage of development (P<0.05). When grouped on the basis of superovulation response, the numbers (M+/-SEM) of recovered one-cell, two-cell and more advanced ova were 3.7+/-0.7, 1.0+/-0.3 and 0.5+/-0.3, respectively, for donors with up to 15 ovulations. The corresponding numbers for donors with more than 15 ovulations were 7.2+/-1.8, 6.0+/-1.3 and 2.8+/-1.2, respectively. Following centrifugation, pronuclei were visible in 68% of one-cell ova, and nuclei were visible in 80% of two-cell ova. Approximately 20% of ova were destroyed during DNA microinjection. A total of 66 centrifuged and DNA-injected ova were transferred to the oviducts of 26 crossbred beef heifers, each receiving two, three or four ova. Echography at Day 55 confirmed that 14 (54%) heifers were pregnant with 26 (39%) fetuses. Eleven heifers were held to calve and produced 21 calves.