|[Frontiers in Bioscience 2, d298-308, June 15, 1997]|
TRANSGENIC RABBIT MODELS FOR THE STUDY OF ATHEROSCLEROSIS
John M. Taylor and Jianglin Fan
Gladstone Institute of Cardiovascular Disease, the Department of Physiology, and the Cardiovascular Research Institute, University of California, San Francisco, CA
The most common breeds of rabbits used for research are descended from the European rabbit (Order Lagomorpha, Family Leporidae, Subfamily Leporinae, Genus Oryctolagus, Species cuniculus) (31). The European rabbit is the only domesticated species of this animal, but there are more than 50 established breeds. Uniform stocks of several breeds have been developed for laboratory research, including the albino New Zealand White (5-6 kg adult body weight) and the agouti Dutch Belted (~2.5 kg adult body weight). Homozygous inbred rabbits have reduced reproductive efficiency. Many partially inbred substrains having desired genotypes are maintained by various suppliers. Important variants like the WHHL rabbits are maintained as partially inbred closed colonies, with sublines developing distinct phenotypic characteristics (32).
Figure 1. Production of transgenic rabbits. Specific pathogen-free New Zealand White donor females at five months of age are superovulated by the injection of 400 units of pregnant mare serum followed four days later by 150 units of human chorionic gonadotropin (13). The donors are mated to fertile males; single-cell embryos are flushed from the oviducts 19 h later. A DNA solution (~5 mg/ml) of the construct of interest is microinjected into the male pronucleus of the embryo while it is immobilized by a holding pipette under a gentle vacuum. Injected embryos are implanted through the fimbrial end of the oviduct (10-20 embryos per oviduct) of a pseudopregnant recipient that had been mated with a vasectomized male 24 hours earlier. Founder pups are identified one month after birth by DNA screening using Southern blot analysis or polymerase chain reaction.
The domestic rabbit may be ready for mating activity by ~4.5 months of age. The rabbit ovulates in response to mating activity, and cyclic estrous behavior can occur with 5-6 day intervals. The gestation period is ~31 days. A few days prior to parturition, the pregnant mother will build a nest with her own body hair and straw if it is available. A nesting box and a quiet room with restricted access facilitate this activity. The typical litter size for New Zealand White rabbits is 8-10 pups. Litters larger than 10 pups do not thrive.
Successful breeding of rabbits requires careful attention to animal husbandry (summarized in ref. (33)). Rabbits are highly susceptible to respiratory diseases, caused mainly by Pasteurella multocida and Bordetella bronchiseptica. These pathogens are endemic in most colonies. Another major problem for rabbits is coccidiosis in the liver or intestine caused by various protozoa, the most widespread being Eimeria and Encephalitozoa. Minimizing the occurrence of these diseases and maintaining a tightly regulated housing environment are crucial elements of a successful transgenic rabbit colony. These conditions generally can be met by housing specific pathogen-free rabbits in a restricted barrier facility with close veterinary monitoring.