56 ESTABLISHMENT OF TRANSGENIC RED FLUORESCENCE PROTEIN (RFP) CLONE DOGS THROUGH A STABLE TRANSMISSION OF RFP GENE TO NEXT GENERATION

Abstract

Somatic cell nuclear transfer (SCNT) technology has been spotlighted not only for its advantage in producing unlimited numbers of genetically identical animals, but also the possibility of producing complex genetic modifications in animals. However, a few reports showed that mosaic expression of transgene in transgenic animals produced by SCNT (Park et al. 2002) and down-regulated gene expression is sometimes irreversible in their offspring (Bordignon et al. 2003). Therefore, we investigated reproductive ability by a breeding between female transgenic beagles and wild-type beagles. When female transgenic beagles (R1, R2, R3, and R5) expressing red fluorescence protein (RFP) gene reached puberty at 373, 353, 283, and 354 days after birth, serum progesterone concentration was monitored for detecting timing of ovulation. Approximately 72 to 79 h after ovulation, the beagles were naturally mated or artificially inseminated. Pregnancy was confirmed by ultrasonography at Day 30 after insemination. The transgenic bitches (R1, R2, R3, and R5) were then bred with wild-type male dogs, became pregnant, and successfully delivered 13 puppies (9 female and 4 male). In order to prove integration of RFP gene in all offspring, DNA was extracted from the blood of pups on Day 7 after birth. For PCR analysis, a primer pair for the RFP gene, forward primer (5′CGTGAAGCTGAAGGTGA-3′) and reverse primer (5′-CTCGTACTGCTCCACGA-3′), were used to amplify a 517-bp DNA fragment. The initial denaturation was performed at 94°C for 5 min, followed by 30 cycles at 94°C for 40 s (denaturation), 58°C for 40 s (annealing), and 72°C for 40 s (extension), and a final incubation at 72°C for 10 min to ensure complete strand extension. Presence of the RFP transgene in 7 of the puppies was confirmed by PCR and the puppies expressed RFP upon UV illumination. It was not different from the 53.8% expected Mendelian ratio. The present result demonstrated a stable transmission of the RFP gene into 5 female and 2 male offspring in the second generation. Among the second generation, 2 female puppies integrated with the RFP gene were in heat at ∼1-year-old. They were then bred with the semen of a wild-type beagle and bore 6 puppies. In the third generation, 3 puppies carried the RFP gene and results showed the expected Mendelian ratio. In conclusion, the present study demonstrates that female transgenic beagles have normal reproductive ability and a stable insertion of the transgene to the next generation.