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Mosaic Gene Expression in Nuclear Transfer-Derived Embryos: DISCUSSION(3)

Recently, a transgenic pig has been cloned from ear skin fibroblasts. However, those researchers used in vivo matured oocytes for recipient cytoplasts, and in vitro culture data were not available. Therefore, in vitro developmental ability of NT embryos derived from ear skin fibroblasts was conducted by using in vitro matured oocytes. The developmental ability of NT embryos was not different between fetal fibroblast and ear skin fibroblasts as donor cells. However the percentage of blastocyst formation was still low (about 10%, Table 1).

Increased placental and embryonic weights have been reported in cloned calves, lambs, and mice. However, the birth weights of these piglets (1300, 1300, 1300, and 850 g, respectively), if anything, were lower than normal for our recipient sow herd (1450 g). These weights are also similar to those reported by Park et al.. We did not find any placental abnormalities. Unfortunately, two piglets died. NT8 had contracture of the flexor tendon of one front limb and died at 3 days of age due to a bacterial infection. NT9 died at 7 days of age from congestive heart failure. Her birth weight (850 g) was the lightest among the litter. NT7 had a hoof deformity; one of the dewclaws of the front left leg was abnormally large, and the front right leg had three dewclaws (polydactylia, Fig. 4). It is interesting that 402-2 had a contracture of the flexor tendons of her front legs at birth. She was the result of in vitro embryo production and culture to the blastocyst stage before embryo transfer, and, to our knowledge, the first pig resulting from such a procedure. She has since given birth, and none of her offspring exhibit this phenotype.