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Gene targeting in sheep
Genome Biologyvolume 1, Article number: spotlight-20000629-00 (2000)
PPL Therapeutics Ltd of Roslin, Scotland, show in the 29 June issue of Nature how they succeeded a year ago (the delay was to secure a patent) in targeting a gene to a chosen location in embryonic sheep fibroblasts (Nature 2000, 405: 1066-1099). They then transferred the nucleus from cultured fetal cells to stem cells to create gene-targeted sheep. Cloning sheep, goats, cows, pigs and mice has succeeded, but gene targeting has not previously been achieved except in mice. But it is proving difficult to clone whole animals efficiently, as the science involved is obscure, and of some 100 attempts to clone an animal, typically just two or three live offspring result (see Science 2000, 288: 1722- 1727). Even when an embryo does successfully implant in the womb, pregnancies often end in miscarriage. A significant fraction of the animals that are born die shortly after birth. And some of those that survive have serious developmental abnormalities. So there is still much work to do before this technology yields herds of animals producing therapeutically important proteins.