Most attempts to solve those problems have focused on the nuclear donor cell, which is fused with an egg cell that has had its nucleus removed. "What has come to pass is that whether you take a cell from an adult, from skin, from liver, muscle, or a variety of differentiated tissue types... they can contribute to the formation of a clone, albeit at low efficiency," Overström says. "There was this original thinking that a 'silver bullet' cell type may exist that would be substantially more adept at giving rise to successful cloned offspring. To date, however, there is little evidence to suggest that that is the case." He and his team began to suspect that the state of activation of the egg cell could be a key to improved success.
Overström and colleagues bred a transgenic goat with the goal of accessing antithrombin III (ATIII), a protein normally found ...
