The stage was set for Ian to work on translating these early findings to domestic animals for agricultural and biomedical applications. A highly sought-after goal at the time was to create transgenic animals capable of producing human recombinant proteins at an affordable cost. After Ian moved to Edinburgh to what is now known as the Roslin Institute, he and his team pursued a two-pronged approach: generating sheep embryonic stem cells to make germline chimeric animals and developing direct pronuclear microinjection into embryos. The interest was driven by the biopharmaceutical company Pharming, which sought to manufacture large quantities of the human enzyme α1-antitrypsin in animals for the treatment of the lung diseases cystic fibrosis and emphysema. Using a technique for injecting human DNA into the pronuclei of single-celled embryos, Ian and his team produced Tracy, a genetically engineered sheep that secreted the human enzyme in her milk11.

Among other things, his group became proficient at culturing embryo-derived cells with normal karyotypes12. After the arrival of Keith Campbell, a frog nuclear-transfer researcher who was aware of the importance of coordinating the cell cycle of the donor nucleus with that of the recipient oocyte, they first introduced Megan and Morag, two sheep derived from embryonic cells that had been cultured in vitro and rendered quiescent by serum starvation13. Only a year later, in 1997, they reported Dolly, cloned from a cell taken from an adult sheep14 — perhaps the most astonishing development in embryology of all time. Ian told one of us (A.T.) about Dolly during a hike in the hills above Edinburgh. I could not believe what he was saying because the great scientists working on amphibia and mice had, after exhaustive experimentation, dismissed the possibility that completely competent offspring could be cloned from differentiated adult cells. I remember saying to Ian that we would need to change the lecture notes on nuclear commitment in development — hardly an appropriate response.

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