The hGH produced by the mice is to be used in the production of medical drugs. The Canadian geneticists had achieved this through the use of a DNA gene promoter sequence, P12, which is only active in male sex glands such as the seminal vesicle. They injected fertilized mouse eggs with DNA encoding hGH linked up to the P12 DNA sequence. This ensured that the hormone was secreted specifically into the semen of male animals. A subsequent analysis showed that hGH was expressed in the seminal vesicle and the kidney, and in no other organs.
Experiments are currently under way to test the technique in boars.
Until now, only females were used in the production of hGH, which was secreted along with the animals' milk. Females were of limited use for this task, because they only produce milk during lactation, whereas males produce sperm year-round.