The study on transgenic mice.
The structural gene coding for human growth hormone (hGH) was fused to the promoter of the mouse gene for metallothionein-1. These fusion genes were introduced into pronuclei of the fertilized eggs of mice by micro-injection. We have injected MT-hGH genes into 121 mouse eggs which were transferred into the oviducts of eleven pseudo-mothers. Seven out of eleven mothers gave birth. Forty-three litters were born. These litters were grown-up and their tails were cut for isolating the DNA. The DNA of each mouse was examined by dot hybridization and Southern blotting. We found that eighteen mice had incorporated the fusion genes and grew larger than control mice. Synthesis of human growth hormone was induced further by zinc, which normally induces metallothionein gene expression. We also isolated the RNA from the livers of transgenic mice. The RNA was hybridized with hGH gene. It showed that on the transcription level the hGH gene was transcribed into mRNA in the transgenic mice. Using the same method to examine the second and third generation of the transgenic mice, we found that the incorporated gene could be inherited for generations. But the body-weight of transgenic mice appeared to decrease in the progeny. The offspring obtained from different combinations of parents (carrying or not carrying hGH gene) were different.