Introduction of Rat Growth Hormone Gene into Mice
Page 835 fragment was designed so that the fragment could be ligated in front of a restriction fragment of growth hormone cDNA that provided the rest of the coding sequence, including the termination codon. The other end of the synthetic fragment was chosen so that the composite coding sequence could easily be inserted into a site immediately downstream of the promoter–operator–ribosome binding site of the lactose operon cloned in a plasmid. After the introduction into bacteria, the bacteria were induced with IPTG to transcribe this foreign coding region and the greatly overproduced human growth hormone subsequently was purified away from the bacterial proteins. 19.14— Introduction of Rat Growth Hormone Gene into Mice The previous section described the use of bacteria to produce large quantities of human proteins for treatment of disease. It is possible to microinject molecules of purified RNA or DNA directly into eukaryotic cells. This provides a very powerful approach for identifying conditions under which specific genes are expressed in eukaryotic cells. One of the most dramatic illustrations of this approach was the microinjection of a chromosomal DNA fragment containing the structural gene for rat growth hormone into the pronuclei of fertilized mouse eggs. The eggs were then reimplanted into the reproductive tracts of foster mouse mothers. Some of the mice that developed from this procedure were transgenic; one or more copies of the microinjected growth hormone gene integrated into a host mouse chromosome at an early stage of embryo development. These foreign genes were transmitted through the germline and became a permanent feature in the host chromosomes of the progeny (Figure 19.30). Figure 19.30 Schematic illustration of the introduction of rat growth hormone gene into mice. Copies of a recombinant plasmid DNA containing rat growth hormone gene were microinjected into fertilized mouse eggs that were reimplanted into foster mothers. Some of the resulting progeny contained the foreign gene integrated into their own genome and greatly overexpressed growth hormone, growing much larger than their normalsized littermates. Redrawn from Palmiter, R. D., Brinster, R. L., Hammer, R. E. et al. Nature 300:611, 1982.