Purification of plasmid and BAC transgenic DNA constructs.

Pronuclear microinjection is the most used method for generating transgenic mice. The quality of DNA to be microinjected is a key determinant of the success rate of this method. DNA purity is a critical factor because trace amounts of many substances, when microinjected into the pronucleus of the fertilized egg, can kill or prevent the further development of the embryo. Avoiding all contaminants is not a trivial issue, because most transgenic fragments need to be purified from agarose gels. Small particles and viscous materials in the DNA solution can also dramatically reduce the efficiency of microinjection because they tend to clog the injection needles. DNA shearing or breakage during purification and microinjection is also a potential problem, particularly when linearized bacterial artificial chromosomes (BAC) DNAs are used. The overall quantity and the final DNA concentration are also important considerations, because egg -pronuclei are very sensitive to the amount of foreign DNA. In this chapter, we first discuss the general guidelines and cautions for preparing microinjection-quality DNA, and then describe in detail two -protocols, one for gel purification of transgenic fragments from plasmid vectors and the other for isolating high-quality BAC DNA from bacteria.