Transgenic Techniques

Techniques now exist that allow the role of gene function to be addressed in mammalian systems in vivo. The major mammalian species in which transgenic techniques have been applied is the mouse. Pronuclear microinJection techniques have allowed the analysis of elements important for correctly regulated gene expression, selective ablation of particular cell types, spatiotemporal control of transgene expression, the effect of overexpression of parttcular genes to generate models of human disease, and testing of potential gene-therapy constructs for complementation of mutations. These techniques have now been extended to a range of other species to allow the generation of animal bioreactors for the in vivo production of pharmaceutical proteins and may in the future allow the use of animal organs for xenotransplantation. The existence of ES cell lines that may be modified in vitro and subsequently used to generate offspring possessing the modification have created the ability to knockout gene function in the mouse. Homologous recombination can be used to disrupt specific genes and create null alleles. Genes can also be knocked out in a random manner using gene-trap approaches and screened for interesting patterns of expression to generate novel mouse mutants. Site-specific recombinase activities can be used to generate conditional knockouts and induce chromosomal rearrangements or translocatlons to allow an exammatlon of the effects of these gross rearrangements. Alternatively, techniques now exist that allow the precise introduction of single-codon changes into genes to examine the effect of missense mutations on gene function in vlvo. Such a wide range of possibilities can now be contemplated by the use of the transgenic techniques now available that the maJor limitation to further progress is an understanding of the developmental, biological, and physlologlcal consequencesof the intervention.