DNA-mediated genetic transformation of mouse embryos and bone marrow--a review

In recent years, new gene transfer systems have been developed which allow molecularly cloned genetic material to be introduced into whole organisms. These systems include the microinjection of DNA into mammalian embryos, transfection of DNA into mouse bone marrow cells, and the infection of early embryos with retroviruses. Exogenous DNA appears to integrate randomly into the host genome. The production of transgenic mice by injection of DNA into mouse embryos has rapidly gained importance as an experimental tool for the study of gene regulation during development. Through this technique, recombinant molecules of any type can be introduced into one-celled embryos, and thus can be used to study development from its earliest stages. DNA sequences have been shown to integrate and transmit through the germ line to subsequent generations as mendelian traits. Transgenic mice carrying various gene constructs have been successfully exploited for the elucidation of factors which determine tissue specificity of gene expression as well as the level of gene control. Phenotypic changes related to expression of foreign genes have also been observed. This experimental approach thus promises to rapidly solve many of the heretofore most challenging problems in developmental genetics. Insertion of foreign genes has also made possible the creation of insertional mutants which manifest themselves most frequently as recessives. Such mutations can be readily studied at the molecular level by using the transferred material as a probe for recovery of the affected host sequence from genomic libraries. Many of these same problems have been addressed by introducing retroviral DNA into mouse embryos. Here, the sequences used for transfer have been limited to retroviral genes, but nonetheless these experiments have been profitably exploited for studies both of gene regulation and mutagenesis. Gene transfer systems are being developed allowing the experimenter to transfer DNA into bone marrow cells of mice, after which the recipient cells can be reintroduced into lethally irradiated histocompatible animals. This system has the advantage that selection can be applied during the gene transfer process such that the expression of the foreign material is assured. In addition, these experiments have created a model system for production of animals carrying a subpopulation of cells which is highly resistant to a toxic agent. This system has the potential for therapeutic application to man.