Characterization of a retrovirus shuttle vector capable of either proviral integration or extrachromosomal replication in mouse cells

Polyomavirus-based shuttle vectors for studying mechanisms of mutagenesis in rodent cells

We have constructed a series of polyomavirus-based shuttle vectors for analyzing mechanisms of mutagenesis in rodent cell systems. These vectors contain the supF suppressor tRNA gene which serves as the mutagenesis target; the pBR327 replication functions and ampr gene for replication and selection in bacteria; and the polyomavirus genome which permits replication in rodent cells. The polyoma genomes used in these vectors vary in their enhancer regions, causing varying efficiencies of replication in different types of rodent cells. One of the vectors (pPySLPT-2) which replicates particularly well in several different rodent cell types (i.e., Chinese hamster ovary, mouse hepatoma and mouse lymphoma) was used to compare mutation induction by UV radiation in UV repair-deficient mouse lymphoma L5178Y-R cells with mutagenesis in the related UV repair-proficient line, L5178Y-S. In both cell types, UV-induced mutants could be recovered at frequencies up to 50-fold higher than that of the spontaneous background. At a given UV fluence the L5178Y-R cells were more highly mutable than the L5178Y-S cells. Our results indicate that these new polyomavirus-based vectors should be useful for analysis of the molecular mechanisms of mutation induction in rodent cell systems, and in particular should allow detailed analysis of mutagenesis in the well characterized rodent somatic cell mutants.

Retroviral-mediated gene transfer. Applications in neurobiology

There are now many examples of the successful expression of genes transduced by retroviruses in studies from outside the field of neuroscience. Retroviruses will undoubtedly also prove to be effective tools for neuro-scientists interested in expressing cloned neurotransmitter and receptor genes. There are also other less obvious applications of retroviruses, such as their insertional mutagenic effects, which may be useful in studies of the genetic factors and biochemical mechanisms involved in, for example, neurotoxicity. Strong cellular promoters have been identified by retroviral infection and subsequent rescue of the flanking genomic DNA. Retroviruses can be employed again to reintroduce these regulatory sequences back into cells. In this way the complexities of gene expression in the many subpopulations of neurons may be unraveled. Retroviruses can also serve as very useful genetic markers in studies of development and lineage relationships. Retroviruses may be used to efficiently transfer oncogenes into neuronal cells to create new cell lines. This application exploits one of the natural traits of retroviruses--oncogenesis--which led to their original discovery. Finally, there are neurotropic retroviruses that could serve as important vectors for delivering genes into neurons. Studying these retroviruses may lead to an understanding of how they cause neuropathologic changes in the CNS.

SV40-based Escherichia coli shuttle vectors infectious for monkey cells

We describe SV40-based Escherichia coli shuttle vectors which can be packaged as pseudovirions without excision of plasmid sequences and which can be rescued in bacteria. These vectors replicate and are transmitted as virus in monkey COS cells without requiring a helper virus. Extrachromosomal vector DNA isolated from infected cells can be rescued in E. coli, so that DNA alterations can be easily screened. Indeed, some of the constructions give rise to very stable plasmids with no detectable rearrangements after multiple lytic cycles in COS cells. The spontaneous mutation frequency measured in bacteria, on the lacO target, is smaller than those usually found with shuttle vectors. We also constructed an expression vector derived from one of our infectious viruses by inserting the chloramphenicol acetyl transferase gene, expressed from the SV40 early promoter, which is efficiently transduced to cells by infection. In this system, the shuttle virus combines the convenience of plasmid rescue and analysis in bacteria, with the advantages of infectious virus.