Investigation of Schizosaccharomyces pombe as a cloning host for human telomere and alphoid DNA

Retrofitting BACs with G418 resistance, luciferase, and oriP and EBNA-1 - new vectors for in vitro and in vivo delivery

BACKGROUND

Bacterial artificial chromosomes (BACs) have been used extensively for sequencing the human and mouse genomes and are thus readily available for most genes. The large size of BACs means that they can generally carry intact genes with all the long range controlling elements that drive full levels of tissue-specific expression. For gene expression studies and gene therapy applications it is useful to be able to retrofit the BACs with selectable genes such as G418 resistance, reporter genes such as luciferase, and oriP/EBNA-1 from Epstein Barr virus which allows long term episomal maintenance in mammalian cells.

RESULTS

We describe a series of retrofitting plasmids and a protocol for in vivo loxP/Cre recombination. The vector pRetroNeo carries a G418 resistance cassette, pRetroNeoLuc carries G418 resistance and a luciferase expression cassette, pRetroNeoLucOE carries G418 resistance, luciferase and an oriP/EBNA-1 cassette and pRetroNeoOE carries G418 resistance and oriP/EBNA-1. These vectors can be efficiently retrofitted onto BACs without rearrangement of the BAC clone. The luciferase cassette is expressed efficiently from the retrofitting plasmids and from retrofitted BACs after transient transfection of B16F10 cells in tissue culture and after electroporation into muscles of BALB/c mice in vivo. We also show that a BAC carrying GFP, oriP and EBNA-1 can be transfected into B16F10 cells with Lipofectamine 2000 and can be rescued intact after 5 weeks.

CONCLUSION

The pRetro vectors allow efficient retrofitting of BACs with G418 resistance, luciferase and/or oriP/EBNA-1 using in vivo expression of Cre. The luciferase reporter gene is expressed after transient transfection of retrofitted BACs into cells in tissue culture and after electroporation into mouse muscle in vivo. OriP/EBNA-1 allows stable maintenance of a 150-kb BAC without rearrangement for at least 5 weeks.

Simple and efficient vectors for retrofitting BACs and PACs with mammalian neoR and EGFP marker genes

Bacterial artificial chromosomes (BACs) and P1 artificial chromosomes (PACs) are widely used to investigate the functions of genes and genomes in mammalian cells in vitro and in vivo. We have developed a series of vectors which can simply and efficiently be retrofitted onto BACs or PACs. These vectors carry a neoR gene for selection in cells in tissue culture, including ES cells, and also an EGFP gene driven by the strong CAG promoter for quick detection of the DNA in cells. All the plasmids are retrofitted using the loxP site and Cre recombinase and some carry the gamma origin of plasmid R6K which does not function in commonly used bacteria such as DH10B. Retrofitting of PACs and BACs carrying alphoid DNA was very efficient with almost no rearrangement of the highly repetitive alphoid DNA. Following transfer into HT1080 cells and mouse oocytes in tissue culture the DNA could easily be monitored by the EGFP fluorescence.