The Tol2 FLEX conditional Cre-Switch gene expression vector combines VectorBuilder’s highly efficient Tol2 vector system with the Cre-responsive FLEX conditional gene expression system to help you achieve transfection-mediated permanent integration of FLEX switch into the host genome for Cre-induced switching between the expression of two ORFs. The FLEX Cre-Switch system utilizes two pairs of LoxP-variant recombination sites flanking two antiparallel ORFs in an arrangement which facilitates activation of one gene while repressing the other by Cre-dependent inversion of both ORFs.
The FLEX Cre-Switch system consists of two pairs of heterotypic LoxP-variant recombination sites, namely LoxP, having the wild type sequence and Lox2272, having a mutated sequence flanking a pair of ORFs. Both LoxP variants are recognized by Cre, but only identical pairs of LoxP sites can recombine with each other and not with any other variant. The two ORFs are in an opposite orientation with respect to one-another, such that one ORF is in its proper sense orientation, while the other is in an antisense orientation. The LoxP and Lox2272 sites are organized in an alternating fashion, with an antiparallel orientation for each pair. In the absence of Cre recombinase, while the first ORF is expressed under the control of the user-selected promoter, the second ORF is not expressed due to its antisense orientation. In the presence of Cre, the LoxP and Lox2272 sites undergo recombination with the other LoxP and Lox2272 sites respectively, resulting in the inversion of both ORFs and excision of one from each pair of identical recombination sites. Inversion of the ORFs results in silencing of the first ORF (which will now be in an antisense orientation) and allows expression of the second ORF (which will now be in a sense orientation).
The Tol2 vector system is technically simple, utilizing plasmid transfection (rather than viral transduction) to permanently integrate your gene(s) of interest into the host genome. The Tol2 FLEX conditional Cre-Switch gene expression system contains two vectors, both engineered as E. coli plasmids. One vector, referred to as the helper plasmid, encodes the transposase. The other vector, referred to as the transposon plasmid, contains two terminal repeats (TRs) bracketing the region to be transposed. The FLEX Cre-Switch described above is cloned into this region.
When the transposon and helper plasmids are co-transfected into target cells, the transposase produced from the helper plasmid would recognize the two ITRs on the transposon and inserts the flanked FLEX Cre-Switch including the two ITRs into the host genome. Insertion occurs without any significant bias with respect to insertion site sequence. This is unlike transposon systems which have specific target consensus sites. For example, piggyBac transposons typically inserts at sites containing the sequence TTAA. Expression of the second ORF in the FLEX Cre-Switch can then be activated while silencing the first ORF in the presence of Cre recombinase, upon Cre-mediated inversion of both ORF sequences.
While this vector system can be used in tissue culture cells, it is particularly suitable for the generation of transgenic animals. Transgenic animals carrying such a vector originally express the first user-selected ORF, however when crossed to an animal carrying a tissue-specific Cre transgene, expression of the second user-selected ORF will be activated while silencing the first ORF in the progeny animals carrying both types of transgenes, specifically in cells where the tissue-specific Cre is expressed and the user-selected promoter is active.
Tol2 is a class II transposon, meaning that it moves in a cut-and-paste manner, hopping from place to place without leaving copies behind. (In contrast, class I transposons move in a copy-and-paste manner.) Tol2 integrates as a single copy through a cut-and-paste mechanism. At each insertion site, the Tol2 transposase creates an 8 bp duplication, resulting in identical 8 bp direct repeats flanking each transposon integration site in the genome.
For further information about this vector system, please refer to the papers below.