Knockout First Allele Design
Since 1998, ingenious targeting laboratory has generated over 2,500 custom mouse models employing diverse targeting strategies, with hundreds specifically utilizing knockout first allele designs to maximize flexibility and enable generation of multiple derivative alleles from single ES cell clone. This strategic approach reduces overall project costs while providing researchers maximal options for downstream experimental applications.
Knockout first alleles represent a paradigm shift in mouse model design, where a single initial targeting event creates an allele capable of generating conditional knockout, conventional knockout, and reporter knockin variations through complementary recombination strategies. This methodology has become standard practice for most modern mouse genetics projects where experimental questions might evolve during multiyear research programs.
Start your project today
Our scientific consultants are ready to discuss your research requirements and recommend the optimal approach for your program. Initial consultation is provided at no charge.
Frequently asked questions
tm1a represents the original targeted allele with selection cassette and reporter intact. tm1b and tm1c are FLP excised derivatives with selection markers removed. tm1d represents Cre mediated exon excision creating conventional null allele. tm1a is hypomorphic/null, tm1b and tm1c are conditional ready, and tm1d is conventional null.
Standard knockout first alleles with LacZ reporters provide reporter knockin function in tm1a configuration. More complex reporter combinations or fluorescent proteins require custom vector design beyond standard knockout first approach, though knockout first framework provides foundation for these applications.
FLP transgenic crosses typically achieve 90 to 95% conversion of tm1a to tm1c in F1 generation. Incomplete conversion reflects low background FLP mediated recombination in wild type tissues. Researchers should screen F1 pups to identify fully converted tm1c mice.
Standard knockout first design works well for typical single exon targeting (5 to 10 kilobases). Large insert applications require custom vector engineering but can incorporate knockout first principles. BAC targeting typically employs alternative approaches due to vector size constraints, though some BAC projects incorporate LoxP sites for conditional design.
Initial characterization often benefits from tm1d conventional null to establish gene essential role before tissue specific studies identify where function occurs. However, if embryonic lethality is anticipated, tissue specific tm1c lines may provide earlier research progress than null approaches.