Application of droplet digital PCR in the analysis of genome integration and organization of the transgene in BAC transgenic mice

Transgenic (Tg) mice containing bacterial artificial chromosome (BAC) DNA are widely used for gene expression analysis and gene therapy models because BAC transgenes provide gene expression at physiological levels with the same developmental timing as endogenous genes. To ensure correct interpretation of transgene functions, investigation of the genomic organisation and integration of the BAC transgene is required. Here, we describe a reliable method based on droplet digital PCR (ddPCR) and inverse PCR to estimate copy number, genomic organisation and insertion sites of BAC transgenes in the mouse genome. We generated BAC Tg mice containing fragments of BAC clone RP23-59P20. ddPCR and iPCR analysis showed that the transgene consisted of five fragments of the BAC clone containing the Mkrn3 gene region, and that the transgene was inserted into Bckdhb, homozygous deletion of which causes the maple syrup urine disease phenotype. The ddPCR method described here should prove useful for analysis of genomic organisation and integration of BAC transgenes.