Cre-Lox manipulation is the gold standard for cell-specific expression or knockout of selected genes. However, it is not unusual to deal with conditions of low Cre expression or transient activation, which can often go undetected by conventional Cre- reporters. We designed Beatrix, a general-purpose tool specifically devised to amplify weak Cre recombinase activity, and we used it to develop a powerful approach for the in vivo generation and detection of sparse mosaics of mutant and wild type cells.

A Cre-amplifier to generate and detect genetic mosaics in vivo