In vivo binary genetic mosaics via Beatrix: a reliable sensor of cell genome obtained by a regenerative amplifier of Cre activity

Genetic mosaicism is a condition in which an organ includes cells with different genotypes. The difference can be due to the mutation of a single gene, as it is often the case with several monogenic diseases of the central nervous system, where the mosaicism is caused either by somatic mutations affecting only a subset of cells, or by the random inactivation of the X chromosome, in the case of X-linked pathologies. The understanding of the mechanistic basis of these diseases would benefit by the creation of models where the genotype of each cell is univocally identified by the expression of a fluorescent reporter. The most used strategy for the control of gene expression relies on the use of the CRE-LoxP system, where the gene of interest can be turned on or off by the activity of CRE recombinase. Here we developed a Cre fluorescent reporter system capable of enhancing Cre recombinase activity that provides increased sensitivity and absolute specificity. This reporter system is designed for the creation of genetic mosaics that can be analyzed in vivo by means of two-photon microscopy. This system allows the study of cell-autonomous effects produced by the mutation of a single gene in vivo by a variety of imaging and electrophysiological techniques.