Activation of EGFP expression by Cre-mediated excision in a new ROSA26 reporter mouse strain

Reporter mouse strains are important tools for monitoring Cre recombinase-m ediated excision in vivo. In practice, excision may be incomplete in a give n population due to threshold level or variegated expression of Cre, Hence, it is desirable in many experimental contexts to isolate cells that have u ndergone excision to assess the consequences of gene ablation, To generate alternative reporter mice, an enhanced green fluorescent protein (EGFP) gen e was targeted to the retroviral-trapped ROSA26 locus, Upon Cre-mediated ex cision of "Stop" sequences, EGFP was expressed ubiquitously during embryoge nesis and in adult tissues (including T cells, B cells, and myeloid cells). Using this new reporter strain, separation of excised from nonexcised cell s in vitro was achieved in thymocytes in a noninvasive manner based on acti vated EGFP expression. This new EGFP reporter strain should facilitate a va riety of conditional gene-targeting experiments, including the functional s tudies of hematopoietic cells in lineage-specific knockout mice. (C) 2001 b y The American Society of Hematology.