DIMERIZABLE CRE (DICRE) AS A TOOL FOR CONDITIONAL TRANSGENESIS: A FIRST EVALUATION
Nicolas JULLIEN, Samia SELMI-RUBY*, Isabelle GODDARD@, Jean-Luc FINA@, Harold CREMER# and Jean-Paul HERMAN
UMR 6544 – ICNE CNRS-Université de la Méditerranée and @ Centre de Transgenèse, IFR Jean-Roche, Faculté de
Médecine Nord, 13916 Marseille Cedex 20, France; *: INSERM UMR 664, Faculté de Médecine RTH-Laennec, 69372
Lyon Cedex 08, France; #: UMR 6216 – IBDML CNRS-Université de la Méditerranée, Parc Scientifique de Luminy,
13288 Marseille Cedex 9, France.
Cre recombinase is extensively used to engineer the genome of experimental animals. However, its usefulness is still
limited by the lack of an efficient temporal control over its activity. To overcome this, we have developed DiCre, a
regulatable fragment complementation system for Cre. The enzyme was split into two moieties that were fused to
FKBP12 (FK506-binding protein) and FRB (binding domain of the FKBP12-rapamycin associated protein),
respectively. These latter can be efficiently hetero-dimerized by rapamycin. After testing several variants, we have been
able to show, using in vitro approaches, that ligand-induced dimerization is an efficient way to regulate Cre activity,
and presents a low background activity together with a high efficiency of recombination following dimerization. We
have knocked-in the best pair into the ROSA26 locus of mice. To evaluate the performance of this system, mice have
been mated with indicator mice (Z/EG or R26R) and Cre-induced recombination was examined following activation of
DiCre by rapamycin during embryonic development or after birth of progenies. Recombination could be observed in
several (liver, heart, kidney, muscle), but far from all, tissues of progenies. Moreover, this recombination was highly
mosaic and did not extend to the whole extent of the tissue. It was also less important than that observed using another
conditional Cre-deleter mouse line that we have created for comparison, and that had the tamoxifene-regulated ERT2iCre-ERT2 construct expressed from the ROSA26 locus. In conclusion, we have documented that DiCre has indeed the
potentiality to be used to establish conditional Cre-deleter mice, however, its performance should be ameliorated before
its use could be generalized.