Use of ERT2‐iCre‐ERT2 for conditional transgenesis

Abstract We examined the use of ERT2‐iCre‐ERT2 (Cre2ERT2), a tamoxifen‐regulated form of Cre that has been described to have a background activity lower than that of other tamoxifen‐regulated Cre constructs, for establishing performant conditional deleter mouse lines. Cre2ERT2 was inserted by homologous recombination into the Rosa26 locus. These mice were mated with R26R Cre‐reporter mice. No recombination could be observed in the progenies in the absence of tamoxifen treatment. Tamoxifen treatment at E13‐14 led to a high level, albeit variable, recombination in most of the tissues examined: liver, heart, kidney, brain, lung etc. Treatment of adult animals also induced recombination in these tissues, although at a lower level. Northern blot and qPCR studies suggested that these differences are not linked to significant variations of the level of expression of Cre2ERT2. Thus, Cre2ERT2 appears to be a good alternative to existing modulatable Cre systems, displaying a lack of background activity and a high‐level inducibility in vivo. genesis 46:193–199, 2008. © 2008 Wiley‐Liss, Inc.