Experimental Animal Division

The Cre-loxP and Flp-FRT systems are very useful tools for time- and space-specific gene knockout [1]. Drs. Imayoshi and Kageyama generated multifunctional fluorescent reporter mice that strongly express monomeric teal fluorescent protein (mTFP1) after Cre- and/or Flp-mediated recombination [2]. mTFP1 is an improved variant of tetrameric cyan fluorescent protein (CFP) cFP484 from Clavularia coral. The reporter cassette was inserted into the Gt(ROSA)26Sor locus (R26-CAG-LF-mTFP1). The germline excision of the Frt-flanked stop cassette in R26-CAG-LFmTFP1 generates a Cre-dependent reporter (R26-CAG-LoxP-mTFP1). Similarly, R26-CAG-FRT-mTFP1, in which the loxP-flanked stop cassette is excised in the germline, requires only Flp to activate mTFP1 expression. These reporter mice are useful for monitoring Cre/Flp expression in tissues, and tracing the lineage of cells in embryos and adult mice at desired time points.

Drs. Imayoshi and Kageyama recently reported new mouse strains that express modifiedNatronomonas pharaonis halorhodopsin (eNpHR2)-EYFP fusion proteins after Cre- and/or Flp-mediated recombination in order to silence neural activity in vivo [3]. Optogenetic strategies for controlling neuronal activity have been widely employed for mapping functional circuits within the nervous system. These mouse strains also offer powerful tools for light-induced silencing of neural activity in genetically defined cell populations.