Junko mice are transgenic mice expressing nucleus-localized förster (or fluorescence) resonance energy transfer (FRET) biosensor JNKAREV-NLS monitoring PKA kinase activity under the control of CAG promoter in whole body. The c-Jun N-terminal kinase (JNK) is belong to MAPK family and activated by environmental stress such as UV or temperature, inflammatory cytokine, growth factor, etc. It's possible to measure JNK kinase activity spatially and temporally in fetal or adult various tissues by live imaging observation of this strain in the two-photon microscopy. This strain expects not only to analyze the signal transduction cascade in live animals, but also apply drug development such as the pharmacodynamic analysis targeting signal molecules, because these mice are showed rich expression in primary cultured cells derived from various tissues. In the case of using epithelial tissues when you detect the difference of JNK activity in cell lines, nucleus-localized FRET biosensor is easier to use. However, this strain is difficult to observe cell forms, therefore it's necessary to coincidentally express the marker for identifing cells in some tissues. FRET biosensor generally can't use for fixed samples.