Genetic and spectrally distinct in vivoimaging: embryonic stem cells and mice with widespread expression of a monomeric red fluorescent protein

Fluorescent proteins with excitation and/or emission profiles in the red part of the visible spectrum represent distinct partners, or longer wavelength substitutes for GFP. Not only do DsRed-based RFPs provide a genetically and spectrally distinct addition to the available repertoire of autoflorescent proteins, but by virtue of their spectral properties they permit deeper tissue imaging. Our work in generating CAG::mRFP1 transgenic ES cells and mice demonstrates the developmental neutrality of mRFP1 in an organismal context. It paves the way for the use of DsRed-based monomeric RFPs in transgenic and gene targeted approaches which often necessitate spatially and/or temporally restricted reporter expression. Moreover animals of the CAG::mRFP1 transgenic strain serve as a source of RFP tagged tissue for the derivation of cell lines and explant, transplant and embryo chimera experiments.