The HEK293 tau biosensor cells express both cyan fluorescent protein (CFP) and yellow fluorescent protein (YFP) tagged forms of the tau K18 fragment with the P301S mutation and form bright FRET+ (Förster resonance energy transfer) tau aggregates upon lipofection of exogenous tau seeds isolated from the brains of Tg2541 (P301S) tauopathy mice (24). The gene discussed is CFP; the disease is tauopathy.