Design and in vitro validation of the Kaleidoscope reporter. (A) The Kaleidoscope reporter construct diagram showing three fluorescent fusion proteins connected with 2A self-cleaving sequences (P2A and T2A) driven by a strong, constitutive promoter (CAG), interrupted by a transcriptional stop flanked by LoxP sites, followed by a stabilizing Woodchuck hepatitis virus posttranscriptional regulatory element (WPRE) and sandwiched between left and right homology arms targeting the ROSA26 locus (R26L and R26R). (B) Representative images of HEK 293T cells co-transfected with ROSA-Kaleidoscope and pCAG-Cre, showing distinct subcellular localization of the three fusion proteins, color coded as in A. Scale: 10 μm. (C) Sporadic epithelial cells in an E14.5 mouse lung electroporated with Cre-recombined ROSA-Kaleidoscope and cultured for 24 h. The enlarged cell is truncated by physical sectioning and thus does not reach the airway lumen, as the dimmer cell behind it does. Scale: 10 μm.