Intensity Modulation of Trichromatic Split Fluorescent Proteins for Live Cell Mapping

Multiplexed live cell-labeling technologies are essential tools for investigating complex biological systems, yet existing approaches face limitations in achieving reliable discrimination of multiple cell populations. Here, we present color and intensity modulation with split fluorescent proteins for cell labeling (Caterpie), a live cell labeling system that enables high-fidelity identification of multiple cell populations through rational design of split fluorescent proteins. Drawing inspiration from human trichromatic vision, we engineered optimized split fluorescent protein variants--split CFP2, split mNG3A, and split sfCherry3C--and developed a comprehensive library of the 11th {beta}-strand (FP11) tags comprising variable numbers of tandem repeats. Structure-guided protein engineering enhanced the performance of split mNG3A and split sfCherry3C through targeted modifications of their C-terminal sequences and binding interfaces, respectively. By systematically varying the composition and arrangement of FP11 repeats, we selected 20 distinct FP11 tags that enable robust cell population discrimination with 97% accuracy using conventional fluorescence microscopy. In these FP11 tag-expressing cells, we expressed multiple EGF ligands and their receptors and cultured them in bulk to examine the effects of EGF signaling on chemotaxis within the cell population. The results showed that chemotaxis changes according to the intensity of EGFR signaling. The Caterpie system holds significant potential for applications requiring precise identification and tracking of multiple cell populations in complex biological systems.