Three-color flow cytometry analysis of tricistronic expression of eBFP, eGFP, and eYFP using EMCV-IRES linkages

Abstract

The ability to quickly analyze and sort double or triple fluorescent reporter constructs using simultaneous analysis provides significant flexibility in the solution of analytical and process-related questions in biotechnology. Bicistronic eBFP/eGFP and eBFP/eYFP constructs were made on two mammalian episomal plasmids using an internal ribosomal entry sequence from encephalomyocarditis virus (EMCV-IRES) to link two GFP expressions. Simultaneous two-color flow cytometry (FCM) analysis was accomplished using a dual Argon-laser multi-line configuration set at excitation wavelengths of 360 and 488 nm. Blue fluorescence emission (440 nm) and green fluorescence emission (507 nm) were detected using 405/20 (FL4) and 510/20 (FL1) bandpass filters. Dual eBFP/eYFP and three-color simultaneous analysis of eBFP/eGFP/eYFP was accomplished using the dual-laser configuration but also using a short-pass (525-nm) dichroic mirror and 550/30 bandpass filter configuration to detect yellow fluorescence emission (527 nm) in a third channel (FL2). Human 293 cells transfected with the bicistronic construct of eBFP-IRES-eGFP were easily detected using simultaneous analysis, and the signals were well separated with a mean blue fluorescent intensity (MFI) in the 2nd-log decade (FL4) and green MFI in the 4th-log decade (FL1). Likewise, eBFP-IRES-eYFP transfected cells were as easily detected and also demonstrated very good signal separation. A tricistronic construct of eBFP-IRES-eGFP-IRES-eYFP was also made and transfected into 293 cells. Triple-color fluorescent cells were easily detected using the cytometer configuration for simultaneous analysis. All three signals separated with only moderate compensation required for green and yellow emission spectra. The respective MFI for each of the fluorescent proteins was correlative to what had been observed with the separate bicistronic constructs. Our results demonstrate that we have developed a novel fluorescent flow cytometry method that can be used as a powerful tool to differentiate and analyze three colors simultaneously from either a dual or a triple cistronic construct which has been transfected into living cells.