Development of CRTEIL and CETRIZ, Cre-loxP-Based Systems, Which Allow Change of Expression of Red to Green or Green to Red Fluorescence upon Transfection with a Cre-Expression Vector

Table 1

Summary of efficiency of Cre-mediated recombination in NIH3T3 cells after cotransfection with tester and Cre-expression constructs.

		No gene switching^1	Complete gene switching^1	Incomplete gene switching^1
Plasmid construct(s) used	Total number of cells examined	No. of cells expressing only HcRed1-derived fluorescence (%)	No. of cells expressing only EGFP-derived fluorescence (%)	No. of cells expressing both types of fluorescence (%)
pCRTEIL	102	36 (35)	0 (0)	0 (0)
pCRTEIL + pCAG/NCre	112	27 (24)	4 (4)	10 (9)

¹Cells one day after transfection were observed for fluorescence under a fluorescence microscope, and regions containing fluorescent and neighboring nonfluorescent cells were photographed. The fluorescent cells were classified into groups with no gene switching (cells exhibiting only red fluorescence; as exemplified by the cells (arrowed) in Figure 2(b)), complete gene switching (cells exhibiting only green fluorescence; as exemplified by the cell (indicated by arrowheads) in Figures 2(e), 2(f)), or incomplete gene switching (cells exhibiting both fluorescence; as exemplified by the cell (arrowed) in Figures 2(e), 2(f)). Regions comprising 30–40 cells were photographed, and fluorescent cells were scored. The numbers of cells in a total of 3 regions are listed in the table.