The present invention relates to the use of split fluorescent proteins to determine whether promoters are coordinately active, whereby the transcriptional expression of incomplete portions of a fluorescent protein is controlled by different promoters and coordinate (not necessarily contemporaneous) promoter activity results in the reconstitution of a fluorescent protein. The present invention, in non-limiting embodiments, may be used to selectively label cells and cell structures in vivo and to demonstrate changes in promoter activity (for example, in developmental biology and drug discovery applications).