Four-color, 4-D time-lapse confocal imaging of chick embryos.

Our understanding of the molecular mechanisms that direct cell motility, cell division, and cell shaping has benefited from innovations in cell labeling and the ability to resolve intracellular dynamics with multispectral, high-resolution imaging. However, due to difficulties with in vivo cell marking and monitoring, most studies have been restricted to fixed tissue or cells in culture. Here, we report the delivery of multiple (up to four), multicolor fluorescent protein (FP) constructs and four-dimensional (4-D), multispectral time-lapse confocal imaging of cell movements in living chick embryos. Cell cytoskeletal components are fluorescently tagged after microinjection and electroporation of a cocktail of FP constructs into specific regions of chick embryos. We tested 11 different FP constructs in various two-, three-, and four-color combinations using multispectral imaging and linear unmixing to limit the crosstalk between different emission spectra. We monitored intracellular dynamics in individual multicolored migrating cells in vivo and developed a set of advantageous imaging parameters for 4-D time-lapse confocal microscopy. We find that the number of four-color labeled cells in a typical embryo is approximately 10% of the total number of fluorescently labeled cells; this value consistently increases showing that approximately 50% of the total labeled cells have only one-color. We find that multicolored cells are photostable for time-lapses of approximately 2-3 h. Thus, cell labeling with up to four FP color schemes combined with multispectral, 4-D confocal time-lapse imaging offers a powerful tool to simultaneously analyze cellular and molecular dynamics during chick embryogenesis.