Visualizing compound transgenic zebrafish in development: a tale of green fluorescent protein and KillerRed.

Optically translucent embryos of model vertebrates expressing transgenic fluorescent proteins provide a possibility to unravel developmental events, particularly when combined with live imaging. An introduction of transposon-mediated transgenesis resulted in generation of a number of transgenics expressing cytosolic green fluorescent protein in a tissue-specific manner. The recent generation of photodynamic and differentially tagged fluorescent proteins opened a possibility not only to mix-and-match living markers of different color, but also to employ them as powerful experimental tools for studies of cell physiology. Using this approach, transgenic lines expressing membrane-tagged KillerRed (memKR), a genetically encoded photosensitizer, with little or no inducible phototoxicity under confocal imaging were generated. Phototoxicity is only induced by intense green or white light generated by the mercury lamp in a widefield mode. Here, we discuss new ideas born from experimentation using the zebrafish Tol2 transposon-mediated enhancer trap transgenic lines expressing memKR. Because of accumulation on the cell membrane, memKR reveals fine details of cellular morphology. In combination with cytosolic green fluorescent protein, the multicolor in vivo imaging of memKR transgenics reveals complex developmental processes and provides a possibility to manipulate them by regulated generation of reactive oxygen species.