Combining near-infrared fluorescence with Brainbow to visualize expression of specific genes within a multicolor context.

Fluorescent proteins are a powerful experimental tool, allowing the visualization of gene expression and cellular behaviors in a variety of systems. Multicolor combinations of fluorescent proteins, such as Brainbow, have expanded the range of possible research questions and are useful for distinguishing and tracking cells. The addition of a separately driven color, however, would allow researchers to report expression of a manipulated gene within the multicolor context to investigate mechanistic effects. A far-red or near-infrared protein could be particularly suitable in this context, as these can be distinguished spectrally from Brainbow. We investigated five far-red/near-infrared proteins in zebrafish: TagRFP657, mCardinal, miRFP670, iRFP670, and mIFP. Our results show that both mCardinal and iRFP670 are useful fluorescent proteins for zebrafish expression. We also introduce a new transgenic zebrafish line that expresses Brainbow under the control of the neuroD promoter. We demonstrate that mCardinal can be used to track the expression of a manipulated bone morphogenetic protein receptor within the Brainbow context. The overlay of near-infrared fluorescence onto a Brainbow background defines a clear strategy for future research questions that aim to manipulate or track the effects of specific genes within a population of cells that are delineated using multicolor approaches.