Long-term in vivo single-cell lineage tracing of deep structures using three-photon activation

Activating a labeling compound using three rather than two photons permits the progeny of cells in deep tissues to be traced. Genetic labeling techniques are powerful methods for identifying the progeny of a cell in vivo. Previously, protein expression in cells had been activated by two photons, but it is limited to cells near the surface due to the high scattering of the red photons used. Now, Angel Raya of the Center of Regenerative Medicine in Barcelona, Dobryna Zalvidea of the Institute for Bioengineering of Catalonia and co-workers in Spain and France show experimentally and theoretically that this limitation can be overcome by using three photons of longer wavelength. They labeled heart muscle cells in zebrafish embryos and found that progeny of these cells in adult fish were permanently labeled without causing noticeable tissue damage. This technique is promising for activating different proteins in vivo.