Reaching new depths: a non-invasive solution for the activation of proteins in deep tissues

Manipulating protein expression to monitor cell behavior is a powerful tool in the field of biology.

Until now, protein expression in cells had been activated by two photon illumination, but it was limited to cells near the surface due to the high scattering of the red photons used. The new study, published in a new high-impact Nature group journal Light: Science & Applications, reveals for the first time that activating a labeling compound using three photons of longer wavelength implies less scattering of photons traveling through tissues, therefore permitting the cell lineages in much deeper tissues to be manipulated.

“This innovative technique, based on photoactivation by three photon illumination, is a solution to the dispersion problem and enables the activation of proteins found in the cells in deeper tissues in vivo without interfering with the life expectancy of the animal,” says Dobryna Zalvidea, who led the study at IBEC.

The researchers labeled the heart muscle cells of zebrafish embryos and found that the cell lineages in adult fish were permanently marked without causing any noticable tissue damage. The method can also be extended to other tissues and animal models, as well as being useful to activate, with spatial and temporal resolution, the expression of different proteins to control the long-term behavior of individual cells or cell groups in vivo.

The method is based on a photoactivation system that uses an inactive encapsulated inductor (Cre-loxP) that penetrates deep inside the body but only becomes functional when activated by light. Once activated, the inductor is able to modify certain parts of the DNA of particular cells whose behaviour is being studied. In this way, protein expression is controlled and changes can be targeted to specific cell types by using an external stimulus as a trigger. The genetic modification persists throughout the life of the cell and is transmitted to its descendants.

The study was made possible thanks to MINECO, Programa I3, ISCII/FEDER, AGAUR, LA Fundación la Marató de TV3 and the ERC.

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Source article: Isil Tekeli, Isabelle Aujard, Xavier Trepat, Ludovic Jullien, Angel Raya & Dobryna Zalvidea (2016) Long-term in vivo single-cell lineage tracing of Deep structures using three-photon activation. Light: Science & applications, 5, 1-7

Image:Left: a heart from an adult zebrafish where the descendants of the labelled cells are visible in green. Right: magnification of the labelled area, showing photoactivated heart muscle cells in green, interspersed with unlabelled cells.