One of the grant challenges for biological research is to visualize the localization and function of cells in live mammals with high resolution; the same is true for visualizing the distribution of the chemicals that drive life. Such imaging on the level of organs, tissues or the whole animal is indispensable to understand the “bigger picture”. Current whole animal imaging techniques are either limited in the richness of detail (resolution), their ability to capture a whole tissue in a holistic fashion (volume-of-view / penetration depth), the availability of labels for unperturbed and targeted imaging of specific cells or chemical distributions and finally their potential to work in vivo.
A methodology that can overcome those limitations can be an indispensable driver to advance our fundamental understanding of organismal functioning and advance bio-medical research necessary to counter pathophysiologies. In this regard, the tumor micro-environment (TME) is a prime example of a pathophysiological state characterized by a complex and highly interdependent mosaic. High resolution imaging (resolving single cells or small populations) of immune cell infiltration with respect to concentrations of specific chemicals in the tumor, for example, is crucial in understanding the disease and develop therapeutic strategies. The same is true for numerous other questions in immunology, developmental- or neurobiology. All are characterized by the necessity to resolve spatial and temporal patterns of cell populations and chemical distributions on the level of whole tissues or the animal in vivo.
The project aims to advance an in vivo imaging modality that combines high resolution, large volume of views and availability of genetically encoded labels. The project builds on opto- or photoacoustic imaging; a young methodology that affords deep penetration in tissue at comparably high resolution by detecting ultrasound signals upon illumination. The technique already proofed to be valuable in research and clinical imaging by visualizing for example the vessel infrastructure whose aberrations are indicative of many pathophysiologies. To date optoacoustic imaging however lacks a successful way to employ targeted labels alike fluorescent proteins in fluorescence microscopy (Nobel Prize 2008). We seek to implement such genetically encoded labels tailored for optoacoustic imaging and with this enable the use of optoacoustic as a method for high resolution in vivo research imaging of labeled cells and molecular distribution allowing us to see the “bigger picture”. This goal will be achieved by relying on protein-engineered photoswitching proteins. This class of proteins can be switched between an ON and OFF state by illumination with two different wavelengths. Accordingly, alternating illumination results in the modulation of the optoacoustic signal. Thus, the modulating signal of cells expressing a photoswitchable reporter can be used to discriminate those cells from the non-modulating tissue background in vivo – rendering the latter virtually invisible – hence, Switch2See.
