Fluorescence-detected linear dichroism microscopy allows observing various molecular processes in living cells, as well as obtaining quantitative information on orientation of fluorescent molecules associated with cellular features. Such information can provide insights into protein structure, aid in development of genetically encoded probes, and allow determinations of lipid membrane properties. However, quantitating and interpreting linear dichroism in biological systems has been laborious and unreliable. Here we present a set of open source ImageJ-based software tools that allow fast and easy linear dichroism visualization and quantitation, as well as extraction of quantitative information on molecular orientations, even in living systems. The tools were tested on model synthetic lipid vesicles and applied to a variety of biological systems, including observations of conformational changes during G-protein signaling in living cells, using fluorescent proteins. Our results show that our tools and model systems are applicable to a wide range of molecules and polarization-resolved microscopy techniques, and represent a significant step towards making polarization microscopy a mainstream tool of biological imaging.

Center for Nanobiology and Structural Biology Institute of Microbiology Czech Academy of Science Nove Hrady Czech Republic

CNRS Université de Paris UPR 9080 Laboratoire de Biochimie Théorique 13 rue Pierre et Marie Curie Paris France

Faculty of Sciences Charles University Prague Czech Republic

Groningen Biomolecular Sciences and Biotechnology Institute and the Zernike Institute for Advanced Materials University of Groningen Groningen Netherlands

Institut de Biologie Physico Chimique Fondation Edmond de Rothschild PSL Research University Paris France

Institute of Organic Chemistry and Biochemistry Czech Academy of Science Praha 6 Czech Republic

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