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Polarized fluorescence microscopy is a valuable tool for measuring molecular orientations in biological samples, but techniques for recovering three-dimensional orientations and positions of fluorescent ensembles are limited. We report a polarized dual-view light-sheet system for determining the diffraction-limited three-dimensional distribution of the orientations and positions of ensembles of fluorescent dipoles that label biological structures. We share a set of visualization, histogram, and profiling tools for interpreting these positions and orientations. We model the distributions based on the polarization-dependent efficiency of excitation and detection of emitted fluorescence, using coarse-grained representations we call orientation distribution functions (ODFs). We apply ODFs to create physics-informed models of image formation with spatio-angular point-spread and transfer functions. We use theory and experiment to conclude that light-sheet tilting is a necessary part of our design for recovering all three-dimensional orientations. We use our system to extend known two-dimensional results to three dimensions in FM1-43-labeled giant unilamellar vesicles, fast-scarlet-labeled cellulose in xylem cells, and phalloidin-labeled actin in U2OS cells. Additionally, we observe phalloidin-labeled actin in mouse fibroblasts grown on grids of labeled nanowires and identify correlations between local actin alignment and global cell-scale orientation, indicating cellular coordination across length scales. 

Significance Tumor progression to enable metastasis includes remodeling the wavy bundles of collagen making up the tissue stromal extracellular matrix (ECM) into straight bundles within the tumor microenvironment. While wavy collagen bundles are thought to be inhibitory to cell polarization and migration in tissue, straight ECM fibers are thought to be conducive, thereby mediating metastasis. We used nanofabricated cell culture substrates that mimic the ECM fiber waveforms seen in both benign- and metastases-promoting tumor ECMs. Large amplitude ECM waves depolarized tumor cells and decreased directional migration via cell contractility-mediated organization of the cytoskeleton and adhesions. Thus, ECM architecture of normal tissue and benign tumors may generally inhibit tumor cell exit, but this may be overcome by increasing tumor cell contractility.