Modulated polarization microscopy: A promising new approach to visualizingcytoskeletal dynamics in living cells

In an effort to visualize cytoskeletal filaments in living cells, we have d eveloped modulated polarization microscopy. Modulated polarization microsco py visualizes cytoskeletal filaments based on their birefringence but diffe rs from the standard polarization microscopy by exploiting the angle depend ence of birefringence, A prototype instrument has been developed using two Faraday rotators under computer control to change the angle of plane polari zed light at a known rate. By placing one Faraday rotator before and one af ter the specimen, rotation produced by the first Faraday rotator is cancell ed by the second. This allows the use of fixed polarizer and analyzer in a crossed configuration and continuous imaging of the specimen between crosse d polarizers. The variation in polarization angle of light illuminating the specimen causes birefringent elements to oscillate in brightness. Images a cquired as polarization angle is varied are then processed by a Fourier fil ter image-processing algorithm. The Fourier filtering algorithm isolates th ose signals that vary at the proper rate, whereas static or random signals are removed. Here we show that the modulated polarization microscope can re veal cytoskeletal elements including stress fibers and microtubules in livi ng cells.