Analysis of Myosin II Minifilament Orientation at Epithelial Zonula Adherens

Non-muscle myosin II (NMII) form bipolar filaments, which bind F-actin to exert cellular contractility during physiological processes (Vicente-Manzanares et al., 2009). Using a combinatorial approach to fluorescently label both N- and C-termini of the NMII heavy chain, recent works have demonstrated the ability to visualize NMII bipolar filaments at various subcellular localizations (Ebrahim et al., 2013; Beach et al., 2014). At the zonula adherens (ZA) of epithelia, NMII minifilaments bind the circumferential actin bundles in a pseudo-sarcomeric manner (Ebrahim et al., 2013), a conformation required to maintain junctional tension and tissue integrity (Ratheesh et al., 2012). By expressing green fluorescent protein (GFP)-NMIIA heavy chain and immunolabel it using a NMIIA C-terminus specific antibody, we were able to visualize the NMII minifilaments bound to F-actin bundles in Caco-2 cells (Michael et al., 2016), as previously reported (Ebrahim et al., 2013; Beach et al., 2014). In addition, we designed an FIJI/MATLAB analysis module to quantify the size, distance and alignment of these minifilaments with respect to junctional F-actin at the ZA. Measurements of the dispersion of minifilaments angles were proven to be a useful parameter that closely correlated to the extent of contractility at junctions (Michael et al., 2016).