Myosin VI facilitates connexin 43 gap junction accretion

Abstract

In this study, we demonstrate myosin VI enrichment at Cx43 gap junctions in heart tissue, primary cardiomyocytes and cell culture models. The loss of myosin VI via siRNA-mediated knock down or isolation of primary cardiac tissue and fibroblasts from the myosin VI-null mouse results in reduced GJ plaque size with a concomitant reduction in intercellular communication as shown by FRAP and a new method of selective calcein administration. Analysis of the molecular role of myosin VI in Cx43 trafficking indicates that myosin VI is dispensable in the delivery of Cx43 to the cell surface and connexon movement in the plasma membrane. Furthermore, we cannot corroborate clathrin or Dab2 localization at gap junctions and we do not observe myosin VI/Dab2 complex function in clathrin-dependent endocytosis of annular gap junctions. Instead, we visualize myosin VI at the edge of Cx43 plaques using TIRF microscopy and use FRAP to identify a plaque accretion defect as the primary manifestation of myosin VI loss in Cx43 homeostasis. A fuller understanding of this derangement may explain the cardiomyopathy or astrogliosis associated with the loss of myosin VI.