Connexin57 is expressed in dendro‐dendritic and axo‐axonal gap junctions of mouse horizontal cells and its distribution is modulated by light

Abstract

Mouse horizontal cells are coupled by gap junctions composed of connexin57. These gap junctions are regulated by ambient light via multiple neuromodulators including dopamine. In order to analyze the distribution and structure of horizontal cell gap junctions in the mouse retina, and examine the effects of light adaptation on gap junction density, we developed antibodies that detect mouse retinal connexin57. Using immunohistochemistry in retinal slices, flat-mounted retinas, and dissociated retinal cells, we showed that connexin57 is expressed in the dendrites and axon terminal processes of mouse horizontal cells. No staining was found in retinas of connexin57-deficient mice. Significantly more connexin57-positive puncta were found in the distal than in the proximal outer plexiform layer, indicating a higher level of expression in axon terminal processes than in the dendrites. We also examined the gap junctions using immunoelectron microscopy and showed that connexin57 does not form hemichannels in the horizontal cell dendritic tips. Light adaptation resulted in a significant increase in the number of connexin57-immunoreactive plaques in the outer plexiform layer, consistent with previously reported effects of light adaptation on connexin57 expression in the mouse retina. This study shows for the first time the detailed location of connexin57 expression within mouse horizontal cells, and provides the first ultrastructural data on mouse horizontal cell gap junctions.

ZO-1 and the Spatial Organization of Gap Junctions and Glutamate Receptors in the Outer Plexiform Layer of the Mammalian Retina

“…The connexin of dendrites of B-type cells is not yet known. In mouse, Cx57 is expressed on both dendrites and axon terminals of the horizontal cells (Janssen-Bienhold et al, 2009). However, ZO-1 is only expressed and colocalized with Cx57 on the horizontal cell dendrites beneath the cone pedicles, and not on the axon terminals.…”

“…Horizontal cell coupling is regulated by ambient light (Xin and Bloomfield, 1999) via neuromodulators such as dopamine and retinoic acid (Teranishi et al, 1983;Perlman and Ammermüller, 1994;He et al, 2000;Pottek and Weiler, 2000). Horizontal cells in mouse are coupled by gap junctions composed of Cx57 (Hombach et al, 2004;Shelley et al, 2006;Janssen-Bienhold et al, 2009); A-type horizontal cells in rabbit retina are coupled by Cx50 (O'Brien et al, 2006). Furthermore, numerous proteins have been identified that may be involved in the mechanism of gap-junctional coupling.…”

Ablation of Retinal Horizontal Cells from Adult Mice Leads to Rod Degeneration and Remodeling in the Outer Retina

“…Immunohistochemistry and confocal image acquisition were performed as described previously (Janssen-Bienhold et al, 2009). Briefly, eyecups of Cx57ϩ/ϩ (n ϭ 6) and Cx57ϩ/DTR mice (n ϭ 6) were fixed with 2% paraformaldehyde in 0.1 M phosphate buffer (PB) for 20 min.…”

“…Mouse horizontal cells are electrically coupled by gap junctions made of connexin57 (Cx57) (Hombach et al, 2004;Shelley et al, 2006;Janssen-Bienhold et al, 2009), forming an extensive network that feeds back onto photoreceptors and feeds forward to bipolar cells. In photoreceptors, two morphologically distinct types of synaptic contacts have been characterized: flat contacts and invaginating synapses called "triads."…”

Expression and modulation of connexin30.2, a novel gap junction protein in the mouse retina

“…As we found the coupling of RG A1 and displaced amacrine cells also unimpaired in Cx45-deficient and Cx40 À/À mice, we conclude that the displaced amacrine cells did not express Cx36, Cx45, or Cx40. Since the only other known neuronal connexin in the mouse retina, Cx57, is expressed exclusively in horizontal cells (Hombach et al, 2004;Janssen-Bienhold et al, 2009), we conclude that the displaced amacrine cells coupled to RG A1 cells most likely express a yet unidentified connexin.…”