Cx29 and Cx32, two connexins expressed by myelinating glia, do not interact and are functionally distinct

Abstract

In rodents, oligodendrocytes and myelinating Schwann cells express connexin32 (Cx32) and Cx29, which have different localizations in the two cell types. We show here that, in contrast to Cx32, Cx29 does not form gap junction plaques or functional gap junctions in transfected cells. Furthermore, when expressed together, Cx29 and Cx32 are not colocalized and do not coimmunoprecipitate. To determine the structural basis of their divergent behavior, we generated a series of chimeric Cx32-Cx29 proteins by exchanging their intracellular loops and/or their C-terminal cytoplasmic tails. Although some chimerae reach the cell membrane, others appear to be largely localized intracellularly; none form gap junction plaques or functional gap junctions. Substituting the C-terminus or the intracellular loop and the C-terminus of Cx32 with those of Cx29 does not disrupt their colocalization or coimmunoprecipitation with Cx32. Substituting the C-terminus of Cx29 with that of Cx32 does not disrupt the coimmunoprecipitation or the colocalization with Cx29, whereas substituting both the intracellular loop and the C-terminus of Cx32 with those of Cx29 diminishes the coimmunoprecipitation with Cx29. Conversely, the Cx32 chimera that contains the intracellular loop of Cx29 coimmunoprecipitates with Cx29, indicating that the intracellular loop participates in Cx29-Cx29 interactions. These data indicate that homomeric interactions of Cx29 and especially Cx32 largely require other domains: the N-terminus, transmembrane domains, and extracellular loops. Substituting the intracellular loop and/or tail of Cx32 with those of Cx29 appears to prevent Cx32 from forming functional gap junctions.

Human oligodendrocytes express Cx31.3: Function and interactions with Cx32 mutants

“…Rather, Cx32 and Cx47 are the primary connexins on the oligodendrocyte side of A:O GJs. Like Cx29 (Ahn et al 2007), Cx31.3 does not form GJ plaques or functional GJs by either dye transfer or electrophysiological assays in transfected cells. How Cx29/Cx31.3 functions in oligodendrocytes is unknown, but its localization on the adaxonal membrane of small myelinated axons (facing the periaxonal space) leads to the speculation that it forms hemichannels (Altevogt et al 2002;Kamasawa et al 2005;Kleopa et al 2004;Menichella et al 2006).…”

Panglial Gap Junctional Communication is Essential for Maintenance of Myelin in the CNS

“…Gap junction channels are formed among astrocytes (A/A), among oligodendrocytes (O/ O), and between oligodendrocytes and astrocytes (O/A), which results in formation of panglial networks (Wallraff et al, 2006;Maglione et al, 2010;Wasseff and Scherer, 2011). Since Cx29 does not form functional gap junction channels in cell culture experiments and Cx26 expression is limited to few gray matter astrocytes, panglial networks are mainly formed by astrocytic Cx43 and Cx30 and oligodendrocytic Cx47 and Cx32 (Ahn et al, 2008;Giaume and Theis, 2010;Nagy et al, 2011).…”

Analysis of human alternative first exons and copy number variation of the GJA12 gene in patients with Pelizaeus–Merzbacher‐like disease

“…The observed variation of most of the analyzed samples is between 0.80 and 1.20 regarding to the calibrator sample. All RQ results of this analysis are listed in Supplementary Table I. display any abnormalities [Eiberger et al, 2006], and it was shown that the protein does not form fully functional intercellular channels [Ahn et al, 2008]. Another gap junction protein seems to be important for oligodendrocytic homeostasis although not expressed by oligodendrocytes: GJA1 is expressed by astrocytes, but was shown to be the interacting hemichannel partner of GJA12 [Orthmann-Murphy et al, 2007b].…”