Coupling of astrocyte connexins Cx26, Cx30, Cx43 to oligodendrocyte Cx29, Cx32, Cx47: Implications from normal and connexin32 knockout mice

Abstract

Oligodendrocytes in vivo form heterologous gap junctions with astrocytes. These oligodendrocyte/ astrocyte (A/O) gap junctions contain multiple connexins (Cx), including Cx26, Cx30, and Cx43 on the astrocyte side, and Cx32, Cx29, and Cx47 on the oligodendrocyte side. We investigated connexin associations at A/O gap junctions on oligodendrocytes in normal and Cx32 knockout (KO) mice. Immunoblotting and immunolabeling by several different antibodies indicated the presence of Cx32 in liver and brain of normal mice, but the absence of Cx32 in liver and brain of Cx32 KO mice, confirming the specificity and efficacy of the antibodies, as well as allowing the demonstration of Cx32 expression by oligodendrocytes. Oligodendrocytes throughout brain were decorated with numerous Cx30-positive puncta, which also were immunolabeled for both Cx32 and Cx43. In Cx32 KO mice, astrocytic Cx30 association with oligodendrocyte somata was nearly absent, Cx26 was partially reduced, and Cx43 was present in abundance. In normal and Cx32 KO mice, oligodendrocyte Cx29 was sparsely distributed, whereas Cx47-positive puncta were densely localized on oligodendrocyte somata. These results demonstrate that astrocyte Cx30 and oligodendrocyte Cx47 are widely present at A/O gap junctions. Immunolabeling patterns for these six connexins in Cx32 KO brain have implications for deciphering the organization of heterotypic connexin coupling partners at A/O junctions. The persistence and abundance of Cx43 and Cx47 at these junctions after Cx32 deletion, together with the paucity of Cx29 normally present at these junctions, suggests Cx43/Cx47 coupling at A/O junctions. Reductions in Cx30 and Cx26 after Cx32 deletion suggest that these astrocytic connexins likely form junctions with Cx32 and that their incorporation into A/O gap junctions is dependent on the presence of oligodendrocytic Cx32.

Connexin36 vs. connexin32, “miniature” neuronal gap junctions, and limited electrotonic coupling in rodent suprachiasmatic nucleus

“…We show that neuronal gap junctions in SCN were present in two major classes -a few large "conventional" gap junctions vs. more abundant miniature ("mini") gap junctions, most of which were smaller than 50 connexons. Our data also support the hypothesis of cell-type-specific expression of the other three connexins tested, with Cx32 confined to oligodendrocyte gap junctions; Cx30 and Cx43 in astrocyte gap junctions; and Cx43 (but none of the other connexins) in ependymocyte junctions, extending similar data from other regions of the CNS (Rash et al, 2001a(Rash et al, , 2001bNagy et al, 2003aNagy et al, ., 2003bNagy et al, , 2004Kamasawa et al, 2005Kamasawa et al, , 2006. The physiological data in the current study also demonstrate that the proportion of cell pairs that show evidence for electrotonic or tracer coupling or spike-to-spike synchrony is quite low (i.e., no spike synchrony in our study and only one pair of tracer-coupled neurons).…”

“…6C,D; paranodal loops are numbered 1-4), and on the outer surface of myelin (Fig. 6E) Nagy et al, 2003aNagy et al, , 2003bNagy et al, , 2004. In high-magnification stereoscopic views (Fig.…”

Loss-of-function GJA12/Connexin47 mutations cause Pelizaeus–Merzbacher-like disease

“…Cx43/Cx47 and Cx30/Cx32 likely form two parallel sets of heterotypic channels that constitute A/O coupling. These two pairs of connexins colocalize at A/O gap junction plaques in WT brains, but Cx30 (and not Cx43) is mislocalized in Gjb1/cx32-null brains (Nagy et al 2003;Altevogt and Paul 2004). Cx30 and Cx32 can form functional heterotypic channels in oocytes (Dahl et al 1996), but it remains to be shown whether Cx43 and Cx47 can also form functional heterotypic channels.…”

“…Astrocyte/astrocyte (A/ A) coupling is likely mediated by Cx43/Cx43 and Cx30/Cx30 homotypic channels, and astrocyte/oligodendrocyte (A/O) coupling is most likely mediated by Cx43/Cx47 and Cx30/ Cx32 heterotypic channels, with an uncertain contribution of Cx26/Cx32 channels (Rash et al 2001;Nagy et al 2003;Altevogt and Paul 2004;Li et al 2004). Cx32/Cx32 homotypic channels appear to form gap junctions between layers of CNS myelin sheaths (Kamasawa et al 2005), as previously described in PNS myelin sheaths (Bergoffen et al 1993;Scherer et al 1995;Balice-Gordon et al 1998;Meier et al 2004).…”

Modulation of connexin expression and gap junction communication in astrocytes by the gram‐positive bacterium S. aureus

“…Gap junction channels are formed by the joining of two hemichannels (connexons) between adjacent cells each composed of hexameric protein subunits called connexins (Cx). Several connexins have been reported to be expressed by astrocytes including connexin 43 (Cx43), connexin 26 (Cx26), and connexin 30 (Cx30) (Altevogt and Paul, 2004;Dermietzel et al, 2000;Nagy et al, 2001Nagy et al, , 2003.…”