Connexin26 in adult rodent central nervous system: Demonstration at astrocytic gap junctions and colocalization with connexin30 and connexin43

The connexin family of proteins (Cx) that form intercellular gap junctions in vertebrates is well represented in the mammalian central nervous system. Among these, Cx30 and Cx43 are present in gap junctions of astrocytes. Cx3 2 is expressed by oligodendrocytes and is present in heterologous gap junct ions between oligodendrocytes and astrocytes as well as at autologous gap j unctions between successive myelin layers. Cx36 mRNA has been identified in neurons, and Cx36 protein has been localized at ultrastructurally defined interneuronal gap junctions. Cx26 is also expressed in the CNS, primarily i n the leptomeningeal linings, but is also reported in astrocytes and in neu rons of developing brain and spinal cord. To establish further the regional , cellular, and subcellular localization of Cx26 in neural tissue, we inves tigated this connexin in adult. mouse brain and in rat brain and spinal cor d using biochemical and immunocytochemical methods. Northern blotting, west ern blotting, and immunofluorescence studies indicated widespread and heter ogeneous Cx26 expression in numerous subcortical areas of both species. By confocal microscopy, Cx26 was colocalized with both Cx30 and Cx43 in leptom eninges as well as along blood vessels in cortical and subcortical structur es. It was; also localized at the surface of oligodendrocyte cell bodies, w here it was coassociated with Cx32. Freeze-fracture replica immunogold labe ling (FRIL) demonstrated Cx26 in most gap junctions between cells of the pi a mater, by postnatal day 4. By postnatal day 18 and thereafter, Cx26 was p resent at gap junctions between astrocytes and in the astrocyte side-of mos t gap junctions between astrocytes and oligodendrocytes. In perinatal spina l cord and in five regions of adult brain and spinal cord examined by FRIL, no evidence was obtained for the presence of Cx26 in neuronal gap junction s. In addition to its established localization in leptomeningeal gap juncti ons, these results identify Cx26 as a third connexin (together with Cx30 an d Cx43) within astrocytic gap junctions and suggest a further level of comp lexity to the heterotypic connexin channel combinations formed at these jun ctions. (C) 2001 Wiley-Liss, Inc.