Connexin30, expression in astrocytes, co-localization with connexin43 at gap junctions, and late developmental appearance in rat brain
Evidence has been presented (Nagy et al., 1997a) that in addition to connexin43, astrocytes express a second connexin, suggested to be connexin30 (Cx30), a recently discovered member of the family of gap junction proteins. A Cx30 specific antibody was developed and used to confirm this observation using Western blots and immunohistochemical techniques. On Western blots, this antibody detected a 30,000 mol. wt protein in rat, mouse, cat and human brain. It did not exhibit cross-reaction with connexin43 (Cx43), connexin26 (Cx26), or any other known connexins expressed in brain. Immunohistochemically, Cx30 was localized to astrocytes, at gap junctions of these cells, and on the astrocytic side of gap junctions between astrocytes and oligodendrocytes. Double labeling revealed co-expression of Cx30 with Cx43 at astrocytic gap junctions. The punctate immunolabeling patterns of these two connexins was similar, but differences were evident. In contrast to regional Cx43 expression, diencephalic and hindbrain areas showed a greater expression of Cx30 than did forebrain areas. Subcortical perivascular astrocytic endfeet were more heavily labeled for Cx30. White matter tracts such as corpus callosum, internal capsule, and anterior commissure were devoid of Cx30 labeling. During development, Cx30 was not detected until about 15 days postnatal. These results indicate that Cx30 is expressed in gray matter, but not in white matter astrocytes, the distribution of Cx30 is highly heterogeneous in gray matter, it is co-localized with Cx43 at astrocytic gap junctions where it forms homotypic or heterotypic junctions, and its emergence is delayed until late brain maturation. The results suggest that astrocytic Cx30 expression at regional and cellular levels is subject to regulation in adult brain as well as during brain development.