Differential expression of three gap junction proteins in developing and mature brain tissues.

Abstract

By using antibodies directed against gapjunction proteins of liver (connexins 26 and 32) and heart (connexin 43), we have localized immunoreactivity to specific cell types in frozen sections of adult rodent brains. Connexin 32 reactivity was found in oligodendrocytes and also in a few neurons, whereas reactivity to connexins 26 and 43 was localized to leptomeningeal cells, ependymal cells, and pineal gland. Immunoreactivity with antibodies to connexin 43 also occurred in astrocytes. Furthermore, during embryonic and postnatal maturation of brain tissues, gap junction proteins were differentially expressed. Connexins 43 and 26 predominated in the neuroepithelium of embryonic brains, whereas connexin 32 was virtually absent. Between 3 and 6 weeks after birth, connexin 26 largely disappeared from immature brain; this time course corresponded to the increased expression of connexin 32. Expression of connexin 43 remained high throughout embryonic and postnatal development. These findings demonstrate that gap junction expression in the brain is diverse, with specific cell types expressing different connexins; this cell-specific distribution may imply differences in the function of these intercellular channels in different loci and developmental stages.Gap junctions are the structural domains through which electrical transmission and metabolic and ionic cooperation between contiguous cells are thought to be mediated. Recent progress in the understanding of the molecular composition of at least four types of gapjunctions found in liver, heart, and lens fibers has been derived from immunochemical (1-5) and molecular biological studies (6-10). The message emerging from these discoveries is that gap junctions are composed of a family of homologous proteins that are expressed in various amounts in different cell types (11,12). We have shown (11, 12) that at least two gap junction proteins are present in liver.Nervous tissue was among the first organs where gap junction membrane contacts were structurally and physiologically characterized (for review, see ref. 13). Recent studies using antibodies against multiple determinants have demonstrated that gap junctions are abundant in brain (14,15), but the composition of these gap junction proteins was not unambiguously determined.By using affinity-purified polyclonal and monoclonal anticonnexin-32 antibodies, an antibody to the liver protein connexin 26, and a polyclonal antibody directed to the carboxylterminal domain of the heart protein connexin 43, we have evaluated the patterns of expression of these proteins in adult and embryonic brains. Our data provide evidence that specific sets of gap junction proteins are expressed by specific brain cell populations. In addition, we found that during development relative amounts of connexin 26 and connexin 32 shift. Connexin 26, which is abundant in embryonic brain, becomes confined to leptomeningeal and ependymal cells and to pinealocytes. Connexin 32, which is not expressed to a large extent in embryonic brain, is expressed ...

Identification of connexin36 in gap junctions between neurons in rodent locus coeruleus

“…0−4 per replica), which is similar to densities found in spinal cord, inferior olive, and suprachiasmatic nucleus (Rash et al, 1996(Rash et al, ,2001bNagy et al, 2004;and Rash, Nagy and Dudek, unpublished observations). Third, in contrast to purported abundance Cx32 in astrocytes (Alvarez-Maubecin et al, 2000), Cx32 was not found by FRIL in astrocytes at any age, paralleling observations in all other brain regions (Dermietzel et al, 1989;Nelles et al, 1996;Kunzelmann et al, 1997;Dermietzel, 1998;Rash et al, 2001b;Nagy et al, 2003b;Kamasawa et al, 2005). Fourth, consistent with our reports that detection of Cx26 and Cx32 is particularly sensitive to tissue fixation conditions (Li et al, 1997;Nagy et al, 2001Nagy et al, , 2003a, we found that the stronger 3.75% acrolein/2% formaldehyde fixative of AlvarezMaubecin (2000) applied under our conditions of immunohistochemistry abolished all labeling of Cx32 and Cx26 in brain parenchyma and greatly reduced Cx26 labeling in leptomeninges.…”

Gap junctions formed by connexins 26 and 32 alone and in combination are differently affected by applied voltage.

“…Of the cloned connexins, Cx26 has been unique in that, with the possible exception of pinealocytes (22), it has consistently been found to be coexpressed with other connexins (2,13,14,23 Oocyte Preparation. Oocytes were prepared as described (25).…”

Neonatal CX26 removal impairs neocortical development and leads to elevated anxiety

“…However, whether CX26-mediated electrical coupling regulates the development and synapse formation of excitatory neurons in vivo remains unclear. In addition, although functional electrical coupling between excitatory neurons is largely eliminated after the first postnatal week, CX26 proteins remain abundantly present in excitatory neurons even at the mature stage (13,16). Therefore, the precise role of CX26 proteins in excitatory neurons after the disappearance of electrical coupling is unclear.…”