| Mouse knockouts and human genetic diseases illustrate that the maintenance of CNS myelin requires the expression of connexins involved in gap junctions between astrocytes and oligodendrocytes. As these two cell types express non-overlapping sets of connexins, the intercellular channels formed between them must be asymmetric with regard to connexin content, defined as heterotypic.;Since not all heterotypic connexin pairings are functional, we assessed the ability of astrocyte and oligodendrocyte connexins to form functional heterotypic channels by expressing each connexin in communication negative cell lines and using neurobiotin transfer as an assay for junctional communication. We found that oligodendrocyte Cx47 can form functional channels with either astrocyte Cx43 or Cx30, but not Cx26. On the other hand, oligodendrocyte Cx32 can form function channels with astrocyte Cx30 or astrocyte Cx26, but not Cx32. Therefore, as many as four pathways for gap junctional communication are possible between astrocytes and oligodendrocytes.;In addition to junctions between astrocytes and oligodendrocytes (A/O), gap junctions are also formed in the CNS between neighboring astrocytes (A/A), and between layers of myelin in oligodendrocytes (reflexive). However, the relative importance of each type of junctional interaction has not been established. In order to directly assess the role of A/O junctions in the health and maintenance of the CNS, we generated a double knockout mouse (dKO) lacking one astrocyte and one oligodendrocyte connexin, where A/A and reflexive coupling should be partially preserved but A/O coupling should be absent.;These dKO mice demonstrated seizures, sensorimotor impairment, and early mortality. They also showed marked vacuolation specifically associated with white matter structures without any obvious disruption of myelin. Ultrastructural analysis revealed disorganized cell bodies and processes that often contained intermediate filaments. To verify that these pathological cells are astrocytic in origin, we performed a morphometric analysis to establish glial cell numbers and observed significant astrocyte loss in the dKO compared to controls. Together, these data suggest a critical role for A/O coupling in the maintenance of white matter astrocytes. |
