Disease relevance of Gja9

• It blocked Cx36 channels, expressed in transfected N2A neuroblastoma cells, at low concentrations (IC(50) approximately 300 nM) [1].
• In this study, we show alteration of Cx43 and Cx36 in the hippocampus after traumatic brain injury in rats [2].
• PURPOSE: The selective contribution of neuronal gap junction (GJ) communication via connexin 36 (Cx36) channels to epileptogenesis and to the maintenance and propagation of seizures was investigated in both the primary focus and the mirror focus by using pharmacologic approaches with the 4-aminopyridine in vivo epilepsy model [3].

High impact information on Gja9

• All these synapses require the gap junction protein connexin36 (Cx36) for robust electrical coupling [4].
• Cx36 appears to interconnect neurons exclusively, and it is expressed widely along the mammalian neuraxis, implying that there are undiscovered electrical synapses throughout the central nervous system [4].
• Both developmental gap junction uncoupling and Cx36 downregulation are prevented by the blockade of NMDA glutamate receptors, action potentials and the calcium-cyclic AMP response element binding protein (CREB), and are accelerated by CREB overexpression [5].
• Here we report that developmental uncoupling of gap junctions in the rat hypothalamus in vivo and in vitro is associated with a decrease in connexin 36 (Cx36) protein expression [5].
• Thus, mefloquine is expected to be a useful tool to study the functional roles of Cx36 and Cx50 [1].

Biological context of Gja9

• We investigated the contribution of this protein in normal beta-cell function by using a viral gene transfer approach to alter Cx36 content in the insulin-producing line of INS-1E cells and rat pancreatic islets [6].
• After infection with a sense viral vector, which induced de novo Cx36 expression in the Cx-defective HeLa cells we used to control the transgene expression, Western blot, immunofluorescence, and freeze-fracture analysis showed a large increase of Cx36 within INS-1E cell membranes [6].
• Taken together, these data provide evidence that glucose represses the expression of Cx36 through the cAMP-PKA pathway, which activates a member of the CRE binding protein family [7].
• Moreover, KCl-induced depolarization of beta-cells had no effect on Cx36 expression, indicating that glucose metabolism and ATP production are not mandatory for glucose-induced Cx36 downregulation [7].
• Reporter-gene activity driven by various Cx36 promoter fragments indicated that Cx36 repression requires the presence of a highly conserved cAMP responsive element (CRE) [7].

Anatomical context of Gja9

• Conversely, Cx43 but not Cx36 was detected in astrocyte and ependymocyte gap junctions [8].
• To address this question directly, freeze-fracture replica immunogold labeling (FRIL) and immunofluorescence (IF) were used to visualize the subcellular and regional localization of Cx36 in rat brain and spinal cord [8].
• By IF, Cx36 labeling was widely distributed in neuropil, including along dendritic processes and within neuronal somata [8].
• Using probes that permitted the original identification of Cx36 in the central nervous system, we show that a transcript for Cx36 is clearly detectable in rat pancreatic islets [9].
• Glucose caused a significant reduction of Cx36 in insulin-secreting cell lines and freshly isolated pancreatic rat islets [7].

Associations of Gja9 with chemical compounds

• The data indicate that large changes in Cx36 alter insulin content and, at least in INS-1E cells, also affect glucose-induced insulin release [6].
• Glucose or forskolin effects on Cx36 expression were not suppressed by the L-type Ca(2+)-channel blocker nifedipine but were fully blunted by the cAMP-dependent protein kinase (PKA) inhibitor H89 [7].
• Brain coronal sections were used for immunohistochemistry with Cx43 and Cx36 antibodies [2].
• The NRSF-mediated repression of Cx36 in HeLa cells was abolished by trichostatin A, confirming the functional importance of histone deacetylase activity [10].
• METHODS: ECoG recording was performed on anesthetized adult rats, in which either quinine, a selective blocker of Cx36, or the broad-spectrum GJ blockers carbenoxolone and octanol were applied locally, before the induction or at already active epileptic foci [3].

Other interactions of Gja9

• Among at least six gap junction-forming connexin proteins in adult rat brain, connexin- (Cx) 32, Cx36, and Cx43 have been reported to occur in neurons [8].
• In 4 and 18 day postnatal rat spinal cord, neuronal gap junctions contained Cx36, whereas Cx26 was present in leptomenigeal gap junctions [11].
• No Cx32 or Cx36 transcripts were amplified [12].

Analytical, diagnostic and therapeutic context of Gja9

• By Western blotting, these antibodies detected protein at 36 and 66 kDa, corresponding to Cx36 monomer and dimer forms, respectively [8].
• Multisite electromyography revealed that blocking Cx36 in the IO impaired the coherence of muscle firing during harmaline tremor without affecting its rhythm [13].
• In addition, none of the tested SNc cells (n = 12) showed expression of connexin 36 (the "neuronal" connexin) when tested with single-cell RT-PCR [14].
• The distribution of connexin36 (Cx36) in the adult rat brain and retina has been analysed at the protein (immunofluorescence) and mRNA (in situ hybridization) level [15].
• Co-immunoprecipitation experiments with monkey COS-7 cells transiently transfected with both mutant and wild-type Cx36 cDNAs demonstrated that the mutant protein bound to the wild-type [16].

References