In vivo evidence for the involvement of the carboxy terminal domain in assembling connexin 36 at the electrical synapse

Abstract

Connexin 36 (Cx36)-containing electrical synapses contribute to the timing and amplitude of neural responses in many brain regions. A Cx36-EGFP transgenic was previously generated to facilitate their identification and study. In this study we demonstrate that electrical coupling is normal in transgenic mice expressing Cx36 from the genomic locus and suggest that fluorescent puncta present in brain tissue represent distributed electrical synapses. These qualities emphasize the usefulness of the Cx36-EGFP reporter as a tool for the detailed anatomical characterization of electrical synapses in fixed and living tissue. However, though the fusion protein is able to form gap junctions between Xenopus laevis oocytes it is unable to restore electrical coupling to interneurons in the Cx36-deficient mouse. Further experiments in transgenic tissue and non-neural cell lines reveal impaired transport to the plasma membrane as the possible cause. By analyzing the functional deficits exhibited by the fusion protein in vivo and in vitro, we identify a motif within Cx36 that may interact with other trafficking or scaffold proteins and thereby be responsible for its incorporation into electrical synapses.

Trafficking of gap junction channels at a vertebrate electrical synapse in vivo

“…Alternatively, interference with dynamin and SNAP might affect the surface expression of other proteins that, in turn, could modify synaptic transmission. It has been suggested that the last amino acids of the CT of Cx36 are necessary for the correct surface expression of these channels (44). We hypothesized that, if GJ channels are added rapidly by exocytosis, interference with this region of the molecule will, like the SNAP-25-blocking peptide, block connexon insertion and, as a consequence, result in a rundown of electrical transmission.…”

Electrical synapses and their functional interactions with chemical synapses

“…ZO-1 is a scaffold protein of the MAGUK family that is known to associate to many connexins 60 , and that might have a similar role to PSD-95 at glutamatergic synapses 1 . Conserved regions of the carboxy-terminus of Cx36 (and its two teleost homologs) 58,59,61 mediate interactions with ZO-1 and are required for the insertion of new gap junction proteins into electrical synapses 40,61 . ZO-1 has been also proposed to have an essential role regulating the transition from connexon to intercellular gap junction channel formation in the periphery of Cx43-containing junctions 62 .…”

<b><i>TOP3B</i></b>: A Novel Candidate Gene in Juvenile Myoclonic Epilepsy?

“…So far, 29 chromosomal loci have been linked to JME, and variations have been identified in several genes (e.g., CACNB4 , CASR , GABRA1 , GABRD , CLCN2 , SLC2A1 , and EFHC1 ) [Koepp et al, 2014]. In addition, chromosomal rearrangements such as microdeletions in 15q13.3, 15q11.2, and 16p13.11 have been reported to be associated with JME [Escayg et al, 2000;Delgado-Escueta, 2007;Helbig et al, 2010;Delgado-Escueta et al, 2013;Thomas and Berkovic, 2014]. The deletion in chromosome 22q11.2 was originally assigned to DiGeorge syndrome and velocardiofacial syndrome [Ben-Sachar et al, 2008].…”