Mutations in genes coding for connexin26 (Cx26) and/or Cx30 are linked to approximately half of all cases of human autosomal nonsyndromic prelingual deafness. Cx26 and Cx30 are the two major Cx isoforms found in the cochlea, and they coassemble to form hybrid (heteromeric and heterotypic) gap junctions (GJs). This molecular arrangement implies that homomeric GJs would remain in the cochlea if one of the coassembly partners were mutated resulting in null expression. We generated mice in which extra copies of the Cx26 gene were transgenically expressed from a modified bacterial artificial chromosome in a Cx30 ؊/؊ background. In the absence of the Cx30 gene, Cx26 expressed from extra alleles completely restored hearing sensitivity and prevented hair cell death in deaf Cx30 ؊/؊ mice. The results indicated that hybrid GJs consisting of Cx26 and Cx30 were not essential for normal hearing in mice and suggested that up-regulation of Cx26 or slowing down its protein degradation might be a therapeutic strategy to prevent and treat deafness caused by Cx30 mutations.gap junction ͉ hearing rescue ͉ hereditary deafness

The primary effect of G45E Cx26 mutation is to cause leaky GJ hemichannels when cells are bathed in normal [Ca2+]0. Our data showed that abnormally open hemichannels with resultant cell death, in addition to GJ and hemichannel uncoupling, is a novel molecular mechanism by which Cx26 mutations may result in hearing impairment. One plausible therapeutic strategy for this type of Cx mutation, therefore, is to manipulate [Ca2+]0 and/or the Ca-binding affinity of GJ hemichannels.

The molecular mechanisms underlying polarized sorting of proteins in neurons are poorly understood. Here we report the identification of a 16 amino-acid, dileucine-containing motif that mediates dendritic targeting in a variety of neuronal cell types in slices of rat brain. This motif is present in the carboxy (C) termini of Shal-family K+ channels and is highly conserved from C. elegans to humans. It is necessary for dendritic targeting of potassium channel Kv4.2 and is sufficient to target the axonally localized channels Kv1.3 and Kv1.4 to the dendrites. It can also mediate dendritic targeting of a non-channel protein, CD8.

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Abstract. Stable isotope records from speleothems provide information on past climate changes, most particularly information that can be used to reconstruct past changes in precipitation and atmospheric circulation. These records are increasingly being used to provide “out-of-sample” evaluations of isotope-enabled climate models. SISAL (Speleothem Isotope Synthesis and Analysis) is an international working group of the Past Global Changes (PAGES) project. The working group aims to provide a comprehensive compilation of speleothem isotope records for climate reconstruction and model evaluation. The SISAL database contains data for individual speleothems, grouped by cave system. Stable isotopes of oxygen and carbon (δ18O, δ13C) measurements are referenced by distance from the top or bottom of the speleothem. Additional tables provide information on dating, including information on the dates used to construct the original age model and sufficient information to assess the quality of each data set and to erect a standardized chronology across different speleothems. The metadata table provides location information, information on the full range of measurements carried out on each speleothem and information on the cave system that is relevant to the interpretation of the records, as well as citations for both publications and archived data. The compiled data are available at https://doi.org/10.17864/1947.147.

Guinea-pig liver gap junctions are constructed from approximately equal amounts of connexins 26 and 32. The assembly of these connexins into connexon hemichannels and gap junctions was studied using antibodies specific to each connexin. Intracellular membranes were shown to contain low amounts of connexin 26 relative to connexin 32 in contrast to the equal connexin ratios detected in lateral plasma membranes and gap junctions. Assembly of gap junctions requires oligomerization of connexins into connexons that may be homomeric or heteromeric. Immunoprecipitation using antibodies to connexins 26 and 32 showed that liver gap junctions were heteromeric. A chemical cross-linking procedure showed that connexons solubilized from guinea-pig liver gap junctions were constructed of hexameric assemblies of connexin subunits. The intracellular site of oligomerization of connexins was investigated by velocity sedimentation in sucrose±detergent gradients. Oligomers of connexins 26 and 32 were extensively present in Golgi membranes and oligomeric intermediates, especially of connexin 26, were detected in the endoplasmic reticulum±Golgi intermediate subcellular fraction. Two intracellular trafficking pathways that may account for the delivery of connexin 26 to the plasma membrane and explain the heteromeric nature of liver gap junctions are discussed.Keywords: cell±cell communication; connexins; gap junctions; intracellular trafficking routes; secretory pathway.Key issues in studying the arrangement of protein subunits in multimeric channels are the cellular location where subunit oligomerization occurs and the underlying mechanisms ensuring subunit correct stoichiometry during channel assembly. Gap junctions are pervasive intercellular channels providing direct signalling pathways integrating and co-ordinating cellular activities in tissues and organs [1,2]. They are constructed of apposed connexon hemichannels that have been shown, primarily on the basis of the structural features revealed by X-ray scattering and by electron microscopy of paracrystalline arrays [3], to consist of a hexameric assembly of connexin protein subunits arranged around a central aqueous channel. Connexon hemichannels, located in the contacting plasma membranes dock, provide a direct intercellular communication pathway across which electrolytes, metabolites and signalling molecules, with a size of <1 kDa, are able to pass [4]. Fourteen connexin isoforms have been identified in rodents [5,6] and nine in humans [5,7,8] with many homologues from other species [5].Previous work has shown that connexin (Cx) 32, the major constituent of rat liver gap junctions, was present at low levels in subcellular fractions deriving from the constituent compartments of the secretory pathway and it was concluded that these results reflected the synthesis, trafficking and rapid turnover of gap junctions [9]. In the present work guinea-pig liver was selected as a model system to study, using subcellular fractionation techniques, aspects of the intracellular trafficking and...

Mutations in the genes coding for connexin 26 (Cx26) and connexin 31 (Cx31) cause non-syndromic deafness. Here, we provide evidence that mutations at these two connexin genes can interact to cause hearing loss in digenic heterozygotes in humans. We have screened 108 GJB2 heterozygous Chinese patients for mutations in GJB3 by sequencing. We have excluded the possibility that mutations in exon 1 of GJB2 and the deletion of GJB6 are the second mutant allele in these Chinese heterozygous probands. Two different GJB3 mutations (N166S and A194T) occurring in compound heterozygosity with the 235delC and 299delAT of GJB2 were identified in three unrelated families (235delC/N166S, 235delC/A194T and 299delAT/A194T). Neither of these mutations in Cx31 was detected in DNA from 200 unrelated Chinese controls. Direct physical interaction of Cx26 with Cx31 is supported by data showing that Cx26 and Cx31 have overlapping expression patterns in the cochlea. In addition, by coimmunoprecipitation of mouse cochlear membrane proteins, we identified the presence of heteromeric Cx26/Cx31 connexons. Furthermore, by cotransfection of mCherry-tagged Cx26 and GFP-tagged Cx31 in human embryonic kidney-293 cells, we demonstrated that the two connexins were able to co-assemble in vitro in the same junction plaque. Together, our data indicate that a genetic interaction between these two connexin genes can lead to hearing loss.