Molecular Cloning and Functional Expression of zfCx52.6

Zoidl, Georg; Bruzzone, Roberto; Weickert, Svenja; Kremer, Marian; Zoidl, Christiane; Mitropoulou, Georgia; Srinivas, Miduturu; Spray, David C.; Dermietzel, Rolf

doi:10.1074/jbc.m304850200

Cited by 48 publications

(8 citation statements)

References 74 publications

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“…Application of 100 µM cobalt produced a reduction in the inward current in wild-type horizontal cells similar in magnitude to the reduction in inward current observed in Cx55.5 mutant horizontal cells (Figure S1). The voltage dependence of the hemichannel currents in dissociated horizontal cells of wild-type and mutant zebrafish are in agreement with the known voltage-dependence of Cx55.5 and Cx52.6 hemichannels [7],[17].…”

Section: Resultssupporting

confidence: 84%

Synaptic Transmission from Horizontal Cells to Cones Is Impaired by Loss of Connexin Hemichannels

et al. 2011

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In the vertebrate retina, horizontal cells generate the inhibitory surround of bipolar cells, an essential step in contrast enhancement. For the last decades, the mechanism involved in this inhibitory synaptic pathway has been a major controversy in retinal research. One hypothesis suggests that connexin hemichannels mediate this negative feedback signal; another suggests that feedback is mediated by protons. Mutant zebrafish were generated that lack connexin 55.5 hemichannels in horizontal cells. Whole cell voltage clamp recordings were made from isolated horizontal cells and cones in flat mount retinas. Light-induced feedback from horizontal cells to cones was reduced in mutants. A reduction of feedback was also found when horizontal cells were pharmacologically hyperpolarized but was absent when they were pharmacologically depolarized. Hemichannel currents in isolated horizontal cells showed a similar behavior. The hyperpolarization-induced hemichannel current was strongly reduced in the mutants while the depolarization-induced hemichannel current was not. Intracellular recordings were made from horizontal cells. Consistent with impaired feedback in the mutant, spectral opponent responses in horizontal cells were diminished in these animals. A behavioral assay revealed a lower contrast-sensitivity, illustrating the role of the horizontal cell to cone feedback pathway in contrast enhancement. Model simulations showed that the observed modifications of feedback can be accounted for by an ephaptic mechanism. A model for feedback, in which the number of connexin hemichannels is reduced to about 40%, fully predicts the specific asymmetric modification of feedback. To our knowledge, this is the first successful genetic interference in the feedback pathway from horizontal cells to cones. It provides direct evidence for an unconventional role of connexin hemichannels in the inhibitory synapse between horizontal cells and cones. This is an important step in resolving a long-standing debate about the unusual form of (ephaptic) synaptic transmission between horizontal cells and cones in the vertebrate retina.

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Section: Resultssupporting

confidence: 84%

Synaptic Transmission from Horizontal Cells to Cones Is Impaired by Loss of Connexin Hemichannels

et al. 2011

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“….. but not others?'' (Zoidl et al, 2004). It seems this issue can now be extended into the Xenopus field.…”

Section: Interspecies Comparisonsmentioning

confidence: 98%

“…As stated earlier, by others for zebrafish, “this observation raises the question why evolution does conserve some Cxs …. but not others?” (Zoidl et al, 2004). It seems this issue can now be extended into the Xenopus field.…”

Section: Interspecies Comparisonsmentioning

confidence: 99%

Xenopus connexins: how frogs bridge the gap

Boer

Heyden

2005

Differentiation

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Animal species use specialized cell-to-cell channels, called gap junctions, to allow for a direct exchange of ions and small metabolites between their cells' cytoplasm. In invertebrates, gap junctions are formed by innexins, while vertebrates use connexin (Cx) proteins as gap-junction-building blocks. Recently, innexin homologs have been found in vertebrates and named pannexins. From progress in the different genome projects, it has become evident that every class of vertebrates uses their own unique set of Cxs to build their gap junctions. Here, we review all known Xenopus Cxs with respect to their expression, regulation, and function. We compare Xenopus Cxs with those of zebrafish and mouse, and provide evidence for the existence of several additional, non-identified, amphibian Cxs. Finally, we identify two new Xenopus pannexins by screening EST libraries.

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“…Additionally, mRNA of hCx62, the putative human ortholog of mCx57 (Gja10), was found after Northern blot hybridization. HCx59 (GJA9), having no ortholog in the mouse genome [20,33], shows a high phylogenetic sequence relationship to zebrafish Cx52.6 [34], zebrafish Cx55.5 [35] but much less to mCx57 and porcine Cx60 [55]. However, in contrast the hCx62, hCx59 transcripts could not be detected after Northern blot hybridization, presumably due to their very low abundance.…”

Section: Methodsmentioning

confidence: 99%

Expression of connexin genes in the human retina

et al. 2010

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BackgroundGap junction channels allow direct metabolically and electrical coupling between adjacent cells in various mammalian tissues. Each channel is composed of 12 protein subunits, termed connexins (Cx). In the mouse retina, Cx43 could be localized mostly between astroglial cells whereas expression of Cx36, Cx45 and Cx57 genes has been detected in different neuronal subtypes. In the human retina, however, the expression pattern of connexin genes is largely unknown.MethodsNorthern blot hybridizations, RT-PCR as well as immunofluorescence analyses helped to explore at least partially the expression pattern of the following human connexin genes GJD2 (hCx36), GJC1 (hCx45), GJA9 (hCx59) and GJA10 (hCx62) in the human retina.ResultsHere we report that Northern blot hybridization signals of the orthologuous hCx36 and hCx45 were found in human retinal RNA. Immunofluorescence signals for both connexins could be located in both inner and outer plexiform layer (IPL, OPL). Expression of a third connexin gene denoted as GJA10 (Cx62) was also detected after Northern blot hybridization in the human retina. Interestingly, its gene structure is similar to that of Gja10 (mCx57) being expressed in mouse horizontal cells. RT-PCR analysis suggested that an additional exon of about 25 kb further downstream, coding for 12 amino acid residues, is spliced to the nearly complete reading frame on exon2 of GJA10 (Cx62). Cx59 mRNA, however, with high sequence identity to zebrafish Cx55.5 was only weakly detectable by RT-PCR in cDNA of human retina.ConclusionIn contrast to the neuron-expressed connexin genes Gjd2 coding for mCx36, Gjc1 coding for mCx45 and Gja10 coding for mCx57 in the mouse, a subset of 4 connexin genes, including the unique GJA9 (Cx59) and GJA10 (Cx62), could be detected at least as transcript isoforms in the human retina. First immunofluorescence analyses revealed a staining pattern of hCx36 and hCx45 expression both in the IPL and OPL, partially reminiscent to that in the mouse, although additional post-mortem material is needed to further explore their sublamina-specific distribution. Appropriate antibodies against Cx59 and Cx62 protein will clarify expression of these proteins in future studies.

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Molecular Cloning and Functional Expression of zfCx52.6

Cited by 48 publications

References 74 publications

Synaptic Transmission from Horizontal Cells to Cones Is Impaired by Loss of Connexin Hemichannels

Synaptic Transmission from Horizontal Cells to Cones Is Impaired by Loss of Connexin Hemichannels

Xenopus connexins: how frogs bridge the gap

Expression of connexin genes in the human retina

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