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Mouse connexin37: cloning and functional expression of a gap junction gene highly expressed in lung.

ABSTRACT: The coding sequence (333 amino acids) of a new connexin protein, designated mouse connexin37 (Cx37 or Cx37.6) due to the deduced theoretical molecular mass of 37.600 kD, has been determined from cDNA and genomic clones. As seen in other connexins, its gene has no introns within the coding region and the deduced amino acid sequence is predicted to have similar topology to other connexins that form intercellular channels. The amino acid sequence of mouse Cx37 is most similar to rat connexin43 (59% identity) and Xenopus connexin38 (66% identity) when compared from the NH2 terminus to the end of the fourth putative transmembrane region. When expressed in Xenopus oocytes Cx37 forms functional intercellular channels that exhibit more sensitive and rapid gating in response to voltage than any previously characterized vertebrate gap junction. Under stringent conditions the Cx37 cDNA hybridizes to an mRNA of 1.7 kb that is found highly abundant in lung and to progressively lesser extents in brain, kidney, skin, spleen, liver, intestine, and heart. Embryonic brain, kidney, and skin express two to fivefold higher levels of the Cx37 transcript than the corresponding adult tissues. Cx37 transcripts were also found to increase two to threefold in response to retinoic acid treatment of cultured embryonic carcinoma F9 cells.

SUBMITTER: Willecke K

PROVIDER: S-EPMC2289105 | biostudies-other | 1991 Sep

REPOSITORIES: biostudies-other

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Molecular cloning and functional expression of mouse connexin40, a second gap junction gene preferentially expressed in lung.

Project description:From a mouse genomic library, a clone has been isolated that codes for a connexin-homologous sequence of 358 amino acids. Because of its theoretical molecular mass of 40.418 kD it is named connexin40 (Cx40). Based on both protein and nucleotide sequence, mouse Cx40 is more closely related to mouse Cx43 (alpha subgroup of connexins) than to mouse Cx32 (beta subgroup). The highest overall homology detected, however, was to chick Cx42 (67% amino acid and 86% nucleotide identity), raising the possibility that Cx40 may be the mouse analogue. The coding region of Cx40 is uninterrupted by introns and is detected as a single copy gene in the mouse genome. High stringency hybridization of Northern blots with the coding sequence of Cx40 identified a single transcript of 3.5 kb that is at least 16-fold more abundant in lung-similar to mouse Cx37-than in other adult tissues (kidney, heart, and skin). In embryonic kidney, skin, and liver the level of the Cx40 transcript is two- to fourfold higher than in the corresponding adult tissues. Microinjection of Cx40 cRNA into Xenopus oocytes induced functional cell-to-cell channels between pairs. These channels show a symmetrical and markedly cooperative closure in response to transjunctional voltage (Boltzmann parameters of Vo = +/- 35 mV; A = 0.32) which is also fast relative to other connexin channels recorded similarly (tau = 580 ms at Vj of +/- 50 mV). Although Cx40-expressing oocytes did not couple efficiently with oocytes expressing endogenous connexins, they did couple well to Cx37-expressing oocytes. The heterotypic channels which formed had voltage-gating properties modified from those of the original homotypic forms. Transfection of mouse Cx40 DNA, under control of the SV-40 early promoter, into coupling-deficient human HeLa or SK-Hep-1 cells resulted in expression of the expected transcript and restoration of fluorescent dye transfer in transfected clones.

| S-EPMC2289506 | biostudies-other

Zebrafish cx30.3: identification and characterization of a gap junction gene highly expressed in the skin.

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Project description:The potential gap junction forming mouse connexin29 (Cx29) protein is concomitantly expressed with connexin32 (Cx32) in peripheral myelin forming Schwann cells and together with both Cx32 and connexin47 (Cx47) in oligodendrocytes of the CNS. To study the genomic structure and functional expression of Cx29, either primary cells or cell culture systems might be selected, from which the latter are easier to cultivate. Both structure and expression of Cx29 is still not fully understood. In the mouse sciatic nerve, brain and the oligodendroglial precursor cell line Oli-neu the Cx29 gene is processed in two transcript isoforms both harboring a unique reading frame. In contrast to Cx32 and Cx47, only Cx29 protein is abundantly expressed in undifferentiated as well as differentiated Oli-neu cells but the absence of Etbr dye transfer after microinjection concealed the function of Cx29-mediated gap junction communication between those cells. Although HeLa cells stably transfected with Cx29 or Cx29-eGFP neither demonstrated any permeability for Lucifer yellow nor for neurobiotin, blocking of Etbr uptake from the media by gap junction blockers does suppose a role of Cx29 in hemi-channel function. Thus, we conclude that, due to its high abundance of Cx29 expression and its reproducible culture conditions, the oligodendroglial precursor cell line Oli-neu might constitute an appropriate cell culture system to study molecular mechanisms or putative extracellular stimuli to functionally open Cx29 channels or hemi-channels.

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Strain-specific Variation in Mouse Gene Expression and the Onset of Gap Junction Mutation-induced Cataracts

Project description:Disruption of the mouse gene encoding the gap junction subunit alpha3 connexin 46 (Cx46) results in the formation of lens cataracts. The timing of the onset of this lens opacity is affected by the genetic background, i.e. the mouse strain. To elucidate the mechanism by which cataracts form in the 129Sv/Jae strain earlier than in the C57BL/6J strain, global gene expression was quantitated in the lenses of these strains. Lens cDNAs were analyzed by hybridization to DNA microarrays and with real time-PCR. Theories are proposed based on the observed higher level of expression of the stress-response genes in the C57BL/6J strain and variations in the expression levels of genes involved in protein synthesis, metabolism, catabolism and cell proliferation. How these variations in gene expression might affect the response of lens fiber cells to the increased calcium, caused by lack of alpha3Cx46, is considered. The possibility that the proteins coded by the strain-variable genes might influence the cataract-associated proteolysis of gamma-crystallin is also addressed. Keywords: Lens, cataract, microarray, connexin 46, gene knock out

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Modulation of cardiac gap junction expression and arrhythmic susceptibility.

Project description:Connexin43 (Cx43), the predominant ventricular gap junction protein, is critical for maintaining normal cardiac electrical conduction, and its absence in the mouse heart results in sudden arrhythmic death. The mechanisms linking reduced Cx43 abundance in the heart and inducibility of malignant ventricular arrhythmias have yet to be established. In this report, we investigate arrhythmic susceptibility in a murine model genetically engineered to express progressively decreasing levels of Cx43. Progressively older cardiac-restricted Cx43 conditional knockout (CKO) mice were selectively bred to produce a heart-specific Cx43-deficient subline ("O-CKO" mice) in which the loss of Cx43 in the heart occurs more gradually. O-CKO mice lived significantly longer than the initial series of CKO mice but still died suddenly and prematurely. At 25 days of age, cardiac Cx43 protein levels decreased to 59% of control values (P<0.01), but conduction velocity was not significantly decreased and no O-CKO mice were inducible into sustained ventricular tachyarrhythmias. By 45 days of age, cardiac Cx43 abundance had decreased in a heterogeneous fashion to 18% of control levels, conduction velocity had slowed to half of that observed in control hearts, and 80% of O-CKO mice were inducible into lethal tachyarrhythmias. Enhanced susceptibility to induced arrhythmias was not associated with altered invasive hemodynamic measurements or changes in ventricular effective refractory period. Thus, moderately severe reductions in Cx43 abundance are associated with slowing of impulse propagation and a dramatic increase in the susceptibility to inducible ventricular arrhythmias.

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PTEN Expression Regulates Gap Junction Connectivity in the Retina.

Project description:Manipulation of the phosphatase and tensin homolog (PTEN) pathway has been suggested as a therapeutic approach to treat or prevent vision loss due to retinal disease. In this study, we investigated the effects of deleting one copy of Pten in a well-characterized class of retinal ganglion cells called α-ganglion cells in the mouse retina. In Pten +/- retinas, α-ganglion cells did not exhibit major changes in their dendritic structure, although most cells developed a few, unusual loop-forming dendrites. By contrast, α-ganglion cells exhibited a significant decrease in heterologous and homologous gap junction mediated cell coupling with other retinal ganglion and amacrine cells. Additionally, the majority of OFF α-ganglion cells (12/18 cells) formed novel coupling to displaced amacrine cells. The number of connexin36 puncta, the predominant connexin that mediates gap junction communication at electrical synapses, was decreased by at least 50% on OFF α-ganglion cells. Reduced and incorrect gap junction connectivity of α-ganglion cells will affect their functional properties and alter visual image processing in the retina. The anomalous connectivity of retinal ganglion cells would potentially limit future therapeutic approaches involving manipulation of the Pten pathway for treating ganglion cell degeneration in diseases like glaucoma, traumatic brain injury, Parkinson's, and Alzheimer's diseases.

| S-EPMC8172595 | biostudies-literature

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