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E C Beyer

Publications and source records attributed to E C Beyer.

At least 55 records · Page 3Linked to original sources
PubMed1996

Rat uterine myometrium contains the gap junction protein connexin45, which has a differing temporal expression pattern from connexin43.

OBJECTIVE: Our purpose was to determine whether myometrial cell lines and rat myometrial tissue contained additional gap junction proteins besides connexin43. STUDY DESIGNS: Syrian hamster myocytes (SHM-ER) and human SK-UT-1 myometrial cell lines were analyzed for intercellular coupling by microinjection of Lucifer yellow. These cell lines and myometrial tissue isolated from pregnant rats were analyzed for connexin expression by ribonucleic acid blotting and immunofluorescence. RESULTS: SHM-ER and SK-UT-1 cells showed functional gap junctional coupling by intercellular passage of microinjected dye. Both cell lines contained connexin43 and connexin45 messenger ribonucleic acids but did not contain any other detectable connexin messenger ribonucleic acids. Immunofluorescence confirmed the presence of connexin43 and connexin45 proteins in these cells. Connexin 43 and connexin45 messenger ribonucleic acids and immunoreactive proteins were detected in pregnant rat myometrium. Connexin 43 messenger ribonucleic acid levels increased dramatically at term. In contrast, connexin45 messenger ribonucleic acid was present in nonpregnant myometrium, remained relatively constant early in gestation, fell just before term, and more than doubled post partum. CONCLUSIONS: Rat uterine myometrium contains connexin45 and connexin43. Coexpression of connexin45 with connexin43 in uterine myometrium may regulate gap junctional coupling between these cells. The different temporal expression patterns suggest that connexin45 and connexin43 may have different roles or that the ratio of these connexins may be important in the increased cellular coupling coincident with the onset of labor.

Animals↗
PubMed1996

Functional and structural assessment of intercellular communication. Increased conduction velocity and enhanced connexin expression in dibutyryl cAMP-treated cultured cardiac myocytes.

Remodeling of conduction pathways in the hypertrophic response to myocardial injury is a potential mechanism leading to the development of anatomic substrates of lethal arrhythmias. To delineate the responsible mechanisms and to directly relate changes in intercellular coupling at gap junctions with electrophysiological alterations, we studied the effects of cAMP, a mediator of cardiac hypertrophy, on action potential conduction velocity and connexin expression in neonatal rat ventricular myocyte cultures. Conduction velocity was measured with an optical activation mapping technique in cells loaded with the voltage-sensitive dye RH-237. Action potentials were conducted 24% to 29% more rapidly (P < .005) after incubating cultures for 24 hours with the cAMP analogue dibutyryl cAMP (db-cAMP, 1 mmol/L). However, db-cAMP caused no change in the maximum rate of rise of the action potential upstroke, Vmax. Electron and immunofluorescence microscopy revealed a significant increase in the number and size of gap junctions in db-cAMP-treated cells. Immunoblotting showed that the total amounts of the ventricular gap junction proteins connexin43 and connexin45 (Cx43 and Cx45, respectively) increased 2- to 4-fold. Immuno-precipitation of metabolically labeled connexin proteins revealed a dose-dependent increase in the rate of Cx45 protein synthesis in myocytes exposed to db-cAMP ( > 2-fold after a 4-hour exposure) but no change in the Cx43 synthesis rate. Northern blot analysis demonstrated a time-dependent increase in the amount of Cx43 mRNA, with a maximum 3.3-fold increase after 4 hours of exposure to 1 mmol/L db-cAMP; cycloheximide did not block this effect. In contrast, Cx45 mRNA levels were not altered significantly after db-cAMP treatment. Thus, cAMP causes a significant increase in conduction velocity that appears to be attributable largely to enhanced expression of proteins responsible for intercellular communication. Cx43 and Cx45 levels appear to be upregulated by cAMP by disparate molecular mechanisms.

Action Potentials↗
PubMed1995

The extent of heterocellular communication mediated by gap junctions is predictive of bystander tumor cytotoxicity in vitro.

Herpes simplex virus thymidine kinase (HSV-tk)/ganciclovir (GCV) viral-directed enzyme prodrug gene therapy causes potent, tumor-selective cytotoxicity in animal models in which HSV-tk gene transduction is limited to a minority of tumor cells. The passage of toxic molecules from HSV-tk+ cells to neighboring HSV-tk- cells during GCV therapy is one mechanism that may account for this "bystander" cytotoxicity. To investigate whether gap junction-mediated intercellular coupling could mediate this bystander effect, we used a flow cytometry assay to quantitate the extent of heterocellular coupling between HSV-tk+ murine fibroblasts and both rodent and human tumor cell lines. Bystander tumor cytotoxicity during GCV treatment in a coculture assay was highly correlated (P < 0.001) with the extent of gap junction-mediated coupling. These findings show that gap junction-mediated intercellular coupling contributes to the in vitro bystander effect during HSV-tk/GCV therapy and that retroviral transduction of tumor cells is not required for bystander cytotoxicity.

Animals↗
PubMed1995

The gap junction protein connexin43 is degraded via the ubiquitin proteasome pathway.

We investigated the degradation of the gap junction protein connexin43 in E36 Chinese hamster ovary cells and rat cardiomyocyte-derived BWEM cells. Treatment of E36 cells with the lysosomotropic amine, primaquine, for 16 h doubled the amount of connexin43 detected by immunoblotting and modestly increased the half-life of connexin43 in pulse-chase studies, suggesting that the lysosome played a minor role in connexin43 proteolysis. In contrast, treatment with the proteasomal inhibitor N-acetyl-L-leucyl-L-leucinyl-norleucinal led to a 6-fold accumulation of connexin43 and increased the half-life of connexin43 to approximately 9 h. The role of ubiquitin in connexin43 degradation was examined in an E36-derived mutant, ts20, which contains a thermolabile ubiquitin-activating enzyme, E1. E36 and ts20 cells grown at the permissive temperature contained similar amounts of connexin43 detectable by immunoblotting. Heat treatment dramatically reduced the amount of connexin43 detected in E36 cells, while connexin43 levels in heat-treated ts20 cells did not change. E36 cells that were heat-treated in the presence of N-acetyl-L-leucyl-L-leucinyl-norleucinal did not lose their connexin43. Pulse-chase experiments showed the reversibility of the block to connexin43 degradation in ts20 cells that were returned to the permissive temperature. Finally, sequential immunoprecipitation using anti-connexin43 and anti-ubiquitin antibodies demonstrated polyubiquitination of connexin43. These results indicate that ubiquitin-mediated proteasomal proteolysis may be the major mechanism of degradation of connexin43.

Animals↗
PubMed1995

Structural and molecular determinants of intercellular coupling in cardiac myocytes.

Electrical activation of the heart requires intercellular transfer of current through gap junctions connecting individual cardiac myocytes. Using a combination of light and electron microscopic techniques and molecular approaches, we have characterized the number, size, and spatial distribution of intercellular connections at gap junctions in cardiac myocytes and have also cloned, sequenced, and elucidated the subcellular distribution of three physiologically distinct gap junction channel proteins. In this review, we present evidence to suggest that the spatial distribution of myocyte interconnections and the molecular composition of gap junction channels may confer distinct conduction properties on specific tissues of the mammalian heart such as atrial and ventricular myocardium, and the nodes and bundles of the cardiac conduction system.

Animals↗
PubMed1995

Distinct behavior of connexin56 and connexin46 gap junctional channels can be predicted from the behavior of their hemi-gap-junctional channels.

The gap-junctional protein rat connexin46 (Cx46) has the unusual ability to form voltage-gated channels in the nonjunctional plasma membrane of Xenopus oocytes (Paul et al., 1991; Ebihara and Steiner, 1993). These have been suggested to be gap-junctional hemichannels or connexons. The Xenopus oocyte system was used to characterize the functional properties of a closely related lens gap-junctional protein, chicken connexin56 (Cx56) (Rup et al., 1993) and to contrast them to those of rat Cx46. Single oocytes injected with either Cx56 or Cx46 cRNA developed time-dependent, outward currents that activated on depolarization. The currents induced by Cx56 and Cx46 showed differences in steady-state voltage dependence and in their degree of rectification. Furthermore, the voltage-dependent properties of the nonjunctional channels induced by the connexin cRNAs in external solutions containing low concentrations of calcium ions could account remarkably well for the behavior of the intercellular channels formed by Cx56 and Cx46 in paired oocytes. These results suggest that many of the voltage-dependent properties of the hemi-gap-junctional channels are retained by the intercellular channels.

Animals↗
PubMed1995

Transfected connexin45 alters gap junction permeability in cells expressing endogenous connexin43.

Many cells express multiple connexins, the gap junction proteins that interconnect the cytosol of adjacent cells. Connexin43 (Cx43) channels allow intercellular transfer of Lucifer Yellow (LY, MW = 443 D), while connexin45 (Cx45) channels do not. We transfected full-length or truncated chicken Cx45 into a rat osteosarcoma cell line ROS-17/2.8, which expresses endogenous Cx43. Both forms of Cx45 were expressed at high levels and colocalized with Cx43 at plasma membrane junctions. Cells transfected with full-length Cx45 (ROS/Cx45) and cells transfected with Cx45 missing the 37 carboxyl-terminal amino acids (ROS/Cx45tr) showed 30-60% of the gap junctional conductance exhibited by ROS cells. Intercellular transfer of three negatively charged fluorescent reporter molecules was examined. In ROS cells, microinjected LY was transferred to an average of 11.2 cells/injected cell, while dye transfer between ROS/Cx45 cells was reduced to 3.9 transfer between ROS/Cx45 cells was reduced to 3.9 cells. In contrast, ROS/Cx45tr cells transferred LY to > 20 cells. Transfer of calcein (MW = 623 D) was also reduced by approximately 50% in ROS/Cx45 cells, but passage of hydroxycoumarin carboxylic acid (HCCA; MW = 206 D) was only reduced by 35% as compared to ROS cells. Thus, introduction of Cx45 altered intercellular coupling between cells expressing Cx43, most likely the result of direct interaction between Cx43 and Cx45. Transfection of Cx45tr and Cx45 had different effects in ROS cells, consistent with a role of the carboxyl-terminal domain of Cx45 in determining gap junction permeability or interactions between connexins. These data suggest that coexpression of multiple connexins may enable cells to achieve forms of intercellular communication that cannot be attained by expression of a single connexin.

Animals↗
PubMed1995

Gap junction protein phenotypes of the human heart and conduction system.

INTRODUCTION: Gap junction channels are major determinants of intercellular resistance to current flow between cardiac myocytes. Alterations in gap junctions may contribute to development of arrhythmia substrates in patients. However, there is significant interspecies variation in the types and amounts of gap junction subunit proteins (connexins) expressed in disparate regions of mammalian hearts. To elucidate determinants of conduction properties in the human heart, we characterized connexin phenotypes of specific human cardiac tissues with different conduction properties. METHODS AND RESULTS: The distribution and relative abundance of Cx37, Cx40, Cx43, Cx45, and Cx46 were studied immunohistochemically using monospecific antibodies and frozen sections of the sinoatrial node and adjacent atria. AV node and His bundle, the bundle branches, and the left and right ventricular walls. Patterns of expression of these connexins in the human heart differed from those in previous animal studies. Sinus node gap junctions were small and sparse and contained Cx45 and apparently smaller amounts of Cx40 but no Cx43. AV node gap junctions were also small and contained mainly Cx45 and Cx40 but, unlike the sinus node, also expressed Cx43. Atrial gap junctions were larger than nodal junctions and contained moderate amounts of Cx40, Cx43, and Cx45. Junctions in the bundle branches were the largest in size and contained abundant amounts of Cx40, Cx43, and Cx45. Gap junctions in ventricular myocardium contained mainly Cx43 and Cx45; only a very small and amount of ventricular Cx40 was detected in subendocardial myocyte junctions and endothelial cells of small to medium sized intramural coronary arteries. Minimal Cx37 and Cx46 immunoreactivity was detected between occasional atrial or ventricular myocytes. CONCLUSIONS: The relative amounts of individual connexins and the number and size of gap junctions vary greatly in specific regions of the human heart with different conduction properties. These differences likely play a role in regulating cardiac conduction velocity. Differences in the connexin phenotypes of specific regions of the human heart and experimental animal hearts must be considered in future experimental or modeling studies of cardiac conduction.

Adult↗
PubMed1995

The molecular basis of anisotropy: role of gap junctions.

Electrical activation of the heart requires transfer of current from one discrete cardiac myocyte to another, a process that occurs at gap junctions. Recent advances in knowledge have established that, like most differentiated cells, individual cardiac myocytes express multiple gap junction channel proteins that are members of a multigene family of channel proteins called connexins. These proteins form channels with unique biophysical properties. Furthermore, functionally distinct cardiac tissues such as the nodes and bundles of the conduction system and atrial and ventricular muscle express different combinations of connexins. Myocytes in these tissues are interconnected by gap junctions that differ in tissue-specific manner in terms of their number, size, and three-dimensional distribution. These observations suggest that both molecular and structural aspects of gap junctions are critical determinants of the anisotropic conduction properties of different cardiac tissues. Expression of multiple connexins also creates the possibility that "hybrid" channels composed of more than one connexin protein type can form, thus greatly increasing the potential for fine control of intercellular ion flow and communication within the heart.

Anisotropy↗
PubMed1995

Modulation of connexin43 expression: effects on cellular coupling.

INTRODUCTION: Gap junctions connect cardiac myocytes allowing propagation of action potentials. They contain intercellular channels formed by multiple different connexin proteins. The arrangement and type of gap junctions and the types, function, and interaction of connexin proteins determine intercellular resistance and can thereby influence conduction velocity and the potential for reentrant arrhythmias. Our goal was to develop genetically manipulable models to test the effects of altering expression of a major cardiac connexin (connexin43) on intercellular coupling and expression of other connexin proteins. METHODS AND RESULTS: BHK cells that are poorly coupled and BWEM cells that are well coupled were stably transfected with plasmids containing connexin43 cDNA in antisense and sense orientations. RNA blots confirmed expression of the transfected transcripts. Immunoblots showed that connexin43 protein was reduced in the BHK antisense transfectants and increased in the BHK sense transfectants compared to the parental cells. It was not detectably changed in the BWEM antisense transfectant line compared to the BWEM parental cells. Transfection of connexin43 cDNA did not affect production of connexin45 mRNA and protein nor did transfection induce expression of other previously unexpressed connexin mRNAs. Cell coupling was assessed by intercellular diffusion of microinjected Lucifer yellow in confluent cell populations. Lucifer yellow passed to a mean of 3 +/- 3 neighboring parental BHK cells, to 8 +/- 8 neighbors in the sense connexin43 transfected BHK cells, and to only 2 +/- 2 neighbors in the antisense connexin43 transfected BHK cells (P < 0.05). In contrast, dye transfer did not differ significantly between the parental BWEM cells (mean transfer = 19 +/- 14 cells) and the BWEM connexin43 antisense transfectants (mean transfer = 15 +/- 12 cells) (P = 0.20). CONCLUSIONS: These data demonstrate that stable transfection with connexin43 cDNA constructs can result in detectable changes in connexin43 expression and cellular coupling without inducing compensatory changes in the cell's connexin phenotype and, therefore, may provide a basis for future attempts at specifically modulating connexin expression and intercellular resistance in cardiac tissues.

Animals↗
PubMed1995

Properties of gap junction channels formed of connexin 45 endogenously expressed in human hepatoma (SKHep1) cells.

We have evaluated the voltage dependence and unitary conductance of gap junctional channels that were recorded in a clone isolated from the hepatoma cell line SKHep1. In this clonal population (designated SKHep1A), Northern blots, immunoprecipitation, and immunohistochemical staining demonstrated the expression of connexin (Cx) 45; no other gap junction protein was identified by these techniques, although weak hybridization with Cx40 was detected. Macroscopic junctional conductance (gj) in these cells was low, averaging 1.3 nS, and was steeply voltage dependent. Parameters of voltage sensitivity were as follows: voltage at which voltage-sensitive conductance is reduced by 50%, 13.4 mV; steepness of relation, 0.115 (corresponding to 2.7 gating charges), and voltage-insensitive fraction of residual to total conductance approximately 0.06. Unitary conductance (gamma j) of these junctional channels averaged 32 +/- 8 pS; although gamma j was independent of transjunctional voltage (Vj), at high Vj values (> 50 mV), smaller conductance values were also detected. Open probabilities of the 30-pS channels at various Vj values closely matched the predicted voltage-dependent component of macroscopic gj, the residual conductance at high Vj might be attributable to the smaller conductance events. The voltage dependence of human Cx45 gap junction channels is as steep as that seen for channels formed by Xenopus Cx38 and is much steeper than that previously reported for channels formed of the highly homologous chick Cx45 and for other mammalian connexins expressed either endogenously or exogenously.

Carcinoma, Hepatocellular↗
PubMed1995

Connexin 43 and connexin 40 gap junctional proteins are present in arteriolar smooth muscle and endothelium in vivo.

The distributions of connexin 43 (Cx43) and connexin 40 (Cx40) in smooth muscle and endothelium of resistance vessels were examined using indirect immunofluorescence techniques coupled with confocal microscopy. Cx43 and Cx40 were found in smooth muscle and endothelium. Similar staining patterns were found in microvessel samples from brain and cremaster of the rat and from arterioles of the hamster cheek pouch. Double-labeling studies showed a high degree of colocalization of Cx40 with Cx43, suggesting the presence of multiple connexins within a single junctional plaque. Quantitative comparisons were made of the fluorescent patterns in the endothelium and smooth muscle of rat brain arterioles. Cx43 and Cx40 plaque diameters were 0.9 +/- 0.1 and 0.8 +/- 0.1 (SE) microns, respectively, in the endothelial layer and 0.5 +/- 0.1 and 0.5 +/- 0.1 microns, respectively, in the smooth muscle. There was no difference between mean plaque diameters of Cx43 and Cx40 in endothelium or smooth muscle. However, plaques were significantly larger in endothelium than in smooth muscle (P < 0.05). These findings demonstrate the potential for cell-cell communication in both cell types of the wall of arterioles from three different tissues. The data also suggest a greater level of coupling within the endothelium.

Animals↗
PubMed1995

Expression of multiple connexins in cultured neonatal rat ventricular myocytes.

Three gap junction proteins have been identified in mammalian cardiac myocytes: connexin43 (Cx43), connexin45 (Cx45), and connexin40 (Cx40). These proteins form channels with different electrophysiological properties and have different distributions in cardiac tissues with disparate conduction properties. We characterized the expression, phosphorylation, turnover, and subcellular distribution of these connexins in primary cultures of neonatal rat ventricular myocytes. Cx43, Cx45, and Cx40 mRNA were specifically detected in RNA blots. Immunofluorescent staining with antibodies specific for Cx43 and Cx45 revealed punctate labeling at appositional membranes, but no immunoreactive Cx40 was detected. Double-label immunofluorescence confocal microscopy of cultured myocytes revealed colocalization of Cx43 and Cx45. Cx43 and Cx45 were both identified by immunoprecipitation from [35S]methionine-labeled cultures, but anti-Cx40 antibodies did not precipitate any radiolabeled protein. Phosphorylated forms of both Cx45 and Cx43 were immunoprecipitated from cultures metabolically labeled with [32P]orthophosphate. Phosphoamino acid analysis demonstrated that Cx45 was modified on serine residues, and Cx43 was phosphorylated on serine and threonine residues. Pulse-chase labeling experiments demonstrated that the half-lives of Cx43 and Cx45 were 1.9 and 2.9 hours, respectively. Thus, both Cx43 and Cx45 turn over relatively rapidly, suggesting that myocardial gap junctions have the potential for dynamic remodeling. The results implicate multiple mechanisms of gap junction regulation that may differ for different connexins.

Animals↗
PubMed1995

Unique conductance, gating, and selective permeability properties of gap junction channels formed by connexin40.

Connexin40 is selectively expressed in specialized cardiac conduction (nodal and His-Purkinje) tissues and the atrium, yet the channel properties formed by this gap junction protein have not been investigated. The conductance, gating, and selective permeability of rat connexin40 (Cx40) gap junction channels between pairs of Cx40-transfected mouse neuroblastoma (N2A) cells in culture were studied by using dual whole-cell voltage-clamp techniques. The macroscopic steady state junctional conductance gating was dependent on transjunctional voltage with a Boltzmann half-inactivation voltage of +/- 50 mV, a residual voltage-insensitive normalized junctional conductance of 35% of maximum, and a gating charge valence of 3. In the presence of 120 mmol/L potassium glutamate, the slope conductance of single rat Cx40 gap junction channels measured 158 +/- 2 pS (n = 4). Lower conductance states equal to 21% to 48% of the main open-state conductance were also occasionally observed in two of the four cell pairs. Multichannel open probabilities were found to be heterogeneous. Ion substitution and dye transfer experiments were performed to determine the relative chloride/potassium conductance and dye permeability of anionic fluorescein derivatives in rat Cx40 channels. The rat Cx40 channel had a maximum conductance of 180 +/- 18 pS (n = 3) in 120 mmol/L KCl and a detectable chloride permeability of 0.29 relative to potassium, indicating some selectivity for cations over anions. Cx40 gap junctions were permeable to 2',7'-dichlorofluorescein (diCl-F) and also to the more polar 6-carboxyfluorescein dye; however, diCl-F dye transfer was not observed to increase with increasing junctional conductance.

Animals↗
PubMed1995

Selectivity of connexin-specific gap junctions does not correlate with channel conductance.

Connexins form a variety of gap junction channels that vary in their developmental and tissue-specific levels of expression, modulation of gating by transjunctional voltage and posttranslational modification, and unitary channel conductance (gamma j). Despite a 10-fold variation in gamma j, whether connexin-specific channels possess distinct ionic and molecular permeabilities is presently unknown. A major assumption of the conventional model for a gap junction channel pore is that gamma j is determined primarily by pore diameter. Hence, molecular size permeability limits should increase and ionic selectivity should decrease with increasing channel gamma j (and pore diameter). Equimolar ion substitution of 120 mmol/L KCl for potassium glutamate was used to determine the unitary conductance ratios for rat connexin40 and connexin43, chicken connexin43 and connexin45, and human connexin37 channels functionally expressed in communication-deficient mouse neuroblastoma (N2A) cells. Comparison of experimental and predicted conductance ratios based on the aqueous mobilities of all ions according to the Goldman-Hodgkin-Katz current equation was used to determine relative anion-to-cation permeability ratios. Direct correlation of junctional conductance with dye transfer of two fluorescein-derivatives (2 mmol/L 6-carboxyfluorescein or 2',7'-dichlorofluorescein) was also performed. Both approaches revealed a range of selectivities and permeabilities for all five different connexins that was independent of channel conductance. These results are not consistent with the conventional simple aqueous pore model of a gap junction channel and suggest a new model for connexin channel conductance and permselectivity based on electrostatic interactions. Divergent conductance and permeability properties are features of other classes of ion channels (eg, Na+ and K+ channels), implying similar mechanisms for selectivity.

Animals↗
PubMed1995

Cardiac intercellular communication: consequences of connexin distribution and diversity.

Gap junctions contain channels which allow the exchange of ions and small molecules between adjacent cells. In the heart, these channels are crucial for normal intercellular current flow and the propagation of action potentials throughout the myocardium. Molecular cloning studies have demonstrated that these channels are formed by members of a family of related proteins called connexins each containing conserved and unique regions. There are several consequences of this multiplicity of connexins. Multiple connexins are expressed in differing, but sometimes overlapping, distributions within cardiovascular and other tissues. Connexin40, connexin43, and connexin45 are all found in cardiac myocytes, but their abundance differs in specialized cardiac regions with disparate conductive properties. Individual connexins form channels with differing voltage-dependence, conductance, and permeability properties, as demonstrated by functional expression of the cloned sequences. Connexins differ in their modification by phosphorylation, which may contribute to physiological regulation of intercellular communication. Expression of multiple connexins may lead to the formation of multiple channel types in a single tissue or cell and potentially allows mixing to form heterotypic and/or heteromeric channels. Thus, multiple connexins may contribute to the differences in intercellular resistance in cardiac regions with differing conductive properties and possibly may allow differences in the signalling molecules that pass between cells.

Animals↗
PubMed1994

Expression patterns of mRNAs for the gap junction proteins connexin43 and connexin42 suggest their involvement in chick limb morphogenesis and specification of the arterial vasculature.

Gap junctions which comprise a family of proteins called connexins have been implicated in the morphogenesis of the chick limb bud. We have examined the expression patterns of two members of the connexin family, connexin43 (Cx43) and connexin42 (Cx42), during the early development of the chick limb bud and embryo by in situ hybridization. Cx43 mRNA is expressed in high amounts in the apical ectodermal ridge (AER), which promotes the outgrowth of the mesodermal cells of the limb bud, and in the ectopic AER of the limb buds of polydactylous diplopodia-5 mutant embryos. In contrast, little Cx43 expression is detectable in nonridge limb ectoderm at early stages of limb development. These results suggest that Cx43 gap junctions may integrate the activity of the cells comprising the AER and compartmentalize them into a functionally distinct entity capable of directing limb outgrowth. In addition, Cx43 exhibits high expression in the posterior subridge mesoderm of the early limb bud that is growing out in response to the AER, but little expression in the anterior mesoderm. This graded distribution of Cx43 transcripts correlates with a functional gradient of gap junctional communication along the anteroposterior (AP) axis, and suggests that Cx43 gap junctions may be involved in pattern formation across the AP axis. At later stages of development, Cx43 is transiently expressed in high amounts in the precartilage condensations of the carpals and metacarpals, at a time when critical cell-cell interactions are occurring that trigger cartilage differentiation. In contrast, in the developing limb, Cx42 is expressed exclusively by the central artery. In the remainder of the chick embryo, Cx42 is expressed in high amounts by the vessels comprising the arterial vasculature, but is not expressed by the venous vasculature. Thus, Cx42 gap junctions may be involved in specification of the arterial vasculature of the limb and embryo. Cx42, but not Cx43, is expressed in the ventricle of the heart, and by cells along the intrasclerotomal fissure that separates the rostral and caudal halves of the sclerotome of somites into distinct communication compartments.

Animals↗