BMP regulation of the mouse connexin43 promoter in osteoblastic cells and embryos

Regulation of connexin 43 expression in human gingival fibroblasts

AIMS

Abundance of connexin 43 (Cx43), a transmembrane protein that forms hemichannels (HCs) and gap junctions (GJs), is dynamically regulated in human gingival fibroblasts (GFBLs) during wound healing. This may be important for fast and scarless gingival wound healing as Cx43 is involved in key cell functions important during this process. Our aim was to uncover the factors that regulate Cx43 expression and abundance in GFBLs. We hypothesized that cytokines and growth factors released during wound healing coordinately regulate Cx43 abundance in GFBLs.

RESULTS

TGF-β1, -β2, -β3, PGE2 and IL-1β significantly upregulated, while TNF-α and IFN-γ downregulated Cx43 in cultured GFBLs. TGF-β1, -β2, -β3, IL-1β and IFN-γ modulated Cx43 abundance at both mRNA and protein levels, while TNF-α and PGE2 regulated only Cx43 protein abundance, suggesting involvement of distinct transcriptional/post-transcriptional and translational/post-translational mechanisms, respectively. TGF-β1-induced upregulation of Cx43 was mediated by TGFβRI (ALK5) and SMAD2/3 signaling, and this was potently suppressed by PGE2, IL-1β, TNF-α and IFN-γ that inhibited SMAD2/3 phosphorylation.

CONCLUSION

Regulation of Cx43 abundance in GFBLs involves transcriptional/post-transcriptional and translational/post-translational mechanisms that are distinctly modulated by an interplay between TGF-β isoforms and PGE2, IL-1β, TNF-α and IFN-γ.

Joint diseases: from connexins to gap junctions

Connexons form the basis of hemichannels and gap junctions. They are composed of six tetraspan proteins called connexins. Connexons can function as individual hemichannels, releasing cytosolic factors (such as ATP) into the pericellular environment. Alternatively, two hemichannel connexons from neighbouring cells can come together to form gap junctions, membrane-spanning channels that facilitate cell-cell communication by enabling signalling molecules of approximately 1 kDa to pass from one cell to an adjacent cell. Connexins are expressed in joint tissues including bone, cartilage, skeletal muscle and the synovium. Indicative of their importance as gap junction components, connexins are also known as gap junction proteins, but individual connexin proteins are gaining recognition for their channel-independent roles, which include scaffolding and signalling functions. Considerable evidence indicates that connexons contribute to the function of bone and muscle, but less is known about the function of connexons in other joint tissues. However, the implication that connexins and gap junctional channels might be involved in joint disease, including age-related bone loss, osteoarthritis and rheumatoid arthritis, emphasizes the need for further research into these areas and highlights the therapeutic potential of connexins.

Bone morphogenetic protein 2 regulates cell-cell communication by down-regulating connexin43 expression in luteinized human granulosa cells

STUDY QUESTION

Does bone morphogenetic protein 2 (BMP2) regulate connexin43 (Cx43) and modulate cell-cell communication in luteinized human granulosa cells?

SUMMARY ANSWER

BMP2 decreases gap junction intercellular communication (GJIC) of luteinized human granulosa cells by down-regulating Cx43 expression through an activin receptor-like kinase (ALK)2/ALK3-mediated Sma- and Mad-related protein (SMAD)-dependent signaling pathway.

WHAT IS KNOWN ALREADY

BMP2 and its putative receptors are highly expressed in the human corpus luteum and are involved in the process of luteolysis. Cx43-coupled gap junctions play a critical role in the development and maintenance of corpus luteum.

STUDY DESIGN DURATION

This is a laboratory study conducted over a 1-year period. At least three independent experiments with three replicates were conducted and the experimental samples were compared with the appropriate vehicle controls for all of the inhibition-approach, concentration-dependent or time-course studies.

PARTICIPANTS/MATERIALS, SETTING, METHODS

SVOG cell line (immortalized human granulosa-lutein cells derived from in vitro fertilization patients in an academic research center) was used as the study model. The changes of Cx43 expression and levels of phosphorylated SMAD1/5/8 protein were evaluated after exposure to recombinant human BMP2. Real-time quantitative PCR and Western blot analysis were used to examine the specific mRNA and protein levels, respectively. The BMP/TGF-β type I receptor inhibitors (Dorsomorphin, DMH-1 and SB431542) and target depletion small interfering RNAs (ALK2, ALK3, ALK6 and SMAD4) were used to investigate the underlying molecular mechanisms. A scrape loading and dye transfer assay was used to evaluate the GJIC between the SVOG cells.

MAIN RESULTS AND THE ROLE OF CHANCE

Treatment with BMP2 down-regulated the expression of Cx43 and decreased the GJIC activity, whereas it increased the phosphorylated SMAD1/5/8 protein in SVOG cells (P < 0.05). These biological effects were abolished by pre-treatment with the BMP type I receptor inhibitors, Dorsomorphin and DMH-1 (P < 0.05), but not SB431542. Additionally, the individual or concomitant small interfering RNA-mediated knockdown of ALK2 and ALK3, but not ALK6 attenuated the BMP2-induced increases in phosphorylated SMAD1/5/8 and down-regulation of Cx43 expression (P < 0.05). The knockdown of SMAD4 completely abolished the BMP2-induced down-regulation of Cx43 expression (P < 0.05).

LIMITATIONS REASONS FOR CAUTION

This experimental study was conducted in an in vitro cell culture system, and may not reflect a realistic intra-ovarian environment.

WIDER IMPLICATIONS OF THE FINDINGS

Our results suggested that BMP2 may be involved in the local modulation of cell-cell communication in the luteal phase. This study also represents the first comprehensive research of molecular mechanisms of BMP2 in the down-regulation Cx43 in luteinized human granulosa cells. Such data may provide valuable insights into ovarian physiology and benefit the development of potential therapeutic methods for patients suffering from luteal insufficiency.

LARGE SCALE DATA

N/A.

STUDY FUNDING AND COMPETING INTEREST(s)

This research was supported by an operating grant from the China-Canadian Joint Health Research Initiative Grants Program to P.C.K. Leung and J.Z. Sheng. The authors declare no competing interest with the contents of this article.

BMP Signaling Mediated by BMPR1A in Osteoclasts Negatively Regulates Osteoblast Mineralization Through Suppression of Cx43

Osteoblasts and osteoclasts are well orchestrated through different mechanisms of communication during bone remodeling. Previously, we found that osteoclast-specific disruption of one of the BMP receptors, Bmpr1a, results in increased osteoblastic bone formation in mice. We hypothesized that BMPR1A signaling in osteoclasts regulates production of either membrane bound proteins or secreted molecules that regulated osteoblast differentiation. In our current study, we co-cultured wild-type osteoblasts with either control osteoclasts or osteoclasts lacking BMPR1A signaling activity. We found that loss of Bmpr1a in osteoclasts promoted osteoblast mineralization in vitro. Further, we found that the expression of Cx43/Gja1 in the mutant osteoclasts was increased, which encoded for one of the gap junction proteins connexin 43/gap junction alpha 1. Knockdown of Gja1 in the mutant osteoclasts for Bmpr1a reduced osteoblastic mineralization when co-cultured. Our findings suggest that GJA1 may be one of the downstream targets of BMPR1A signaling in osteoclasts that mediates osteoclast-osteoblast communication during bone remodeling. J. Cell. Biochem. 118: 605-614, 2017. © 2016 Wiley Periodicals, Inc.

Osterix plays a critical role in BMP4-induced promoter activity of connexin43

Osterix is an essential transcription factor for osteogenesis and is expressed in osteoblasts. Although Osterix has been shown to be induced by bone morphogenetic protein 4, the molecular mechanism underlying Osterix function during osteoblast differentiation remains unclear. Connexin43 (Cx43) is the most abundant gap junction protein in bone cells and plays a critical role in osteoblast differentiation. However, little is known about the functional interactions between Osterix and the Cx43 promoter. In the present study, we investigated the relationship between Osterix and Cx43 in HEK293 and C2C12 cells. Cx43 expression was significantly repressed by the addition of shRNA against Osterix, whereas overexpression of Osterix resulted in enhanced Cx43 expression. Furthermore, Osterix directly occupied the promoter region of Cx43 and subsequently increased Cx43 promoter activity in a dose-dependent manner. In addition, phosphorylation of the Ser76 and Ser80 residues in Osterix were found to be critical for its activity on the Cx43 promoter. Our results suggest that Osterix plays an important role in increasing bone morphogenetic protein 4-induced Cx43 activity.

Transforming growth factor-β1 up-regulates connexin43 expression in human granulosa cells

STUDY QUESTION

Does transforming growth factor-β1 (TGF-β1) up-regulate connexin43 (Cx43) to promote cell-cell communication in human granulosa cells?

SUMMARY ANSWER

TGF-β1 up-regulates Cx43 and increases gap junction intercellular communication activities (GJIC) in human granulosa cells, and this effect occurs via the activin receptor-like kinase (ALK)5-mediated Sma- and Mad-related protein (SMAD)2/3-SMAD4-dependent pathway.

WHAT IS KNOWN ALREADY

TGF-β1 and its receptors are expressed in human granulosa cells, and follicular fluid contains TGF-β1 protein. In human granulosa cells, Cx43 gap junctions play an important role in the development of follicles and oocytes.

STUDY DESIGN, SIZE, DURATION

This is an experimental study which was performed over a 1-year period.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Immortalized human granulosa cells (SVOG cells) and primary human granulosa-lutein cells obtained from women undergoing IVF in an academic research center were used as the study models. Cx43 mRNA and protein expression levels were examined after exposure of SVOG cells to recombinant human TGF-β1. An activin/TGF-β type I receptor inhibitor, SB431542, and small interfering RNAs targeting ALK4, ALK5, SMAD2, SMAD3 and SMAD4 were used to verify the specificity of the effects and to investigate the molecular mechanisms. Real-time-quantitative PCR and western blot analysis were used to detect the specific mRNA and protein levels, respectively. GJIC between SVOG cells were evaluated using a scrape loading and dye transfer assay. Results were analyzed by one-way analysis of variance.

MAIN RESULTS AND THE ROLE OF CHANCE

TGF-β1 treatment increased phosphorylation of SMAD2/3 (P < 0.0001) and up-regulated Cx43 mRNA and protein levels (P < 0.001) in SVOG cells and these stimulatory effects were abolished by the TGF-β type I receptor inhibitor SB431542. In addition, the up-regulatory effect of TGF-β1 on Cx43 expression (mRNA and protein) was confirmed in primary cultures of human granulosa-lutein cells (P < 0.05). The small interfering RNA-mediated knockdown of ALK5, but not ALK4, abolished the TGF-β1-induced phosphorylation of SMAD2/3 and the up-regulation of Cx43. Furthermore, knockdown of SMAD2/3 or the common SMAD, SMAD4, abolished the stimulatory effects of TGF-β1 on Cx43 expression in SVOG cells. The TGF-β1-induced up-regulation of Cx43 contributed to the increase of GJIC between SVOG cells (P < 0.001).

LIMITATIONS, REASONS FOR CAUTION

The results of this study were generated from in vitro system and may not reflect the intra-ovarian microenvironment in vivo.

WIDER IMPLICATIONS OF THE FINDINGS

Our studies represent the first comprehensive research of molecular mechanisms of TGF-β1 in the regulation of Cx43 expression and GJIC in human granulosa cells and demonstrate that TGF-β1 may play a crucial role in the local modulation of cell-cell communication. Deepening our understanding of the molecular determinants will offer important insights into ovarian physiology and lead to the development of potential therapeutic methods for fertility regulation.

STUDY FUNDING/COMPETING INTERESTS

This research was supported by an operating grant from the Canadian Institutes of Health Research to P.C.K.L. There are no conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

NA.

miRNA-17 members that target Bmpr2 influence signaling mechanisms important for embryonic stem cell differentiation in vitro and gastrulation in embryos

Body axes and germ layers evolve at gastrulation, and in mammals are driven by many genes; however, what orchestrates the genetic pathways during gastrulation remains elusive. Previously, we presented evidence that microRNA-17 (miRNA-17) family members, miR-17-5p, miR-20a, miR-93, and miR-106a were differentially expressed in mouse embryos and functioned to control differentiation of the stem cell population. Here, we identify function(s) that these miRNAs have during gastrulation. Fluorescent in situ hybridization miRNA probes reveal that these miRNAs are localized at the mid/posterior primitive streak (ps) in distinct populations of primitive ectoderm, mesendoderm, and mesoderm. Seven different miRNA prediction algorithms are identified in silico bone morphogenic protein receptor 2 (Bmpr2) as a target of these miRNAs. Bmpr2 is a member of the TGFβ pathway and invokes stage-specific changes during gastrulation. Recently, Bmpr2 was shown regulating cytoskeletal dynamics, cell movement, and invasion. Our previous and current data led to a hypothesis by which members of the miR-17 family influence gastrulation by suppressing Bmpr2 expression at the primitive streak. This suppression influences fate decisions of cells by affecting genes downstream of BMPR2 as well as mesoderm invasion through regulation of actin dynamics.

Combined biophysical and soluble factor modulation induces cardiomyocyte differentiation from human muscle derived stem cells

Cellular cardiomyoplasty has emerged as a novel therapy to restore contractile function of injured failing myocardium. Human multipotent muscle derived stem cells (MDSC) can be a potential abundant, autologous cell source for cardiac repair. However, robust conditions for cardiomyocyte (CM) differentiation are not well established for this cell type. We have developed a new method for CM differentiation from human MDSC that combines 3-dimensional artificial muscle tissue (AMT) culture with temporally controlled biophysical cell aggregation and delivery of 4 soluble factors (microRNA-206 inhibitor, IWR-1, Lithium Chloride, and BMP-4) (4F-AG-AMT). The 4F-AG-AMT displayed cardiac-like response to β-adrenergic stimulation and contractile properties. 4F-AG-AMT expressed major cardiac (NKX2-5, GATA4, TBX5, MEF2C) transcription factors and structural proteins. They also express cardiac gap-junction protein, connexin-43, similar to CMs and synchronized spontaneous calcium transients. These results highlight the importance of temporal control of biophysical and soluble factors for CM differentiation from MDSCs.

Theca-derived BMP4 and BMP7 down-regulate connexin43 expression and decrease gap junction intercellular communication activity in immortalized human granulosa cells

CONTEXT

Connexin43 (Cx43)-coupled gap junctions in granulosa cells play important roles in follicular and oocyte development and may be modulated by theca cell-derived bone morphogenic protein (BMP) 4 and BMP7.

OBJECTIVE

The aim of this study was to examine the effects of BMP4 and BMP7 on Cx43 expression in human granulosa cells and its potential mediation by the Smad-dependent pathway.

DESIGN

An immortalized human granulosa (SVOG) cell was used to investigate Cx43 expression and gap junction intercellular communication (GJIC) activity after exposure to BMP4 and BMP7. A BMP type I inhibitor, dorsomorphin, and small interfering RNAs targeting Smad4 were used to verify the specificity of the effects.

SETTING

The study was conducted in an academic center.

MAIN OUTCOME MEASURES

Extracts were prepared from cultured cells, the Cx43 mRNA levels were examined using RT-quantitative real-time PCR, and the levels of Cx43 protein and phosphorylated Smad1/5/8 were assayed using Western blot analyses. GJIC activities between SVOG cells were evaluated using a scrape loading and dye transfer assay.

RESULTS

Treatment with BMP4 and BMP7 significantly decreased Cx43 mRNA and protein levels, as well as GJIC activities. These suppressive effects were attenuated by cotreatment with the BMP type I receptor inhibitor dorsomorphin. Furthermore, Smad4 knockdown reversed the effects of BMP4 and BMP7 on Cx43 expression.

CONCLUSION

Theca cell-derived BMP4 and BMP7 down-regulate Cx43 expression and decrease GJIC activity in human granulosa cells. Our findings indicate that this biological effect is most likely mediated by a Smad-dependent pathway.

Gap junctions and hemichannels in signal transmission, function and development of bone

Gap junctional intercellular communication (GJIC) mediated by connexins, in particular connexin 43 (Cx43), plays important roles in regulating signal transmission among different bone cells and thereby regulates development, differentiation, modeling and remodeling of the bone. GJIC regulates osteoblast formation, differentiation, survival and apoptosis. Osteoclast formation and resorptive ability are also reported to be modulated by GJIC. Furthermore, osteocytes utilize GJIC to coordinate bone remodeling in response to anabolic factors and mechanical loading. Apart from gap junctions, connexins also form hemichannels, which are localized on the cell surface and function independently of the gap junction channels. Both these channels mediate the transfer of molecules smaller than 1.2kDa including small ions, metabolites, ATP, prostaglandin and IP(3). The biological importance of the communication mediated by connexin-forming channels in bone development is revealed by the low bone mass and osteoblast dysfunction in the Cx43-null mice and the skeletal malformations observed in occulodentodigital dysplasia (ODDD) caused by mutations in the Cx43 gene. The current review summarizes the role of gap junctions and hemichannels in regulating signaling, function and development of bone cells. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.

Cell communication and tissue engineering

Gap junction intercellular communication (GJIC) is ubiquitous in the majority of cells and is indispensable for proper development and function of most tissues. The loss of gap junction mediated cell to cell communication leads to compromised development in many tissues and organs, and also facilitates tumorigenesis and autonomous cell behavior in cancerous cells. Because cells embedded in an extracellular matrix constantly interact through gap junctions to coordinate normal tissue functions and homeostasis, our group hypothesized that increasing cell to cell communication, via genetically engineering cells to overexpress gap junction proteins, could improve cell signaling and increase differentiation in interior regions of engineered tissue equivalents. In a recent paper,1 we presented a platform to regenerate full 3D equivalents of engineered tissue, providing a strategy to overcome a barrier in regenerative medicine. These findings suggest that both targeted delivery and cell-based strategies can be used as treatments to enhance communication in 3D living tissue.2 In this addendum, we address the effects of extracellular calcium (Ca(2+) (e)) on intracellular calcium (Ca(2+) (i)), GJIC and osteogenic differentiation under conditions in which bone marrow stromal cells (BMSCs) also exhibit higher cell-to-cell communication. As a key secondary messenger in many biological processes, the levels of Ca(2+) (e) and Ca(2+) (i) play a role in cell differentiation and may be a tunable signal in tissue regeneration. Higher cell-to-cell communication was achieved by both genetically engineering cells to overexpress connexin 43 (Cx43) and by a high density cell seeding technique, denoted micromass seeding (MM). The results presented in this addendum show that the intensity and duration of a second messenger, like calcium, can be augmented in a platform that enables higher cell-to-cell communication. The ability to modulate calcium signaling, combined with our previous approaches to modulate GJIC, may have an impact on tissue regeneration and therapies for communication incompetent cells, such as those associated with heart disease and certain types of cancer.

Dedifferentiation of human articular chondrocytes is associated with alterations in expression patterns of GDF-5 and its receptors

Human articular chondrocytes are expanded in monolayer culture in order to obtain sufficient cells for matrix-associated cartilage transplantation. During this proliferation process, the cells change their shape as well as their expression profile. These changes resemble those that occur during embryogenesis, when the limb anlagen form the interzone that later develops the joint cleft. We analysed the expression profile of genes that are reportedly important for these changes during embryogenesis within the dedifferentiation process of adult articular chondrocytes. We found GDF-5, BMPR-Ib and connexin 43 up-regulated, as well as a down-regulation of BMPR-Ia and noggin. Connexin 32 could not be detected in either native cartilage or in dedifferentiated cells. The newly synthesized proteins were detected by immunofluorescence. There is evidence from our results that dedifferentiated chondrocytes resemble the cells from the interzone in developing synovial joints.

Connexin 43 as a signaling platform for increasing the volume and spatial distribution of regenerated tissue

Gap junction intercellular communication (GJIC) is ubiquitous in the majority of vertebrate cells and is required for the proper development of most tissues. The loss of gap junction-mediated cell-to-cell communication leads to compromised development in many tissues and organs. Because cells constantly interact through gap junctions to coordinate tissue functions and homeostasis, we hypothesized that increasing cell-to-cell communication, via genetically engineering cells to overexpress gap junction proteins, could enhance cell differentiation in the interior regions of 3D tissue equivalents, thereby increasing the ability to regenerate larger and more uniform volumes of tissue. To test this hypothesis, we used bone as a model tissue because of the difficulty in achieving spatially uniform bone regeneration in 3D. In bone marrow stromal cells (BMSC), GJIC and osteogenic differentiation were compromised in 3D cultures relative to 2D monolayers and in the core of 3D cultures relative to the surface. Overexpression of connexin 43 (Cx43) via transduction of BMSCs with a lentivirus overcame this problem, enhancing both the magnitude and spatial distribution of GJIC and osteogenic differentiation markers throughout 3D constructs. Transplantation of cells overexpressing Cx43 resulted in an increased volume fraction and spatial uniformity of bone in vivo, relative to nontransduced BMSCs. Increased GJIC also enhanced the effect of a potent osteoinductive agent (BMP-7), suggesting a synergism between the soluble factor and GJIC. These findings present a platform to improve cell-to-cell communication in 3D and to achieve uniformly distributed tissue regeneration in 3D.

Differences in gene expression profiles from asbestos-treated SPARC-null and wild-type mouse lungs

The role of SPARC in the in vivo lung response to crocidolite asbestos was addressed by instillation of crocidolite asbestos in a series of wild-type or SPARC-null mice. Animals were sacrificed at one week, one month, and three months post-instillation to assess the impact of SPARC on multiple stages in the development of fibrosis. RNA was harvested from 10 animals/time point, pooled, and used to probe a mouse array containing approximately 10,000 probes. Gene expression data were analyzed for fold change, and for broader functional group alterations. As expected, the one-week time point displayed alterations in genes involved in immune recognition, energy utilization, and growth factor production. Later time points showed expression alterations for genes involved in protein degradation, Wnt receptor signaling, membrane protein activity, and transport. Molecules in the Wnt pathway have been implicated in bone growth, mediation of fibroblast activity, and have been directly linked to SPARC regulation.

Acute stress regulation of neuroplasticity genes in mouse hippocampus CA3 area--possible novel signalling pathways

Stress exposure can lead to the precipitation of psychiatric disorders in susceptible individuals, but the molecular underpinnings are incompletely understood. We used forced swimming in mice to reveal stress-regulated genes in the CA3 area of the hippocampus. To determine changes in the transcriptional profile 4 h and 8 h after stress exposure microarrays were used in the two mouse strains C57BL/6J and DBA/2J, which are known for their differential stress response. We discovered a surprisingly distinct set of regulated genes for each strain and followed selected ones by in situ hybridisation. Our results support the concept of a phased transcriptional reaction to stress. Moreover, we suggest novel stress-elicited pathways, which comprise a number of genes involved in the regulation of neuronal plasticity. Furthermore, we focused in particular on dihydropyrimidinase like 2, to which we provide evidence for its regulation by NeuroD, an important factor for neuronal activity-dependent dendritic morphogenesis.

Gap junctional communication in morphogenesis

Gap junctions permit the direct passage of small molecules from the cytosol of one cell to that of its neighbor, and thus form a system of cell-cell communication that exists alongside familiar secretion/receptor signaling. Because of the rich potential for regulation of junctional conductance, and directional and molecular gating (specificity), gap junctional communication (GJC) plays a crucial role in many aspects of normal tissue physiology. However, the most exciting role for GJC is in the regulation of information flow that takes place during embryonic development, regeneration, and tumor progression. The molecular mechanisms by which GJC establishes local and long-range instructive morphogenetic cues are just beginning to be understood. This review summarizes the current knowledge of the involvement of GJC in the patterning of both vertebrate and invertebrate systems and discusses in detail several morphogenetic systems in which the properties of this signaling have been molecularly characterized. One model consistent with existing data in the fields of vertebrate left-right patterning and anterior-posterior polarity in flatworm regeneration postulates electrophoretically guided movement of small molecule morphogens through long-range GJC paths. The discovery of mechanisms controlling embryonic and regenerative GJC-mediated signaling, and identification of the downstream targets of GJC-permeable molecules, represent exciting next areas of research in this fascinating field.

Connexin 32 and 43 gap junctions differentially modulate tenocyte response to cyclic mechanical load

Gap junctions allow rapid exchange of ions and small metabolites between cells. They can occur between connective tissue cells, and in tendons there are two prominent types, composed of connexin 32 or 43. These form distinct networks - tenocyte rows are linked by both longitudinally, but only by connexin 43 laterally. We hypothesised that the junctions had different roles in cell response to mechanical loading, and measured the effects of inhibitors of gap junction function on secretion of collagen by tenocyte cultures exposed to mechanical strain. Chicken tendon fibroblasts were exposed to cyclic tensile loading in the presence or absence of general gap junction inhibitors (halothane or the biomimetic peptide gap27), or antisense oligonucleotides to chicken connexin 32 or 43. Untreated cultures increased collagen secretion by around 25% under load. Halothane eliminated this response but caused cell damage. Gap27 peptide reduced secretion but maintained loading effects - strained cultures secreting more collagen than unstrained. Antisense downregulation showed major differences between connexins: antisense 32 reduced, and antisense 43 increased, collagen secretion. In both cases loading effects were maintained. This shows that (i) gap junctional integration of signals is important in load response of tenocyte populations - mechanotransduction occurs in individual cells but integration of signals markedly enhances it and (ii) communication via connexin 32 and 43 have differential effects on the load response, with connexin 32 being stimulatory and connexin 43 being inhibitory. Cells coordinate and control their response to mechanical signals at least in part by differential actions of these two types of gap junction.

Developmental regulation and expression of the zebrafish connexin43 gene

We cloned and sequenced the zebrafish (Danio rerio) connexin43 (Cx43alpha1) gene. The predicted protein sequence shows a high degree of sequence conservation. Transcript analyses revealed multiple transcription start sites and a potential alternative transcript encoding a N-terminally truncated Cx43alpha1 protein. Maternal Cx43alpha1 transcripts were detected, with zygotic expression initiated before gastrulation. In situ hybridization revealed many Cx43alpha1 expression domains, including the notochord and brain, heart and vasculature, many resembling patterns seen in mammalian embryos. Of interest, a reporter construct under control of the mouse Cx43alpha1 promoter was observed to drive green fluorescent protein expression in zebrafish embryos in domains mimicking the native Cx43alpha1 expression pattern in fish and mice. Sequence comparison between the mouse and zebrafish Cx43alpha1 promoter sequences showed the conservation of several transcription factor motifs, which otherwise shared little overall sequence homology. The conservation of protein sequence and developmental gene regulation would suggest that Cx43alpha1 gap junctions are likely to have conserved roles in vertebrate embryonic development.

Mutations in connexin43 (GJA1) perturb bone growth in zebrafish fins

Mechanisms that regulate the size and shape of bony structures are largely unknown. The molecular identification of the fin length mutant short fin (sof), which causes defects in the length of bony fin ray segments, may provide insights regarding the regulation of bone growth. In this report, we demonstrate that the sof phenotype is caused by mutations in the connexin43 (cx43) gene. This conclusion is supported by genetic mapping, reduced expression of cx43 in the original sof allele (sofb123), identification of missense mutations in three ENU-induced alleles, and by demonstration of partially abrogated cx43 function in sofb123 embryos. Expression of cx43 was identified in cells flanking the germinal region of newly growing segments as well as in the osteoblasts at segment boundaries. This pattern of cx43 expression in cells lateral to new segment growth is consistent with a model where cx43-expressing cells represent a biological ruler that measures segment size. This report identifies the first gene identification for a fin length mutation (sof) as well as the first connexin mutations in zebrafish, and therefore reveals a critical role for local cell-cell communication in the regulation of bone size and growth.

The complex of ciliary neurotrophic factor-ciliary neurotrophic factor receptor alpha up-regulates connexin43 and intercellular coupling in astrocytes via the Janus tyrosine kinase/signal transducer and activator of transcription pathway

Cytokines regulate numerous cell processes, including connexin expression and gap junctional coupling. In this study, we examined the effect of ciliary neurotrophic factor (CNTF) on connexin43 (Cx43) expression and intercellular coupling in astrocytes. Murine cortical astrocytes matured in vitro were treated with CNTF (20 ng/ml), soluble ciliary neurotrophic factor receptor alpha (CNTFRalpha) (200 ng/ml), or CNTF-CNTFRalpha. Although CNTF and CNTFRalpha alone had no effect on Cx43 expression, the heterodimer CNTF-CNTFRalpha significantly increased both Cx43 mRNA and protein levels. Cx43 immunostaining correlated with increased intercellular coupling as determined by dye transfer analysis. By using the pharmacological inhibitor alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide (AG490), the increase in Cx43 was found to be dependent on the Janus tyrosine kinase/signal transducer and activator of transcription (JAK/STAT) pathway. Immunocytochemical analysis revealed that CNTF-CNTFRalpha treatment produced nuclear localization of phosphorylated STAT3, whereas CNTF treatment alone did not. Transient transfection of constructs containing various sequences of the Cx43 promoter tagged to a LacZ reporter into ROS 17/2.8 cells confirmed that the promoter region between -838 to -1693 was deemed necessary for CNTF-CNTFRalpha to induce heightened expression. CNTF-CNTFRalpha did not alter Cx30 mRNA levels, suggesting selectivity of CNTF-CNTFRalpha for connexin signaling. Together in the presence of soluble receptor, CNTF activates the JAK/STAT pathway leading to enhanced Cx43 expression and intercellular coupling.

Correlation of GDF5 and connexin 43 mRNA expression during embryonic development

Growth/differentiation factor 5 (GDF5) regulates connexin expression and enhances embryonic chondrogenesis in a gap junction-dependent manner, suggesting that GDF5 action on developmental skeletogenesis is coordinated with gap junction activities. The results shown here demonstrate concordance between the mRNA expression profiles of GDF5 and the gap junction gene, Cx43, in the mouse embryonic limb, spine, and heart, consistent with coordinated functions for these gene products during developmental organogenesis.