151
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Abstract
Gap junctions that allow the direct communication between cytoplasmic compartments of neighboring cells are present in a variety of tissues and organs and play pivotal roles in a wide range of physiological processes. In the ovary, gap junctions consist mainly of connexin (Cx) 43 and Cx37, and their indispensable role in regulating folliculogenesis and oogenesis is well established. The ovarian Cx43 is regulated by gonadotropins at the transcriptional, translational and post-translational levels whereas the regulation of the ovarian Cx37 is yet unknown. In addition to their involvement in normal ovarian functions, gap junction proteins, particularly Cx43, seem to act as cancer suppressors. A summary of our present knowledge regarding gap junctional communication (GJC) and the ovarian gap junction proteins in normally developing ovaries and under pathological conditions is presented in this review.
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Affiliation(s)
- Eran Gershon
- Department of Biological Regulation, Weizmann Institute of Science, Rehovot 76100, Israel
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152
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Hong SM, Kang SW, Goo TW, Kim NS, Lee JS, Kim KA, Nho SK. Two gap junction channel (innexin) genes of the Bombyx mori and their expression. JOURNAL OF INSECT PHYSIOLOGY 2008; 54:180-191. [PMID: 17950307 DOI: 10.1016/j.jinsphys.2007.09.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2007] [Revised: 09/01/2007] [Accepted: 09/03/2007] [Indexed: 05/25/2023]
Abstract
Gap junctions are clusters of intercellular channels that are associated with embryonic development and neural signaling. Innexins, invertebrate gap junction proteins, have been identified in Drosophila and Caenorhabditis. Here, we report the isolation and characterization of two novel members of the insect innexin family, Bm inx2 and Bm inx4, from embryos of the silkworm, Bombyx mori, during the germ-band formation stage. Bm inx2 is a single copy gene with one exon, while Bm inx4 is a single copy gene with four exons and three introns. The predicted proteins show structural similarities with other innexin family members, including four transmembrane (TM) domains, two extracellular loops (ELs), one cytoplasmic loop (CL), and typical conserved amino acids. Bm inx2 is phylogenetically orthologous to the other insect inx2 genes, but Bm inx4 is not orthologous to any known innexin including Dm inx4. Interestingly, Northern blotting and in situ hybridization showed that Bm inx2 was variously expressed across all developmental stages and in various tissues, with high expression seen in the nervous system at the time of embryogenesis. In contrast, Bm inx4 was transiently expressed at the germ-band formation stage of embryogenesis, and was specifically expressed in the ovary and testis during the larval and pupal stages. The isolation and characterization of these novel genes should form the basis for further study of the functional events that occur during development and neuronal communication in B. mori.
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Affiliation(s)
- Sun-Mee Hong
- College of Agriculture and Life Sciences, Kyungpook National University, Daegu 702701, Republic of Korea
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153
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Iovine MK, Gumpert AM, Falk MM, Mendelson TC. Cx23, a connexin with only four extracellular-loop cysteines, forms functional gap junction channels and hemichannels. FEBS Lett 2007; 582:165-70. [PMID: 18068130 DOI: 10.1016/j.febslet.2007.11.079] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2007] [Revised: 11/07/2007] [Accepted: 11/28/2007] [Indexed: 11/18/2022]
Abstract
Gap junction channels may be comprised of either connexin or pannexin proteins (innexins and pannexins). Membrane topologies of both families are similar, but sequence similarity is lacking. Recently, connexin-like sequences have been identified in mammalian and zebrafish genomes that have only four conserved cysteines in the extracellular domains (Cx23), a feature of the pannexins. Phylogenetic analyses of the non-canonical "C4" connexins reveal that these sequences are indeed connexins. Functional assays reveal that the Cx23 gap junctions are capable of sharing neurobiotin, and further, that Cx23 connexins form hemichannels in vitro.
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Affiliation(s)
- M Kathryn Iovine
- Department of Biological Sciences, Lehigh University, 111 Research Drive, Bethlehem, PA 18015, USA.
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154
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Kumar S, Chaudhary K, Foster JM, Novelli JF, Zhang Y, Wang S, Spiro D, Ghedin E, Carlow CKS. Mining predicted essential genes of Brugia malayi for nematode drug targets. PLoS One 2007; 2:e1189. [PMID: 18000556 PMCID: PMC2063515 DOI: 10.1371/journal.pone.0001189] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2007] [Accepted: 10/25/2007] [Indexed: 12/02/2022] Open
Abstract
We report results from the first genome-wide application of a rational drug target selection methodology to a metazoan pathogen genome, the completed draft sequence of Brugia malayi, a parasitic nematode responsible for human lymphatic filariasis. More than 1.5 billion people worldwide are at risk of contracting lymphatic filariasis and onchocerciasis, a related filarial disease. Drug treatments for filariasis have not changed significantly in over 20 years, and with the risk of resistance rising, there is an urgent need for the development of new anti-filarial drug therapies. The recent publication of the draft genomic sequence for B. malayi enables a genome-wide search for new drug targets. However, there is no functional genomics data in B. malayi to guide the selection of potential drug targets. To circumvent this problem, we have utilized the free-living model nematode Caenorhabditis elegans as a surrogate for B. malayi. Sequence comparisons between the two genomes allow us to map C. elegans orthologs to B. malayi genes. Using these orthology mappings and by incorporating the extensive genomic and functional genomic data, including genome-wide RNAi screens, that already exist for C. elegans, we identify potentially essential genes in B. malayi. Further incorporation of human host genome sequence data and a custom algorithm for prioritization enables us to collect and rank nearly 600 drug target candidates. Previously identified potential drug targets cluster near the top of our prioritized list, lending credibility to our methodology. Over-represented Gene Ontology terms, predicted InterPro domains, and RNAi phenotypes of C. elegans orthologs associated with the potential target pool are identified. By virtue of the selection procedure, the potential B. malayi drug targets highlight components of key processes in nematode biology such as central metabolism, molting and regulation of gene expression.
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Affiliation(s)
- Sanjay Kumar
- Division of Parasitology, New England Biolabs, Inc., Ipswich, Massachusetts, United States of America
| | - Kshitiz Chaudhary
- Division of Parasitology, New England Biolabs, Inc., Ipswich, Massachusetts, United States of America
| | - Jeremy M. Foster
- Division of Parasitology, New England Biolabs, Inc., Ipswich, Massachusetts, United States of America
| | - Jacopo F. Novelli
- Division of Parasitology, New England Biolabs, Inc., Ipswich, Massachusetts, United States of America
| | - Yinhua Zhang
- Division of Parasitology, New England Biolabs, Inc., Ipswich, Massachusetts, United States of America
| | - Shiliang Wang
- The Institute for Genomic Research, Rockville, Maryland, United States of America
| | - David Spiro
- The Institute for Genomic Research, Rockville, Maryland, United States of America
| | - Elodie Ghedin
- The Institute for Genomic Research, Rockville, Maryland, United States of America
- Division of Infectious Diseases, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States of America
| | - Clotilde K. S. Carlow
- Division of Parasitology, New England Biolabs, Inc., Ipswich, Massachusetts, United States of America
- * To whom correspondence should be addressed. E-mail:
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155
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Penuela S, Bhalla R, Gong XQ, Cowan KN, Celetti SJ, Cowan BJ, Bai D, Shao Q, Laird DW. Pannexin 1 and pannexin 3 are glycoproteins that exhibit many distinct characteristics from the connexin family of gap junction proteins. J Cell Sci 2007; 120:3772-83. [PMID: 17925379 DOI: 10.1242/jcs.009514] [Citation(s) in RCA: 331] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Pannexins are mammalian orthologs of the invertebrate gap junction proteins innexins and thus have been proposed to play a role in gap junctional intercellular communication. Localization of exogenously expressed pannexin 1 (Panx1) and pannexin 3 (Panx3), together with pharmacological studies, revealed a cell surface distribution profile and life cycle dynamics that were distinct from connexin 43 (Cx43, encoded by Gja1). Furthermore, N-glycosidase treatment showed that both Panx1 (approximately 41-48 kD species) and Panx3 (approximately 43 kD) were glycosylated, whereas N-linked glycosylation-defective mutants exhibited a decreased ability to be transported to the cell surface. Tissue surveys revealed the expression of Panx1 in several murine tissues--including in cartilage, skin, spleen and brain--whereas Panx3 expression was prevalent in skin and cartilage with a second higher-molecular-weight species present in a broad range of tissues. Tissue-specific localization patterns of Panx1 and Panx3 ranging from distinct cell surface clusters to intracellular profiles were revealed by immunostaining of skin and spleen sections. Finally, functional assays in cultured cells transiently expressing Panx1 and Panx3 were incapable of forming intercellular channels, but assembled into functional cell surface channels. Collectively, these studies show that Panx1 and Panx3 have many characteristics that are distinct from Cx43 and that these proteins probably play an important biological role as single membrane channels.
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Affiliation(s)
- Silvia Penuela
- Department of Anatomy and Cell Biology, University of Western Ontario, London, ON, N6A 5C1, Canada
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156
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Kim Y, Sun H. Functional genomic approach to identify novel genes involved in the regulation of oxidative stress resistance and animal lifespan. Aging Cell 2007; 6:489-503. [PMID: 17608836 DOI: 10.1111/j.1474-9726.2007.00302.x] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Genetic studies in many organisms suggest that an increased animal lifespan phenotype is often accompanied by enhanced resistance toward reactive oxygen species (ROS). In Caenorhabditis elegans, mutations in daf-2, which encode an insulin/insulin-like growth factor 1 receptor-like molecule, lead to an extended animal lifespan and increased resistance to ROS. We have optimized an assay to monitor ROS resistance in worms using the ROS-generating chemical paraquat. We have employed this assay to screen the RNAi library along chromosomes III and IV for genes that, when silenced, confer paraquat resistance. The positive RNAi clones were subsequently screened for a lifespan extension phenotype. Using this approach, we have identified 84 genes that, when inactivated by RNAi, lead to significant increases in animal lifespan. Among the 84 genes, 29 were found to act in a manner dependent on daf-16. DAF-16, a forkhead transcription factor, is known to integrate signals from multiple pathways, including the daf-2 pathway, to regulate animal lifespan. Most of the 84 genes have not been previously linked to aging, and potentially participate in important cellular processes such as signal transduction, cell-cell interaction, gene expression, protein degradation, and energy metabolism. Our screen has also identified a group of genes that potentially function in a nutrient-sensing pathway to regulate lifespan in C. elegans. Our study provides a novel approach to identify genes involved in the regulation of aging.
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Affiliation(s)
- Yongsoon Kim
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06520, USA
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157
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Oviedo NJ, Levin M. smedinx-11 is a planarian stem cell gap junction gene required for regeneration and homeostasis. Development 2007; 134:3121-31. [PMID: 17670787 DOI: 10.1242/dev.006635] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The largely unknown mechanisms that regulate adult stem cells probably involve signals from neighboring differentiated cells. Gap junction channels providing direct cell-cell communication via small molecules are a crucial component of morphogenesis and normal physiology. However, no specific gap junction protein has yet been functionally linked to adult/somatic stem cell behavior in vivo or to organ regeneration. We report the identification and characterization of smedinx-11--an innexin gap junction channel gene expressed in the adult stem cells (neoblasts) of the planarian Schmidtea mediterranea. smedinx-11 RNAi treatment inhibits regeneration and abrogates neoblast maintenance. Moreover, smedinx-11 expression is enriched in an irradiation-sensitive subpopulation (;X2') and is required for proper expression of other stem cell-specific markers. Analyses of the smedinx-11 downregulation phenotype revealed a striking anterior-posterior neoblast gradient. Our data demonstrate a novel role for gap junction proteins and suggest gap junction-mediated signaling as a new and tractable control point for adult, somatic stem cell regulation.
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Affiliation(s)
- Néstor J Oviedo
- Center for Regenerative and Developmental Biology, Forsyth Institute, Harvard School of Dental Medicine, Boston, MA 02115, USA
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158
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Chuang CF, Vanhoven MK, Fetter RD, Verselis VK, Bargmann CI. An innexin-dependent cell network establishes left-right neuronal asymmetry in C. elegans. Cell 2007; 129:787-99. [PMID: 17512411 DOI: 10.1016/j.cell.2007.02.052] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2006] [Revised: 01/27/2007] [Accepted: 02/26/2007] [Indexed: 02/03/2023]
Abstract
Gap junctions are widespread in immature neuronal circuits, but their functional significance is poorly understood. We show here that a transient network formed by the innexin gap-junction protein NSY-5 coordinates left-right asymmetry in the developing nervous system of Caenorhabditis elegans. nsy-5 is required for the left and right AWC olfactory neurons to establish stochastic, asymmetric patterns of gene expression during embryogenesis. nsy-5-dependent gap junctions in the embryo transiently connect the AWC cell bodies with those of numerous other neurons. Both AWCs and several other classes of nsy-5-expressing neurons participate in signaling that coordinates left-right AWC asymmetry. The right AWC can respond to nsy-5 directly, but the left AWC requires nsy-5 function in multiple cells of the network. NSY-5 forms hemichannels and intercellular gap-junction channels in Xenopus oocytes, consistent with a combination of cell-intrinsic and network functions. These results provide insight into gap-junction activity in developing circuits.
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Affiliation(s)
- Chiou-Fen Chuang
- Howard Hughes Medical Institute, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA
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159
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Lechner H, Josten F, Fuss B, Bauer R, Hoch M. Cross regulation of intercellular gap junction communication and paracrine signaling pathways during organogenesis in Drosophila. Dev Biol 2007; 310:23-34. [PMID: 17707365 DOI: 10.1016/j.ydbio.2007.07.008] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2007] [Revised: 06/22/2007] [Accepted: 07/12/2007] [Indexed: 01/09/2023]
Abstract
The spatial and temporal coordination of patterning and morphogenesis is often achieved by paracrine morphogen signals or by the direct coupling of cells via gap junctions. How paracrine signals and gap junction communication cooperate to control the coordinated behavior of cells and tissues is mostly unknown. We found that hedgehog signaling is required for the expression of wingless and of Delta/Notch target genes in a single row of boundary cells in the foregut-associated proventriculus organ of the Drosophila embryo. These cells coordinate the movement and folding of proventricular cells to generate a multilayered organ. hedgehog and wingless regulate gap junction communication by transcriptionally activating the innexin2 gene, which encodes a member of the innexin family of gap junction proteins. In innexin2 mutants, gap junction-mediated cell-to-cell communication is strongly reduced and the proventricular cell layers fail to fold and invaginate, similarly as in hedgehog or wingless mutants. We further found that innexin2 is required in a feedback loop for the transcriptional activation of the hedgehog and wingless morphogens and of Delta in the proventriculus primordium. We propose that the transcriptional cross regulation of paracrine and gap junction-mediated signaling is essential for organogenesis in Drosophila.
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Affiliation(s)
- Hildegard Lechner
- LIMES Institute, Laboratory of Molecular Developmental Biology, University of Bonn, Meckenheimer Allee 169, Poppelsdorfer Schloss, D-53115 Bonn, Germany
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160
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Zoidl G, Petrasch-Parwez E, Ray A, Meier C, Bunse S, Habbes HW, Dahl G, Dermietzel R. Localization of the pannexin1 protein at postsynaptic sites in the cerebral cortex and hippocampus. Neuroscience 2007; 146:9-16. [PMID: 17379420 DOI: 10.1016/j.neuroscience.2007.01.061] [Citation(s) in RCA: 123] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2006] [Revised: 01/22/2007] [Accepted: 01/22/2007] [Indexed: 10/23/2022]
Abstract
Pannexins (Panx) constitute a new family of gap junction type proteins. Functional expression in paired Xenopus oocytes indicated that pannexins are capable of forming communicating junctions but also proved to be active in forming of unopposed hemichannels. In the vertebrate brain pannexins have been found in neurons. However, the subcellular cerebral localization of pannexin proteins which could gain first clues on their putative function is essentially unknown. Here we demonstrate by light and electron microscopical immunohistochemistry that Panx1 reveals postsynaptic localization in rodent hippocampal and cortical principal neurons accumulating at postsynaptic densities. The postsynaptic localization was corroborated by co-localization of Panx1 with postsynaptic density protein 95 (PSD-95), a prominent postsynaptic scaffolding protein, in hippocampal neurons expressing tagged versions of these proteins. The asymmetric synaptic distribution of Panx1 suggests that it may function in neurons as non-junctional channels (pannexons) at postsynaptic sites and comprises a novel component of the postsynaptic protein complex.
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Affiliation(s)
- G Zoidl
- Department of Neuroanatomy and Molecular Brain Research, Ruhr University Bochum, Universitystreet 150, D-44780 Bochum, Germany
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161
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Levin M. Gap junctional communication in morphogenesis. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2007; 94:186-206. [PMID: 17481700 PMCID: PMC2292839 DOI: 10.1016/j.pbiomolbio.2007.03.005] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
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.
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Affiliation(s)
- Michael Levin
- Forsyth Center for Regenerative and Devlopmental Biology, Forsyth Institute, and Developmental Biology Department, Harvard School of Dental Medicine, Boston, MA 02115, USA.
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162
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Yen MR, Saier MH. Gap junctional proteins of animals: the innexin/pannexin superfamily. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2007; 94:5-14. [PMID: 17507077 PMCID: PMC2592087 DOI: 10.1016/j.pbiomolbio.2007.03.006] [Citation(s) in RCA: 118] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
There has been some controversy as to whether vertebrate pannexins are related to invertebrate innexins. Using statistical, topological and conserved sequence motif analyses, we establish that these proteins belong to a single superfamily. We also demonstrate the occurrence of large homologues with C-terminal proline-rich domains that may have arisen by gene fusion events. Phylogenetic analyses reveal the orthologous and paralogous relationships of these homologues to each other. We show that different sets of orthologous paralogues underwent sequence divergence at markedly different rates, suggesting differential pressures through evolutionary time promoting or restricting sequence divergence. We further show that the first 2 TMS-containing halves of these homologues underwent sequence divergence more slowly than the second 2 TMS-containing halves and analyze these differences. These bioinformatic analyses should serve as useful guides for future studies of structure, function and evolutionary aspects of this important superfamily.
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Affiliation(s)
| | - Milton H. Saier
- *Corresponding author: Telephone: 858-534-4084, Fax: 858-534-7108, E-mail:
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163
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Neijssen J, Pang B, Neefjes J. Gap junction-mediated intercellular communication in the immune system. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2007; 94:207-18. [PMID: 17467043 DOI: 10.1016/j.pbiomolbio.2007.03.008] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Immune cells are usually considered non-attached blood cells, which would exclude the formation of gap junctions. This is a misconception since many immune cells express connexin 43 (Cx43) and other connexins and are often residing in tissue. The role of gap junctions is largely ignored by immunologists as is the immune system in the field of gap junction research. Here, the current knowledge of the distribution of connexins and the function of gap junctions in the immune system is discussed. Gap junctions appear to play many roles in antibody productions and specific immune responses and may be important in sensing danger in tissue by the immune system. Gap junctions not only transfer electrical and metabolical but also immunological information in the form of peptides for a process called cross-presentation. This is essential for proper immune responses to viruses and possibly tumours. Until now only 40 research papers on gap junctions in the immune system appeared and this will almost certainly expand with the increased mutual interest between the fields of immunology and gap junction research.
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Affiliation(s)
- Joost Neijssen
- Division of Tumor Biology, The Netherlands Cancer Institute, Plesmanlaan 121, Amsterdam, The Netherlands
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164
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Zhu X, Stevens LM, Stein D. Synthesis of the sulfate donor PAPS in either the Drosophila germline or somatic follicle cells can support embryonic dorsal-ventral axis formation. Development 2007; 134:1465-9. [PMID: 17344226 DOI: 10.1242/dev.003426] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The establishment of dorsal-ventral (DV) polarity in the Drosophila embryo depends upon a localized signal that is generated in the perivitelline space of the egg through the action of a serine proteolytic cascade. Spatial regulation of this pathway is determined by the expression of the pipe gene in a subpopulation of ventral follicle cells in the developing egg chamber. The Pipe protein exhibits homology to vertebrate glycosaminoglycan sulfotransferases. In a previous study, we demonstrated that embryonic DV polarity depends upon the sulfotransferase activity of Pipe. Surprisingly, however, our results also indicated that formation of the embryonic DV axis does not require the synthesis of the high-energy sulfate donor, 3'-phosphoadenosine 5'-phosphosulfate (PAPS) in the follicle cells in which Pipe is presumed to function. Here, we resolve this apparent paradox by demonstrating that dorsalized embryos are only produced by egg chambers in which both germline and follicle cells lack PAPS synthetase activity. Thus, PAPS produced either in the germline or in the follicular epithelium can support the requirement for Pipe sulfotransferase activity in embryonic DV patterning. This finding indicates the existence of a conduit for the movement of PAPS between the germline and the follicle cells, which highlights a previously unappreciated mechanism of soma/germline cooperation affecting pattern formation.
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Affiliation(s)
- Xianjun Zhu
- Section of Molecular Cell and Developmental Biology, University of Texas at Austin, Austin, TX 78712, USA
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165
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Schlurmann M, Hausen K. Motoneurons of the flight power muscles of the blowflyCalliphora erythrocephala: Structures and mutual dye coupling. J Comp Neurol 2007; 500:448-64. [PMID: 17120285 DOI: 10.1002/cne.21182] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The morphologies of the motoneurons of the dorsolongitudinal and the three dorsoventral flight power muscles (DLM, DVM 1-3) of Calliphora were investigated by means of cobalt backfills and intracellular biocytin stainings. The DLM is innervated by four prothoracic motoneurons supplying the four ventral muscle fibers and one mesothoracic motoneuron supplying the two dorsal fibers. The three fibers of the DVM 1 and the two fibers of the DVM 2 are innervated by five mesothoracic motoneurons, whereas the two fibers of the DVM 3 are innervated by two prothoracic motoneurons. In general, the motoneurons of each muscle have a common ventral soma cluster located in a characteristic position on the ipsilateral side of the thoracic ganglion, show similar dendritic arborizations in the mesothoracic wing neuropil, and have the same axon pathway. Only the soma of the common motoneuron of two dorsal fibers of the DLM is situated dorsally in the contralateral hemiganglion. The motoneurons of each muscle were found to be strongly dye coupled with each other, indicating that they are connected by gap junctions. In addition, the motoneurons of each muscle establish characteristic coupling patterns with the motoneurons of the other flight power muscles on both sides of the thorax and with two bilateral groups of local mesothoracic interneurons. The revealed coupling patterns are assumed to be of major relevance for the generation the characteristic, rhythmic flight activity of the motoneurons described in previous studies.
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Affiliation(s)
- M Schlurmann
- Zoologisches Institut, Universität Köln, 50923 Köln, Germany.
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166
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Litvin O, Tiunova A, Connell-Alberts Y, Panchin Y, Baranova A. What is hidden in the pannexin treasure trove: the sneak peek and the guesswork. J Cell Mol Med 2007; 10:613-34. [PMID: 16989724 PMCID: PMC3933146 DOI: 10.1111/j.1582-4934.2006.tb00424.x] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Connexins had been considered to be the only class of the vertebrate proteins capable of gap junction formation; however, new candidates for this function with no homology to connexins, termed pannexins were discovered. So far three pannexins were described in rodent and human genomes: Panx1, Panx2 and Panx3. Expressions of pannexins can be detected in numerous brain structures, and now found both in neuronal and glial cells. Hypothetical roles of pannexins in the nervous system include participating in sensory processing, hippocampal plasticity, synchronization between hippocampus and cortex, and propagation of the calcium waves supported by glial cells, which help maintain and modulate neuronal metabolism. Pannexin also may participate in pathological reactions of the neural cells, including their damage after ischemia and subsequent cell death. Recent study revealed non-gap junction function of Panx1 hemichannels in erythrocytes, where they serve as the conduits for the ATP release in response to the osmotic stress. High-throughput studies produced some evidences of the pannexin involvement in the process of tumorigenesis. According to brain cancer gene expression database REMBRANDT, PANX2 expression levels can predict post diagnosis survival for patients with glial tumors. Further investigations are needed to verify or reject hypotheses listed.
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Affiliation(s)
- Oxana Litvin
- Stowers Institute for Medical ResearchKansas City, MO, USA
| | - Anya Tiunova
- P. K. Anokhin Institute of Normal Physiology, Russian Academy of Medical SciencesMoscow, Russia
| | - Yvette Connell-Alberts
- Molecular and Microbiology Department, George Mason UniversityFairfax, VA, USA
- NCI/MCGP, FrederickMD, USA
| | - Yuri Panchin
- Institute for Information Transmission Problems, RAS, Moscow, Russia and A. N. Belozersky Institute, Moscow State UniversityMoscow, Russia
| | - Ancha Baranova
- Molecular and Microbiology Department, George Mason UniversityFairfax, VA, USA
- Russian Center of Medical Genetics, Russian Academy of Medical SciencesMoscow, Russia
- * Correspondence to: Dr. A.BARANOVA Molecular Biology and Microbiology, David King Hall, MSN 3E1, George Mason University, Fairfax, VA, 22030, USA. Tel.: 703-993-42-93 E-mail:
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167
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Abstract
Pannexin1 and pannexin2 are members of the pannexin gene family which are widely expressed in the central nervous system. Here we present an overview of pannexin expression and distribution in the mouse cerebellum. Pannexin1 and pannexin2 are expressed in the Purkinje cells and in some cells of the granule cell layer. Pannexin2 is also expressed in the stellate cells of the molecular layer. A differential expression of pannexin1 and pannexin2 mRNA is observed during cerebellar development. These findings constitute the first indication of the involvement of pannexin molecules in the developing cerebellum. Although the functional relevance of these molecules remains currently unknown, the abundance of pannexins in the Purkinje cells suggests that they may contribute to the generation of cerebellar rhythms.
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Affiliation(s)
- Arundhati Ray
- Department of Neuroanatomy and Molecular Brain Research, Faculty of Medicine, Ruhr University, Bochum, Germany
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168
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Abstract
"Hemichannels" are defined as the halves of gap junction channels (also termed connexons) that are contributed by one cell; "hemichannels" are considered to be functional if they are open in nonjunctional membranes in the absence of pairing with partners from adjacent cells. Several recent reviews have summarized the blossoming literature regarding functional "hemichannels", in some cases encyclopedically. However, most of these previous reviews have been written with the assumption that all data reporting "hemichannel" involvement really have studied phenomena in which connexons actually form the permeability or conductance pathway. In this review, we have taken a slightly different approach. We review the concept of "hemichannels", summarize properties that might be expected of half gap junctions and evaluate the extent to which the properties of presumptive "hemichannels" match expectations. Then we consider functions attributed to hemichannels, provide an overview of other channel types that might fulfill similar roles and provide sets of criteria that might be applied to verify involvement of connexin hemichannels in cell and tissue function. One firm conclusion is reached. The study of hemichannels is technically challenging and fraught with opportunities for misinterpretation, so that future studies must apply rigorous standards for detection of hemichannel expression and function. At the same time there are reasons to expect surprises, including the possibility that some time honored techniques for studying gap junctions may prove unsuitable for detecting hemichannels. We advise hemichannel researchers to proceed with caution and an open mind.
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Affiliation(s)
- David C Spray
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York
| | - Zu-Cheng Ye
- Department of Neurology, University of Washington School of Medicine, Seattle, Washington
| | - Bruce R Ransom
- Department of Neurology, University of Washington School of Medicine, Seattle, Washington
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169
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de Boer TP, Kok B, Roël G, van Veen TAB, Destrée OHJ, Rook MB, Vos MA, de Bakker JMT, van der Heyden MAG. Cloning, embryonic expression, and functional characterization of two novel connexins from Xenopus laevis. Biochem Biophys Res Commun 2006; 349:855-62. [PMID: 16950205 DOI: 10.1016/j.bbrc.2006.08.121] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2006] [Accepted: 08/20/2006] [Indexed: 11/26/2022]
Abstract
Vertebrate gap junctions are constituted of connexin (Cx) proteins. In Xenopus laevis, only seven different Cxs have been described so far. Here, we identify two new Cxs from X. laevis. Cx28.6 displays > 60% amino acid identity with human Cx25, Cx29 displays strong homology with mouse Cx26 and Cx30. Cx29 is expressed throughout embryonic development. Cx28.6 mRNA is only transiently found from stage 22 to 26 of development. While no Cx28.6 expression could be detected by whole mount in situ hybridization, expression of Cx29 was found in the developing endoderm, lateral mesoderm, liver anlage, pronephros, and proctodeum. Ectopic expression of Cx28.6 failed to produce functional gap-junctions. In contrast, ectopic expression of full-length Cx29 in HEK293 and COS-7 cells resulted in the formation of gap junction-like structures at the cell-cell interfaces. Ectopic expression of Cx29 in communication deficient N2A cell pairs led to functional electrical coupling.
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Affiliation(s)
- Teun P de Boer
- Department of Medical Physiology, HLCU, University Medical Center Utrecht, Yalelaan 50, 3584 CM Utrecht, The Netherlands
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170
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Whitten SJ, Miller MA. The role of gap junctions in Caenorhabditis elegans oocyte maturation and fertilization. Dev Biol 2006; 301:432-46. [PMID: 16982048 DOI: 10.1016/j.ydbio.2006.08.038] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2006] [Revised: 08/03/2006] [Accepted: 08/17/2006] [Indexed: 10/24/2022]
Abstract
We have investigated the role of gap junctions in Caenorhabditis elegans oocyte maturation and fertilization. Gap junctions are observed between oocytes and the surrounding ovarian sheath cells in wild-type gonads. The sheath transcription factor CEH-18 is required to negatively regulate oocyte maturation, mitogen-activated protein kinase (MAPK) activation, and ovulation. Transmission electron microscopy (TEM) indicates that sheath/oocyte gap junctions are rare or absent in ceh-18(mg57) null mutant gonads. To test the hypothesis that gap junctions negatively regulate oocyte maturation, we performed an RNAi screen of innexin genes, which encode channel-forming proteins. Here we show that INX-14 and INX-22 are required in the female germ line to inhibit oocyte maturation, MAPK activation, and ovulation. Genetic analysis and TEM are consistent with INX-14 and INX-22 being components of sheath/oocyte gap junctions. Our results support the hypothesis that gap junctions maintain oocytes in meiotic prophase I when sperm are absent. We also implicate these channels in regulating sheath cell contractile activity and sperm recruitment to the spermatheca, the site of sperm storage and fertilization. Together with previous studies, our results help establish the C. elegans gonad as a model system for investigating the molecular mechanism(s) by which gap junctions regulate meiosis and fertilization.
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Affiliation(s)
- Scott J Whitten
- Division of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
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171
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Barbe MT, Monyer H, Bruzzone R. Cell-cell communication beyond connexins: the pannexin channels. Physiology (Bethesda) 2006; 21:103-14. [PMID: 16565476 DOI: 10.1152/physiol.00048.2005] [Citation(s) in RCA: 181] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Direct cell-to-cell communication through specialized intercellular channels is a characteristic feature of virtually all multi-cellular organisms. The remarkable functional conservation of cell-to-cell coupling throughout the animal kingdom, however, is not matched at the molecular level of the structural protein components. Thus protostomes (including nematodes and flies) and deuterostomes (including all vertebrates) utilize two unrelated families of gap-junction genes, innexins and connexins, respectively. The recent discovery that pannexins, a novel group of proteins expressed by several organisms, are able to form intercellular channels has started a quest to understand their evolutionary relationship and functional contribution to cell communication in vivo. There are three pannexin genes in mammals, two of which are co-expressed in the developing and adult brain. Of note, pannexin1 can also form Ca2+-activated hemichannels that open at physiological extracellular Ca2+ concentrations and exhibit distinct pharmacological properties.
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Affiliation(s)
- Michael T Barbe
- Department of Clinical Neurobiology and Interdisciplinary Center for Neuroscience, University of Heidelberg, Heidelberg, Germany
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172
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Franks CJ, Holden-Dye L, Bull K, Luedtke S, Walker RJ. Anatomy, physiology and pharmacology of Caenorhabditis elegans pharynx: a model to define gene function in a simple neural system. INVERTEBRATE NEUROSCIENCE 2006; 6:105-22. [PMID: 16862440 DOI: 10.1007/s10158-006-0023-1] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2006] [Accepted: 06/26/2006] [Indexed: 12/31/2022]
Abstract
Invertebrate neuroscience has provided a number of very informative model systems that have been extensively utilized in order to define the neurobiological bases of animal behaviours (Sattelle and Buckingham in Invert Neurosci 6:1-3, 2006). Most eminent among these are a number of molluscs, including Aplysia californica, Lymnaea stagnalis and Helix aspersa, crustacean systems such as the crab stomatogastric ganglion and a wide-range of other arthropods. All of these have been elegantly exploited to shed light on the very important phenomenon of the molecular and cellular basis for synaptic regulation that underpins behavioural plasticity. Key to the successful use of these systems has been the ability to study well-defined, relatively simple neuronal circuits that direct and regulate a quantifiable animal behaviour. Here we describe the pharyngeal system of the nematode C. elegans and its utility as a model for defining the genetic basis of behaviour. The circuitry of the nervous system in this animal is uniquely well-defined. Furthermore, the feeding behaviour of the worm is controlled by the activity of the pharynx and this in turn is regulated in a context-dependent manner by a simple nervous system that integrates external signals, e.g. presence or absence of food, and internal signals, e.g. the nutritional status of the animal to direct an appropriate response. The genetics of C. elegans is being effectively exploited to provide novel insight into genes that function to regulate the neuronal network that controls the pharynx. Here we summarise the progress to date and highlight topics for future research. Two main themes emerge. First, although the anatomy of the pharyngeal system is very well-defined, there is a much poorer understanding of its neurochemistry. Second, it is evident that the neurochemistry is remarkably complex for such a simple circuit/behaviour. This suggests that the pharyngeal activity may be subject to exquisitely precise regulation depending on the animal's environment and status. This therefore provides a very tractable genetic model to investigate neural mechanisms for signal integration and synaptic plasticity in a well-defined neuronal network that directs a quantifiable behaviour, feeding.
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Affiliation(s)
- Christopher J Franks
- School of Biological Sciences, Bassett Crescent East, University of Southampton, Southampton, SO16 7PX, UK
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173
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Dykes IM, Macagno ER. Molecular characterization and embryonic expression of innexins in the leech Hirudo medicinalis. Dev Genes Evol 2006; 216:185-97. [PMID: 16440200 DOI: 10.1007/s00427-005-0048-1] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2005] [Accepted: 11/21/2005] [Indexed: 10/25/2022]
Abstract
Gap junctions are direct intercellular channels that permit the passage of ions and small signaling molecules. The temporal and spatial regulation of gap junctional communication is, thus, one mechanism by which cell interactions, and hence cell properties and cell fate, may be regulated during development. The nervous system of the leech, Hirudo medicinalis, is a particularly advantageous system in which to study developmental mechanisms involving gap junctions because interactions between identified cells may be studied in vivo in both the embryo and the adult. As in most invertebrates, gap junctions in the leech are composed of innexin proteins, which are distantly related to the vertebrate pannexins and are encoded by a multi-gene family. We have cloned ten novel leech innexins and describe the expression of these, plus two other previously reported members of this gene family, in the leech embryo between embryonic days 6 and 12, a period during which the main features of the central nervous system are established. Four innexins are expressed in neurons and two in glia, while several innexins are expressed in the excretory, circulatory, and reproductive organs. Of particular interest is Hm-inx6, whose expression appears to be restricted to the characterized S cell and two other neurons putatively identified as presynaptic to this cell. Two other innexins also show highly restricted expressions in neurons and may be developmentally regulated.
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Affiliation(s)
- Iain M Dykes
- Section of Cell and Developmental Biology, Division of Biological Sciences, NSB 6213, University of California, San Diego, La Jolla, 92093-0376, USA
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174
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Lehmann C, Lechner H, Löer B, Knieps M, Herrmann S, Famulok M, Bauer R, Hoch M. Heteromerization of innexin gap junction proteins regulates epithelial tissue organization in Drosophila. Mol Biol Cell 2006; 17:1676-85. [PMID: 16436513 PMCID: PMC1415333 DOI: 10.1091/mbc.e05-11-1059] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Gap junctions consist of clusters of intercellular channels, which enable direct cell-to-cell communication and adhesion in animals. Whereas deuterostomes, including all vertebrates, use members of the connexin and pannexin multiprotein families to assemble gap junction channels, protostomes such as Drosophila and Caenorhabditis elegans use members of the innexin protein family. The molecular composition of innexin-containing gap junctions and the functional significance of innexin oligomerization for development are largely unknown. Here, we report that heteromerization of Drosophila innexins 2 and 3 is crucial for epithelial organization and polarity of the embryonic epidermis. Both innexins colocalize in epithelial cell membranes. Innexin3 is mislocalized to the cytoplasm in innexin2 mutants and is recruited into ectopic expression domains defined by innexin2 misexpression. Conversely, RNA interference (RNAi) knockdown of innexin3 causes mislocalization of innexin2 and of DE-cadherin, causing cell polarity defects in the epidermis. Biochemical interaction studies, surface plasmon resonance analysis, transgenesis, and biochemical fractionation experiments demonstrate that both innexins interact via their C-terminal cytoplasmic domains during the assembly of heteromeric channels. Our data provide the first molecular and functional demonstration that innexin heteromerization occurs in vivo and reveal insight into a molecular mechanism by which innexins may oligomerize into heteromeric gap junction channels.
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Affiliation(s)
- Corinna Lehmann
- Institut für Molekulare Physiologie und Entwicklungsbiologie der Universität Bonn, 53115 Bonn, Germany
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175
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Allen MJ, Godenschwege TA, Tanouye MA, Phelan P. Making an escape: development and function of the Drosophila giant fibre system. Semin Cell Dev Biol 2005; 17:31-41. [PMID: 16378740 DOI: 10.1016/j.semcdb.2005.11.011] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Flies escape danger by jumping into the air and flying away. The giant fibre system (GFS) is the neural circuit that mediates this simple behavioural response to visual stimuli. The sensory signal is received by the giant fibre and relayed to the leg and wing muscle motorneurons. Many of the neurons in the Drosophila GFS are uniquely identifiable and amenable to cell biological, electrophysiological and genetic studies. Here we review the anatomy and development of this system and highlight its utility for studying many aspects of nervous system biology ranging from neural development and synaptic plasticity to the aetiology of neural disorder.
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Affiliation(s)
- Marcus J Allen
- Department of Biosciences, University of Kent, Canterbury CT2 7NJ, UK
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176
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Hervé JC, Phelan P, Bruzzone R, White TW. Connexins, innexins and pannexins: Bridging the communication gap. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2005; 1719:3-5. [PMID: 16359939 DOI: 10.1016/j.bbamem.2005.11.013] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
- Jean-Claude Hervé
- Communications jonctionnelles, UMR CNRS 6187, Université de Poitiers, 40 av. du Recteur Pineau, 86022 Poitiers, France
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177
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Chiusano ML, Di Giaimo R, Potenza N, Russo GMR, Geraci G, del Gaudio R. A possible flip-flop genetic mechanism for reciprocal gene expression. FEBS Lett 2005; 579:4919-22. [PMID: 16139277 DOI: 10.1016/j.febslet.2005.07.094] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2005] [Revised: 07/04/2005] [Accepted: 07/07/2005] [Indexed: 10/25/2022]
Abstract
Innexins are a family of transmembrane proteins involved in the formation of gap junctions, specific intercellular channels, in invertebrates. Analyses of the entire innexin family during Drosophila melanogaster embryonic development shows the occurrence of complex and specific patterns of expression of the different genes. Innexins inx-2 and inx-7, in general, do not appear to exhibit extensive co-expression in different D. melanogaster cellular compartments. We propose here a new and robust mechanism, based on our analysis of the genomic organization of inx-2 and inx-7, that structurally justifies the reciprocal expression of genes.
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Affiliation(s)
- Maria Luisa Chiusano
- Department of Genetics, General and Molecular Biology, University of Naples Federico II, Via Mezzocannone, 8, 80134 Naples, Italy.
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178
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