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Abstract
The inner side of the nuclear envelope (NE) is lined with lamins, a meshwork of intermediate filaments that provides structural support for the nucleus and plays roles in many nuclear processes. Lamins, classified as A- or B-types on the basis of biochemical properties, have a conserved globular head, central rod and C-terminal domain that includes an Ig-fold structural motif. In humans, mutations in A-type lamins give rise to diseases that exhibit tissue-specific defects, such as Emery-Dreifuss muscular dystrophy. Drosophila is being used as a model to determine tissue-specific functions of A-type lamins in development, with implications for understanding human disease mechanisms. The GAL4-UAS system was used to express wild-type and mutant forms of Lamin C (the presumed Drosophila A-type lamin), in an otherwise wild-type background. Larval muscle-specific expression of wild type Drosophila Lamin C caused no overt phenotype. By contrast, larval muscle-specific expression of a truncated form of Lamin C lacking the N-terminal head (Lamin C DeltaN) caused muscle defects and semi-lethality, with adult 'escapers' possessing malformed legs. The leg defects were due to a lack of larval muscle function and alterations in hormone-regulated gene expression. The consequences of Lamin C association at a gene were tested directly by targeting a Lamin C DNA-binding domain fusion protein upstream of a reporter gene. Association of Lamin C correlated with localization of the reporter gene at the nuclear periphery and gene repression. These data demonstrate connections among the Drosophila A-type lamin, hormone-induced gene expression and muscle function.
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Affiliation(s)
- George Dialynas
- Department of Biochemistry, University of Iowa, Iowa City, IA 52241, USA
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Schulze SR, Curio-Penny B, Speese S, Dialynas G, Cryderman DE, McDonough CW, Nalbant D, Petersen M, Budnik V, Geyer PK, Wallrath LL. A comparative study of Drosophila and human A-type lamins. PLoS One 2009; 4:e7564. [PMID: 19855837 PMCID: PMC2762312 DOI: 10.1371/journal.pone.0007564] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2009] [Accepted: 10/04/2009] [Indexed: 11/24/2022] Open
Abstract
Nuclear intermediate filament proteins, called lamins, form a meshwork that lines the inner surface of the nuclear envelope. Lamins contain three domains: an N-terminal head, a central rod and a C-terminal tail domain possessing an Ig-fold structural motif. Lamins are classified as either A- or B-type based on structure and expression pattern. The Drosophila genome possesses two genes encoding lamins, Lamin C and lamin Dm0, which have been designated A- and B-type, respectively, based on their expression profile and structural features. In humans, mutations in the gene encoding A-type lamins are associated with a spectrum of predominantly tissue-specific diseases known as laminopathies. Linking the disease phenotypes to cellular functions of lamins has been a major challenge. Drosophila is being used as a model system to identify the roles of lamins in development. Towards this end, we performed a comparative study of Drosophila and human A-type lamins. Analysis of transgenic flies showed that human lamins localize predictably within the Drosophila nucleus. Consistent with this finding, yeast two-hybrid data demonstrated conservation of partner-protein interactions. Drosophila lacking A-type lamin show nuclear envelope defects similar to those observed with human laminopathies. Expression of mutant forms of the A-type Drosophila lamin modeled after human disease-causing amino acid substitutions revealed an essential role for the N-terminal head and the Ig-fold in larval muscle tissue. This tissue-restricted sensitivity suggests a conserved role for lamins in muscle biology. In conclusion, we show that (1) localization of A-type lamins and protein-partner interactions are conserved between Drosophila and humans, (2) loss of the Drosophila A-type lamin causes nuclear defects and (3) muscle tissue is sensitive to the expression of mutant forms of A-type lamin modeled after those causing disease in humans. These studies provide new insights on the role of lamins in nuclear biology and support Drosophila as a model for studies of human laminopathies involving muscle dysfunction.
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Affiliation(s)
- Sandra R. Schulze
- Department of Biology, Western Washington University, Bellingham, Washington, United States of America
| | - Beatrice Curio-Penny
- Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America
| | - Sean Speese
- Department of Neurobiology, University of Massachusetts, Wochester, Massachusetts, United States of America
| | - George Dialynas
- Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America
| | - Diane E. Cryderman
- Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America
| | - Caitrin W. McDonough
- Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America
| | - Demet Nalbant
- Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America
| | - Melissa Petersen
- Department of Biology, Western Washington University, Bellingham, Washington, United States of America
| | - Vivian Budnik
- Department of Neurobiology, University of Massachusetts, Wochester, Massachusetts, United States of America
| | - Pamela K. Geyer
- Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America
| | - Lori L. Wallrath
- Department of Biochemistry, University of Iowa, Iowa City, Iowa, United States of America
- * E-mail:
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Speese S, Petrie M, Schuske K, Ailion M, Ann K, Iwasaki K, Jorgensen EM, Martin TFJ. UNC-31 (CAPS) is required for dense-core vesicle but not synaptic vesicle exocytosis in Caenorhabditis elegans. J Neurosci 2007; 27:6150-62. [PMID: 17553987 PMCID: PMC6672138 DOI: 10.1523/jneurosci.1466-07.2007] [Citation(s) in RCA: 219] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Previous studies indicated that CAPS (calcium-dependent activator protein for secretion) functions as an essential component for the Ca2+-dependent exocytosis of dense-core vesicles in neuroendocrine cells. However, recent mouse knock-out studies suggested an alternative role in the vesicular uptake or storage of catecholamines. To genetically assess the functional role of CAPS, we characterized the sole Caenorhabditis elegans CAPS ortholog UNC-31 (uncoordinated family member) and determined its role in dense-core vesicle-mediated peptide secretion and in synaptic vesicle recycling. Novel assays for dense-core vesicle exocytosis were developed by expressing a prepro-atrial natriuretic factor-green fluorescent protein fusion protein in C. elegans. unc-31 mutants exhibited reduced peptide release in vivo and lacked evoked peptide release in cultured neurons. In contrast, cultured neurons from unc-31 mutants exhibited normal stimulated synaptic vesicle recycling measured by FM4-64 [N-(3-triethylammoniumpropyl)-4-(6-(4-diethylamino)phenyl)hexatrienyl)pyridinium dibromide] dye uptake. Conversely, UNC-13, which exhibits sequence homology to CAPS/UNC-31, was found to be essential for synaptic vesicle but not dense-core vesicle exocytosis. These findings indicate that CAPS/UNC-31 function is not restricted to catecholaminergic vesicles but is generally required for and specific to dense-core vesicle exocytosis. Our results suggest that CAPS/UNC-31 and UNC-13 serve parallel and dedicated roles in dense-core vesicle and synaptic vesicle exocytosis, respectively, in the C. elegans nervous system.
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Affiliation(s)
- Sean Speese
- Department of Biology, University of Utah, Salt Lake City, Utah 84112
| | - Matt Petrie
- Department of Biochemistry, University of Wisconsin–Madison, Madison, Wisconsin 53706, and
| | - Kim Schuske
- Department of Biology, University of Utah, Salt Lake City, Utah 84112
| | - Michael Ailion
- Department of Biology, University of Utah, Salt Lake City, Utah 84112
| | - Kyoungsook Ann
- Department of Biochemistry, University of Wisconsin–Madison, Madison, Wisconsin 53706, and
| | - Kouichi Iwasaki
- Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, Chicago, Illinois 60611
| | - Erik M. Jorgensen
- Department of Biology, University of Utah, Salt Lake City, Utah 84112
| | - Thomas F. J. Martin
- Department of Biochemistry, University of Wisconsin–Madison, Madison, Wisconsin 53706, and
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Gorczyca D, Ashley J, Speese S, Gherbesi N, Thomas U, Gundelfinger E, Gramates LS, Budnik V. Postsynaptic membrane addition depends on the Discs-Large-interacting t-SNARE Gtaxin. J Neurosci 2007; 27:1033-44. [PMID: 17267557 PMCID: PMC4664082 DOI: 10.1523/jneurosci.3160-06.2007] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Targeted membrane addition is a hallmark of many cellular functions. In the nervous system, modification of synaptic membrane size has a major impact on synaptic function. However, because of the complex shape of neurons and the need to target membrane addition to very small and polarized synaptic compartments, this process is poorly understood. Here, we show that Gtaxin (GTX), a Drosophila t-SNARE (target-soluble N-ethylmaleimide-sensitive factor attachment protein receptor), is required for expansion of postsynaptic membranes during new synapse formation. Mutations in gtx lead to drastic reductions in postsynaptic membrane surface, whereas gtx upregulation results in the formation of complex membrane structures at ectopic sites. Postsynaptic GTX activity depends on its direct interaction with Discs-Large (DLG), a multidomain scaffolding protein of the PSD-95 (postsynaptic density protein-95) family with key roles in cell polarity and formation of cellular junctions as well as synaptic protein anchoring and trafficking. We show that DLG selectively determines the postsynaptic distribution of GTX to type I, but not to type II or type III boutons on the same cell, thereby defining sites of membrane addition to this unique set of glutamatergic synapses. We provide a mechanistic explanation for selective targeted membrane expansion at specific synaptic junctions.
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Affiliation(s)
- David Gorczyca
- Department of Neurobiology, University of Massachusetts Medical School, Worcester, Massachusetts 01605
| | - James Ashley
- Department of Neurobiology, University of Massachusetts Medical School, Worcester, Massachusetts 01605
| | - Sean Speese
- Department of Neurobiology, University of Massachusetts Medical School, Worcester, Massachusetts 01605
| | - Norberto Gherbesi
- Department of Neurobiology, University of Massachusetts Medical School, Worcester, Massachusetts 01605
| | - Ulrich Thomas
- Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany, and
| | | | - L. Sian Gramates
- Molecular and Cellular Biology Graduate Program, University of Massachusetts at Amherst, Amherst, Massachusetts 01003
| | - Vivian Budnik
- Department of Neurobiology, University of Massachusetts Medical School, Worcester, Massachusetts 01605
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