1
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Gregory EF, Ragle JM, Ward JD, Starr DA. Split-GFP lamin as a tool for studying C. elegans LMN-1 dynamics in vivo. MicroPubl Biol 2023; 2023:10.17912/micropub.biology.001022. [PMID: 38152058 PMCID: PMC10751582 DOI: 10.17912/micropub.biology.001022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Figures] [Subscribe] [Scholar Register] [Received: 10/10/2023] [Revised: 11/10/2023] [Accepted: 12/01/2023] [Indexed: 12/29/2023]
Abstract
We engineered a fluorescent fusion protein of C. elegans lamin, by fusing the eleventh beta strand of GFP to the N-terminus of LMN-1 at the endogenous lmn-1 locus. When co-expressed with GFP1-10, GFP11::LMN-1 was observed at the nuclear periphery of a wide variety of somatic cells. Homozygous gfp11::lmn-1 animals had normal numbers of viable embryos. However, the gfp11::lmn-1 animals had a mild swimming defect. While not completely functional, the GFP11::LMN-1 strain is more healthy than other published fluorescent LMN-1 lines, making it a valuable reagent for studying lamins.
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Affiliation(s)
- Ellen F. Gregory
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, California, United States
| | - James Matthew Ragle
- Department of Molecular, Cell, and Developmental Biology, University of California, Santa Cruz, Santa Cruz, California, United States
| | - Jordan D. Ward
- Department of Molecular, Cell, and Developmental Biology, University of California, Santa Cruz, Santa Cruz, California, United States
| | - Daniel A. Starr
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, California, United States
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2
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McGillivary RM, Starr DA, Luxton GWG. Building and breaking mechanical bridges between the nucleus and cytoskeleton: Regulation of LINC complex assembly and disassembly. Curr Opin Cell Biol 2023; 85:102260. [PMID: 37857179 PMCID: PMC10859145 DOI: 10.1016/j.ceb.2023.102260] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [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] [Received: 08/04/2023] [Revised: 09/15/2023] [Accepted: 09/20/2023] [Indexed: 10/21/2023]
Abstract
The nucleus is physically coupled to the cytoskeleton through LINC complexes, macromolecular bridges composed of SUN and KASH proteins that span the nuclear envelope. LINC complexes are involved in a wide variety of critical cellular processes. For these processes to occur, cells regulate the composition, assembly, and disassembly of LINC complexes. Here we discuss recent studies on the regulation of the SUN-KASH interaction that forms the core of the LINC complex. These new findings encompass the stages of LINC complex assembly, from the formation of SUN-KASH heterooligomers to higher-order assemblies of LINC complexes. There is also new work on how components of the LINC complex are selectively dismantled, particularly by proteasomal degradation. It is becoming increasingly clear that LINC complexes are subject to multiple layers of regulation.
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Affiliation(s)
| | - Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, USA.
| | - G W Gant Luxton
- Department of Molecular and Cellular Biology, University of California, Davis, USA.
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3
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Ho J, Guerrero LA, Libuda DE, Luxton GWG, Starr DA. Actin and CDC-42 contribute to nuclear migration through constricted spaces in C. elegans. Development 2023; 150:dev202115. [PMID: 37756590 PMCID: PMC10617605 DOI: 10.1242/dev.202115] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Accepted: 09/15/2023] [Indexed: 09/29/2023]
Abstract
Successful nuclear migration through constricted spaces between cells or in the extracellular matrix relies on the ability of the nucleus to deform. Little is known about how this takes place in vivo. We have studied confined nuclear migration in Caenorhabditis elegans larval P cells, which is mediated by the LINC complex to pull nuclei towards the minus ends of microtubules. Null mutations of the LINC component unc-84 lead to a temperature-dependent phenotype, suggesting a parallel pathway for P-cell nuclear migration. A forward genetic screen for enhancers of unc-84 identified cgef-1 (CDC-42 guanine nucleotide exchange factor). Knockdown of CDC-42 in the absence of the LINC complex led to a P-cell nuclear migration defect. Expression of constitutively active CDC-42 partially rescued nuclear migration in cgef-1; unc-84 double mutants, suggesting that CDC-42 functions downstream of CGEF-1. The Arp2/3 complex and non-muscle myosin II (NMY-2) were also found to function parallel to the LINC pathway. In our model, CGEF-1 activates CDC-42, which induces actin polymerization through the Arp2/3 complex to deform the nucleus during nuclear migration, and NMY-2 helps to push the nucleus through confined spaces.
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Affiliation(s)
- Jamie Ho
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Leslie A. Guerrero
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Diana E. Libuda
- Department of Biology, University of Oregon, Eugene, OR 97403, USA
| | - G. W. Gant Luxton
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Daniel A. Starr
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
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4
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Ma L, Kuhn J, Chang YT, Elnatan D, Luxton GWG, Starr DA. FLN-2 functions in parallel to LINC complexes and Cdc42/actin pathways during P-cell nuclear migration through constricted spaces in Caenorhabditis elegans. bioRxiv 2023:2023.08.04.552041. [PMID: 37577634 PMCID: PMC10418278 DOI: 10.1101/2023.08.04.552041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/15/2023]
Abstract
Nuclear migration through narrow constrictions is important for development, metastasis, and pro-inflammatory responses. Studies performed in tissue culture cells have implicated LINC (linker of nucleoskeleton and cytoskeleton) complexes, microtubule motors, the actin cytoskeleton, and nuclear envelope repair machinery as important mediators of nuclear movements through constricted spaces. However, little is understood about how these mechanisms operate to move nuclei in vivo. In C. elegans larvae, 6 pairs of hypodermal P cells migrate from lateral to ventral positions through a constricted space between the body wall muscles and the cuticle. P-cell nuclear migration is mediated in part by LINC complexes using a microtubule-based pathway and by an independent CDC-42/actin-based pathway. However, when both LINC complex and actin-based pathways are knocked out, many nuclei still migrate, suggesting the existence of additional pathways. Here we show that FLN-2 functions in a third pathway to mediate P-cell nuclear migration. The predicted N-terminal actin binding domain in FLN-2 that is found in canonical filamins is dispensable for FLN-2 function, this and structural predictions suggest that FLN-2 is not a divergent filamin. The immunoglobulin (Ig)-like repeats 4-8 of FLN-2 were necessary for P-cell nuclear migration. Furthermore, in the absence of the LINC complex component unc-84, fln-2 mutants had an increase in P-cell nuclear rupture. We conclude that FLN-2 functions to maintain the integrity of the nuclear envelope in parallel with the LINC complex and CDC-42/actin-based pathways to move P-cell nuclei through constricted spaces.
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Affiliation(s)
- Linda Ma
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, USA
| | - Jonathan Kuhn
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, USA
| | - Yu-Tai Chang
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, USA
| | - Daniel Elnatan
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, USA
| | - G W Gant Luxton
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, USA
| | - Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, USA
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5
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Gregory EF, Kalra S, Brock T, Bonne G, Luxton GWG, Hopkins C, Starr DA. Caenorhabditis elegans models for striated muscle disorders caused by missense variants of human LMNA. PLoS Genet 2023; 19:e1010895. [PMID: 37624850 PMCID: PMC10484454 DOI: 10.1371/journal.pgen.1010895] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [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] [Received: 04/10/2023] [Revised: 09/07/2023] [Accepted: 08/01/2023] [Indexed: 08/27/2023] Open
Abstract
Striated muscle laminopathies caused by missense mutations in the nuclear lamin gene LMNA are characterized by cardiac dysfunction and often skeletal muscle defects. Attempts to predict which LMNA variants are pathogenic and to understand their physiological effects lag behind variant discovery. We created Caenorhabditis elegans models for striated muscle laminopathies by introducing pathogenic human LMNA variants and variants of unknown significance at conserved residues within the lmn-1 gene. Severe missense variants reduced fertility and/or motility in C. elegans. Nuclear morphology defects were evident in the hypodermal nuclei of many lamin variant strains, indicating a loss of nuclear envelope integrity. Phenotypic severity varied within the two classes of missense mutations involved in striated muscle disease, but overall, variants associated with both skeletal and cardiac muscle defects in humans lead to more severe phenotypes in our model than variants predicted to disrupt cardiac function alone. We also identified a separation of function allele, lmn-1(R204W), that exhibited normal viability and swimming behavior but had a severe nuclear migration defect. Thus, we established C. elegans avatars for striated muscle laminopathies and identified LMNA variants that offer insight into lamin mechanisms during normal development.
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Affiliation(s)
- Ellen F. Gregory
- Department of Molecular and Cellular Biology, University of California, Davis, California, United States of America
| | - Shilpi Kalra
- Department of Molecular and Cellular Biology, University of California, Davis, California, United States of America
| | - Trisha Brock
- InVivo Biosystems, Eugene, Oregon, United States of America
| | - Gisèle Bonne
- Sorbonne Université, Inserm, Institut de Myologie, Centre de Recherche en Myologie, Paris, France
| | - G. W. Gant Luxton
- Department of Molecular and Cellular Biology, University of California, Davis, California, United States of America
| | | | - Daniel A. Starr
- Department of Molecular and Cellular Biology, University of California, Davis, California, United States of America
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6
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Gümüşderelioğlu S, Resch L, Brock T, Luxton GWG, Cope H, Tan QKG, Hopkins C, Starr DA. A humanized Caenorhabditis elegans model of hereditary spastic paraplegia-associated variants in KLC4. Dis Model Mech 2023; 16:dmm050076. [PMID: 37565267 PMCID: PMC10481945 DOI: 10.1242/dmm.050076] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2023] [Accepted: 07/31/2023] [Indexed: 08/12/2023] Open
Abstract
Hereditary spastic paraplegia (HSP) is a group of degenerative neurological disorders. We identified a variant in human kinesin light chain 4 (KLC4) that is suspected to be associated with autosomal-dominant HSP. How this and other variants relate to pathologies is unknown. We created a humanized Caenorhabditis elegans model in which klc-2 was replaced by human KLC4 (referred to as hKLC4) and assessed the extent to which hKLC4 retained function in the worm. We observed a slight decrease in motility but no nuclear migration defects in the humanized worms, suggesting that hKLC4 retains much of the function of klc-2. Five hKLC4 variants were introduced into the humanized model. The clinical variant led to early lethality, with significant defects in nuclear migration when homozygous and a weak nuclear migration defect when heterozygous, possibly correlating with the clinical finding of late-onset HSP when the proband was heterozygous. Thus, we were able to establish humanized C. elegans as an animal model for HSP and to use it to test the significance of five variants of uncertain significance in the human gene KLC4.
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Affiliation(s)
- Selin Gümüşderelioğlu
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616, USA
| | | | | | | | - G. W. Gant Luxton
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616, USA
| | - Heidi Cope
- Division of Medical Genetics, Department of Pediatrics, Duke University Medical Center, Durham, NC 27710, USA
| | - Queenie K.-G. Tan
- Division of Medical Genetics, Department of Pediatrics, Duke University Medical Center, Durham, NC 27710, USA
| | | | - Daniel A. Starr
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616, USA
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7
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Gümüşderelioğlu S, Resch L, Brock T, Luxton GWG, Tan QKG, Hopkins C, Starr DA. A humanized Caenorhabditis elegans model of Hereditary Spastic Paraplegia-associated variants in kinesin light chain KLC4. bioRxiv 2023:2023.01.07.523106. [PMID: 36789438 PMCID: PMC9928042 DOI: 10.1101/2023.01.07.523106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Hereditary spastic paraplegia (HSP) is a group of degenerative neurological disorders. We identified a variant in human kinesin light chain KLC4 that is suspected to be associated with autosomal dominant HSP. How this and other variants relate to pathologies is unknown. We created a humanized C. elegans model where klc- 2 was replaced with human KLC4 and assessed the extent to which hKLC4 retained function in the worm. We observed a slight decrease in motility but no nuclear migration defects in the humanized worms, suggesting that hKLC4 retains much of the function of klc-2 . Five hKLC4 variants were introduced into the humanized model. The clinical variant led to early lethality with significant defects in nuclear migration when homozygous, and a weak nuclear migration defect when heterozygous, possibly correlating with the clinical finding of late onset HSP when the proband was heterozygous. Thus, we were able to establish humanized C. elegans as an animal model for HSP and use it to test the significance of five variants of uncertain significance in the human gene KLC4 . Summary Statement We identified a variant in KLC4 associated with Hereditary Spastic Paraplegia. The variant had physiological relevance in a humanized C. elegans model where we replaced klc-2 with human KLC4 .
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Affiliation(s)
- Selin Gümüşderelioğlu
- Department of Molecular and Cellular Biology, University of California, Davis, CA, USA
| | | | | | - G W Gant Luxton
- Department of Molecular and Cellular Biology, University of California, Davis, CA, USA
| | - Queenie K-G Tan
- Division of Medical Genetics, Department of Pediatrics, Duke University Medical Center, Durham, NC, USA
| | | | - Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, CA, USA
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8
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Fischer NC, Friedman V, Martinez-Reyes MA, Hao H, Chowdhury TA, Starr DA, Quinn CC. The ANC-1 (Nesprin-1/2) organelle-anchoring protein functions through mitochondria to polarize axon growth in response to SLT-1. PLoS Genet 2022; 18:e1010521. [PMID: 36409768 PMCID: PMC9721489 DOI: 10.1371/journal.pgen.1010521] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [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] [Received: 06/06/2022] [Revised: 12/05/2022] [Accepted: 11/11/2022] [Indexed: 11/22/2022] Open
Abstract
A family of giant KASH proteins, including C. elegans ANC-1 and mammalian Nesprin-1 and -2, are involved in organelle anchoring and are associated with multiple neurodevelopmental disorders including autism, bipolar disorder, and schizophrenia. However, little is known about how these proteins function in neurons. Moreover, the role of organelle anchoring in axon development is poorly understood. Here, we report that ANC-1 functions with the SLT-1 extracellular guidance cue to polarize ALM axon growth. This role for ANC-1 is specific to its longer ANC-1A and ANC-1C isoforms, suggesting that it is mechanistically distinct from previously described roles for ANC-1. We find that ANC-1 is required for the localization of a cluster of mitochondria to the base of the proximal axon. Furthermore, genetic and pharmacological studies indicate that ANC-1 functions with mitochondria to promote polarization of ALM axon growth. These observations reveal a mechanism whereby ANC-1 functions through mitochondria to polarize axon growth in response to SLT-1.
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Affiliation(s)
- Nathan C. Fischer
- Department of Biological Sciences, University of Wisconsin-Milwaukee; Milwaukee, Wisconsin, United States of America
| | - Vladislav Friedman
- Department of Biological Sciences, University of Wisconsin-Milwaukee; Milwaukee, Wisconsin, United States of America
| | - Miguel A. Martinez-Reyes
- Department of Biological Sciences, University of Wisconsin-Milwaukee; Milwaukee, Wisconsin, United States of America
| | - Hongyan Hao
- Department of Molecular and Cellular Biology, University of California, Davis, California, United States of America
| | - Tamjid A. Chowdhury
- Department of Biological Sciences, University of Wisconsin-Milwaukee; Milwaukee, Wisconsin, United States of America
| | - Daniel A. Starr
- Department of Molecular and Cellular Biology, University of California, Davis, California, United States of America
| | - Christopher C. Quinn
- Department of Biological Sciences, University of Wisconsin-Milwaukee; Milwaukee, Wisconsin, United States of America
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9
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Taiber S, Gozlan O, Cohen R, Andrade LR, Gregory EF, Starr DA, Moran Y, Hipp R, Kelley MW, Manor U, Sprinzak D, Avraham KB. A Nesprin-4/kinesin-1 cargo model for nuclear positioning in cochlear outer hair cells. Front Cell Dev Biol 2022; 10:974168. [PMID: 36211453 PMCID: PMC9537699 DOI: 10.3389/fcell.2022.974168] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Accepted: 09/07/2022] [Indexed: 11/14/2022] Open
Abstract
Nuclear positioning is important for the functionality of many cell types and is mediated by interactions of cytoskeletal elements and nucleoskeleton proteins. Nesprin proteins, part of the linker of nucleoskeleton and cytoskeleton (LINC) complex, have been shown to participate in nuclear positioning in multiple cell types. Outer hair cells (OHCs) in the inner ear are specialized sensory epithelial cells that utilize somatic electromotility to amplify auditory signals in the cochlea. Recently, Nesprin-4 (encoded by Syne4) was shown to play a crucial role in nuclear positioning in OHCs. Syne4 deficiency in humans and mice leads to mislocalization of the OHC nuclei and cell death resulting in deafness. However, it is unknown how Nesprin-4 mediates the position of the nucleus, and which other molecular components are involved in this process. Here, we show that the interaction of Nesprin-4 and the microtubule motor kinesin-1 is mediated by a conserved 4 amino-acid motif. Using in vivo AAV gene delivery, we show that this interaction is critical for nuclear positioning and hearing in mice. Nuclear mislocalization and cell death of OHCs coincide with the onset of hearing and electromotility and are solely restricted to outer, but not inner, hair cells. Likewise, the C. elegans functional homolog of Nesprin-4, UNC-83, uses a similar motif to mediate interactions between migrating nuclei and kinesin-1. Overall, our results suggest that OHCs require unique cellular machinery for proper nuclear positioning at the onset of electromotility. This machinery relies on the interaction between Nesprin-4 and kinesin-1 motors supporting a microtubule cargo model for nuclear positioning.
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Affiliation(s)
- Shahar Taiber
- Department of Human Molecular Genetics and Biochemistry, Faculty of Medicine and Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel,School of Neurobiology, Biochemistry and Biophysics, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Oren Gozlan
- School of Neurobiology, Biochemistry and Biophysics, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Roie Cohen
- School of Neurobiology, Biochemistry and Biophysics, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Leonardo R. Andrade
- Waitt Advanced Biophotonics Center, Salk Institute for Biological Studies, La Jolla, CA, United States
| | - Ellen F. Gregory
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, United States
| | - Daniel A. Starr
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA, United States
| | - Yehu Moran
- Department of Ecology, Evolution and Behavior, Alexander Silberman Institute of Life Sciences, Faculty of Science, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Rebecca Hipp
- Laboratory of Cochlear Development, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD, United States
| | - Matthew W. Kelley
- Laboratory of Cochlear Development, National Institute on Deafness and Other Communication Disorders, NIH, Bethesda, MD, United States
| | - Uri Manor
- Waitt Advanced Biophotonics Center, Salk Institute for Biological Studies, La Jolla, CA, United States
| | - David Sprinzak
- School of Neurobiology, Biochemistry and Biophysics, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel,*Correspondence: David Sprinzak, ; Karen B. Avraham,
| | - Karen B. Avraham
- Department of Human Molecular Genetics and Biochemistry, Faculty of Medicine and Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel,*Correspondence: David Sprinzak, ; Karen B. Avraham,
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10
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Hao H, Holt LJ, Gant Luxton G, Starr DA. The role of linc complexes in regulating the intracellular concentration of ribosomes and cytoplasmic stiffness in C. elegans. Biophys J 2022. [DOI: 10.1016/j.bpj.2021.11.2760] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022] Open
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11
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Hao H, Kalra S, Jameson LE, Guerrero LA, Cain NE, Bolivar J, Starr DA. The Nesprin-1/-2 ortholog ANC-1 regulates organelle positioning in C. elegans independently from its KASH or actin-binding domains. eLife 2021; 10:e61069. [PMID: 33860766 PMCID: PMC8139857 DOI: 10.7554/elife.61069] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Accepted: 04/11/2021] [Indexed: 12/15/2022] Open
Abstract
KASH proteins in the outer nuclear membrane comprise the cytoplasmic half of linker of nucleoskeleton and cytoskeleton (LINC) complexes that connect nuclei to the cytoskeleton. Caenorhabditis elegans ANC-1, an ortholog of Nesprin-1/2, contains actin-binding and KASH domains at opposite ends of a long spectrin-like region. Deletion of either the KASH or calponin homology (CH) domains does not completely disrupt nuclear positioning, suggesting neither KASH nor CH domains are essential. Deletions in the spectrin-like region of ANC-1 led to significant defects, but only recapitulated the null phenotype in combination with mutations in the transmembrane (TM) span. In anc-1 mutants, the endoplasmic reticulum ER, mitochondria, and lipid droplets were unanchored, moving throughout the cytoplasm. The data presented here support a cytoplasmic integrity model where ANC-1 localizes to the ER membrane and extends into the cytoplasm to position nuclei, ER, mitochondria, and other organelles in place.
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Affiliation(s)
- Hongyan Hao
- Department of Molecular and Cellular Biology, University of California, DavisDavisUnited States
| | - Shilpi Kalra
- Department of Molecular and Cellular Biology, University of California, DavisDavisUnited States
| | - Laura E Jameson
- Department of Molecular and Cellular Biology, University of California, DavisDavisUnited States
| | - Leslie A Guerrero
- Department of Molecular and Cellular Biology, University of California, DavisDavisUnited States
| | - Natalie E Cain
- Department of Molecular and Cellular Biology, University of California, DavisDavisUnited States
| | - Jessica Bolivar
- Department of Molecular and Cellular Biology, University of California, DavisDavisUnited States
| | - Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, DavisDavisUnited States
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12
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Abstract
The mechanisms that control how the two parental pronuclei fuse in the first mitosis of the embryo are poorly understood. In this issue, Rahman et al. (2020. J. Cell Biol.https://doi.org/10.1083/jcb.201909137) found that membrane fusion between pronuclear envelopes, followed by fenestration, promotes pronuclear fusion.
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Affiliation(s)
- Linda Ma
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA
| | - Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA
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13
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Abstract
LINC complexes (Linker of Nucleoskeleton and Cytoskeleton), consisting of inner nuclear membrane SUN (Sad1, UNC-84) proteins and outer nuclear membrane KASH (Klarsicht, ANC-1, and Syne Homology) proteins, are essential for nuclear positioning, cell migration and chromosome dynamics. To test the in vivo functions of conserved interfaces revealed by crystal structures, Cain et al used a combination of Caenorhabditis elegans genetics, imaging in cultured NIH 3T3 fibroblasts, and Molecular Dynamic simulations, to study SUN-KASH interactions. Conserved aromatic residues at the -7 position of the C-termini of KASH proteins and conserved disulfide bonds in LINC complexes play important roles in force transmission across the nuclear envelope. Other properties of LINC complexes, such as the helices preceding the SUN domain, the longer coiled-coils spanning the perinuclear space and higher-order organization may also function to transmit mechanical forces generated by the cytoskeleton across the nuclear envelope.
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Affiliation(s)
- Hongyan Hao
- a Department of Molecular and Cellular Biology , University of California , Davis , CA USA
| | - Daniel A Starr
- a Department of Molecular and Cellular Biology , University of California , Davis , CA USA
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14
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Starr DA. A network of nuclear envelope proteins and cytoskeletal force generators mediates movements of and within nuclei throughout Caenorhabditis elegans development. Exp Biol Med (Maywood) 2019; 244:1323-1332. [PMID: 31495194 PMCID: PMC6880151 DOI: 10.1177/1535370219871965] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Nuclear migration and anchorage, together referred to as nuclear positioning, are central to many cellular and developmental events. Nuclear positioning is mediated by a conserved network of nuclear envelope proteins that interacts with force generators in the cytoskeleton. At the heart of this network are li nker of n ucleoskeleton and c ytoskeleton (LINC) complexes made of S ad1 and UN C-84 (SUN) proteins at the inner nuclear membrane and K larsicht, A NC-1, and S yne homology (KASH) proteins in the outer nuclear membrane. LINC complexes span the nuclear envelope, maintain nuclear envelope architecture, designate the surface of nuclei distinctly from the contiguous endoplasmic reticulum, and were instrumental in the early evolution of eukaryotes. LINC complexes interact with lamins in the nucleus and with various cytoplasmic KASH effectors from the surface of nuclei. These effectors regulate the cytoskeleton, leading to a variety of cellular outputs including pronuclear migration, nuclear migration through constricted spaces, nuclear anchorage, centrosome attachment to nuclei, meiotic chromosome movements, and DNA damage repair. How LINC complexes are regulated and how they function are reviewed here. The focus is on recent studies elucidating the best-understood network of LINC complexes, those used throughout Caenorhabditis elegans development.
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Affiliation(s)
- Daniel A Starr
- Department of Molecular and Cellular Biology,
University of California, Davis, CA 95616, USA
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15
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Abstract
Microtubule-organizing centers move from centrosomes to the nuclear envelope during muscle development. The KASH protein Nesprin-1α recruits pericentriolar material to the surface of myotube nuclei, where it nucleates microtubules to ensure even spacing of nuclei within the developing myotube.
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Affiliation(s)
- Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, USA.
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16
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Jahed Z, Hao H, Thakkar V, Vu UT, Valdez VA, Rathish A, Tolentino C, Kim SCJ, Fadavi D, Starr DA, Mofrad MRK. Role of KASH domain lengths in the regulation of LINC complexes. Mol Biol Cell 2019; 30:2076-2086. [PMID: 30995155 PMCID: PMC6727767 DOI: 10.1091/mbc.e19-02-0079] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The linker of the nucleoskeleton and cytoskeleton (LINC) complex is formed by the conserved interactions between Sad-1 and UNC-84 (SUN) and Klarsicht, ANC-1, SYNE homology (KASH) domain proteins, providing a physical coupling between the nucleoskeleton and cytoskeleton that mediates the transfer of physical forces across the nuclear envelope. The LINC complex can perform distinct cellular functions by pairing various KASH domain proteins with the same SUN domain protein. For example, in Caenorhabditis elegans, SUN protein UNC-84 binds to two KASH proteins UNC-83 and ANC-1 to mediate nuclear migration and anchorage, respectively. In addition to distinct cytoplasmic domains, the luminal KASH domain also varies among KASH domain proteins of distinct functions. In this study, we combined in vivo C. elegans genetics and in silico molecular dynamics simulations to understand the relation between the length and amino acid composition of the luminal KASH domain, and the function of the SUN–KASH complex. We show that longer KASH domains can withstand and transfer higher forces and interact with the membrane through a conserved membrane proximal EEDY domain that is unique to longer KASH domains. In agreement with our models, our in vivo results show that swapping the KASH domains of ANC-1 and UNC-83, or shortening the KASH domain of ANC-1, both result in a nuclear anchorage defect in C. elegans.
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Affiliation(s)
- Zeinab Jahed
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, Berkeley, CA 94720
| | - Hongyan Hao
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616
| | - Vyom Thakkar
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, Berkeley, CA 94720
| | - Uyen T Vu
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, Berkeley, CA 94720
| | - Venecia A Valdez
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616
| | - Akshay Rathish
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, Berkeley, CA 94720
| | - Chris Tolentino
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, Berkeley, CA 94720
| | - Samuel C J Kim
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, Berkeley, CA 94720
| | - Darya Fadavi
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, Berkeley, CA 94720
| | - Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616
| | - Mohammad R K Mofrad
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, Berkeley, CA 94720.,Molecular Biophysics and Integrative Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
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17
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Cain NE, Jahed Z, Schoenhofen A, Valdez VA, Elkin B, Hao H, Harris NJ, Herrera LA, Woolums BM, Mofrad MRK, Luxton GWG, Starr DA. Conserved SUN-KASH Interfaces Mediate LINC Complex-Dependent Nuclear Movement and Positioning. Curr Biol 2018; 28:3086-3097.e4. [PMID: 30245107 DOI: 10.1016/j.cub.2018.08.001] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2017] [Revised: 06/18/2018] [Accepted: 08/01/2018] [Indexed: 12/20/2022]
Abstract
Many nuclear positioning events involve linker of nucleoskeleton and cytoskeleton (LINC) complexes, which transmit forces generated by the cytoskeleton across the nuclear envelope. LINC complexes are formed by trans-luminal interactions between inner nuclear membrane SUN proteins and outer nuclear membrane KASH proteins, but how these interactions are regulated is poorly understood. We combine in vivo C. elegans genetics, in vitro wounded fibroblast polarization, and in silico molecular dynamics simulations to elucidate mechanisms of LINC complexes. The extension of the KASH domain by a single alanine residue or the mutation of the conserved tyrosine at -7 completely blocked the nuclear migration function of C. elegans UNC-83. Analogous mutations at -7 of mouse nesprin-2 disrupted rearward nuclear movements in NIH 3T3 cells, but did not disrupt ANC-1 in nuclear anchorage. Furthermore, conserved cysteines predicted to form a disulfide bond between SUN and KASH proteins are important for the function of certain LINC complexes, and might promote a developmental switch between nuclear migration and nuclear anchorage. Mutations of conserved cysteines in SUN or KASH disrupted ANC-1-dependent nuclear anchorage in C. elegans and Nesprin-2G-dependent nuclear movements in polarizing fibroblasts. However, the SUN cysteine mutation did not disrupt nuclear migration. Moreover, molecular dynamics simulations showed that a disulfide bond is necessary for the maximal transmission of cytoskeleton-generated forces by LINC complexes in silico. Thus, we have demonstrated functions for SUN-KASH binding interfaces, including a predicted intermolecular disulfide bond, as mechanistic determinants of nuclear positioning that may represent targets for regulation.
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Affiliation(s)
- Natalie E Cain
- Department of Molecular and Cellular Biology, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, USA
| | - Zeinab Jahed
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, 208A Stanley Hall, Berkeley, CA 94720, USA
| | - Amy Schoenhofen
- Department of Genetics, Cell Biology, and Development, University of Minnesota, 420 Washington Avenue SE, Minneapolis, MN 55455, USA
| | - Venecia A Valdez
- Department of Molecular and Cellular Biology, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, USA
| | - Baila Elkin
- Department of Genetics, Cell Biology, and Development, University of Minnesota, 420 Washington Avenue SE, Minneapolis, MN 55455, USA
| | - Hongyan Hao
- Department of Molecular and Cellular Biology, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, USA
| | - Nathan J Harris
- Department of Genetics, Cell Biology, and Development, University of Minnesota, 420 Washington Avenue SE, Minneapolis, MN 55455, USA
| | - Leslie A Herrera
- Department of Molecular and Cellular Biology, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, USA
| | - Brian M Woolums
- Department of Genetics, Cell Biology, and Development, University of Minnesota, 420 Washington Avenue SE, Minneapolis, MN 55455, USA
| | - Mohammad R K Mofrad
- Molecular Cell Biomechanics Laboratory, Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, 208A Stanley Hall, Berkeley, CA 94720, USA
| | - G W Gant Luxton
- Department of Genetics, Cell Biology, and Development, University of Minnesota, 420 Washington Avenue SE, Minneapolis, MN 55455, USA
| | - Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, USA.
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18
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Ho J, Valdez VA, Ma L, Starr DA. Characterizing Dynein's Role in P-cell Nuclear Migration using an Auxin-Induced Degradation System. MicroPubl Biol 2018; 2018. [PMID: 32550376 PMCID: PMC7255844 DOI: 10.17912/w2w96j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- Jamie Ho
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Venecia A Valdez
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Linda Ma
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
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19
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Fridolfsson HN, Herrera LA, Brandt JN, Cain NE, Hermann GJ, Starr DA. Genetic Analysis of Nuclear Migration and Anchorage to Study LINC Complexes During Development of Caenorhabditis elegans. Methods Mol Biol 2018; 1840:163-180. [PMID: 30141045 DOI: 10.1007/978-1-4939-8691-0_13] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Studying nuclear positioning in developing tissues of the model nematode Caenorhabditis elegans greatly contributed to the discovery of SUN and KASH proteins and the formation of the LINC model. Such studies continue to make important contributions into both how LINC complexes are regulated and how defects in LINC components disrupt normal development. The methods described explain how to observe and quantify the following: nuclear migration in embryonic dorsal hypodermal cells, nuclear migration through constricted spaces in larval P cells, nuclear positioning in the embryonic intestinal primordia, and nuclear anchorage in syncytial hypodermal cells. These methods will allow others to employ nuclear positioning in C. elegans as a model to further explore LINC complex regulation and function.
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Affiliation(s)
- Heidi N Fridolfsson
- Department of Molecular and Cellular Biology, University of California, Davis, CA, USA
| | - Leslie A Herrera
- Department of Molecular and Cellular Biology, University of California, Davis, CA, USA
| | - James N Brandt
- Department of Biology, Lewis and Clark College, Portland, OR, USA
| | - Natalie E Cain
- Department of Molecular and Cellular Biology, University of California, Davis, CA, USA
| | - Greg J Hermann
- Department of Biology, Lewis and Clark College, Portland, OR, USA
| | - Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, CA, USA.
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20
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Abstract
Moving the nucleus to a specific position within the cell is an important event during many cell and developmental processes. Several different molecular mechanisms exist to position nuclei in various cell types. In this Commentary, we review the recent progress made in elucidating mechanisms of nuclear migration in a variety of important developmental models. Genetic approaches to identify mutations that disrupt nuclear migration in yeast, filamentous fungi, Caenorhabditis elegans, Drosophila melanogaster and plants led to the identification of microtubule motors, as well as Sad1p, UNC-84 (SUN) domain and Klarsicht, ANC-1, Syne homology (KASH) domain proteins (LINC complex) that function to connect nuclei to the cytoskeleton. We focus on how these proteins and various mechanisms move nuclei during vertebrate development, including processes related to wound healing of fibroblasts, fertilization, developing myotubes and the developing central nervous system. We also describe how nuclear migration is involved in cells that migrate through constricted spaces. On the basis of these findings, it is becoming increasingly clear that defects in nuclear positioning are associated with human diseases, syndromes and disorders.
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Affiliation(s)
- Courtney R Bone
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
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21
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Abstract
Starr and Rose discuss work by Saunders et al. demonstrating that torsinA and LAP1 regulate nuclear movement during fibroblast polarization. How LINC complexes are regulated to connect nuclei to the cytoskeleton during nuclear migration is unknown. Saunders et al. (2017. J. Cell Biol.https://doi.org/10.1083/jcb.201507113) show that the AAA+ ATPase torsinA and its partner LAP1 are required for nuclear migration during fibroblast polarization by mediating the dynamics of LINC complexes.
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Affiliation(s)
- Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616
| | - Lesilee S Rose
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616
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22
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Lawrence KS, Tapley EC, Cruz VE, Li Q, Aung K, Hart KC, Schwartz TU, Starr DA, Engebrecht J. LINC complexes promote homologous recombination in part through inhibition of nonhomologous end joining. J Cell Biol 2016; 215:801-821. [PMID: 27956467 PMCID: PMC5166498 DOI: 10.1083/jcb.201604112] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Revised: 09/03/2016] [Accepted: 10/31/2016] [Indexed: 01/23/2023] Open
Abstract
The Caenorhabditis elegans SUN domain protein, UNC-84, functions in nuclear migration and anchorage in the soma. We discovered a novel role for UNC-84 in DNA damage repair and meiotic recombination. Loss of UNC-84 leads to defects in the loading and disassembly of the recombinase RAD-51. Similar to mutations in Fanconi anemia (FA) genes, unc-84 mutants and human cells depleted of Sun-1 are sensitive to DNA cross-linking agents, and sensitivity is rescued by the inactivation of nonhomologous end joining (NHEJ). UNC-84 also recruits FA nuclease FAN-1 to the nucleoplasm, suggesting that UNC-84 both alters the extent of repair by NHEJ and promotes the processing of cross-links by FAN-1. UNC-84 interacts with the KASH protein ZYG-12 for DNA damage repair. Furthermore, the microtubule network and interaction with the nucleoskeleton are important for repair, suggesting that a functional linker of nucleoskeleton and cytoskeleton (LINC) complex is required. We propose that LINC complexes serve a conserved role in DNA repair through both the inhibition of NHEJ and the promotion of homologous recombination at sites of chromosomal breaks.
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Affiliation(s)
- Katherine S Lawrence
- Department of Molecular and Cellular Biology; Biochemistry, Molecular Cellular, and Developmental Biology Graduate Group, University of California, Davis, Davis, CA 95616
| | - Erin C Tapley
- Department of Molecular and Cellular Biology; Biochemistry, Molecular Cellular, and Developmental Biology Graduate Group, University of California, Davis, Davis, CA 95616
| | - Victor E Cruz
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Qianyan Li
- Department of Molecular and Cellular Biology; Biochemistry, Molecular Cellular, and Developmental Biology Graduate Group, University of California, Davis, Davis, CA 95616
| | - Kayla Aung
- Department of Molecular and Cellular Biology; Biochemistry, Molecular Cellular, and Developmental Biology Graduate Group, University of California, Davis, Davis, CA 95616
| | - Kevin C Hart
- Department of Molecular and Cellular Biology; Biochemistry, Molecular Cellular, and Developmental Biology Graduate Group, University of California, Davis, Davis, CA 95616
| | - Thomas U Schwartz
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139
| | - Daniel A Starr
- Department of Molecular and Cellular Biology; Biochemistry, Molecular Cellular, and Developmental Biology Graduate Group, University of California, Davis, Davis, CA 95616
| | - JoAnne Engebrecht
- Department of Molecular and Cellular Biology; Biochemistry, Molecular Cellular, and Developmental Biology Graduate Group, University of California, Davis, Davis, CA 95616
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23
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Bone CR, Chang YT, Cain NE, Murphy SP, Starr DA. Nuclei migrate through constricted spaces using microtubule motors and actin networks in C. elegans hypodermal cells. J Cell Sci 2016. [DOI: 10.1242/jcs.199646] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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24
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Bone CR, Chang YT, Cain NE, Murphy SP, Starr DA. Nuclei migrate through constricted spaces using microtubule motors and actin networks in C. elegans hypodermal cells. Development 2016; 143:4193-4202. [PMID: 27697906 DOI: 10.1242/dev.141192] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Accepted: 09/20/2016] [Indexed: 12/22/2022]
Abstract
Cellular migrations through constricted spaces are a crucial aspect of many developmental and disease processes including hematopoiesis, inflammation and metastasis. A limiting factor in these events is nuclear deformation. Here, we establish an in vivo model in which nuclei can be visualized while moving through constrictions and use it to elucidate mechanisms for nuclear migration. C. elegans hypodermal P-cell larval nuclei traverse a narrow space that is about 5% their width. This constriction is blocked by fibrous organelles, structures that pass through P cells to connect the muscles to cuticle. Fibrous organelles are removed just prior to nuclear migration, when nuclei and lamins undergo extreme morphological changes to squeeze through the space. Both actin and microtubule networks are organized to mediate nuclear migration. The LINC complex, consisting of the SUN protein UNC-84 and the KASH protein UNC-83, recruits dynein and kinesin-1 to the nuclear surface. Both motors function in P-cell nuclear migration, but dynein, functioning through UNC-83, plays a more central role as nuclei migrate towards minus ends of polarized microtubule networks. Thus, the nucleoskeleton and cytoskeleton are coordinated to move nuclei through constricted spaces.
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Affiliation(s)
- Courtney R Bone
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Yu-Tai Chang
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Natalie E Cain
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Shaun P Murphy
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
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25
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Abstract
The nuclear envelope consists of 2 membranes separated by 30–50 nm, but how the 2 membranes are evenly spaced has been an open question in the field. Nuclear envelope bridges composed of inner nuclear membrane SUN proteins and outer nuclear membrane KASH proteins have been proposed to set and regulate nuclear envelope spacing. We tested this hypothesis directly by examining nuclear envelope spacing in Caenorhabditis elegans animals lacking UNC-84, the sole somatic SUN protein. SUN/KASH bridges are not required to maintain even nuclear envelope spacing in most tissues. However, UNC-84 is required for even spacing in body wall muscle nuclei. Shortening UNC-84 by 300 amino acids did not narrow the nuclear envelope space. While SUN proteins may play a role in maintaining nuclear envelope spacing in cells experiencing forces, our data suggest they are dispensable in most cells.
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Affiliation(s)
- Natalie E Cain
- a Department of Molecular and Cellular Biology ; University of California Davis ; Davis , CA USA
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26
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Starr DA. Watching nuclei move: Insights into how kinesin-1 and dynein function together. Bioarchitecture 2014; 1:9-13. [PMID: 21866255 DOI: 10.4161/bioa.1.1.14629] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2010] [Accepted: 12/21/2010] [Indexed: 12/29/2022]
Abstract
Moving nuclei to specific intracellular locations is central to many cell and developmental processes. However, the molecular mechanisms of nuclear migration are poorly understood. We took advantage of the ability to film nuclear migration events in Caenorhabditis elegans embryos to gain insights into the mechanisms of nuclear migration. Mutations in unc-83 blocked the initiation of nuclear migration. UNC-83 recruits kinesin-1 and dynein to the nuclear envelope. Live imaging of mutants showed that kinein-1 provides the major force to move nuclei. Dynein is responsible to move nuclei backwards or to mediate nuclear rolling to by pass cellular roadblocks that impede efficient migration. Live imaging was also used to analyze the microtubule network, which is highly polarized and dynamic. This detailed mechanism of nuclear migration may be applicable to nuclear migration in other systems and for the movement of other large cellular cargo.
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Affiliation(s)
- Daniel A Starr
- Department of Molecular and Cellular Biology; University of California, Davis; Davis, CA USA
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27
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Bone CR, Tapley EC, Gorjánácz M, Starr DA. The Caenorhabditis elegans SUN protein UNC-84 interacts with lamin to transfer forces from the cytoplasm to the nucleoskeleton during nuclear migration. Mol Biol Cell 2014; 25:2853-65. [PMID: 25057012 PMCID: PMC4161519 DOI: 10.1091/mbc.e14-05-0971] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The nucleoplasmic domain of the Caenorhabditis elegans SUN protein UNC-84 interacts with lamin. If this interaction is disrupted, a partial failure in nuclear migration occurs. Nuclear migration is a critical component of many cellular and developmental processes. The nuclear envelope forms a barrier between the cytoplasm, where mechanical forces are generated, and the nucleoskeleton. The LINC complex consists of KASH proteins in the outer nuclear membrane and SUN proteins in the inner nuclear membrane that bridge the nuclear envelope. How forces are transferred from the LINC complex to the nucleoskeleton is poorly understood. The Caenorhabditis elegans lamin, LMN-1, is required for nuclear migration and interacts with the nucleoplasmic domain of the SUN protein UNC-84. This interaction is weakened by the unc-84(P91S) missense mutation. These mutant nuclei have an intermediate nuclear migration defect—live imaging of nuclei or LMN-1::GFP shows that many nuclei migrate normally, others initiate migration before subsequently failing, and others fail to begin migration. At least one other component of the nucleoskeleton, the NET5/Samp1/Ima1 homologue SAMP-1, plays a role in nuclear migration. We propose a nut-and-bolt model to explain how forces are dissipated across the nuclear envelope during nuclear migration. In this model, SUN/KASH bridges serve as bolts through the nuclear envelope, and nucleoskeleton components LMN-1 and SAMP-1 act as both nuts and washers on the inside of the nucleus.
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Affiliation(s)
- Courtney R Bone
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95618
| | - Erin C Tapley
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95618
| | - Mátyás Gorjánácz
- European Molecular Biology Laboratory, 69117 Heidelberg, Germany
| | - Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95618
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28
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Cain NE, Tapley EC, McDonald KL, Cain BM, Starr DA. The SUN protein UNC-84 is required only in force-bearing cells to maintain nuclear envelope architecture. ACTA ACUST UNITED AC 2014; 206:163-72. [PMID: 25023515 PMCID: PMC4107780 DOI: 10.1083/jcb.201405081] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
SUN-KASH bridges that connect the nucleoskeleton to the cytoskeleton are only required to maintain nuclear envelope spacing in cells subjected to increased mechanical forces, such as muscle cells. The nuclear envelope (NE) consists of two evenly spaced bilayers, the inner and outer nuclear membranes. The Sad1p and UNC-84 (SUN) proteins and Klarsicht, ANC-1, and Syne homology (KASH) proteins that interact to form LINC (linker of nucleoskeleton and cytoskeleton) complexes connecting the nucleoskeleton to the cytoskeleton have been implicated in maintaining NE spacing. Surprisingly, the NE morphology of most Caenorhabditis elegans nuclei was normal in the absence of functional SUN proteins. Distortions of the perinuclear space observed in unc-84 mutant muscle nuclei resembled those previously observed in HeLa cells, suggesting that SUN proteins are required to maintain NE architecture in cells under high mechanical strain. The UNC-84 protein with large deletions in its luminal domain was able to form functional NE bridges but had no observable effect on NE architecture. Therefore, SUN-KASH bridges are only required to maintain NE spacing in cells subjected to increased mechanical forces. Furthermore, SUN proteins do not dictate the width of the NE.
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Affiliation(s)
- Natalie E Cain
- Department of Molecular and Cellular Biology and Department of Physics, University of California, Davis, Davis, CA 95616
| | - Erin C Tapley
- Department of Molecular and Cellular Biology and Department of Physics, University of California, Davis, Davis, CA 95616
| | - Kent L McDonald
- Electron Microscope Laboratory, University of California, Berkeley, Berkeley, CA 94720
| | - Benjamin M Cain
- Department of Molecular and Cellular Biology and Department of Physics, University of California, Davis, Davis, CA 95616
| | - Daniel A Starr
- Department of Molecular and Cellular Biology and Department of Physics, University of California, Davis, Davis, CA 95616
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29
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Luxton GWG, Starr DA. KASHing up with the nucleus: novel functional roles of KASH proteins at the cytoplasmic surface of the nucleus. Curr Opin Cell Biol 2014; 28:69-75. [PMID: 24704701 DOI: 10.1016/j.ceb.2014.03.002] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2013] [Revised: 03/05/2014] [Accepted: 03/08/2014] [Indexed: 10/25/2022]
Abstract
Nuclear-cytoskeletal connections are central to fundamental cellular processes, including nuclear positioning and chromosome movements in meiosis. The cytoskeleton is coupled to the nucleoskeleton through conserved KASH-SUN bridges, or LINC complexes, that span the nuclear envelope. KASH proteins localize to the outer nuclear membrane where they connect the nucleus to the cytoskeleton. New findings have expanded the functional diversity of KASH proteins, showing that they interact with microtubule motors, actin, intermediate filaments, a nonconventional myosin, RanGAP, and each other. The role of KASH proteins in cellular mechanics is discussed. Genetic mutations in KASH proteins are associated with autism, hearing loss, cancer, muscular dystrophy and other diseases.
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Affiliation(s)
- G W Gant Luxton
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455, United States.
| | - Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, United States.
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30
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Abstract
SUN proteins accelerate the pathological progression of laminopathies. Although the mechanisms remain to be elucidated, an intriguing possibility is that high levels of SUN proteins lead to a hyperactive DNA damage response.
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Affiliation(s)
- Daniel A Starr
- Department of Molecular and Cellular Biology, University of California at Davis, CA 95616, USA.
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31
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Tapley EC, Starr DA. Connecting the nucleus to the cytoskeleton by SUN-KASH bridges across the nuclear envelope. Curr Opin Cell Biol 2012; 25:57-62. [PMID: 23149102 DOI: 10.1016/j.ceb.2012.10.014] [Citation(s) in RCA: 166] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2012] [Accepted: 10/20/2012] [Indexed: 12/11/2022]
Abstract
The nuclear-cytoskeleton connection influences many aspects of cellular architecture, including nuclear positioning, the stiffness of the global cytoskeleton, and mechanotransduction. Central to all of these processes is the assembly and function of conserved SUN-KASH bridges, or LINC complexes, that span the nuclear envelope. Recent studies provide details of the higher order assembly and targeting of SUN proteins to the inner nuclear membrane. Structural studies characterize SUN-KASH interactions that form the central link of the nuclear-envelope bridge. KASH proteins at the outer nuclear membrane link the nuclear envelope to the cytoskeleton where forces are generated to move nuclei. Significantly, SUN proteins were recently shown to contribute to the progression of laminopathies.
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Affiliation(s)
- Erin C Tapley
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616, United States
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32
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Affiliation(s)
- Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA.
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33
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Morgan JT, Pfeiffer ER, Thirkill TL, Kumar P, Peng G, Fridolfsson HN, Douglas GC, Starr DA, Barakat AI. Nesprin-3 regulates endothelial cell morphology, perinuclear cytoskeletal architecture, and flow-induced polarization. Mol Biol Cell 2011; 22:4324-34. [PMID: 21937718 PMCID: PMC3216658 DOI: 10.1091/mbc.e11-04-0287] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Nesprin-3, a protein that links intermediate filaments to the nucleus, plays a role in vascular endothelial cell (EC) function. Nesprin-3 regulates EC morphology, perinuclear cytoskeletal organization, centrosome–nuclear connectivity, and flow-induced cell polarization and migration. Changes in blood flow regulate gene expression and protein synthesis in vascular endothelial cells, and this regulation is involved in the development of atherosclerosis. How mechanical stimuli are transmitted from the endothelial luminal surface to the nucleus is incompletely understood. The linker of nucleus and cytoskeleton (LINC) complexes have been proposed as part of a continuous physical link between the plasma membrane and subnuclear structures. LINC proteins nesprin-1, -2, and -4 have been shown to mediate nuclear positioning via microtubule motors and actin. Although nesprin-3 connects intermediate filaments to the nucleus, no functional consequences of nesprin-3 mutations on cellular processes have been described. Here we show that nesprin-3 is robustly expressed in human aortic endothelial cells (HAECs) and localizes to the nuclear envelope. Nesprin-3 regulates HAEC morphology, with nesprin-3 knockdown inducing prominent cellular elongation. Nesprin-3 also organizes perinuclear cytoskeletal organization and is required to attach the centrosome to the nuclear envelope. Finally, nesprin-3 is required for flow-induced polarization of the centrosome and flow-induced migration in HAECs. These results represent the most complete description to date of nesprin-3 function and suggest that nesprin-3 regulates vascular endothelial cell shape, perinuclear cytoskeletal architecture, and important aspects of flow-mediated mechanotransduction.
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Affiliation(s)
- Joshua T Morgan
- Department of Mechanical and Aerospace Engineering, University of California, Davis, Davis, CA 95616, USA
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Green RA, Kao HL, Audhya A, Arur S, Mayers JR, Fridolfsson HN, Schulman M, Schloissnig S, Niessen S, Laband K, Wang S, Starr DA, Hyman AA, Schedl T, Desai A, Piano F, Gunsalus KC, Oegema K. A high-resolution C. elegans essential gene network based on phenotypic profiling of a complex tissue. Cell 2011; 145:470-82. [PMID: 21529718 DOI: 10.1016/j.cell.2011.03.037] [Citation(s) in RCA: 132] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2010] [Revised: 12/21/2010] [Accepted: 03/24/2011] [Indexed: 10/18/2022]
Abstract
High-content screening for gene profiling has generally been limited to single cells. Here, we explore an alternative approach-profiling gene function by analyzing effects of gene knockdowns on the architecture of a complex tissue in a multicellular organism. We profile 554 essential C. elegans genes by imaging gonad architecture and scoring 94 phenotypic features. To generate a reference for evaluating methods for network construction, genes were manually partitioned into 102 phenotypic classes, predicting functions for uncharacterized genes across diverse cellular processes. Using this classification as a benchmark, we developed a robust computational method for constructing gene networks from high-content profiles based on a network context-dependent measure that ranks the significance of links between genes. Our analysis reveals that multi-parametric profiling in a complex tissue yields functional maps with a resolution similar to genetic interaction-based profiling in unicellular eukaryotes-pinpointing subunits of macromolecular complexes and components functioning in common cellular processes.
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Affiliation(s)
- Rebecca A Green
- Ludwig Institute for Cancer Research, Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, 92093, USA
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Abstract
The mechanisms of inner nuclear membrane protein trafficking remain mostly unknown. We identified UNC-84 mutants that suggest that moving from the endoplasmic reticulum to the nuclear envelope does not occur by diffusion alone. Three signals need to be disrupted to block localization, suggesting that multiple mechanisms facilitate trafficking to the inner nuclear membrane. Approximately 100 proteins are targeted to the inner nuclear membrane (INM), where they regulate chromatin and nuclear dynamics. The mechanisms underlying trafficking to the INM are poorly understood. The Caenorhabditis elegans SUN protein UNC-84 is an excellent model to investigate such mechanisms. UNC-84 recruits KASH proteins to the outer nuclear membrane to bridge the nuclear envelope (NE), mediating nuclear positioning. UNC-84 has four targeting sequences: two classical nuclear localization signals, an INM sorting motif, and a signal conserved in mammalian Sun1, the SUN—nuclear envelope localization signal. Mutations in some signals disrupt the timing of UNC-84 nuclear envelope localization, showing that diffusion is not sufficient to move all UNC-84 to the NE. Thus targeting UNC-84 requires an initial step that actively transports UNC-84 from the peripheral endoplasmic reticulum to the NE. Only when all four signals are simultaneously disrupted does UNC-84 completely fail to localize and to function in nuclear migration, meaning that at least three signals function, in part, redundantly to ensure proper targeting of UNC-84. Multiple mechanisms might also be used to target other proteins to the INM, thereby ensuring their proper and timely localization for essential cellular and developmental functions.
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Affiliation(s)
- Erin C Tapley
- Department of Molecular and Cellular Biology, University of California, Davis, Davis CA 95616, USA
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Affiliation(s)
- Ana Pombo
- Genome Function Group, MRC Clinical Sciences Centre, Imperial College School of Medicine, Hammersmith Hospital Campus, London W12 0NN, UK.
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37
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Abstract
Kinesin-1 and dynein are recruited to the nuclear envelope by the Caenorhabditis elegans klarsicht/ANC-1/Syne homology (KASH) protein UNC-83 to move nuclei. The mechanisms of how these motors are coordinated to mediate nuclear migration are unknown. Time-lapse differential interference contrast and fluorescence imaging of embryonic hypodermal nuclear migration events were used to characterize the kinetics of nuclear migration and determine microtubule dynamics and polarity. Wild-type nuclei display bidirectional movements during migration and are also able to roll past cytoplasmic granules. unc-83, unc-84, and kinesin-1 mutants have severe nuclear migration defects. Without dynein, nuclear migration initiates normally but lacks bidirectional movement and shows defects in nuclear rolling, implicating dynein in resolution of cytoplasmic roadblocks. Microtubules are highly dynamic during nuclear migration. EB1::green fluorescence protein imaging demonstrates that microtubules are polarized in the direction of nuclear migration. This organization of microtubules fits with our model that kinesin-1 moves nuclei forward and dynein functions to move nuclei backward for short stretches to bypass cellular roadblocks.
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Affiliation(s)
- Heidi N Fridolfsson
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616, USA
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38
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Abstract
The nuclear envelope links the cytoskeleton to structural components of the nucleus. It functions to coordinate nuclear migration and anchorage, organize chromatin, and aid meiotic chromosome pairing. Forces generated by the cytoskeleton are transferred across the nuclear envelope to the nuclear lamina through a nuclear-envelope bridge consisting of SUN (Sad1 and UNC-84) and KASH (Klarsicht, ANC-1 and Syne/Nesprin homology) proteins. Some KASH-SUN combinations connect microtubules, centrosomes, actin filaments, or intermediate filaments to the surface of the nucleus. Other combinations are used in cell cycle control, nuclear import, or apoptosis. Interactions between the cytoskeleton and the nucleus also affect global cytoskeleton organization. SUN and KASH proteins were identified through genetic screens for mispositioned nuclei in model organisms. Knockouts of SUN or KASH proteins disrupt neurological and muscular development in mice. Defects in SUN and KASH proteins have been linked to human diseases including muscular dystrophy, ataxia, progeria, lissencephaly, and cancer.
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Affiliation(s)
- Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, California 95616, USA.
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Affiliation(s)
- Daniel A Starr
- Department of Molecular and Cellular Biology, College of Biological Sciences, University of California, Davis, CA 95616, USA.
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Fridolfsson HN, Ly N, Meyerzon M, Starr DA. UNC-83 coordinates kinesin-1 and dynein activities at the nuclear envelope during nuclear migration. Dev Biol 2010; 338:237-50. [PMID: 20005871 PMCID: PMC2826220 DOI: 10.1016/j.ydbio.2009.12.004] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2009] [Revised: 12/04/2009] [Accepted: 12/04/2009] [Indexed: 11/19/2022]
Abstract
Nuclei migrate during many events, including fertilization, establishment of polarity, differentiation, and cell division. The Caenorhabditis elegans KASH protein UNC-83 localizes to the outer nuclear membrane where it recruits kinesin-1 to provide the major motor activity required for nuclear migration in embryonic hyp7 cells. Here we show that UNC-83 also recruits two dynein-regulating complexes to the cytoplasmic face of the nucleus that play a regulatory role. One consists of the NudE homolog NUD-2 and the NudF/Lis1/Pac1 homolog LIS-1, and the other includes dynein light chain DLC-1, the BicaudalD homolog BICD-1, and the Egalitarian homologue EGAL-1. Genetic disruption of any member of these two complexes caused nuclear migration defects that were enhanced in some double mutant animals, suggesting that BICD-1 and EGAL-1 function in parallel to NUD-2. Dynein heavy chain mutant animals also had a nuclear migration defect, suggesting these complexes function through dynein. Deletion analysis indicated that independent domains of UNC-83 interact with kinesin and dynein. These data suggest a model where UNC-83 acts as the cargo-specific adaptor between the outer nuclear membrane and the microtubule motors kinesin-1 and dynein. Kinesin-1 functions as the major force generator during nuclear migration, while dynein is involved in regulation of bidirectional transport of the nucleus.
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Affiliation(s)
- Heidi N. Fridolfsson
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | - Nina Ly
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | - Marina Meyerzon
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | - Daniel A. Starr
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
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41
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Abstract
Klarsicht, ANC-1 and Syne homology (KASH) proteins localize to the outer nuclear membrane where they connect the nucleus to the cytoskeleton. KASH proteins interact with Sad1-UNC-84 (SUN) proteins to transfer forces across the nuclear envelope to position nuclei or move chromosomes. A new KASH protein, KDP-1, was identified in a membrane yeast two-hybrid screen of a Caenorhabditis elegans library using the SUN protein UNC-84 as bait. KDP-1 also interacted with SUN-1. KDP-1 was enriched at the nuclear envelope in a variety of tissues and required SUN-1 for nuclear envelope localization in the germline. Genetic analyses showed that kdp-1 was essential for embryonic viability, larval growth and germline development. kdp-1(RNAi) delayed the entry into mitosis in embryos, led to a small mitotic zone in the germline, and caused an endomitotic phenotype. Aspects of these phenotypes were similar to those seen in sun-1(RNAi), suggesting that KDP-1 functions with SUN-1 in the germline and early embryo. The data suggest that KDP-1 is a novel KASH protein that functions to ensure the timely progression of the cell cycle between the end of S phase and the entry into mitosis.
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Affiliation(s)
- Matthew D McGee
- Department of Molecular and Cellular Biology, University of California, Davis, CA, USA
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Meyerzon M, Fridolfsson HN, Ly N, McNally FJ, Starr DA. UNC-83 is a nuclear-specific cargo adaptor for kinesin-1-mediated nuclear migration. Development 2009; 136:2725-33. [PMID: 19605495 DOI: 10.1242/dev.038596] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Intracellular nuclear migration is essential for many cellular events including fertilization, establishment of polarity, division and differentiation. How nuclei migrate is not understood at the molecular level. The C. elegans KASH protein UNC-83 is required for nuclear migration and localizes to the outer nuclear membrane. UNC-83 interacts with the inner nuclear membrane SUN protein UNC-84 and is proposed to connect the cytoskeleton to the nuclear lamina. Here, we show that UNC-83 also interacts with the kinesin-1 light chain KLC-2, as identified in a yeast two-hybrid screen and confirmed by in vitro assays. UNC-83 interacts with and recruits KLC-2 to the nuclear envelope in a heterologous tissue culture system. Additionally, analysis of mutant phenotypes demonstrated that both KLC-2 and the kinesin-1 heavy chain UNC-116 are required for nuclear migration. Finally, the requirement for UNC-83 in nuclear migration could be partially bypassed by expressing a synthetic outer nuclear membrane KLC-2::KASH fusion protein. Our data support a model in which UNC-83 plays a central role in nuclear migration by acting to bridge the nuclear envelope and as a kinesin-1 cargo-specific adaptor so that motor-generated forces specifically move the nucleus as a single unit.
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Affiliation(s)
- Marina Meyerzon
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
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Abstract
Positioning the nucleus is essential for the formation of polarized cells, pronuclear migration, cell division, cell migration and the organization of specialized syncytia such as mammalian skeletal muscles. Proteins that are required for nuclear positioning also function during chromosome movement and pairing in meiosis. Defects in these processes lead to human diseases including laminopathies. To properly position the nucleus or move chromosomes within the nucleus, the cell must specify the outer surface of the nucleus and transfer forces across both membranes of the nuclear envelope. KASH proteins are specifically recruited to the outer nuclear membrane by SUN proteins, which reside in the inner nuclear membrane. KASH and SUN proteins physically interact in the perinuclear space, forming a bridge across the two membranes of the nuclear envelope. The divergent N-terminal domains of KASH proteins extend from the surface of the nucleus into the cytoplasm and interact with the cytoskeleton, whereas the N-termini of SUN proteins extend into the nucleoplasm to interact with the lamina or chromatin. The bridge of SUN and KASH across the nuclear envelope functions to transfer forces that are generated in the cytoplasm into the nucleoplasm during nuclear migration, nuclear anchorage, centrosome attachment, intermediate-filament association and telomere clustering.
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Affiliation(s)
- Daniel A Starr
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA.
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Meyerzon M, Gao Z, Liu J, Wu JC, Malone CJ, Starr DA. Centrosome attachment to the C. elegans male pronucleus is dependent on the surface area of the nuclear envelope. Dev Biol 2009; 327:433-46. [PMID: 19162001 PMCID: PMC2668512 DOI: 10.1016/j.ydbio.2008.12.030] [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] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2008] [Revised: 12/13/2008] [Accepted: 12/19/2008] [Indexed: 01/11/2023]
Abstract
A close association must be maintained between the male pronucleus and the centrosomes during pronuclear migration. In C. elegans, simultaneous depletion of inner nuclear membrane LEM proteins EMR-1 and LEM-2, depletion of the nuclear lamina proteins LMN-1 or BAF-1, or the depletion of nuclear import components leads to embryonic lethality with small pronuclei. Here, a novel centrosome detachment phenotype in C. elegans zygotes is described. Zygotes with defects in the nuclear envelope had small pronuclei with a single centrosome detached from the male pronucleus. ZYG-12, SUN-1, and LIS-1, which function at the nuclear envelope with dynein to attach centrosomes, were observed at normal concentrations on the nuclear envelope of pronuclei with detached centrosomes. Analysis of time-lapse images showed that as mutant pronuclei grew in surface area, they captured detached centrosomes. Larger tetraploid or smaller histone::mCherry pronuclei suppressed or enhanced the centrosome detachment phenotype respectively. In embryos fertilized with anucleated sperm, only one centrosome was captured by small female pronuclei, suggesting the mechanism of capture is dependent on the surface area of the outer nuclear membrane available to interact with aster microtubules. We propose that the limiting factor for centrosome attachment to the surface of abnormally small pronuclei is dynein.
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Affiliation(s)
- Marina Meyerzon
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | - Zhizhen Gao
- Department of Biochemistry and Molecular Biology, Penn State University, University Park, PA 16802
| | - Jin Liu
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | - Jui-Ching Wu
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
| | - Christian J. Malone
- Department of Biochemistry and Molecular Biology, Penn State University, University Park, PA 16802
| | - Daniel A. Starr
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616
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45
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Starr DA, Han M. A Genetic Approach to Study the Role of Nuclear Envelope Components in Nuclear Positioning. Nuclear Organization in Development and Disease 2008. [DOI: 10.1002/0470093765.ch14] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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46
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Abstract
In most eukaryotic cells, the nucleus is localized to a specific location. This highlight article focuses on recent advances describing the mechanisms of nuclear migration and anchorage. Central to nuclear positioning mechanisms is the communication between the nuclear envelope and the cytoskeleton. All three components of the cytoskeleton-microtubules, actin filaments and intermediate filaments-are involved in nuclear positioning to varying degrees in different cell types. KASH proteins on the outer nuclear membrane connect to SUN proteins on the inner nuclear membrane. Together they transfer forces between the cytoskeleton and the nuclear lamina. Once at the outer nuclear membrane, KASH proteins can interact with the cytoskeleton. Nuclear migrations are a component of many cellular migration events and defects in nuclear positioning lead to human diseases, most notably lissencephaly.
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Affiliation(s)
- Daniel A Starr
- Section of Molecular and Cellular Biology, University of California-Davis, Davis, CA 95616, USA.
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47
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McGee MD, Rillo R, Anderson AS, Starr DA. UNC-83 IS a KASH protein required for nuclear migration and is recruited to the outer nuclear membrane by a physical interaction with the SUN protein UNC-84. Mol Biol Cell 2006; 17:1790-801. [PMID: 16481402 PMCID: PMC1415293 DOI: 10.1091/mbc.e05-09-0894] [Citation(s) in RCA: 113] [Impact Index Per Article: 6.3] [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: 11/11/2022] Open
Abstract
UNC-84 is required to localize UNC-83 to the nuclear envelope where it functions during nuclear migration. A KASH domain in UNC-83 was identified. KASH domains are conserved in the nuclear envelope proteins Syne/nesprins, Klarsicht, MSP-300, and ANC-1. Caenorhabditis elegans UNC-83 was shown to localize to the outer nuclear membrane and UNC-84 to the inner nuclear membrane in transfected mammalian cells, suggesting the KASH and SUN protein targeting mechanisms are conserved. Deletion of the KASH domain of UNC-83 blocked nuclear migration and localization to the C. elegans nuclear envelope. Some point mutations in the UNC-83 KASH domain disrupted nuclear migration, even if they localized normally. At least two separable portions of the C-terminal half of UNC-84 were found to interact with the UNC-83 KASH domain in a membrane-bound, split-ubiquitin yeast two-hybrid system. However, the SUN domain was essential for UNC-84 function and UNC-83 localization in vivo. These data support the model that KASH and SUN proteins bridge the nuclear envelope, connecting the nuclear lamina to cytoskeletal components. This mechanism seems conserved across eukaryotes and is the first proposed mechanism to target proteins specifically to the outer nuclear membrane.
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Affiliation(s)
- Matthew D McGee
- The Center for Genetics and Development and the Section of Molecular and Cellular Biology, University of California-Davis, Davis, CA 95616, USA
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48
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Yu J, Starr DA, Wu X, Parkhurst SM, Zhuang Y, Xu T, Xu R, Han M. The KASH domain protein MSP-300 plays an essential role in nuclear anchoring during Drosophila oogenesis. Dev Biol 2005; 289:336-45. [PMID: 16337624 DOI: 10.1016/j.ydbio.2005.10.027] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2005] [Revised: 09/28/2005] [Accepted: 10/22/2005] [Indexed: 10/25/2022]
Abstract
During late stages of Drosophila oogenesis, the cytoplasm of nurse cells in the egg chamber is rapidly transferred ("dumped") to oocytes, while the nurse cell nuclei are anchored by a mechanism that involves the actin cytoskeleton. The factors that mediate this interaction between nuclei and actin cytoskeleton are unknown. MSP-300 is the likely Drosophila ortholog of the mammalian Syne-1 and -2 and C. elegans ANC-1 proteins, contained both actin-binding and nuclear envelope localization domains. By using an antibody against C-terminus of MSP-300, we find that MSP-300 is distributed throughout the cytoplasm and accumulates at the nuclear envelope of nurse cells and the oocyte. A GFP fusion protein containing the C-terminal region of MSP-300 is also sufficient to localize protein on the nuclear envelope in oocytes. To eliminate the maternal gene activity during oogenesis, we generated homozygous germ-line clones of a loss-of-function mutation in msp-300 in otherwise heterozygous mothers. In the mutant egg chambers that develop from such clones, cytoplasmic dumping of nurse cells is severely disturbed. The nuclei of nurse cells and the oocyte are mislocalized and the usually well-organized actin structures are severely disrupted. These results indicate that maternal MSP-300 plays an important role in actin-dependent nuclear anchorage during cytoplasmic transport.
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Affiliation(s)
- Juehua Yu
- Institute of Developmental Biology and Molecular Medicine, Morgan-Tan International Center for Life Sciences, School of Life Science, Fudan University, Shanghai, China
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Abstract
Vertebrate skeletal muscle fibers contain hundreds of nuclei, of which three to six are functionally specialized and stably anchored beneath the postsynaptic membrane at the neuromuscular junction (NMJ). The mechanisms that localize synaptic nuclei and the roles they play in neuromuscular development are unknown. Syne-1 is concentrated at the nuclear envelope of synaptic nuclei; its Caenorhabditis elegans orthologue ANC-1 functions to tether nuclei to the cytoskeleton. To test the involvement of Syne proteins in nuclear anchoring, we generated transgenic mice overexpressing the conserved C-terminal Klarsicht/ANC-1/Syne homology domain of Syne-1. The transgene acted in a dominant interfering fashion, displacing endogenous Syne-1 from the nuclear envelope. Muscle nuclei failed to aggregate at the NMJ in transgenic mice, demonstrating that localization and positioning of synaptic nuclei require Syne proteins. We then exploited this phenotype to show that synaptic nuclear aggregates are dispensable for maturation of the NMJ.
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Affiliation(s)
- R Mark Grady
- Department of Anatomy and Neurobiology, Washington University, St. Louis, MO 63110, USA
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50
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Abstract
A diverse family of proteins has been discovered with a small C-terminal KASH domain in common. KASH domain proteins are localized uniquely to the outer nuclear envelope, enabling their cytoplasmic extensions to tether the nucleus to actin filaments or microtubules. KASH domains are targeted to the outer nuclear envelope by SUN domains of inner nuclear envelope proteins. Several KASH protein genes were discovered as mutant alleles in model organisms with defects in developmentally regulated nuclear positioning. Recently, KASH-less isoforms have been found that connect the cytoskeleton to organelles other than the nucleus. A widened view of these proteins is now emerging, where KASH proteins and their KASH-less counterparts are cargo-specific adaptors that not only link organelles to the cytoskeleton but also regulate developmentally specific organelle movements.
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Affiliation(s)
- Daniel A Starr
- Section of Molecular and Cellular Biology, Center for Genetics and Development, University of California, Davis, CA, USA
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