251
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Rothwell WF, Zhang CX, Zelano C, Hsieh TS, Sullivan W. The Drosophila centrosomal protein Nuf is required for recruiting Dah, a membrane associated protein, to furrows in the early embryo. J Cell Sci 1999; 112 ( Pt 17):2885-93. [PMID: 10444383 DOI: 10.1242/jcs.112.17.2885] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
During mitosis of the Drosophila cortical syncytial divisions, actin-based membrane furrows separate adjacent spindles. Our genetic analysis indicates that the centrosomal protein Nuf is specifically required for recruitment of components to the furrows and the membrane-associated protein Dah is primarily required for the inward invagination of the furrow membrane. Recruitment of actin, anillin and peanut to the furrows occurs normally in dah-derived embryos. However, subsequent invagination of the furrows fails in dah-derived embryos and the septins become dispersed throughout the cytoplasm. This indicates that stable septin localization requires Dah-mediated furrow invagination. Close examination of actin and Dah localization in wild-type embryos reveals that they associate in adjacent particles during interphase and co-localize in the invaginating furrows during prophase and metaphase. We show that the Nuf centrosomal protein is required for recruiting the membrane-associated protein Dah to the furrows. In nuf-mutant embryos, much of the Dah does not reach the furrows and remains in a punctate distribution. This suggests that Dah is recruited to the furrows in vesicles and that the recruiting step is disrupted in nuf mutants. These studies lead to a model in which the centrosomes play an important role in the transport of membrane-associated proteins and other components to the developing furrows.
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Affiliation(s)
- W F Rothwell
- Sinsheimer Laboratories, Department of Biology, University of California, Santa Cruz, CA 95064, USA
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252
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Spritz RA. Multi-organellar disorders of pigmentation: intracellular traffic jams in mammals, flies and yeast. Trends Genet 1999; 15:337-40. [PMID: 10461199 DOI: 10.1016/s0168-9525(99)01785-0] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Several different mutant genes in humans, mice and Drosophila, most of which were identified initially on the basis of reduced pigmentation, have been associated with defects of multiple cytoplasmic organelles - melanosomes, lysosomes and granules. Recent discoveries show that several of these mutations directly affect components in the pathway of organelle-specific protein trafficking, and provide new insights into the relationships of these pathways in mammals, flies and yeast.
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Affiliation(s)
- R A Spritz
- Human Medical Genetics Program, University of Colorado Health Sciences Center, 4200 East Ninth Avenue, B161, Denver, CO 80262, USA.
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253
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Mehta AD, Rock RS, Rief M, Spudich JA, Mooseker MS, Cheney RE. Myosin-V is a processive actin-based motor. Nature 1999; 400:590-3. [PMID: 10448864 DOI: 10.1038/23072] [Citation(s) in RCA: 662] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Class-V myosins, one of 15 known classes of actin-based molecular motors, have been implicated in several forms of organelle transport, perhaps working with microtubule-based motors such as kinesin. Such movements may require a motor with mechanochemical properties distinct from those of myosin-II, which operates in large ensembles to drive high-speed motility as in muscle contraction. Based on its function and biochemistry, it has been suggested that myosin-V may be a processive motor like kinesin. Processivity means that the motor undergoes multiple catalytic cycles and coupled mechanical advances for each diffusional encounter with its track. This allows single motors to support movement of an organelle along its track. Here we provide direct evidence that myosin-V is indeed a processive actin-based motor that can move in large steps approximating the 36-nm pseudo-repeat of the actin filament.
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Affiliation(s)
- A D Mehta
- Department of Biochemistry, Stanford University Medical Center, California 94305, USA
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254
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EDGAR ALASDAIRJ, BENNETT JONATHANP. Inhibition of dendrite formation in mouse melanocytes transiently transfected with antisense DNA to myosin Va. J Anat 1999; 195 ( Pt 2):173-84. [PMID: 10529054 PMCID: PMC1467982 DOI: 10.1046/j.1469-7580.1999.19520173.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
In mice a molecular motor of the myosin V class (designated myosin Va) is known to be the product of the dilute locus, where a mutation prevents melanosome transport in melanocytes. There is conflicting evidence about whether it has a role in dendrite outgrowth. We investigated its role by transiently transfecting antisense oligonucleotides to inhibit its expression in a melanocyte cell line. We demonstrated mRNA and protein expression of myosin Va in 3 mouse melanocyte lines and 1 human melanoma cell line, using RT-PCR and immunoblotting. Two splice variants were found in human cells whilst only the longer transcript, containing an additional exon, was present in mouse melanocyte lines. The shorter variant was detected in other mouse tissues. Myosin Va protein levels were similar in 3 melanocyte lines with differing amounts of pigmentation, indicating that expression of myosin Va is not tightly coupled to expression of melanin. Immunocytochemistry showed 2 types of myosin Va localisation. A punctate pattern of staining concentrated in the perinuclear region was indicative of organelle association, and the observation of occasional linear punctate staining aligned with F-actin bundles supported the idea that myosin Va has a role in transporting melanosomes along actin filaments. Staining was also intense at tips of dendrites and at sites of dendrite-cell contact, consistent with a possible role in dendrite growth. Transient transfection of antisense phosphorothioate oligodeoxynucleotides targeted against myosin Va mRNA reduced expression of myosin Va protein in cultured mouse melan-a melanocytes by over 70 % 20 h after transfection whereas a control (shuffled sequence) oligonucleotide did not. Upon trypsinisation and replating these cells the capacity of the transfected cells to extend new dendrites was reduced in the cells containing the specific antisense oligonucleotides but unaffected by the control oligonucleotide. Image analysis confirmed that the effect of transfection on morphology was statistically significant (P < 0.01). In contrast when cells were not trypsinised and replated following transfection so that previously existing dendrites could persist, the normal dendritic morphology continued to be observed. We conclude that in addition to its involvement in melanosome transport, myosin Va has a role in the extension of new dendrites by melanocytes but not in maintenance of pre-existing dendrites.
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Affiliation(s)
- ALASDAIR J.
EDGAR
- Division of Biomedical Sciences, Imperial College School of Medicine, London, UK
- Present address: Department of Histochemistry, Division of Investigative Sciences, Imperial College School of Medicine, Hammersmith Campus, Du Cane Road, London W12 0NN, UK
| | - JONATHAN P.
BENNETT
- Division of Biomedical Sciences, Imperial College School of Medicine, London, UK
- Correspondence to Dr J. P. Bennett, Division of Biomedical Sciences, Imperial College School of Medicine, South Kensington, London SW7 2AZ, UK. Tel.: +44(0)171-594-3166; fax: +44(0)171-594-3169; e-mail:
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255
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Abstract
Research over the past 18 months has revealed that many membranous organelles move along both actin filaments and microtubules. It is highly likely that the activity of the microtubule motors, myosins and static linker proteins present on any organelle are co-ordinately regulated and that this control is linked to the processes of membrane traffic itself.
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Affiliation(s)
- V J Allan
- School of Biological Sciences, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester, M13 9PT, UK.
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256
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Langford GM. ER Muscles Its Way Around Neurons. NEWS IN PHYSIOLOGICAL SCIENCES : AN INTERNATIONAL JOURNAL OF PHYSIOLOGY PRODUCED JOINTLY BY THE INTERNATIONAL UNION OF PHYSIOLOGICAL SCIENCES AND THE AMERICAN PHYSIOLOGICAL SOCIETY 1999; 14:175. [PMID: 11390846 DOI: 10.1152/physiologyonline.1999.14.4.175] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- George M. Langford
- Department of Biological Sciences Dartmouth College Hanover, NH 03755-3576
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257
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258
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Dranoff JA, McClure M, Burgstahler AD, Denson LA, Crawford AR, Crawford JM, Karpen SJ, Nathanson MH. Short-term regulation of bile acid uptake by microfilament-dependent translocation of rat ntcp to the plasma membrane. Hepatology 1999; 30:223-9. [PMID: 10385660 DOI: 10.1002/hep.510300136] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The Na+-taurocholate cotransport polypeptide (ntcp) is the primary transporter for the uptake of bile acids in the liver. The second messenger adenosine 3':5'-cyclic monophosphate (cAMP) rapidly increases ntcp protein concentration in the plasma membrane, yet the mechanism is unknown. To investigate this, HepG2 cells were transiently transfected with a carboxy-terminal-tagged green fluorescence protein (GFP) conjugate of ntcp, and then examined by confocal video microscopy. Transporter activity was directly assayed with 3H-taurocholic acid (TC) scintigraphy. ntcp-GFP targeted to the plasma membrane in transfected cells, and the conjugate protein transported 3H-TC as effectively as unmodified rat ntcp. Stimulation of ntcp-GFP cells with cAMP increased GFP fluorescence in the plasma membrane by 40% (P <.0001) within 2.5 minutes and by 55% within 10 minutes. Similarly, cAMP increased transport of bile acids by 30%. Cytochalasin D, an inhibitor of microfilaments, did not prevent ntcp-GFP from targeting to the plasma membrane, but completely abolished the increase in GFP fluorescence seen in response to cAMP. In contrast, the microtubule inhibitor, nocodazole, prevented development of membrane fluorescence in 48 (96%) of 50 cells. Cells regained plasma membrane fluorescence within 2 hours after nocodazole removal. These findings suggest that targeting of ntcp to the plasma membrane consists of 2 steps: 1) delivery of ntcp to the region of the plasma membrane via microtubules; and 2) insertion of ntcp into the plasma membrane, in a microfilament- and cAMP-sensitive fashion.
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Affiliation(s)
- J A Dranoff
- Department of Medicine, Yale University School of Medicine, New Haven, CT, USA.
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259
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Sider JR, Mandato CA, Weber KL, Zandy AJ, Beach D, Finst RJ, Skoble J, Bement WM. Direct observation of microtubule-f-actin interaction in cell free lysates. J Cell Sci 1999; 112 ( Pt 12):1947-56. [PMID: 10341213 DOI: 10.1242/jcs.112.12.1947] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Coordinated interplay of the microtubule and actin cytoskeletons has long been known to be crucial for many cellular processes including cell migration and cytokinesis. However, interactions between these two systems have been difficult to document by conventional approaches, for a variety of technical reasons. Here the distribution of f-actin and microtubules were analyzed in the absence of fixation using Xenopus egg extracts as an in vitro source of microtubules and f-actin, demembranated Xenopus sperm to nucleate microtubule asters, fluorescent phalloidin as a probe for f-actin, and fluorescent tubulin as a probe for microtubules. F-actin consistently colocalized in a lengthwise manner with microtubules of asters subjected to extensive washing in flow chambers. F-actin-microtubule association was heterogenous within a given aster, such that f-actin is most abundant toward the distal (plus) ends of microtubules, and microtubules heavily labeled with f-actin are found in close proximity to microtubules devoid of f-actin. However, this distribution changed over time, in that 5 minute asters had more f-actin in their interiors than did 15 minute asters. Microtubule association with f-actin was correlated with microtubule bending and kinking, while elimination of f-actin resulted in straighter microtubules, indicating that the in vitro interaction between f-actin and microtubules is functionally significant. F-actin was also found to associate in a lengthwise fashion with microtubules in asters centrifuged through 30% sucrose, and microtubules alone (i.e. microtubules not seeded from demembranated sperm) centrifuged through sucrose, indicating that the association cannot be explained by flow-induced trapping and alignment of f-actin by aster microtubules. Further, cosedimentation analysis revealed that microtubule-f-actin association could be reconstituted from microtubules assembled from purified brain tubulin and f-actin assembled from purified muscle actin in the presence, but not the absence, of Xenopus oocyte microtubule binding proteins. The results provide direct evidence for an association between microtubules and f-actin in vitro, indicate that this interaction is mediated by one or more microtubule binding proteins, and suggest that this interaction may be responsible for the mutual regulation of the microtubule and actomyosin cytoskeletons observed in vivo.
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Affiliation(s)
- J R Sider
- Department of Zoology and Program in Cellular and Molecular Biology, University of Wisconsin, Madison, WI, USA
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260
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Lane JD, Allan VJ. Microtubule-based endoplasmic reticulum motility in Xenopus laevis: activation of membrane-associated kinesin during development. Mol Biol Cell 1999; 10:1909-22. [PMID: 10359605 PMCID: PMC25389 DOI: 10.1091/mbc.10.6.1909] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The endoplasmic reticulum (ER) in animal cells uses microtubule motor proteins to adopt and maintain its extended, reticular organization. Although the orientation of microtubules in many somatic cell types predicts that the ER should move toward microtubule plus ends, motor-dependent ER motility reconstituted in extracts of Xenopus laevis eggs is exclusively a minus end-directed, cytoplasmic dynein-driven process. We have used Xenopus egg, embryo, and somatic Xenopus tissue culture cell (XTC) extracts to study ER motility during embryonic development in Xenopus by video-enhanced differential interference contrast microscopy. Our results demonstrate that cytoplasmic dynein is the sole motor for microtubule-based ER motility throughout the early stages of development (up to at least the fifth embryonic interphase). When egg-derived ER membranes were incubated in somatic XTC cytosol, however, ER tubules moved in both directions along microtubules. Data from directionality assays suggest that plus end-directed ER tubule extensions contribute approximately 19% of the total microtubule-based ER motility under these conditions. In XTC extracts, the rate of ER tubule extensions toward microtubule plus ends is lower ( approximately 0.4 microm/s) than minus end-directed motility ( approximately 1.3 microm/s), and plus end-directed motility is eliminated by a function-blocking anti-conventional kinesin heavy chain antibody (SUK4). In addition, we provide evidence that the initiation of plus end-directed ER motility in somatic cytosol is likely to occur via activation of membrane-associated kinesin.
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Affiliation(s)
- J D Lane
- School of Biological Sciences, University of Manchester, Manchester M13 9PT, United Kingdom
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261
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Affiliation(s)
- R A Spritz
- Human Medical Genetics Program, University of Colorado Health Sciences Center, Denver 80262, USA.
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262
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Spritz RA. Multi-organellar disorders of pigmentation: tied up in traffic. Clin Genet 1999. [DOI: 10.1034/j.1399-0004.2000.57si03.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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