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- Braun, Markus, et al.
(författare)
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Rhizoids and protonemata of characean algae : model cells for research on polarized growth and plant gravity sensing
- 2006
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Ingår i: Protoplasma. - : Springer. - 0033-183X .- 1615-6102. ; 229:2-4, s. 133-142
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Tidskriftsartikel (refereegranskat)abstract
- Gravitropically tip-growing rhizoids and protonemata of characean algae are well-established unicellular plant model systems for research on gravitropism. In recent years, considerable progress has been made in the understanding of the cellular and molecular mechanisms underlying gravity sensing and gravity-oriented growth. While in higherplant statocytes the role of cytoskeletal elements, especially the actin cytoskeleton, in the mechanisms of gravity sensing is still enigmatic, there is clear evidence that in the characean cells actin is intimately involved in polarized growth, gravity sensing, and the gravitropic response mechanisms. The multiple functions of actin are orchestrated by a variety of actin-binding proteins which control actin polymerisation, regulate the dynamic remodelling of the actin filament architecture, and mediate the transport of vesicles and organelles. Actin and a steep gradient of cytoplasmic free calcium are crucial components of a feedback mechanism that controls polarized growth. Experiments performed in microgravity provided evidence that actomyosin is a key player for gravity sensing: it coordinates the position of statoliths and, upon a change in the cell’s orientation, directs sedimenting statoliths to specific areas of the plasma membrane, where contact with membrane-bound gravisensor molecules elicits short gravitropic pathways. In rhizoids, gravitropic signalling leads to a local reduction of cytoplasmic free calcium and results in differential growth of the opposite subapical cell flanks. The negative gravitropic response of protonemata involves actin-dependent relocation of the calcium gradient and displacement of the centre of maximal growth towards the upper flank. On the basis of the results obtained from the gravitropic model cells, a similar fine-tuning function of the actomyosin system is discussed for the early steps of gravity sensing in higher-plant statocytes.
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| 5. |
- Corell, Mikael, et al.
(författare)
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Spatiotemporal Distribution and Function of N-Cadherin in Postnatal Schwann Cells : A Matter of Adhesion?
- 2010
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Ingår i: Journal of Neuroscience Research. - : Wiley. - 0360-4012 .- 1097-4547. ; 88:11, s. 2338-2349
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Tidskriftsartikel (refereegranskat)abstract
- During embryonic development of the peripheral nervous system (PNS), the adhesion molecule neuronal cadherin (N-cadherin) is expressed by Schwann cell precursors and associated with axonal growth cones. N-cadherin expression levels decrease as precursors differentiate into Schwann cells. In this study, we investigated the distribution of N-cadherin in the developing postnatal and adult rat peripheral nervous system. N-cadherin was found primarily in ensheathing glia throughout development, concentrated at neuron glial or glial glial contacts of the sciatic nerve, dorsal root ganglia (DRG), and myenteric plexi. In the sciatic nerve, N-cadherin decreases with age and progress of myelination. In adult animals, N-cadherin was found exclusively in nonmyelinating Schwann cells. The distribution of N-cadherin in developing E17 DRG primary cultures is similar to what was observed in vivo. Functional studies of N-cadherin in these cultures, using the antagonist peptide INPISGQ, show a disruption of the attachment between Schwann cells, but no interference in the initial or long-term contact between Schwann cells and axons. We suggest that N-cadherin acts primarily in the adhesion between glial cells during postnatal development. It may form adherents/junctions between nonmyelinating glia, which contribute to the stable tubular structure encapsulating thin caliber axons and thus stabilize the nerve structure as a whole.
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- Larhammar, Martin, 1985-, et al.
(författare)
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SLC10A4 Is a Vesicular Amine-Associated Transporter Modulating Dopamine Homeostasis
- 2015
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Ingår i: Biological Psychiatry. - : Elsevier BV. - 0006-3223 .- 1873-2402. ; 77:6, s. 526-536
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundThe neuromodulatory transmitters, biogenic amines, have profound effects on multiple neurons and are essential for normal behavior and mental health. Here we report that the orphan transporter SLC10A4, which in the brain is exclusively expressed in presynaptic vesicles of monoaminergic and cholinergic neurons, has a regulatory role in dopamine homeostasis.MethodsWe used a combination of molecular and behavioral analyses, pharmacology, and in vivo amperometry to assess the role of SLC10A4 in dopamine-regulated behaviors.ResultsWe show that SLC10A4 is localized on the same synaptic vesicles as either vesicular acetylcholine transporter or vesicular monoamine transporter 2. We did not find evidence for direct transport of dopamine by SLC10A4; however, synaptic vesicle preparations lacking SLC10A4 showed decreased dopamine vesicular uptake efficiency. Furthermore, we observed an increased acidification in synaptic vesicles isolated from mice overexpressing SLC10A4. Loss of SLC10A4 in mice resulted in reduced striatal serotonin, noradrenaline, and dopamine concentrations and a significantly higher dopamine turnover ratio. Absence of SLC10A4 led to slower dopamine clearance rates in vivo, which resulted in accumulation of extracellular dopamine. Finally, whereas SLC10A4 null mutant mice were slightly hypoactive, they displayed hypersensitivity to administration of amphetamine and tranylcypromine.ConclusionsOur results demonstrate that SLC10A4 is a vesicular monoaminergic and cholinergic associated transporter that is important for dopamine homeostasis and neuromodulation in vivo. The discovery of SLC10A4 and its role in dopaminergic signaling reveals a novel mechanism for neuromodulation and represents an unexplored target for the treatment of neurological and mental disorders.
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- Limbach, Christoph, et al.
(författare)
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Electron tomographic characterization of a vacuolar reticulum and of six vesicle types that occupy different cytoplasmic domains in the apex of tip-growing Chara rhizoids.
- 2008
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Ingår i: Planta. - : Springer Science and Business Media LLC. - 0032-0935 .- 1432-2048. ; 227:5, s. 1101-1114
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Tidskriftsartikel (refereegranskat)abstract
- We provide a 3D ultrastructural analysis of the membrane systems involved in tip growth of rhizoids of the green alga Chara. Electron tomography of cells preserved by high-pressure freeze fixation has enabled us to distinguish six different types of vesicles in the apical cytoplasm where the tip growth machinery is accommodated. The vesicle types are: dark and light secretory vesicles, plasma membrane-associated clathrin-coated vesicles (PM-CCVs), Spitzenkoerper-associated clathrin-coated vesicles (Sp-CCVs) and coated vesicles (Sp-CVs), and microvesicles. Each of these vesicle types exhibits a distinct distribution pattern, which provides insights into their possible function for tip growth. The PM-CCVs are confined to the cytoplasm adjacent to the apical plasma membrane. Within this space they are arranged in clusters often surrounding tubular plasma membrane invaginations from which CCVs bud. This suggests that endocytosis and membrane recycling are locally confined to specialized apical endocytosis sites. In contrast, exocytosis of secretory vesicles occurs over the entire membrane area of the apical dome. The Sp-CCVs and the Sp-CVs are associated with the aggregate of endoplasmic reticulum membranes in the center of the growth-organizing Spitzenkoerper complex. Here, Sp-CCVs are seen to bud from undefined tubular membranes. The subapical region of rhizoids contains a vacuolar reticulum that extends along the longitudinal cell axis and consists of large, vesicle-like segments interconnected by thin tubular domains. The tubular domains are encompassed by thin filamentous structures resembling dynamin spirals which could drive peristaltic movements of the vacuolar reticulum similar to those observed in fungal hyphae. The vacuolar reticulum appears to serve as a lytic compartment into which multivesicular bodies deliver their internal vesicles for molecular recycling and degradation.
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| 9. |
- Limbach, Christoph, et al.
(författare)
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Molecular in situ topology of Aczonin/Piccolo and associated proteins at the mammalian neurotransmitter release site
- 2011
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 108:31, s. E392-E401
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Tidskriftsartikel (refereegranskat)abstract
- The protein machinery of neurotransmitter exocytosis requires efficient orchestration in space and time, for speed and precision of neurotransmission and also for synaptic ontogeny and plasticity. However, its spatial organization in situ is virtually unknown. Aczonin/Piccolo is a putative organizer protein of mammalian active zones. We determined by immunogold electron microscopy (EM) (i) the spatial arrangement (i. e., topology) of 11 segments of the Aczonin polypeptide in situ, and correlated it to (ii) the positioning of Aczonin-interacting domains of Bassoon, CAST/ELKS, Munc13, and RIM and (iii) the ultrastructurally defined presynaptic macromolecular aggregates known as dense projections and synaptic ribbons. At conventional synapses, Aczonin assumes a compact molecular topology within a layer 35 to 80 nm parallel to the plasma membrane (PM), with a "trunk" sitting on the dense projection top and a C-terminal "arm" extending down toward the PM and sideward to the dense projection periphery. At ribbon synapses, Aczonin occupies the whole ribbon area. Bassoon colocalizes with Aczonin at conventional synapses but not at ribbon synapses. At both conventional and ribbon synapses, CAST, Munc13, and RIM are segregated from Aczonin, closer to the PM, and Aczonin is positioned such that it may control the access of neurotransmitter vesicles to the fusion site.
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| 10. |
- Wang, Xiaolu, et al.
(författare)
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A protein interaction node at the neurotransmitter release site : domains of Aczonin/Piccolo, Bassoon, CAST, and rim converge on the N-terminal domain of Munc13-1
- 2009
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Ingår i: Journal of Neuroscience. - 0270-6474 .- 1529-2401. ; 29:40, s. 12584-12596
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Tidskriftsartikel (refereegranskat)abstract
- Multidomain scaffolding proteins organize the molecular machinery of neurotransmitter vesicle dynamics during synaptogenesis and synaptic activity. We find that domains of five active zone proteins converge on an interaction node that centers on the N-terminal region of Munc13-1 and includes the zinc-finger domain of Rim1, the C-terminal region of Bassoon, a segment of CAST1/ELKS2, and the third coiled-coil domain (CC3) of either Aczonin/Piccolo or Bassoon. This multidomain complex may constitute a center for the physical and functional integration of the protein machinery at the active zone. An additional connection between Aczonin and Bassoon is mediated by the second coiled-coil domain of Aczonin. Recombinant Aczonin-CC3, expressed in cultured neurons as a green fluorescent protein fusion protein, is targeted to synapses and suppresses vesicle turnover, suggesting involvements in synaptic assembly as well as activity. Our findings show that Aczonin, Bassoon, CAST1, Munc13, and Rim are closely and multiply interconnected, they indicate that Aczonin-CC3 can actively participate in neurotransmitter vesicle dynamics, and they highlight the N-terminal region of Munc13-1 as a hub of protein interactions by adding three new binding partners to its mechanistic potential in the control of synaptic vesicle priming.
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