The Experts below are selected from a list of 4191 Experts worldwide ranked by ideXlab platform
Sabine Petry - One of the best experts on this subject based on the ideXlab platform.
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branching Microtubule Nucleation is controlled by importin mediated inhibition of tpx2 phase separation
bioRxiv, 2020Co-Authors: Mohammad S Safari, Matthew R King, Clifford P Brangwynne, Sabine PetryAbstract:The Microtubule-based mitotic spindle is responsible for equally partitioning the genome during each cell division, and its assembly is executed by several Microtubule Nucleation pathways. In the spindle center, Targeting Protein for XKlp2 (TPX2) promotes branching Microtubule Nucleation, where new Microtubules are nucleated from pre-existing ones. Until the onset of spindle assembly, TPX2 is sequestered by importins-/{beta}, yet the molecular nature of this regulation remains unclear, particularly since TPX2 was recently found to undergo a liquid-liquid phase separation to execute its function. Here we demonstrate that TPX2 interacts with importins-/{beta} with nanomolar affinity as a 1:1:1 mono-dispersed trimer. We identify a new nuclear localization sequence (NLS) on TPX2, which contributes to its high-affinity interaction with importin-. Interestingly, importin-{beta} alone can also associate with TPX2, and does so via dispersed, weak interactions. Interactions of both importin- and importin-{beta} with TPX2 each inhibit its propensity for phase separation, and consequently its ability to orchestrate branching Microtubule Nucleation. In sum, our study explains how TPX2 is regulated in order to facilitate spindle assembly, and provides novel insight into how a protein phase separation can be inhibited via weak biomolecular interactions. Significance StatementThe discovery that proteins can undergo phase separation is revolutionizing biology. Characterization of dozens of phase separating proteins in vitro over the past several years has mainly focused on how macromolecules undergo liquid-liquid phase separation (LLPS). The next, and possibly bigger challenge is to investigate how LLPS is regulated in the cell, namely how it is inhibited to spatiotemporally control a certain cellular function. Here, we addressed this challenge by identifying how the spindle assembly factor TPX2 is inhibited by importins from undergoing LLPS and thereby turning on spindle assembly.
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biochemical reconstitution of branching Microtubule Nucleation
eLife, 2020Co-Authors: Raymundo Alfaroaco, Akanksha Thawani, Sabine PetryAbstract:Microtubules are nucleated from specific locations at precise times in the cell cycle. However, the factors that constitute these Microtubule Nucleation pathways and their mode of action still need to be identified. Using purified Xenopus laevis proteins we biochemically reconstitute branching Microtubule Nucleation, which is critical for chromosome segregation. We found that besides the Microtubule nucleator gamma-tubulin ring complex (γ-TuRC), the branching effectors augmin and TPX2 are required to efficiently nucleate Microtubules from pre-existing Microtubules. TPX2 has the unexpected capacity to directly recruit γ-TuRC as well as augmin, which in turn targets more γ-TuRC along the Microtubule lattice. TPX2 and augmin enable γ-TuRC-dependent Microtubule Nucleation at preferred branching angles of less than 90 degrees from regularly-spaced patches along Microtubules. This work provides a blueprint for other Microtubule Nucleation pathways and helps explain how Microtubules are generated in the spindle.
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phase separation of tpx2 enhances and spatially coordinates Microtubule Nucleation
Nature Communications, 2020Co-Authors: Matthew R King, Sabine PetryAbstract:Phase separation of substrates and effectors is proposed to enhance biological reaction rates and efficiency. Targeting protein for Xklp2 (TPX2) is an effector of branching Microtubule Nucleation in spindles and functions with the substrate tubulin by an unknown mechanism. Here we show that TPX2 phase separates into a co-condensate with tubulin, which mediates Microtubule Nucleation in vitro and in isolated cytosol. TPX2-tubulin co-condensation preferentially occurs on pre-existing Microtubules, the site of branching Microtubule Nucleation, at the endogenous and physiologically relevant concentration of TPX2. Truncation and chimera versions of TPX2 suggest that TPX2-tubulin co-condensation enhances the efficiency of TPX2-mediated branching Microtubule Nucleation. Finally, the known inhibitor of TPX2, the importin-α/β heterodimer, regulates TPX2 condensation in vitro and, consequently, branching Microtubule Nucleation activity in isolated cytosol. Our study demonstrates how regulated phase separation can simultaneously enhance reaction efficiency and spatially coordinate Microtubule Nucleation, which may facilitate rapid and accurate spindle formation.
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biochemical reconstitution of branching Microtubule Nucleation
bioRxiv, 2019Co-Authors: Raymundo Alfaroaco, Akanksha Thawani, Sabine PetryAbstract:Abstract Microtubules are nucleated from specific locations at precise times in the cell cycle. However, the factors that constitute these Microtubule Nucleation pathways still need to be identified along with their mode of action. Here, using purified Xenopus laevis proteins we biochemically reconstitute branching Microtubule Nucleation, a Nucleation pathway where Microtubules originate from pre-existing Microtubules, which is essential for spindle assembly and chromosome segregation. We found that besides the Microtubule nucleator gamma-tubulin ring complex (γ-TuRC), the two branching effectors augmin and TPX2 are required to efficiently nucleate branched Microtubules. Specifically, TPX2 generates regularly-spaced patches that recruit augmin and γ-TuRC to Microtubules, which then nucleate new Microtubules at preferred branching angles of less than 90 degrees. Our work demonstrates how γ-TuRC is brought to its Nucleation site for branching Microtubule Nucleation. It provides a blueprint for other Microtubule Nucleation pathways and for generating a particular Microtubule architecture by regulating Microtubule Nucleation.
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phase separation of tpx2 enhances and spatially coordinates Microtubule Nucleation
bioRxiv, 2019Co-Authors: Matthew R King, Sabine PetryAbstract:Abstract Phase separation of substrates and effectors is proposed to enhance biological reaction rates and efficiency. TPX2 is an effector of Microtubule Nucleation in spindles, and functions with the substrate tubulin by an unknown mechanism. Here, we show that TPX2 phase separates into a co-condensate with tubulin, which mediates Microtubule Nucleation in vitro and in isolated cytosol. TPX2-tubulin co-condensation preferentially occurs on pre-existing Microtubules at the endogenous and physiologically relevant concentration of TPX2. Truncation and chimera versions of TPX2 directly demonstrate that TPX2-tubulin co-condensation enhances the efficiency of TPX2-mediated Microtubule Nucleation. Finally, the known inhibitor of TPX2, the importin-α/β heterodimer, regulates both co-condensation and activity. Our study demonstrates how regulated phase separation can simultaneously enhance reaction efficiency and spatially coordinate Microtubule Nucleation, which may facilitate rapid and accurate spindle formation.
Robert E. Palazzo - One of the best experts on this subject based on the ideXlab platform.
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aurora a kinase regulates breast cancer associated gene 1 inhibition of centrosome dependent Microtubule Nucleation
Cancer Research, 2007Co-Authors: Satish Sankaran, Robert E. Palazzo, Donna E Crone, Jeffrey D ParvinAbstract:Breast cancer-associated gene 1 (BRCA1) regulates the duplication and the function of centrosomes in breast cells. We have previously shown that BRCA1 ubiquitin ligase activity directly inhibits centrosome-dependent Microtubule Nucleation. However, there is a paradox because centrosome Microtubule Nucleation potential is highest during mitosis, a phase when BRCA1 is most abundant at the centrosome. In this study, we resolve this conundrum by testing whether centrosomes from cells in M phase are regulated differently by BRCA1 when compared with other phases of the cell cycle. We observed that BRCA1-dependent inhibition of centrosome Microtubule Nucleation was high in S phase but was significantly lower during M phase. The cell cycle-specific effects of BRCA1 on centrosome-dependent Microtubule Nucleation were detected in living cells and in cell-free experiments using centrosomes purified from cells at specific stages of the cell cycle. We show that Aurora-A kinase modulates the BRCA1 inhibition of centrosome function by decreasing the E3 ubiquitin ligase activity of BRCA1. In addition, dephosphorylation of BRCA1 by protein phosphatase 1 alpha enhances the E3 ubiquitin ligase activity of BRCA1. These observations reveal that the inhibition of centrosome Microtubule Nucleation potential by the BRCA1 E3 ubiquitin ligase is controlled by Aurora-A kinase and protein phosphatase 1 alpha-mediated phosphoregulation through the different phases of the cell cycle.
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reconstitution of Microtubule Nucleation potential in centrosomes isolated from spisula solidissima oocytes
Journal of Cell Science, 2000Co-Authors: Bradley J. Schnackenberg, Dawn Hull, Ronald D Balczon, Robert E. PalazzoAbstract:Treatment of isolated Spisula solidissima centrosomes with KI removes (gamma)-tubulin, 25 nm rings, and their Microtubule Nucleation potential, revealing the presence of a filamentous lattice, the 'centromatrix'. Treatment of this centromatrix with Spisula oocyte extract results in the binding of (gamma)-tubulin and 25 nm rings, and the recovery of Microtubule Nucleation potential. Fractionation of this extract resulted in the separation of elements that are required for the recovery of Microtubule Nucleation potential. We show that some, but not all, of the elements needed cosediment with Microtubules. Further, extracts prepared from activated (meiotic) and non-activated (interphase) Spisula oocytes, CHO cells blocked in S phase, Drosophila embryos and Xenopus oocytes all support the recovery of Microtubule Nucleation potential by the Spisula centromatrix. These results demonstrate that components necessary for centrosome-dependent Microtubule Nucleation are functionally conserved and abundant in both interphase and meiotic/mitotic cytoplasm.
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the disassembly and reassembly of functional centrosomes in vitro
Proceedings of the National Academy of Sciences of the United States of America, 1998Co-Authors: Bradley J. Schnackenberg, Alexey Khodjakov, Conly L. Rieder, Robert E. PalazzoAbstract:Animal cells contain a single centrosome that nucleates and organizes a polarized array of Microtubules which functions in many cellular processes. In most cells the centrosome is composed of two centrioles surrounded by an ill-defined “cloud” of pericentriolar material. Recently, γ-tubulin-containing 25-nm diameter ring structures have been identified as likely Microtubule Nucleation sites within the pericentriolar material of isolated centrosomes. Here we demonstrate that when Spisula centrosomes are extracted with 1.0 M KI they lose their Microtubule Nucleation potential and appear by three-dimensional electron microscopy as a complex lattice, built from 12- to 15-nm thick elementary fiber(s), that lack centrioles and 25-nm rings. Importantly, when these remnants are incubated in extracts prepared from Spisula oocytes they recover their 25-nm rings, γ-tubulin, and Microtubule Nucleation potential. This recovery process occurs in the absence of Microtubules, divalent cations, and nucleotides. Thus, in animals the centrosome is structurally organized around a KI-insoluble filament-based “centromatrix” that serves as a scaffold to which those proteins required for Microtubule Nucleation bind, either directly or indirectly, in a divalent cation and nucleotide independent manner.
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centrosomes isolated from spisula solidissima oocytes contain rings and an unusual stoichiometric ratio of α β tubulin
Journal of Cell Biology, 1997Co-Authors: Jacalyn M Vogel, Tim Stearns, Conly L. Rieder, Robert E. PalazzoAbstract:Centrosome-dependent Microtubule Nucleation involves the interaction of tubulin subunits with pericentriolar material. To study the biochemical and structural basis of centrosome-dependent Microtubule Nucleation, centrosomes capable of organizing Microtubules into astral arrays were isolated from parthenogenetically activated Spisula solidissima oocytes. Intermediate voltage electron microscopy tomography revealed that each centrosome was composed of a single centriole surrounded by pericentriolar material that was studded with ring-shaped structures ∼25 nm in diameter and a ) proteins that contained M-phase–specific phosphoepitopes (MPM-2), ( b ) α-, β-, and γ-tubulins, ( c ) actin, and ( d ) three low molecular weight proteins of
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Centrosomes isolated from Spisula solidissima oocytes contain rings and an unusual stoichiometric ratio of �/� tubulin
1997Co-Authors: Jacalyn M Vogel, Tim Stearns, Conly L. Rieder, Robert E. PalazzoAbstract:Abstract. Centrosome-dependent Microtubule Nucleation involves the interaction of tubulin subunits with pericentriolar material. To study the biochemical and structural basis of centrosome-dependent Microtubule Nucleation, centrosomes capable of organizing Microtubules into astral arrays were isolated from parthenogenetically activated Spisula solidissima oocytes. Intermediate voltage electron microscopy tomography revealed that each centrosome was composed of a single centriole surrounded by pericentriolar material that was studded with ring-shaped structures �25 nm in diameter and �25 nm in length. A number of proteins copurified with centrosomes including: (a) proteins that contained M-phase–specific phosphoepitopes (MPM-2), (b) �-, �-, and �-tubulins, (c) actin, and (d) three low molecula
Timothy J. Mitchison - One of the best experts on this subject based on the ideXlab platform.
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Microtubule Nucleation remote from centrosomes may explain how asters span large cells
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Aaron C. Groen, Keisuke Ishihara, Timothy J. Mitchison, Phuong Nguyen, Christine M FieldAbstract:A major challenge in cell biology is to understand how nanometer-sized molecules can organize micrometer-sized cells in space and time. One solution in many animal cells is a radial array of Microtubules called an aster, which is nucleated by a central organizing center and spans the entire cytoplasm. Frog (here Xenopus laevis) embryos are more than 1 mm in diameter and divide with a defined geometry every 30 min. Like smaller cells, they are organized by asters, which grow, interact, and move to precisely position the cleavage planes. It has been unclear whether asters grow to fill the enormous egg by the same mechanism used in smaller somatic cells, or whether special mechanisms are required. We addressed this question by imaging growing asters in a cell-free system derived from eggs, where asters grew to hundreds of microns in diameter. By tracking marks on the lattice, we found that Microtubules could slide outward, but this was not essential for rapid aster growth. Polymer treadmilling did not occur. By measuring the number and positions of Microtubule ends over time, we found that most Microtubules were nucleated away from the centrosome and that interphase egg cytoplasm supported spontaneous Nucleation after a time lag. We propose that aster growth is initiated by centrosomes but that asters grow by propagating a wave of Microtubule Nucleation stimulated by the presence of preexisting Microtubules.
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branching Microtubule Nucleation in xenopus egg extracts mediated by augmin and tpx2
Cell, 2013Co-Authors: Ronald D Vale, Aaron C. Groen, Keisuke Ishihara, Sabine Petry, Timothy J. MitchisonAbstract:SUMMARY The Microtubules that comprise mitotic spindles in animal cells are nucleated at centrosomes and by spindle assembly factors that are activated in the vicinity of chromatin. Indirect evidence has suggested that Microtubules also might be nucleated from pre-existing Microtubules throughout the spindle, but this process has not been observed directly. Here, we demonstrate Microtubule Nucleation from the sides of existing Microtubules in meiotic Xenopus egg extracts. Daughter Microtubules grow at a low branch angle and with the same polarity as mother filaments. Branching Microtubule Nucleation requires g-tubulin and augmin and is stimulated by factors previously implicated in chromatin-stimulated Nucleation, guanosine triphosphate(GTP)-bound Rananditseffector,TPX2. Because of the rapid amplification of Microtubule numbers and the preservation of Microtubule polarity, Microtubule-dependent Microtubule Nucleation is well suited for spindle assembly and maintenance.
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xrhamm functions in ran dependent Microtubule Nucleation and pole formation during anastral spindle assembly
Current Biology, 2004Co-Authors: Aaron C. Groen, Timothy J. Mitchison, Lisa A Cameron, Margaret Coughlin, David T Miyamoto, Ryoma OhiAbstract:Abstract Background: The regulated assembly of Microtubules is essential for bipolar spindle formation. Depending on cell type, Microtubules nucleate through two different pathways: centrosome-driven or chromatin-driven. The chromatin-driven pathway dominates in cells lacking centrosomes. Results: Human RHAMM (receptor for hyaluronic-acid-mediated motility) was originally implicated in hyaluronic-acid-induced motility but has since been shown to associate with centrosomes and play a role in astral spindle pole integrity in mitotic systems. We have identified the Xenopus ortholog of human RHAMM as a Microtubule-associated protein that plays a role in focusing spindle poles and is essential for efficient Microtubule Nucleation during spindle assembly without centrosomes. XRHAMM associates both with γ-TuRC, a complex required for Microtubule Nucleation and with TPX2, a protein required for Microtubule Nucleation and spindle pole organization. Conclusions: XRHAMM facilitates Ran-dependent, chromatin-driven Nucleation in a process that may require coordinate activation of TPX2 and γ-TuRC.
Aaron C. Groen - One of the best experts on this subject based on the ideXlab platform.
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Microtubule Nucleation remote from centrosomes may explain how asters span large cells
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Aaron C. Groen, Keisuke Ishihara, Timothy J. Mitchison, Phuong Nguyen, Christine M FieldAbstract:A major challenge in cell biology is to understand how nanometer-sized molecules can organize micrometer-sized cells in space and time. One solution in many animal cells is a radial array of Microtubules called an aster, which is nucleated by a central organizing center and spans the entire cytoplasm. Frog (here Xenopus laevis) embryos are more than 1 mm in diameter and divide with a defined geometry every 30 min. Like smaller cells, they are organized by asters, which grow, interact, and move to precisely position the cleavage planes. It has been unclear whether asters grow to fill the enormous egg by the same mechanism used in smaller somatic cells, or whether special mechanisms are required. We addressed this question by imaging growing asters in a cell-free system derived from eggs, where asters grew to hundreds of microns in diameter. By tracking marks on the lattice, we found that Microtubules could slide outward, but this was not essential for rapid aster growth. Polymer treadmilling did not occur. By measuring the number and positions of Microtubule ends over time, we found that most Microtubules were nucleated away from the centrosome and that interphase egg cytoplasm supported spontaneous Nucleation after a time lag. We propose that aster growth is initiated by centrosomes but that asters grow by propagating a wave of Microtubule Nucleation stimulated by the presence of preexisting Microtubules.
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branching Microtubule Nucleation in xenopus egg extracts mediated by augmin and tpx2
Cell, 2013Co-Authors: Ronald D Vale, Aaron C. Groen, Keisuke Ishihara, Sabine Petry, Timothy J. MitchisonAbstract:SUMMARY The Microtubules that comprise mitotic spindles in animal cells are nucleated at centrosomes and by spindle assembly factors that are activated in the vicinity of chromatin. Indirect evidence has suggested that Microtubules also might be nucleated from pre-existing Microtubules throughout the spindle, but this process has not been observed directly. Here, we demonstrate Microtubule Nucleation from the sides of existing Microtubules in meiotic Xenopus egg extracts. Daughter Microtubules grow at a low branch angle and with the same polarity as mother filaments. Branching Microtubule Nucleation requires g-tubulin and augmin and is stimulated by factors previously implicated in chromatin-stimulated Nucleation, guanosine triphosphate(GTP)-bound Rananditseffector,TPX2. Because of the rapid amplification of Microtubule numbers and the preservation of Microtubule polarity, Microtubule-dependent Microtubule Nucleation is well suited for spindle assembly and maintenance.
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centrosomal Microtubule Nucleation activity is inhibited by brca1 dependent ubiquitination
Molecular and Cellular Biology, 2005Co-Authors: Satish Sankaran, Aaron C. Groen, Lea M Starita, Jeffrey D ParvinAbstract:In this study we find that the function of BRCA1 inhibits the Microtubule Nucleation function of centrosomes. In particular, cells in early S phase have quiescent centrosomes due to BRCA1 activity, which inhibits the association of gamma-tubulin with centrosomes. We find that modification of either of two specific lysine residues (Lys-48 and Lys-344) of gamma-tubulin, a known substrate for BRCA1-dependent ubiquitination activity, led to centrosome hyperactivity. Interestingly, mutation of gamma-tubulin lysine 344 had a minimal effect on centrosome number but a profound effect on Microtubule Nucleation function, indicating that the processes regulating centrosome duplication and Microtubule Nucleation are distinct. Using an in vitro aster formation assay, we found that BRCA1-dependent ubiquitination activity directly inhibits Microtubule Nucleation by centrosomes. Mutant BRCA1 protein that was inactive as a ubiquitin ligase did not inhibit aster formation by the centrosome. Further, a BRCA1 carboxy-terminal truncation mutant that was an active ubiquitin ligase lacked domains critical for the inhibition of centrosome function. These experiments reveal an important new functional assay regulated by the BRCA1-dependent ubiquitin ligase, and the results suggest that the loss of this BRCA1 activity could cause the centrosome hypertrophy and subsequent aneuploidy typically found in breast cancers.
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xrhamm functions in ran dependent Microtubule Nucleation and pole formation during anastral spindle assembly
Current Biology, 2004Co-Authors: Aaron C. Groen, Timothy J. Mitchison, Lisa A Cameron, Margaret Coughlin, David T Miyamoto, Ryoma OhiAbstract:Abstract Background: The regulated assembly of Microtubules is essential for bipolar spindle formation. Depending on cell type, Microtubules nucleate through two different pathways: centrosome-driven or chromatin-driven. The chromatin-driven pathway dominates in cells lacking centrosomes. Results: Human RHAMM (receptor for hyaluronic-acid-mediated motility) was originally implicated in hyaluronic-acid-induced motility but has since been shown to associate with centrosomes and play a role in astral spindle pole integrity in mitotic systems. We have identified the Xenopus ortholog of human RHAMM as a Microtubule-associated protein that plays a role in focusing spindle poles and is essential for efficient Microtubule Nucleation during spindle assembly without centrosomes. XRHAMM associates both with γ-TuRC, a complex required for Microtubule Nucleation and with TPX2, a protein required for Microtubule Nucleation and spindle pole organization. Conclusions: XRHAMM facilitates Ran-dependent, chromatin-driven Nucleation in a process that may require coordinate activation of TPX2 and γ-TuRC.
Elmar Schiebel - One of the best experts on this subject based on the ideXlab platform.
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Microtubule Nucleation the waltz between γ tubulin ring complex and associated proteins
Current Opinion in Cell Biology, 2021Co-Authors: Peng Liu, Martin Wurtz, Erik Zupa, Stefan Pfeffer, Elmar SchiebelAbstract:Abstract Microtubules are essential cytoskeletal elements assembled from αβ-tubulin dimers. In high eukaryotes, Microtubule Nucleation, the de novo assembly of a Microtubule from its minus end, is initiated by the γ-tubulin ring complex (γ-TuRC). Despite many years of research, the structural and mechanistic principles of the Microtubule Nucleation machinery remained poorly understood. Only recently, cryoelectron microscopy studies uncovered the molecular organization and potential activation mechanisms of γ-TuRC. In vitro assays further deciphered the spatial and temporal cooperation between γ-TuRC and additional factors, for example, the augmin complex, the phase separation protein TPX2, and the Microtubule polymerase XMAP215. These breakthroughs deepen our understanding of Microtubule Nucleation mechanisms and will link the assembly of individual Microtubules to the organization of cellular Microtubule networks.
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the Microtubule polymerase stu2 promotes oligomerization of the γ tusc for cytoplasmic Microtubule Nucleation
eLife, 2018Co-Authors: Judith Gunzelmann, Annett Neuner, Diana Ruthnick, Tienchen Lin, Wanlu Zhang, Ursula Jakle, Elmar SchiebelAbstract:Stu2/XMAP215/ZYG-9/Dis1/Alp14/Msps/ch-TOG family members in association with with γ-tubulin complexes nucleate Microtubules, but we know little about the interplay of these Nucleation factors. Here, we show that the budding yeast Stu2 in complex with the γ-tubulin receptor Spc72 nucleates Microtubules in vitro without the small γ-tubulin complex (γ-TuSC). Upon γ-TuSC addition, Stu2 facilitates Spc72-γ-TuSC interaction by binding to Spc72 and γ-TuSC. Stu2 together with Spc72-γ-TuSC increases Microtubule Nucleation in a process that is dependent on the TOG domains of Stu2. Importantly, these activities are also important for Microtubule Nucleation in vivo. Stu2 stabilizes Spc72-γ-TuSC at the minus end of cytoplasmic Microtubules (cMTs) and an in vivo assay indicates that cMT Nucleation requires the TOG domains of Stu2. Upon γ-tubulin depletion, we observed efficient cMT Nucleation away from the spindle pole body (SPB), which was dependent on Stu2. Thus, γ-TuSC restricts cMT assembly to the SPB whereas Stu2 nucleates cMTs together with γ-TuSC and stabilizes γ-TuSC at the cMT minus end.
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gtp regulates the Microtubule Nucleation activity of γ tubulin
Nature Cell Biology, 2013Co-Authors: Linda Gombos, Annett Neuner, Mykhaylo Berynskyy, Luca L Fava, Rebecca C Wade, Carsten Sachse, Elmar SchiebelAbstract:Schiebel and colleagues use in vitro techniques and yeast genetics to study the role of GTP binding in the Microtubule Nucleation activity of γ-tubulin.
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γ tubulin complexes binding to the centrosome regulation and Microtubule Nucleation
Current Opinion in Cell Biology, 2000Co-Authors: Elmar SchiebelAbstract:Microtubule assembly is initiated in vivo by gamma-tubulin complexes. Cytoplasmic gamma-tubulin complexes are targeted to centrosomes or to other Microtubule organizing centers (MTOCs) via a set of so called gamma-tubulin complex binding proteins (GTBPs) that probably interact with the conserved Spc97p/Spc98p protein family of gamma-tubulin complexes. In other cell types, gamma-tubulin complexes may initiate Microtubule formation near chromosomes in a MTOC-independent manner. Recently, major advances have been achieved through the finding that gamma-tubulin, Spc97p and Spc98p form a conserved core that is probably responsible for Microtubule Nucleation, and by the discovery that a yeast GTBP is regulated in a cell-cycle-dependent manner and in response to an external signal. Furthermore, it was found that the small GTPase Ran in its GDP-bound state may promote spindle assembly. In addition, an essential function of gamma-tubulin in basal body duplication has been demonstrated in Paramecium.
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centrosome Microtubule Nucleation
Journal of Cell Science, 1997Co-Authors: Gislene Pereira, Elmar SchiebelAbstract:In many cell types the formation of Microtubules from tubulin subunits is initiated at defined Nucleation sites at the centrosome. These sites contain the conserved gamma-tubulin which is in association with additional not very will characterised proteins, identified as components of a gamma-tubulin ring complex from Xenopus egg extracts or from suppressor screens in the yeast Saccharomyces cerevisiae. In this review we discuss two recently proposed models of how the gamma-tubulin complex assists in the assembly of tubulin to form Microtubules. These models propose different roles for gamma-tubulin and the other proteins in the complex in tubulin assembly. While the structure and composition of a Microtubule Nucleation site is becoming clearer, it is still unknown how the cell-cycle dependent regulation of Microtubule Nucleation sites is achieved and whether they disassemble after Microtubule formation in order to allow Microtubule fluxes towards the centrosome which have been observed in mitotic cells.