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Suggestions for organization of the last paragraph from the section "MT nucleation from MTOCs"

Original: "In the cortical array of plants, as well as in the axons of neurons, scientists believe that microtubules nucleate from existing microtubules via the action of severing enzymes such as katanin. Akin to the action of cofilin in generating actin filament arrays, the severing of microtubules by MAPs creates new (+) ends from which microtubules can grow. In this fashion dynamic arrays of microtubules can be generated without the aid of the γ-TuRC."

This entire paragraph needs to sectioned and moved to other places. The first sentence should be moved to the section proceeding this one titled "Branching MT nucleation" because it essentially describes what MT branching is. The second sentence should be moved to the section titled "role of microtubule associated proteins MAPs" which is the section that describes what a MAP is.

Edits for "MT Nucleation form Microtubule Organization Center (MTOCs)":

In animal cells undergoing mitosis, a similar radial array is generated from two MTOCs called the spindle poles, which produce the bipolar mitotic spindle. Microtubule configuration changes throughout the entire cell division process. Microtubules originate from various places. Spindle microtubules, kinetochores and chromatin all trigger microtubule nucleation. In interphase, microtubules stem from the nuclear envelope to help center the nucleus as the cell divides.[1] Some cells however, such as those of higher plants and oocytes, lack distinct MTOCs and microtubules are nucleated via a non-centrosomal pathway. Other cells, such as neurons, skeletal muscle cells, and epithelial cells, which do have MTOCs, possess arrays of microtubules not associated with a centrosome. Other organelles containing membranes can provide nucleation sites for microtubules in several other types of cells. The nuclear envelope of muscle cells, the cell cortex located in plant cells and the Golgi found in somatic cells.[2] Centrosomes in general are nonessential. For example, in neurons, microtubules help with cargo transportation, and plasticity through remodeling; the configurations of these microtubules differ depending on the type of neuron. Microtubule nucleation also stems from places other than the centrosome. In dendrites, Golgi outposts are used as the primary nucleation center. The centrosome and the dendritic Golgi share many of the same characteristics as far as structural and mechanical similarities. [2] These non-centrosomal microtubule arrays can take on various geometries—such as those lead to the long, slender shape of myotubes, the fine protrusions of an axon, or the strongly polarized domains of an epithelial cell. Microtubules work with the actin cytoskeleton to establish cell polarity.[1] Researchers think that the microtubules in these arrays are generated first by the γ-TuRCs, then transported via motor proteins or treadmilling to their desired location, and finally stabilized in the needed configuration through the action of various anchoring and cross-linking proteins.

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Suggested drafts of "Role of γ-tubulin and the γ-tubulin ring complex (γ-TuRC)" by emw17b

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To this section, I suggest adding more citations, discussion of gamma-TuSC, and possibly changing the title to encompass all gamma-tubulin complexes (gamma-TuCs). Please consider edits below.

Original Text:

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In vivo, cells get around this kinetic barrier by using various proteins to aid microtubule nucleation. The primary pathway by which microtubule nucleation is assisted requires the action of a third type of tubulin, γ-tubulin, which is distinct from the α and β subunits that compose the microtubules themselves. The γ-tubulin combines with several other associated proteins to form a conical structure known as the γ-tubulin ring complex (γ-TuRC). This complex, with its 13-fold symmetry, acts as a scaffold or template for α/β tubulin dimers during the nucleation process—speeding up the assembly of the ring of 13 protofilaments that make up the growing microtubule. The γ-TuRC also acts as a cap of the (−) end while the microtubule continues growth from its (+) end. This cap provides both stability and protection to the microtubule (-) end from enzymes that could lead to its depolymerization, while also inhibiting (-) end growth.

Revisions for "Role of gamma-tubulin and the gamma-tubulin ring complex (gamma-TuRC)" in "Microtubule nucleation" main page:

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"Role of γ-tubulin and γ-tubulin complexes (γ-TuCs)" (Suggested new title for this section)

In vivo, cells get around this kinetic barrier by using various proteins to aid microtubule nucleation. The primary pathway by which microtubule nucleation is assisted requires the action of a third type of tubulin, γ-tubulin, which is distinct from the α and β subunits that compose the microtubules themselves[3]. The γ-tubulin combines with several other associated proteins to form conical structures known as γ-tubulin complexes (γ-TuCs)[1]. The γ-TuCs have 13-fold symmetry and act as a scaffold or template for α/β tubulin dimers during the nucleation process—speeding up the assembly of the ring of 13 protofilaments that make up the growing microtubule[4][5]. The localization of γ-TuCs to MTOCs regulate temporal and spatial MT nucleation[4]. One such γ-TuC, known as the γ-tubulin small complex (γ-TuSC) is comprised of two γ-tubulin molecules that bind to Spc97/GCP2[6] and Spc98/GCP3[7]. These γ-TuSCs are sufficient for MT nucleation and have been shown to self-oligomerize under the control of cell-cycle dependent Spc110-N phosphorylation in S. cerevisiae[8]. In higher eukaryotic model systems, γ-TuSCs oligomerize and can template the formation the γ-tubulin ring complex (γ-TuRC) by the binding of additional proteins containing the conserved Spc97_Spc98 domain, known as GCP4, GCP5, GCP6[9]. In addition, the γ-TuRC also acts as a cap of the (−) end while the microtubule continues growth from its (+) end to provide both stability and protection to the microtubule (-) end from enzymes that could lead to its depolymerization, while also inhibiting (-) end growth[10]. γ-TuSC and γ-TuRCs may have distinct MT nucleation regulatory roles as GCP4, 5, and 6 are absent from interphase MTOCs and restricted to spindle pole bodies in S. pombe[11]. γ-TuC proteins are highly conserved throughout many organisms suggesting an evolutionary conserved mechanism for MT nucleation[2].[1]

Bibliography 

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Emw17b (talk) 18:16, 7 December 2017 (UTC)[reply]

Bibliography

  1. ^ a b c d Lin, Tien-chen; Neuner, Annett; Schiebel, Elmar (2015-05-01). "Targeting of γ-tubulin complexes to microtubule organizing centers: conservation and divergence". Trends in Cell Biology. 25 (5): 296–307. doi:10.1016/j.tcb.2014.12.002. ISSN 0962-8924.
  2. ^ a b c Cite error: The named reference :0 was invoked but never defined (see the help page).
  3. ^ Oakley, C. E.; Oakley, B. R. (1989-04-20). "Identification of gamma-tubulin, a new member of the tubulin superfamily encoded by mipA gene of Aspergillus nidulans". Nature. 338 (6217): 662–664. doi:10.1038/338662a0. ISSN 0028-0836. PMID 2649796.
  4. ^ a b Job, Didier; Valiron, Odile; Oakley, Berl (2003-02-01). "Microtubule nucleation". Current Opinion in Cell Biology. 15 (1): 111–117. doi:10.1016/S0955-0674(02)00003-0.
  5. ^ Kollman, Justin M.; Polka, Jessica K.; Zelter, Alex; Davis, Trisha N.; Agard, David A. (2010-12-08). "Microtubule nucleating γ-TuSC assembles structures with 13-fold microtubule-like symmetry". Nature. 466 (7308): 879–882. doi:10.1038/nature09207. ISSN 1476-4687.
  6. ^ Knop, M; Pereira, G; Geissler, S; Grein, K; Schiebel, E (1997-04-01). "The spindle pole body component Spc97p interacts with the gamma-tubulin of Saccharomyces cerevisiae and functions in microtubule organization and spindle pole body duplication". The EMBO Journal. 16 (7): 1550–1564. doi:10.1093/emboj/16.7.1550. ISSN 0261-4189. PMC 1169759. PMID 9130700.{{cite journal}}: CS1 maint: PMC format (link)
  7. ^ Geissler, S; Pereira, G; Spang, A; Knop, M; Souès, S; Kilmartin, J; Schiebel, E (1996-08-01). "The spindle pole body component Spc98p interacts with the gamma-tubulin-like Tub4p of Saccharomyces cerevisiae at the sites of microtubule attachment". The EMBO Journal. 15 (15): 3899–3911. ISSN 0261-4189. PMID 8670895.
  8. ^ Lin, Tien-Chen; Neuner, Annett; Schlosser, Yvonne T.; Scharf, Annette N. D.; Weber, Lisa; Schiebel, Elmar (2014-04-30). "Cell-cycle dependent phosphorylation of yeast pericentrin regulates γ-TuSC-mediated microtubule nucleation". eLife. 3: e02208. doi:10.7554/eLife.02208. ISSN 2050-084X. PMC 4034690. PMID 24842996.{{cite journal}}: CS1 maint: PMC format (link) CS1 maint: unflagged free DOI (link)
  9. ^ Zheng, Y.; Wong, M. L.; Alberts, B.; Mitchison, T. (1995-12-07). "Nucleation of microtubule assembly by a gamma-tubulin-containing ring complex". Nature. 378 (6557): 578–583. doi:10.1038/378578a0. ISSN 0028-0836. PMID 8524390.
  10. ^ Wiese, C.; Zheng, Y. (June 2000). "A new function for the gamma-tubulin ring complex as a microtubule minus-end cap". Nature Cell Biology. 2 (6): 358–364. doi:10.1038/35014051. ISSN 1465-7392. PMID 10854327.
  11. ^ Venkatram, Srinivas; Tasto, Joseph J.; Feoktistova, Anna; Jennings, Jennifer L.; Link, Andrew J.; Gould, Kathleen L. (2004-05-01). "Identification and Characterization of Two Novel Proteins Affecting Fission Yeast γ-tubulin Complex Function". Molecular Biology of the Cell. 15 (5): 2287–2301. doi:10.1091/mbc.E03-10-0728. ISSN 1059-1524. PMID 15004232.

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