Talk:Microtubule nucleation

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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. 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. 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. 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. 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
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:
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:
"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. The γ-tubulin combines with several other associated proteins to form conical structures known as γ-tubulin complexes (γ-TuCs). 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. The localization of γ-TuCs to MTOC s regulate temporal and spatial MT nucleation. 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 and Spc98/GCP3. 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. 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. 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. 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 . γ-TuC proteins are highly conserved throughout many organisms suggesting an evolutionary conserved mechanism for MT nucleation.

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