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The Organization Of Microtubules ( Mts )

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The organization of microtubules (MTs) in the mitotic spindle apparatus has been shown to involve a combination of centrosomal-based nucleation and hypothesized to involve acentrosomal branching MT nucleation. Here, Petry et al. (2013) uses Xenopus egg extracts to successfully observe branching MT nucleation from existing microtubules utilizing total internal reflection microscopy (TIRF). Direct observation of branching MT nucleation highlighted both the activating effect of RanQ69L and its effector protein TPX2 on branching MT nucleation, and the polarity conservation of daughter MTs. Testing for required molecular factors using immunodepletion, it was shown that the γ-tubulin ring complex (γ-TuRC) is required for primary nucleation while the protein complex augmin is required for branching. Furthermore, components of the RanGTP signaling pathway are shown to induce observed branching MT nucleation. The results by Petry et al clearly demonstrate branching MT nucleation and is a significant achievement, being the first ever visualized in a metazoan system. Further research should focus on deciphering the mechanistic interactions between that RanGTP and TPX2, specifically its C-terminus CT-TPX2, that stimulate MT nucleation. In addition, even though augmin has been shown to play a key role in spindle morphogenesis through branched MT nucleation, its relationship with other molecular factors should be further elucidated.
Background
Mitosis and meiosis are key cellular

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