Abstract
The mitotic spindle, essential for segregating the sister chromatids into the two evolving daughter cells, is composed of highly dynamic cytoskeletal filaments, the microtubules. The dynamics of microtubules are regulated by numerous microtubule associated proteins. We identify here Developmentally regulated GTP binding protein 1 (DRG1) as a microtubule binding protein with diverse microtubule-associated functions. In vitro, DRG1 can diffuse on microtubules, promote their polymerization, drive microtubule formation into bundles, and stabilize microtubules. HeLa cells with reduced DRG1 levels show delayed progression from prophase to anaphase because spindle formation is slowed down. To perform its microtubule-associated functions, DRG1, although being a GTPase, does not require GTP hydrolysis. However, all domains are required as truncated versions show none of the mentioned activities besides microtubule binding.
Highlights
Microtubules are key cytoskeletal structures that play a vital role in a variety of cellular processes such as intracellular trafficking, regulation of cell polarity, cell shape maintenance, and chromatid segregation during cell division
Developmentally regulated GTP-binding protein 1 (DRG1) has been recently shown to localize at the mitotic spindle[25], which raises the question whether the protein can interact with microtubules
Whereas DRG1 and its interaction partner DFRP1 were not pelleted in the absence of microtubules, both proteins were found in the pellet fraction in the presence of microtubules
Summary
Microtubules are key cytoskeletal structures that play a vital role in a variety of cellular processes such as intracellular trafficking, regulation of cell polarity, cell shape maintenance, and chromatid segregation during cell division. Microtubules can nucleate from already existing microtubules within the spindle These other pathways can predominate if no centrosomes are present, e.g. during the second meiotic division in vertebrates, or when centrosomes are artificially removed. Other microtubule associated proteins, and mechanical processes such as cell rounding, are involved in spindle assembly and facilitate the microtubule-kinetochore attachment during mitosis[1, 2]. The presence of numerous diverse yet partially redundant factors and pathways most likely represents an inbuilt security mechanism of the cell It is crucial as well as challenging to identify such partially redundant factors during spindle assembly and maintenance, which are deregulated in many disease contexts[4,5,6]
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