Geisterfer ZM et al. (2021), The Cytoskeleton and Its Roles in Self-Organiza...

XB-ART-58490

Cells 2021 Aug 26;109:. doi: 10.3390/cells10092197.

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The Cytoskeleton and Its Roles in Self-Organization Phenomena: Insights from Xenopus Egg Extracts.

Geisterfer ZM , Guilloux G , Gibeaux R .

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Self-organization of and by the cytoskeleton is central to the biology of the cell. Since their introduction in the early 1980s, cytoplasmic extracts derived from the eggs of the African clawed-frog, Xenopus laevis, have flourished as a major experimental system to study the various facets of cytoskeleton-dependent self-organization. Over the years, the many investigations that have used these extracts uniquely benefited from their simplified cell cycle, large experimental volumes, biochemical tractability and cell-free nature. Here, we review the contributions of egg extracts to our understanding of the cytoplasmic aspects of self-organization by the microtubule and the actomyosin cytoskeletons as well as the importance of cytoskeletal filaments in organizing nuclear structure and function.

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Species referenced: Xenopus laevis
Genes referenced: dppa2 hsp90aa1 lmnb3 nup153 prkca tmpo tpx2
GO keywords: cytoskeleton [+]

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	Figure 1. Reconstitution of cytoskeleton-dependent self-organization processes using the Xenopus egg extract in vitro system. Studies introducing or utilizing the reconstitution system in the context of investigating self-organization are referenced next to corresponding schematics in the order they appear in the text.
	Figure 2. Microtubule-dependent self-organization of Xenopus laevis egg extract. Representative schematics of early and late stage organization of X. laevis egg extract during interphase. In the early stage (left panel), a microtubule aster (green) associated with the nucleus (purple) begins to expand and makes contact with dispersed elements of the cytosol including the ER (yellow), mitochondria (blue), and actin cytoskeleton (red). After reaching steady state (right panel) the microtubule cytoskeleton has centered itself in the region of interest, together with it the associated nucleus and ER. Clustering of mitochondria towards the â€œcellâ€ center through the activities of minus-end directed motors such as cytoplasmic dynein (gray) occurs concurrently with microtubule aster centering and continues until most membranous cargos are cleared from more distal regions.
	Figure 3. Gelation-contraction of the actomyosin network. Representative cartoon showing the distributions and rearrangements of F-actin (red), actin nucleators (blue), and myosin (gray) during early and late stages of actomyosin contraction in interphase X. laevis egg extracts. Shortly after F-actin nucleation (early stage; left panel), the F-actin network undergoes contraction (late stage; right panel), resulting in cytosolic flows towards the aggregate center (green arrows) and an F-actin density gradient.
	Figure 4. The cytoskeleton and nuclear assembly, structure, and breakdown. Overview schematics of the different contributions of the cytoskeleton to the formation and maintenance of the nucleus. Nuclear envelope is shown in purple, chromatin in blue, lamin filaments in brown, actin in red and microtubules in green. (1) Lamin B3 promotes the recruitment of the nucleoporin, Nup153, into nuclear pores and to the nuclear envelope. (2) The Lamina-associated protein LAP2 contributes to DNA-nuclear membrane interactions, and ultimately to the elongation of DNA during replication. (3) F-actin accumulates at the sub-nuclear membranous region to stiffen the nuclear lamina and maintain the binding of chromatin to the nuclear envelope. (4) Nuclear actin helps the release of cargoes from RanGTP-importins. (5) The actin-interacting protein, protein 4.1, relies on its spectrin-actin-binding domain (SABD) to interact with nuclear actin and contribute to the nuclear formation. (6) Minus-end directed motors transport membranous nuclear envelope precursors to assemble the nucleus. (7) The chromatin binding protein, Dppa2, inhibits microtubule polymerization near chromatin to allow for proper nuclear assembly. (8) Microtubules may serve a role in removing membranes during nuclear envelope breakdown.

References [+] :

Adam, Regulation of nuclear lamin polymerization by importin alpha. 2008, Pubmed, Xenbase