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Spontaneous emergence of cell-like organization in Xenopus egg extracts

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Science  01 Nov 2019:
Vol. 366, Issue 6465, pp. 631-637
DOI: 10.1126/science.aav7793

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Order in the cytoplasm

Extracts of the very large eggs of the African clawed frog, Xenopus laevis, have proven a valuable model system for the study of cell division. Cheng and Ferrell found that after homogenization, such cytoplasm can reorganize back into cell-like structures and undergo multiple rounds of division (see the Perspective by Mitchison and Field). This reorganization apparently occurs without the usual factors that are known to lead to such structural changes during cell division, such as F-actin, myosin II, various individual kinesins, aurora kinase A, or DNA. What is required is energy from adenosine triphosphate, microtubule polymerization, cytoplasmic dynein activity, and a specific kinase-involved cell cycle progression. Nongenetic information in the cytoplasm is apparently sufficient for basic spatial organization of the cell.

Science, this issue p. 631; see also p. 569

Abstract

Every daughter cell inherits two things from its mother: genetic information and a spatially organized complement of macromolecular complexes and organelles. The extent to which de novo self-organization, as opposed to inheritance of an already organized state, can suffice to yield functional cells is uncertain. We used Xenopus laevis egg extracts to show that homogenized interphase egg cytoplasm self-organizes over the course of ~30 minutes into compartments 300 to 400 micrometers in length that resemble cells. Formation of these cell-like compartments required adenosine triphosphate and microtubule polymerization but did not require added demembranated sperm nuclei with their accompanying centrosomes or actin polymerization. In cycling extracts with added sperm, the compartments underwent multiple cycles of division and reorganization, with mother compartments giving rise to two daughters at the end of each mitotic cycle. These results indicate that the cytoplasm can generate much of the spatial organization and cell cycle function of the early embryo.

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