A Xenopus egg extract goes through more than 14 cycles in vitro, forming cell-like compartments that divide in each cycle (read more in Xianrui Cheng and James Ferrell, Science 366, 631-637, 2019, [ Ссылка ]). These compartments can be seen directly through bright-field microscopy with a 5x objective (left panel). Microtubules are visualized by SiR-tubulin (middle panel). Nuclei are visualized by mCherry-NLS, a fluorescent protein fused with a nuclear localization sequence that translocates into the nucleus from the cytosol during the interphase of the cell cycle, when the nuclear envelope is intact.
Cell-like compartments form during interphase, and divide into daughter compartments at the end of mitosis. After many cycles, the thin layer of egg extract partitions into many small compartments like cells in a developing embryo. Microtubules form asters during interphase, starting from the centrosome and growing outwards. During mitosis, microtubules organize into a spindle structure in each compartment.
The extract is made from activated Xenopus laevis eggs (see Andrew Murray, Methods in Cell Biology Volume 36, 1991, Pages 581-605). They can carry out cell cycles autonomously without additional special treatment, because the cell cycle regulator protein cyclin B1 is synthesized and degraded periodically driven by a robust biochemical oscillator consisting of many other proteins. The extract is deposited on a plastic Petri dish, and covered with oil before commencing imaging.
See the formation of compartments from scratch here:
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See the details of compartment division here:
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Another example with microtubules and nuclei overlay
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You can also see this phenomenon directly by eye if you look closely:
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Check out more research on my website:
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Video credit: Xianrui Cheng, unpublished data
