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J Cell Biol
2018 Aug 06;2178:2601-2603. doi: 10.1083/jcb.201807016.
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An actin shell delays oocyte chromosome capture by microtubules.
Verlhac MH
.
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The large nuclei and tiny spindles of oocytes create a challenge for chromosome capture at M-phase entry. A contractile F-actin mesh in starfish oocytes delivers chromosomes to the spindle and Burdyniuk et al. (2018. J. Cell Biol. https://doi.org/10.1083/jcb.201802080) show that F-actin delays the capture of chromosomes until they are within reach of microtubules.
Figure 1. Chromosomes organize their own actin shell to delay their capture by microtubules nucleated at the animal pole in the starfish oocyte. The process of chromosome congression occurs in two-phases: phase I is driven by F-actin and phase II by microtubules. In phase I, the contractile actin mesh assembled inside the nucleus collects all chromosomes and progressively delivers them to the animal pole. In parallel, actin patches nucleated by Arp2/3 assembled around each chromosome mass block their capture by spindle microtubules. In phase II, chromosomes are within reach of spindle microtubules, actin patches disassemble, and chromosomes can now be captured by microtubules. Actin filaments are in red, microtubules in green, centrosomes in yellow, and chromosomes in blue. The broken nuclear envelope is represented in a black dotted outline. The oocyte plasma membrane at the animal pole is represented by a black outline.
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