Actin assembly mediated by a nucleation promoting factor WASH is involved in MTOC–TMA formation during
            Xenopus
            oocyte maturation

Formins are a conserved family of actin assembly–promoting factors with diverse biological roles, but how their activities are regulated in vivo is not well understood. In Saccharomyces cerevisiae, the formins Bni1 and Bnr1 are required for the assembly of actin cables and polarized cell growth. Proper cable assembly further requires Bud6. Previously it was shown that Bud6 enhances Bni1-mediated actin assembly in vitro, but the biochemical mechanism and in vivo role of this activity were left unclear. Here we demonstrate that Bud6 specifically stimulates the nucleation rather than the elongation phase of Bni1-mediated actin assembly, defining Bud6 as a nucleation-promoting factor (NPF) and distinguishing its effects from those of profilin. We generated alleles of Bud6 that uncouple its interactions with Bni1 and G-actin and found that both interactions are critical for NPF activity. Our data indicate that Bud6 promotes filament nucleation by recruiting actin monomers to Bni1. Genetic analysis of the same alleles showed that Bud6 regulation of formin activity is critical for normal levels of actin cable assembly in vivo. Our results raise important mechanistic parallels between Bud6 and WASP, as well as between Bud6 and other NPFs that interact with formins such as Spire.

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Opening of glibenclamide-sensitive K+ channels in follicular cells promotes Xenopus oocyte maturation.

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.89.11.5133 ◽

1992 ◽

Vol 89 (11) ◽

pp. 5133-5137 ◽

Cited By ~ 17

Author(s):

F. Wibrand ◽

E. Honore ◽

M. Lazdunski

Keyword(s):

Oocyte Maturation ◽

Xenopus Oocyte ◽

Follicular Cells ◽

K Channels

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Reorganization of actin filaments by ADF/cofilin is involved in formation of microtubule structures during Xenopus oocyte maturation

Molecular Biology of the Cell ◽

10.1091/mbc.e15-01-0035 ◽

2015 ◽

Vol 26 (24) ◽

pp. 4387-4400 ◽

Cited By ~ 7

Author(s):

Yuka Yamagishi ◽

Hiroshi Abe

Keyword(s):

Oocyte Maturation ◽

Actin Filament ◽

Actin Filaments ◽

Xenopus Oocyte ◽

Germinal Vesicle ◽

Meiotic Spindle ◽

Base Region ◽

Microtubule Organizing Center ◽

Cytoplasmic Actin ◽

Organizing Center

We examined the reorganization of actin filaments and microtubules during Xenopus oocyte maturation. Surrounding the germinal vesicle (GV) in immature oocytes, the cytoplasmic actin filaments reorganized to accumulate beneath the vegetal side of the GV, where the microtubule-organizing center and transient microtubule array (MTOC-TMA) assembled, just before GV breakdown (GVBD). Immediately after GVBD, both Xenopus ADF/cofilin (XAC) and its phosphatase Slingshot (XSSH) accumulated into the nuclei and intranuclear actin filaments disassembled from the vegetal side with the shrinkage of the GV. As the MTOC-TMA developed well, cytoplasmic actin filaments were retained at the MTOC-TMA base region. Suppression of XAC dephosphorylation by anti-XSSH antibody injection inhibited both actin filament reorganization and proper formation and localization of both the MTOC-TMA and meiotic spindles. Stabilization of actin filaments by phalloidin also inhibited formation of the MTOC-TMA and disassembly of intranuclear actin filaments without affecting nuclear shrinkage. Nocodazole also caused the MTOC-TMA and the cytoplasmic actin filaments at its base region to disappear, which further impeded disassembly of intranuclear actin filaments from the vegetal side. XAC appears to reorganize cytoplasmic actin filaments required for precise assembly of the MTOC and, together with the MTOC-TMA, regulate the intranuclear actin filament disassembly essential for meiotic spindle formation.

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