The Mos-MAPK pathway regulates Diaphanous-related formin activity to drive cleavage furrow closure during polar body emission in starfish oocytes

Abstract

SummaryMaintenance of spindle attachment to the cortex and formation of the cleavage furrow around the protruded spindle are essential for polar body extrusion (PBE) during meiotic maturation of oocytes. Although spindle movement to the cortex has been well-studied, how the spindle is maintained at the cortex during PBE is unknown. Here, we show that activation of Diaphanous-related formin mediated by mitogen-activated protein kinase (MAPK) is required for tight spindle attachment to the cortex and cleavage furrow closure during PBE in starfish (Asterina pectinifera) oocytes. A. pectinifera Diaphanous-related formin (ApDia) had a distinct localization in immature oocytes and was localized to the cleavage furrow during PBE. Inhibition of the Mos-MAPK pathway or the actin nucleating activity of formin homology 2 domain prevented cleavage furrow closure and resulted in PBE failure. In MEK/MAPK-inhibited oocytes, activation of ApDia by relief of its intramolecular inhibition restored PBE. In summary, this study elucidates a link between the Mos-MAPK pathway and Diaphanous-related formins, that is responsible for maintaining tight spindle attachment to the cortex and cleavage furrow closure during PBE.

A disassembly-driven mechanism explains F-actin-mediated chromosome transport in starfish oocytes

“…We tested this hypothesis by inhibiting all formin-like activities in the oocyte by SMIFH2, a small-molecule inhibitor of the FH2 domain contained and essential for the activity of all known formins ( Rizvi et al, 2009 ), and which has already been evaluated in mouse and starfish oocytes ( Kim et al, 2015 ; Ucar et al, 2013 ). We thus quantified the contraction rate and F-actin mass in oocytes treated with SMIFH2 and compared to DMSO controls ( Figure 9A–D and Figure 4—figure supplement 1D , Table 2 ).…”

Distinct mechanisms eliminate mother and daughter centrioles in meiosis of starfish oocytes

“…We next used high-resolution confocal 3D time-lapse imaging of these markers to follow the fate of centrioles throughout meiosis; previously, this behavior had merely been inferred from imaging of microtubule asters and analysis of fixed specimens ( Kato et al, 1990 ; Uetake et al, 2002 ; Zhang et al, 2004 ; Shirato et al, 2006 ; Ucar et al, 2013 ). Of the two general centriole markers, pmPoc1-mEGFP (and to a lesser extent pmPoc1-mCherry) was preferred for its reliability over a wide range of expression levels, and because it conveniently colabels microtubules and thus simultaneously gives information on spindle dynamics ( Fig.…”

“…After its transport to the cell cortex, the mother centriole associates stably and tightly with the plasma membrane in the MII spindle ( Fig. 4 A ; Ucar et al, 2013 ). This is very different from the configuration in mitotic spindles, where long astral microtubules connect centrosomes to the cell cortex ( Grill et al, 2001 ; von Dassow et al, 2009 ).…”

Small Molecule Inhibitor of Formin Homology 2 Domains (SMIFH2) Reveals the Roles of the Formin Family of Proteins in Spindle Assembly and Asymmetric Division in Mouse Oocytes

“…The formin mDia2, one of the isoforms of the mDia family, is localized to the spindle poles in mouse oocytes[ 33 , 34 ], together with gamma-tubulin, indicating its putative role in meiotic spindle formation; however, the exact role of mDia2 in oocyte maturation has not been characterized yet. In starfish oocytes, the mDia family of formins is involved in the formation of the cleavage furrow during polar body formation and their activity is regulated by phosphorylation via the Mos-MAPK kinase pathway[ 35 ]. However, the exact roles of the other formins in oocyte maturation remain to be characterized.…”