Actin Dynamics in Oocyte Maturation

Oocyte maturation is governed by a finely tuned remodelling of the actin cytoskeleton that underpins asymmetric cell division and ensures faithful chromosome segregation. During the transition from germinal vesicle breakdown to metaphase II, actin filaments assemble into dynamic networks and cables that coordinate spindle migration, polar body extrusion and cytoplasmic organisation. Formin-mediated nucleation and Arp2/3‐driven branching establish a meshwork that interacts with organelles and chromosomes, driving centripetal movement and stabilising spindle orientation in the absence of centrosomes. Concurrently, cortical actin layers undergo local softening and thickening to permit membrane protrusions and to guide the spindle toward the oocyte periphery. These processes collectively safeguard oocyte quality by preventing aneuploidy, facilitating efficient fertilisation and enabling early embryonic development.

Research from Nature Portfolio

Recent studies have illuminated how actin cables promote rapid chromosome clustering prior to spindle assembly. In mammalian oocytes, Formin-2 and Spire collaborate to nucleate dynamic actin bundles within the disassembling nuclear space, interacting with kinetochores to draw chromosomes centrally and prevent losses during the prolonged gap between nuclear envelope breakdown and spindle formation. A complementary stabilisation by microtubule loops finalises clustering, highlighting a sequential interplay between actin and microtubules for accurate meiosis. Foundational work has also revealed how organelle distribution initiates actin‐based spindle migration: spindle-peripheral formin-2 nucleates short actin filaments on endoplasmic reticulum–derived vesicles, whose confinement by surrounding mitochondria generates pushing forces that break symmetry and direct the spindle toward the cortex. Optogenetic manipulation and perturbation of mitochondrial arrangement confirm that spatial bias in actin nucleation is sufficient to propel spindle movement in mouse oocytes.

Actin Dynamics in Oocyte Maturation publication trend

The graph below shows the total number of articles in actin dynamics in oocyte maturation across all publications each year (not limited to Nature Index journals).

Technical terms

Formin-2 (FMNL2): An actin-nucleating protein that catalyses the growth of unbranched filaments critical for spindle positioning and cytokinesis.

Spire: A WH2 domain-containing actin nucleator that cooperates with formins to assemble cytoplasmic actin networks.

Arp2/3 complex: A seven-subunit assembly that initiates branched actin filament networks, key to cortical remodelling and cell polarity.

Acentrosomal spindle: A meiotic spindle that forms without centrosomes, relying on actin and microtubule interactions for correct positioning.

Chromosome clustering: The consolidation of dispersed chromosomes into a tight group before spindle capture, driven by actin–microtubule interplay.

Polar body extrusion: The asymmetric cytokinesis event in oocyte maturation that expels half the chromosomal complement, facilitated by actin-driven membrane protrusion.

References

1. Actin-driven chromosome clustering facilitates fast and complete chromosome capture in mammalian oocytes. Nature Cell Biology (2023).
2. Dynamic organelle distribution initiates actin-based spindle migration in mouse oocytes. Nature Communications (2020).
3. Aberrant cortex contractions impact mammalian oocyte quality. Developmental Cell (2024).
4. FMNL2 regulates actin for endoplasmic reticulum and mitochondria distribution in oocyte meiosis. eLife (2024).