The spatial and mechanical challenges of female meiosis

Abstract

Recent work shows that cytokinesis and other cellular morphogenesis events are tuned by an interplay among biochemical signals, cell shape, and cellular mechanics. In cytokinesis, this includes cross-talk between the cortical cytoskeleton and the mitotic spindle in coordination with cell cycle control, resulting in characteristic changes in cellular morphology and mechanics through metaphase and cytokinesis. The changes in cellular mechanics affect not just overall cell shape, but also mitotic spindle morphology and function. This review will address how these principles apply to oocytes undergoing the asymmetric cell divisions of meiosis I and II. The biochemical signals that regulate cell cycle timing during meiotic maturation and egg activation are crucial for temporal control of meiosis. Spatial control of the meiotic divisions is also important, ensuring that the chromosomes are segregated evenly and that meiotic division is clearly asymmetric, yielding two daughter cells – oocyte and polar body – with enormous volume differences. In contrast to mitotic cells, the oocyte does not undergo overt changes in cell shape with its progression through meiosis, but instead maintains a relatively round morphology with the exception of very localized changes at the time of polar body emission. Placement of the metaphase-I and -II spindles at the oocyte periphery is clearly important for normal polar body emission, although this is likely not the only control element. Here, consideration is given to how cellular mechanics could contribute to successful mammalian female meiosis, ultimately affecting egg quality and competence to form a healthy embryo.

Non-muscle tropomyosin (Tpm3) is crucial for asymmetric cell division and maintenance of cortical integrity in mouse oocytes

“…36 Membrane tension increases again after fertilization. 36,38,39 These results suggest that membrane tension is an important factor for controlling fertilization and, therefore, also Tpm3, and it may help to regulate fertilization via modulating cortex remodeling.…”

PGRMC1 participates in late events of bovine granulosa cells mitosis and oocyte meiosis

“…Extrusion of the PB is essential for the formation of the mature egg. 23,25 Nonetheless late mitotic and oocyte meiotic division share many similarities. 23 In both systems, microtubules of the anaphase spindle play important roles in the formation of the actino-myosin contractile ring and the formation of the cytokinetic furrow at this site, allowing the physical separation of the two daughter cells (reviewed in 23 ).…”

Amino Acid Turnover by Bovine Oocytes Provides an Index of Oocyte Developmental Competence In Vitro1

“…The preovulatory surge of gonadotropins triggers the final maturation of the oocyte, which includes the nuclear changes that lead to the production of a fertile metaphase II (MII) gamete, namely, resumption of meiosis, spindle formation, chromatin condensation, chromosome segregation, and extrusion of the first polar body [37]. Nuclear maturation is accompanied by cytoplasmic maturation of the oocyte and the expansion and mucification of the cumulus cells [38,39].…”