Animal Female Meiosis: The Challenges of Eliminating Centrosomes

Centrosome elimination poses two key questions:

first, how can the centrosome be re-established after fertilisation?

Second, how do most metazoan oocytes manage to build up meiotic spindles without centrosomes?

This review summarises our current understanding of the molecular mechanism underlying self-assembly of meiotic spindles, its spatio-temporal regulation, and the key players governing this process in animal oocytes.

Loss and rebirth of the animal MTOC, the centrosome, accompanies meiosis and fertilisation in metazoan organisms. In most metazoans, centrosome elimination precedes meiosis, which necessitates a pathway for meiotic spindle formation in the absence of centrosomes. The mechanisms of spindle self-assembly in meiosis have evolved using mostly the same molecular determinants that are found to nucleate and organise microtubules in the PCM of centrosomes. Centrosome-free microtubule assembly requires RanGTP produced around chromatin, the nucleation promoting activity of kinetochores, as well as positive feedback loops of microtubule nucleation from pre-existing polymers. Analysing spindle assembly in the absence of centrosomes has not only helped to comprehend the biological challenges of meiosis, fertilisation and fertility, it has also highlighted the idea of a cooperation of different microtubule assembly pathways, both centrosomal and non-centrosomal, for spindle assembly in all our somatic cells.