F-actin mechanics, spindle morphogenesis and chromosome behavior in mouse oocyte – ACTOOMIC

Mitotic cells possess two centrosomes that rapidly promote spindle bipolarization, as they form the spindle poles, and influence spindle positioning through the nucleation of astral microtubules connecting the spindle to the cell cortex. Although almost all animal cells contain centrosomes, oocytes are devoid of them, imposing alternative modes of spindle assembly and positioning that could predispose oocytes to errors in chromosome segregation. Indeed, the production of oocytes is an essential process in the propagation of species but is poorly controlled. It ends up with a strong percentage of abnormal female gametes with the wrong ploidy.

In mouse oocytes, F-actin networks replace astral microtubules for spindle positioning, connecting the spindle to the cell cortex. They exert forces on the spindle, embarking it to the cortex. In addition to their contribution to spindle motion, these forces might also provide robustness to spindle morphogenesis and contribute to chromosome alignment. If the role of actin in spindle positioning is very well known and established in oocytes, its role in spindle morphogenesis and chromosome alignment is completely unknown. Yet, mounting evidences suggest that actin plays a role in spindle positioning but also in spindle morphogenesis in mammalian cells.

In this project, we want to assess the contribution of F-actin to spindle morphogenesis and chromosome alignment in oocytes. These results will have implications in Reproductive science, but it will also be relevant to other actin-based divisions where actin plays a role in spindle assembly and function, essential processes maintaining a correct ploidy in the daughter cells.