CV Science

Marie-Emilie TERRET PhD in molecular and cellular developmental biology

Course and current status

- 2018- present : DR2 Inserm and PI in the team oocyte mechanics and morphogenesis, CIRB, U1050/UMR7241, Collège de France, Paris.

- sept 2009- sept 2018: Post doctoral fellow then CR1 Inserm in the team asymmetric divisions in oocytes, UMR7622, UPMC, Paris until 2011 then CIRB, U1050/UMR7241, Collège de France, Paris.

- sept 2004- sept 2009: Post doctoral fellow in the team Chromosomal Instability and Cancer at the Memorial Sloan Kettering Cancer Center, New-York, USA.

- sept 2000- juillet 2004: Master 2 followed by a PhD in UMR7622, UPMC, Paris.

Scientific summary

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. All oocytes undergo extremely asymmetric divisions, leading to the formation of a large cell, the oocyte, and two small polar bodies. This size asymmetry is essential to maintain the maternal stores accumulated during oogenesis in the oocyte in order to sustain embryo development. For this, oocytes rely on very asymmetric spindle positioning.

In the mouse, spindle positioning depends on a cortical actin thickening connected to an actin cytoplasmic meshwork and an actin cage that surrounds the microtubule spindle. We have shown that the cortical actin thickening excludes myosin-II from the cortex, decreasing cortical tension. This change in cortex mechanics amplifies an initial imbalance of pulling forces exerted by myosin-II at the poles of the actin cage, leading to the migration of the microtubule spindle towards the closest cortex. However, cortical tension has to be tightly gated since only a narrow window of cortical tension allows spindle movement. The first embryonic division after fertilization in the mouse also occurs in the absence of canonical centrosomes but achieves a complete opposite geometry since it is symmetrical. We have shown that similar cellular processes involving F-actin and cortical tension are used to position the spindle at the cell center in one-cell embryos. Thus F-actin mechanics are crucial to mediate the geometry of the division in absence of true centrosomes and operate the asymmetric to symmetric division switch at the oocyte to embryo transition.