Publication in Journal of Cell Science : Cofilin regulates actin network homeostasis and microvillus length in mouse oocytes.

During meiosis, the oocytes that have completed their growth undergo a maturation process that allows them to become fertile gametes suitable for embryonic development. Oocyte maturation involves in particular a major reorganization of the actin cytoskeleton, leading in particular to polarization of the oocyte. This actin remodeling involves a number of molecules responsible for the polymerization of actin filaments according to different architectures. However, actin filaments are dynamic structures in constant renewal, because polymerization at one end is counterbalanced by depolymerization at the other end. The role of depolymerization mechanisms in the reorganization of oocyte actin is poorly understood.

In this new study, the authors investigated the contribution of the protein Cofilin, which has been extensively described in somatic cells as promoting actin filament depolymerization. It is shown that in mouse oocytes, Cofilin is activated (by dephosphorylation) during early maturation. Cofilin was then inactivated by injecting the LIMK1 kinase into the oocytes - which phosphorylates Cofilin and prevents it from binding to actin. Under these conditions, the oocyte membrane microvilli become disproportionately elongated, while the cytoplasmic actin network disappears, resulting in maturation defects and inhibition of cytokinesis. Cofilin also regulates the dynamics of actin filaments for the correct establishment of cortical polarization. In conclusion, Cofilin activation represents a new key process in oocyte maturation.

This study also suggests that Cofilin regulates the length of membrane microvilli, structures found in particular in epithelial cells and whose dynamics are still poorly understood.