A single bivalent efficiently inhibits cyclin B1 degradation and polar body extrusion in mouse oocytes indicating robust SAC during female meiosis I.

The Spindle Assembly Checkpoint (SAC) inhibits anaphase until microtubule-to-kinetochore attachments are formed, thus securing correct chromosome separation and preventing aneuploidy. Whereas in mitosis even a single unattached chromosome keeps the SAC active, the high incidence of aneuploidy related to maternal meiotic errors raises a concern about the lower efficiency of SAC in oocytes. Recently it was suggested that in mouse oocytes, contrary to somatic cells, not a single chromosome but a critical mass of chromosomes triggers efficient SAC pointing to the necessity of evaluating the robustness of SAC in oocytes.

The conformation and activation of Fyn kinase in the oocyte determine its localisation to the spindle poles and cleavage furrow.

Several lines of evidence imply the involvement of Fyn, a Src family kinase, in cell-cycle control and cytoskeleton organisation in somatic cells. By live cell confocal imaging of immunostained or cRNA-microinjected mouse oocytes at metaphase of the second meiotic division, membrane localisation of active and non-active Fyn was demonstrated. However, Fyn with a disrupted membrane-binding domain at its N-terminus was targeted to the cytoplasm and spindle in its non-active form and concentrated at the spindle poles when active.

Fyn kinase is involved in cleavage furrow ingression during meiosis and mitosis.

Fertilization of mammalian oocytes triggers their exit from the second meiotic division metaphase arrest. The extrusion of the second polar body (PBII) that marks the completion of meiosis is followed by the first mitotic cleavage of the zygote. Several lines of evidence in somatic cells imply the involvement of Fyn, an Src family kinase (SFK), in cell cycle control and actin functions.

The involvement of Fyn kinase in resumption of the first meiotic division in mouse oocytes.

The process of resumption of the first meiotic division (RMI) in mammalian oocytes includes germinal vesicle breakdown (GVBD), spindle formation during first metaphase (MI), segregation of homologous chromosomes, extrusion of the first polar body (PBI) and an arrest at metaphase of the second meiotic division (MII). Previous studies suggest a role for Fyn, a non-receptor Src family tyrosine kinase, in the exit from MII arrest. In the current study we characterized the involvement of Fyn in RMI.

Orientation of mitotic spindles during the 8- to 16-cell stage transition in mouse embryos.

Background: Asymmetric cell divisions are involved in the divergence of the first two lineages of the pre-implantation mouse embryo. They first take place after cell polarization (during compaction) at the 8-cell stage. It is thought that, in contrast to many species, spindle orientation is random, although there is no direct evidence for this.