The role of Fyn kinase in the release from metaphase in mammalian oocytes.
Meiosis in mammalian oocytes starts during embryonic life and arrests for the first time before birth, at prophase of the first meiotic division. The second meiotic arrest occurs after spindle formation at metaphase of the second meiotic division (MII) in selected oocytes designated for ovulation. The fertilizing spermatozoon induces the release from MII arrest only after the oocyte's spindle assembly checkpoint (SAC) was deactivated. Src family kinases (SFKs) are nine non-receptor protein tyrosine kinases that regulate many key cellular functions. Fyn is an SFK expressed in many cell types, including oocytes. Recent studies, including ours, imply a role for Fyn in exit from meiotic and mitotic metaphases. Other studies demonstrate that SFKs, particularly Fyn, are required for regulation of microtubules polymerization and spindle stabilization. Altogether, Fyn is suggested to play an essential role in signaling events that implicate SAC pathway and hence in regulating the exit from metaphase in oocytes and zygote.