Regulation of division in mammalian oocytes: implications for polar body formation.

Meiosis in mammalian oocytes includes two asymmetric meiotic divisions that result in extrusion of the first and second polar bodies (PBI and PBII, respectively). Fyn, an Src family kinase (SFK), colocalizes with filamentous actin (F-actin) at the meiotic cleavage furrow area of mouse oocytes. In this paper, these studies are extended to rat oocytes. Furthermore, inhibition of Fyn decreased the rate of PBs extrusion and led to formation of larger PBs (PBI and PBII). This effect differs from the effect of Fyn inhibition on the first mitotic symmetric cell division where only the rate of cleavage was affected but the two daughter cells were of regular size. Inhibition of Fyn resulted in a significant decrease in cortical F-actin in the oocytes. We suggest a meiotic model for mammalian oocytes in which Fyn is recruited to the meiotic area of cleavage furrow formation and induces polymerization and stabilization of F-actin, possibly by regulating F-actin effectors, such as RhoA, Arp2/3 and formins, thus allowing ingression of the cleavage furrow. In the context of PB formation, we suggest that SFKs are involved in maintaining the precise temporal restrains of the asymmetric divisions and in regulation of PBs size by inducing polymerization and stabilization of F-actin during the formation and ingression of the cleavage furrow.