The Src family kinases contribute to MII arrest maintenance in aging porcine oocytes

Mature mammalian oocytes arrest meiosis in metaphase II (MII). If the oocyte is not fertilized, it can spontaneously break the MII arrest. Spontaneous activation and postovulatory aging hinder precisely timed and regulated embryonic development. To elucidate the role of Src family protein tyrosine kinases (SFKs) in porcine oocyte MII arrest, activation, and aging, we used a specific SFK inhibitor and immunolocalization. The 24h-prolonged oocyte culture in the presence of SFK inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) increased (P < 0.05) the proportion of spontaneously activated porcine oocytes compared to controls. Further culture with PP2 inhibitor led to an increase (P < 0.05) in the parthenogenetic embryos and a decrease (P < 0.05) in lytic oocytes. SFK inhibition did not affect (P > 0.05) the proportion of ionophore A23187-activated oocytes. SFKs were localized in the perichromosomal region, in the pronuclei, in the cytoplasm, and on the plasma membrane of oocytes and parthenogenetic embryos after 24, 48, and 72 h of prolonged in vitro culture. The greatest SFKs fluorescence was detected after a 24h-prolonged culture on the plasma membrane of MII oocytes. In embryos and fragmented oocytes, intense fluorescence was detected in the cleavage furrow region and on the membrane of apoptotic vesicles, respectively.

Our results reveal the involvement of SFKs in MII arrest maintenance, though they don't appear to modulate the early processes of ionophore-stimulated parthenogenetic activation. Changes in the distribution of SFKs during prolonged culture suggest their role in signaling cascades associated with actin filament cytoskeleton organization.