Abstract
Zinc is an extremely important trace element that plays important roles in several biological processes. However, the function of zinc in meiotic division of porcine oocytes is unknown. In this study, we investigated the role of zinc during meiotic resumption in in vitro matured porcine oocytes. During meiotic division, a massive release of zinc was observed. The level of free zinc in the cytoplasm significantly increased during maturation. Depletion of zinc using N, N, N′, N′-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN), a Zn2+ chelator, blocked meiotic resumption in a dose dependent manner. The level of phosphorylated mitogen activated protein kinase (MAPK) and p34cdc2 kinase activity were reduced when zinc was depleted. Moreover, zinc depletion reduced the levels of phosphorylated protein kinase C (PKC) substrates in a dose dependent manner. Real-time PCR analysis showed that expression of the MAPK- and maturation promoting factor related genes C-mos, CyclinB1, and Cdc2 was downregulated following zinc depletion. Treatment with the PKC agonist phorbol 12-myristate 13-acetate (PMA) increased phosphorylation of PKC substrates and MAPK and increased p34cdc2 kinase activity. This rescued the meiotic arrest, even in the presence of TPEN. Activation of PKC by PMA increased the level of zinc in the cytoplasm. These data demonstrate that zinc is required for meiotic resumption in porcine oocytes, and this appears to be regulated via a PKC related pathway.
Highlights
During mammal oogenesis, follicle enclosed oocytes arrest at prophase I during the first meiosis
Meiotic resumption is facilitated by maturation promoting factor (MPF), a heterodimeric protein composed as Cyclin B1 and Cdc2 ( known as cyclin dependent kinase (CDK)-1 or p34cdc2) [1]
To investigate the effect of zinc depletion on meiotic resumption in porcine oocytes arrested at prophase I, free zinc in these oocytes was depleted by treatment with tetrakis (2pyridylmethyl) ethylenediamine (TPEN)
Summary
Follicle enclosed oocytes arrest at prophase I during the first meiosis. Meiosis resumes once oocytes are released from follicles or are stimulated by specific stimuli, such as gonadotropins. Meiotic resumption is regulated by several protein kinases. Meiotic resumption is facilitated by maturation promoting factor (MPF), a heterodimeric protein composed as Cyclin B1 and Cdc ( known as cyclin dependent kinase (CDK)-1 or p34cdc2) [1]. Microinjection of heterologous maturating cytoplasm into immature porcine oocytes results in GVBD after 8 h of culture [2], whereas inhibition of MPF activation blocks GVBD. Cyclin B1 and Cdc are associated with each other in GV stage oocytes [3], the increase in the level of active MPF requires protein synthesis [4]
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