301 ZINC IS INVOLVED IN PORCINE OOCYTE MEIOTIC MATURATION

Abstract

Zinc is an extremely important trace element that plays important roles in several biological processes. In this study, we investigated the role of zinc during meiotic resumption and metaphase arrest in in vitro-matured porcine oocytes. Oocytes at either germinal vesicle (GV) or MII stage were treated with TPEN, a Zn²⁺ chelator. Meiotic resumption and activation were assayed. Effect of PMA, a PKC activator, on GV breakdown (GVBD) and oocytes activation after TPEN treatment were checked. Results showed that depletion of zinc with 3 µM TPEN-blocked oocytes at GV stage (60.85 ± 5.15 v. 15.60 ± 0.20%; P < 0.05) after 25 h of maturation. The 10-µM TPEN treatment at MII stage significantly (P < 0.05) increased pronucleus formation (90.61 ± 9.10 v. 5.56 ± 9.62%; P < 0.05) and the second polar body extrusion (93.64 ± 5.53 v. 8.59 ± 8.34%; P < 0.05). The p34cdc2 activity was decreased in both MII and GVBD oocytes that were treated with TPEN as compared to control. Phosphorylated MAPK measured by Western blot was also decreased in GVBD oocytes when zinc was depleted. This might be explained by the low expression of C-mos Cyclin B1 and Cdc2 at this stage. Treatment of the oocytes with PKC agonist PMA (100 nM) rescued the meiotic resumption arrest observed after TPEN treatment (GV stage: 26.91 ± 3.10 v. 83.89 ± 11.94%; P < 0.05). The level of phosphorylation of MAPK and p34cdc2 activity were rescued when PMA were used. Treatment oocytes with 100 nM PMA in the GV stage also increased the signal of zinc indicator, fluozin-3-a.m., by about 4-fold in cytoplasm (P < 0.05). These results showed that zinc regulates meiotic resumption probably through PKC. However, although the TPEN treatment reduced phosphorylation of PKC substrates in both meiotic resumption and the MII stage, rescue of PKC substrates phosphorylation with PMA did not prevent the activation of oocytes caused by zinc depletion. These data demonstrate that zinc regulates meiotic resumption via a PKC-dependent pathway, but independent of that in maintaining of metaphase arrest in porcine oocytes.

This work was supported by the Bio-industry Technology Development Program, Ministry of Agriculture, Food and Rural Affairs, Republic of Korea, and by a grant from the Next-Generation BioGreen 21 Program (No. PJ009601 and PJ009098), Rural Development Administration, Republic of Korea.