Expression and cellular distribution of zona pellucida glycoproteins in canine oocytes before and after in vitro maturation

This study was aimed at investigating zona pellucida glycoproteins (ZP) ZP2, ZP3 mRNA expression as well as ZP3, ZP4 (ZPB) protein distribution before and after in vitro maturation (IVM) in canine oocytes. The cumulus-oocyte complexes (COCs) were recovered from 27 anoestrous mongrel bitches and matured for 72 h in TCM199 medium. The canine COCs were analysed before and after IVM. Using real-time quantitative polymerase chain reaction (RQ-PCR), both groups of oocytes were analysed for detection of ZP2 and ZP3 mRNA profiles as well as using confocal microscopic analysis for observation of ZP3 and ZP4 protein distribution. In post-IVM canine oocytes an increase in transcript content of ZP2 and ZP3 genes as well as a decrease in ZP3 and ZP4 protein levels were observed when compared with pre-IVM oocytes. Moreover, the ZP4 protein before IVM was significantly distributed in the peripheral area of cytoplasm, whereas after IVM it was localized rather than in the entire cytoplasm. In contrast, the ZP3 protein was found both before and after IVM was distributed in the peripheral area of the cytoplasm. In conclusion, we suggest that the expression of ZP2 and ZP3 genes is associated with the maturation stage of canine oocytes, as higher mRNAs levels were found after IVM. However, a decreased expression of ZP3 and ZP4 proteins after IVM suggests maturation-dependent down-regulation of these protein translations, which may result in disturbed fertilization.