Equine zona protein synthesis and ZP structure during folliculogenesis, oocyte maturation, and embryogenesis.

This research focuses on the synthesis and structure of zona proteins in horses during egg cell development and embryogenesis. These proteins play a crucial role in successful in vitro fertilization and the study outlines specific attributes of these proteins according to the developmental stage.

Research Aim and Method

• The central objective of this study was to investigate the distinct characteristics of the equine zona pellucida (ZP), an outer layer surrounding mammalian eggs, crucial for fertilization. The research examined the structure as well as the expression sites of the ZP glycoproteins ZPB and ZPC during the oocyte (egg cell) development and embryogenesis.
• The research found high immunological cross-reactivity between horse and pig ZPB and ZPC proteins.

ZP Protein Synthesis During Development

• This study demonstrated that the distribution of ZPB and ZPC proteins on an ovary corresponded with the follicle’s developmental stage. Expression of these proteins started during the late primordial and primary follicle stages in the oocyte.
• Interestingly, both oocyte and the supporting cumulus cells contributed to the synthesis of ZPB and ZPC during the secondary follicle stage.

ZP Protein Synthesis During Maturation

• After in vivo (within the body) maturation, the oocyte stopped producing ZPB and ZPC proteins. Instead, cumulus cells continued the synthesis.
• In contrast, in vitro maturation (closely managed in a lab setting) showed an opposing expression pattern. These differences linked with changes in the structure, number, and size of pores in ZP.

ZP Protein Synthesis During Embryogenesis

• In the zona, N-acetylglucosamine residues were found together with ZPC.
• The study observed that ZPB and ZPC proteins were absent in the acellular glycoprotein capsule encompassing early equine embryos.

Conclusions from the Study

• The regulation of synthesis of ZPC and ZPB glycoproteins in horses differs during folliculogenesis, oocyte maturation, and embryogenesis.
• In comparison with cows and pigs, the zona protein synthesis during in vivo maturation in horses depends entirely on the cumulus cells, indicating that these cells are essential for ZP integrity.
• During in vitro maturation, cumulus cells lose their ability to synthesize glycoproteins, leading to changes in the zona structure.