Quantification and distribution of equine oocyte cortical granules during meiotic maturation and after activation.

The research focuses on the statement that while In Vitro Fertilization (IVF) is common in humans and many domestic animals, it proves to be less successful in horses. The research aims to understand the migration and quantification of cortical granules (CG), a key indicator of cytoplasmic maturity, during the in vitro meiotic maturation of horse oocytes.

Background

• The study begins by noting that although immature horse oocytes can complete the process of meiosis in vitro, there are issues with subsequent fertilization and embryonic development.
• This could be due to an impaired cytoplasmic maturity. Studying this in horses is difficult however, due to the limitations in IVF progress. In animals, the movement of cortical granules (CGs) within oocytes is often used to evaluate cytoplasmic maturity.

Aim and Methodology

• The goal of the study was to describe CG distribution in horse oocytes during in vitro meiotic maturation, and assess oocyte activation based on FITC-labeled Lentil lectin (Lens culinaris agglutinin) and laser confocal microscopy.

Findings

• According to the study’s findings, CGs distribute throughout the cytoplasm of oocytes at the germinal vesicle (GV) stage, which means when the oocytes are immature.
• As maturation proceeds, there is a significant centripetal migration of these CGs to the oocyte cortex, forming a monolayer next to the plasma membrane at the end of a 30-hour incubation period, and this significantly increases after 36 hours.
• The study’s findings suggest that when the oocytes are activated, the number of CGs significantly reduces, indicating that oocytes cultured in the current conditions have the ability to release CGs in response to increased intracellular free calcium levels.