Cytoplasmic maturation in human oocytes: an ultrastructural study †.

Area of Science:

• Reproductive Biology
• Cell Biology
• Developmental Biology

Background:

• Female fertility depends on successful egg development, which involves cytoplasmic changes beyond chromosome segregation.
• The morphological basis of cytoplasmic maturation in human oocytes is not well understood.
• Oocyte quality is crucial for fertilization and embryonic development.

Purpose of the Study:

• To investigate the ultrastructural changes in the cytoplasm of human oocytes during meiotic maturation in vitro.
• To establish a morphological map of cytoplasmic maturation for reference in future studies.

Main Methods:

• Ultrastructural analysis of 69 unfertilized human oocytes from healthy egg donors.
• Comparison of oocytes at three consecutive developmental stages of in vitro maturation.
• Morphometric image analysis to quantify cytoplasmic reorganization.

Main Results:

• Significant cytoplasmic reorganization occurs before polar body extrusion, with organelles redistributing from the nucleus to the periphery.
• Secretory apparatus transforms into cortical granules beneath the oocyte surface.
• Heterologous complexes of endoplasmic reticulum and primitive mitochondria form during maturation.

Conclusions:

• This study provides essential insights into the morphological changes during human oocyte cytoplasmic maturation.
• The findings enhance understanding of intracellular factors influencing human egg quality.
• A proposed morphological map serves as a reference for comparative studies on oocyte development.