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The human zona pellucida and scanning electron microscopy. Reality or artifacts?
G Familiari1, M Relucenti, M Ermini
1Department of Anatomy, University of Rome La Sapienza, Italy. giuseppe.familiari@uniroma1.it
Summary
Human oocyte zona pellucida (ZP) surface morphology varies, with porous and net-like structures being common. These ZP variations reflect oocyte maturation status, not artifacts, challenging previous interpretations.
Area of Science:
- Reproductive Biology
- Cell Biology
- Human Embryology
Background:
- The zona pellucida (ZP) is crucial for human fertilization.
- Understanding ZP surface micro-morphology is key to assessing oocyte quality in assisted reproduction.
- Previous studies have yielded conflicting interpretations of ZP surface structures.
Purpose of the Study:
- To investigate the surface micro-morphology of human oocytes.
- To differentiate between genuine ZP features and potential artifacts.
- To correlate ZP structure with oocyte maturation status.
Main Methods:
- Scanning electron microscopy (SEM) with traditional gold coating and conductive staining.
- Saponin-ruthenium red-osmium tetroxide-thiocarbohydrazide (Sap-RR-Os-TC) method for enhanced ultrastructural preservation.
- Analysis of 158 unfertilized human oocytes from assisted reproduction trials.
Main Results:
- Traditional SEM revealed a predominantly porous, net-like ZP structure (79.5%) in 122 oocytes, with a minority showing a smooth or compact ZP (20.5%).
- The Sap-RR-Os-TC method on 36 oocytes showed alternating tight and large meshed networks (86.1%) versus only tight meshed networks (13.9%).
- Consistent results across methods suggest these ZP morphologies are genuine and linked to oocyte maturation.
Conclusions:
- ZP surface micro-morphology, characterized by porous or compact appearances, reflects genuine features related to oocyte maturation status.
- The observed ZP structures are not artifacts but represent variations in the underlying microfilaments network.
- A modern understanding of the ZP surface emphasizes its filamentous network, with apparent 'spongy' or 'compact' states resulting from network collapse.