Imaging transzonal projections in the cumulus-oocyte complexes: challenges and solutions†

Area of Science:

• Reproductive Biology
• Microscopy and Imaging
• Cell Biology

Background:

• Deep 3D imaging of oocytes faces challenges like depth-dependent shadows and optical aberrations.
• Refractive index mismatches from organelles and lipid droplets hinder clear visualization of fine structures, including transzonal projections (TZPs).

Purpose of the Study:

• To compare various sample preparation and confocal microscopy settings for improved oocyte imaging.
• To identify methods for overcoming optical limitations in deep 3D imaging of cumulus-oocyte complexes (COCs).

Main Methods:

• Utilized a clearing protocol on fixed embryos to demonstrate depth limitations.
• Compared imaging of cleared versus uncleared specimens.
• Investigated the impact of cumulus density, fixation protocols, and permeabilization on image quality.
• Optimized confocal parameters and evaluated mounting media and slide assembly.

Main Results:

• Clearing, lipid droplet removal, and medium harmonization improved staining and distribution.
• Gentle stripping and low fixation reduced image noise.
• Triton permeabilization enhanced antibody penetration for efficient protein labeling of TZPs.
• Optimal confocal settings and slide assembly are crucial for specimen resolution.

Conclusions:

• Sample preparation and confocal settings critically impact the quality of deep 3D oocyte imaging.
• Optimized protocols enhance visualization of fine structures like TZPs within cumulus-oocyte complexes.
• Findings offer practical solutions for researchers in reproductive biology and microscopy.