The versatile electron microscope: an ultrastructural overview of autophagy

Area of Science:

• Cell Biology
• Microscopy Techniques
• Autophagy Research

Background:

• Light microscopy (LM) and electron microscopy (EM) provide insights into autophagic compartment formation and function.
• Advanced EM techniques are crucial for detailed ultrastructural analysis.

Purpose of the Study:

• To outline emerging EM techniques for studying autophagic compartments.
• To focus on volume electron microscopy (volume EM) for 3D morphology and protein localization methods.
• To highlight the impact of EM on understanding phagophore biogenesis.

Main Methods:

• Volume EM techniques: Serial Block-face Scanning Electron Microscopy (SB-SEM) and Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) for large volume visualization.
• Dual-axis electron tomography (ET) for high-resolution reconstruction of smaller volumes, like membrane contact sites.
• Immunolabeling (pre-embedding and post-embedding) for sub-cellular antigen localization.
• Correlative light-electron microscopy (CLEM) for combined LM and EM imaging.
• Cryofixation for preserving near-native cellular states and minimizing artifacts.

Main Results:

• Volume EM methods enable 3D visualization of autophagic compartments and their relationship with surrounding organelles.
• ET provides nano-structural detail for specific regions of interest.
• Immunolabeling confirms the identity of autophagic compartments through antigen localization.
• Cryofixation significantly improves sample preservation, reducing fixation-induced artifacts.

Conclusions:

• Emerging EM techniques significantly advance the study of autophagy.
• Volume EM, immunolabeling, and cryofixation provide powerful tools for dissecting autophagic compartment morphology and biogenesis.
• These methods are essential for detailed investigations into the phagophore and its development.