Electron beam-induced changes in vitreous sections of biological samples

Area of Science:

• Cryo-electron microscopy
• Biological sample preparation
• Electron beam interactions

Background:

• High pressure freezing and cryosectioning are crucial for preserving biological ultrastructure.
• Electron irradiation can induce changes in biological specimens during microscopy.
• Understanding these changes is vital for accurate interpretation of cryo-electron microscopy data.

Purpose of the Study:

• To investigate the effects of electron irradiation on cryosectioned biological samples.
• To assess the impact of electron doses on sample integrity and image quality.
• To differentiate between genuine structural features and beam-induced artifacts.

Main Methods:

• Cryosectioning of nonpretreated high pressure frozen samples (Zea mays, cartilage, human erythrocytes).
• Observation at 110K in a cryoelectron microscope.
• Exposure to medium doses of electron irradiation (< 10 ke nm-2).

Main Results:

• Electron irradiation (< 10 ke nm-2) reduced cutting artifacts, enhancing organelle visibility.
• Irradiation induced shrinkage in the cutting direction, dependent on section support.
• Differential shrinkage occurred in mitochondria, chromatin, and nucleoli, improving gross structure visibility.
• This apparent improvement was identified as a beam-induced artifact, accompanied by a loss of high-resolution information.

Conclusions:

• Electron irradiation can paradoxically improve the appearance of cryosectioned biological samples by reducing artifacts.
• The observed improvements are artifacts due to differential shrinkage, not genuine structural changes.
• Researchers must be aware of these beam-induced artifacts to avoid misinterpretation of high-resolution cryo-electron microscopy data.