CLEM

CLEM stands for Correlative Light and Electron Microscopy, a set of correlated imaging methods that combine fluorescence light microscopy with electron microscopy to relate molecular or functional information to cellular ultrastructure.

In a typical CLEM workflow, regions of interest are first identified by light microscopy after labeling target molecules with fluorescent tags. The same sample is then processed for electron microscopy and imaged at higher resolution. Variants include sequential CLEM, where modalities are performed separately and aligned post hoc, and integrated CLEM, where light and electron imaging are performed on the same instrument or specimen stage, including cryo-CLEM for preserved, near-native states.

Applications include cell biology, neuroscience, virology, and pathology, enabling localization of proteins within organelles and mapping dynamic processes to ultrastructure.

Advantages and limitations: Provides molecular specificity with nanometer-scale ultrastructure, but requires careful sample handling and alignment; potential artifacts from fixation and labeling; specialized equipment and expertise; time-consuming.

History: The approach emerged in the late 1990s and 2000s as fluorescence imaging was integrated with electron microscopy to bridge light- and electron-based analyses.