In situ high-resolution cryo-EM reconstructions from CEMOVIS

Vitreous sectioning (CEMOVIS) is an alternative to FIB milling for generating thin samples suitable for cryo-EM imaging. We show that CEMOVIS samples preserve the high-resolution structural details of macromolecular complexes such as the 60S ribosome, despite the visible macroscopic damage visible in the samples.

Cryo-electron microscopy can be used to image cells and tissue at high resolution. To ensure electron transparency, the sample thickness must not exceed 500 nm. Focused-ion-beam (FIB) milling has become the standard method for preparing thin samples (lamellae); however, the material removed by the milling process is lost, the imageable area is usually limited to a few square micrometres and the surface layers sustain damage from the ion beam. We have examined cryo-electron microscopy of vitreous sections (CEMOVIS), a technique based on cutting thin sections with a knife, as an alternative to FIB milling. Vitreous sections also sustain damage, including compression, shearing and cracks. However, samples can be sectioned in series, producing many orders of magnitude more imageable area compared to lamellae, making CEMOVIS an alternative to FIB milling with distinct advantages. Using two-dimensional template matching on images of vitreous sections of Saccharomyces cerevisiae cells, we reconstructed the 60S ribosomal subunit at near-atomic resolution, demonstrating that, in many regions of the sections, the molecular structure of these subunits is largely intact, comparable to FIB-milled lamellae.