To tilt or not to tilt? Strategies for in situ cryo-EM data collection

Recent breakthroughs in single-particle cryogenic electron microscopy (cryo-EM) and protein structure prediction have transformed our ability to resolve molecular structures. Since we have now experimentally determined, or can confidently predict, the structures of a significant portion of the proteome, and since workflows for imaging in cells are established, the stage is set for applying cryo-EM to understand the molecular basis of complex cellular functions. This review explores a spectrum of data collection strategies-from 2D approaches to tomography-used for in situ cryo-EM. We discuss their relative merits in addressing key biological questions and the need to tailor them towards experimental goals. Improvements in theoretical and practical understanding of the challenges for in situ cryo-EM are necessary for optimizing data collection strategies and pushing the boundaries of structural cell biology.