Is EM dead?

Cryo-soft X-ray tomography: a journey into the world of the native-state cell

One of the ultimate aims of imaging in biology is to achieve molecular localisation in the context of the structure of cells in their native state. Here, we review the current state of the art in cryo-soft X-ray tomography (cryo-SXT), which is the only imaging modality that can provide nanoscale 3D information from cryo-preserved, unstained, whole cells thicker than 1 μm. Correlative cryo-fluorescence and cryo-SXT adds functional information to structure, enabling studies of cellular events that cannot be captured using light, electron or X-ray microscopes alone.

Molecular probes to visualize the location, organization and dynamics of lipids

Cellular lipids play crucial roles in the cell, including in energy storage, the formation of cellular membranes, and in signaling and vesicular trafficking. To understand the functions and characteristics of lipids within cells, various methods to image lipids have been established. In this Commentary, we discuss the four main types of molecular probes that have significantly contributed to our understanding of the cell biology of lipids. In particular, genetically encoded biosensors and antibodies will be discussed, and how they have been used extensively with traditional light and electron microscopy to determine the subcellular localization of lipids and their spatial and temporal regulation. We highlight some of the recent studies that have investigated the distribution of lipids and their ability to cluster using super-resolution and electron microscopy. We also examine methods for analyzing the movement and dynamics of lipids, including single-particle tracking (SPT), fluorescence recovery after photobleaching (FRAP) and fluorescence correlation spectroscopy (FCS). Although the combination of these lipid probes and the various microscopic techniques is very powerful, we also point out several potential caveats and limitations. Finally, we discuss the need for new probes for a variety of phospholipids and cholesterol.