ExAPC Microscopy Visualizes Intracellular Structures with High Clarity

A research team from the University of Tsukuba has demonstrated how ExAPC microscopy enables precise visualization of cellular architecture without fluorescent labeling. The study, published in The FEBS Journal, highlights how this technique overcomes long‑standing imaging challenges to reveal fine details of organelle organization and behavior in living cells.

Cells contain numerous organelles that perform essential functions, including the nucleus and mitochondria. In addition to these membrane‑bound components, cells include nonmembranous organelles formed through the assembly of molecules without enclosing membranes. The size, shape, and distribution of these structures play important roles in maintaining cell function and determining cellular responses.

Fluorescence microscopy has been widely used to study such organelles but is limited by phototoxic effects from strong illumination, dye bleaching, and the restricted number of structures that can be observed simultaneously. Phase contrast microscopy, which allows visualization of transparent structures without staining, offers a safer approach yet traditionally suffers from halo artifacts that blur images.

In their study, the Tsukuba researchers used ExAPC microscopy, an advanced version of phase contrast imaging that contains optical adjustments to suppress halo formation. This innovation provided clear, high‑resolution, label‑free views of multiple organelles, including nuclei, nucleoli, and mitochondria, throughout dynamic processes such as the cell cycle. For the first time, ExAPC also allowed the distinct visualization of biomolecular condensate‑like structures whose compositions remain unknown.

Examination of lipid droplet growth, mitochondrial fission and fusion, and cellular responses to drugs revealed that while individual organelles display diverse behaviors, the overall system maintains a high degree of order and stability.

The authors note that ExAPC microscopy provides a valuable tool for examining living cells in their native state, free from fluorescent dyes or phototoxic damage. Its capacity to visualize the spatial and temporal dynamics of intracellular structures can shed light on how changes in organelle morphology or positioning contribute to disease.