In our research, we have combined theoretical modeling with confocal fluorescence microscopy to study podosomes, small, actin-rich structures that immune cells use to contact, probe, and remodel the biomaterial beneath them, and to ask how these structures sense the mechanical properties of their surroundings. On the cover of the September 1 issue of Biophysical Journal, we show a single living cell alongside a time-lapse view of its podosomes, capturing the restless, oscillatory motion at the heart of our work.
The image shows one cell spread across its substrate, its ruffled edge fanning outward. The bright, textured field covering the cell body is a dense population of podosomes, each a tiny point of concentrated actin. Running down the center of the image is a time-lapse montage: a sequence of narrow vertical strips, each sampled at a slightly later moment, that follows the same region as its podosomes cycle through protrusion and retraction. Read across, the strips trace the rhythm of the podosome population, turning a fleeting, sub-micron motion into something that the eye can take in within a single still frame.
The raw data behind the cover were collected by confocal imaging of a living cell whose actin cytoskeleton was fluorescently labeled and then rendered in color to bring out the cell’s spreading edge and the granular texture of its podosomes. What looks at first like a static portrait is in fact a record of movement: individual podosomes do not stay fixed but continually rise and fall against the surface, and it is this collective, oscillatory behavior that the central montage is meant to reveal.
Podosomes are among the primary tools that cells use to feel their physical surroundings, and that sense of touch matters well beyond a single field. Immune cells such as dendritic cells and macrophages rely on podosomes to move through the body's tissues, and closely related structures appear when cells cross tissue barriers or when tumor cells invade the tissue around them. In all of these settings, cells must continually read the mechanical state of their environment—soft or stiff, relaxed or under tension—and podosomes are where much of that reading takes place. For anyone curious about how something as small as a cell can touch and interpret the world around it, the cover offers a glimpse of that process in motion. You can find more about our work at https://faculty.ustc.edu.cn/gongze.
— Chenxia Zhao, Xiaopeng Fan, Ruihao Xue, Keshu Feng, Liu Wang, and Ze Gong