Figure 5.

Actin-based structures in cell adhesion and fusion. (A) After establishing a fusion area between fusing partners, the cell-initiating fusion extends different size actin-based (red lines) protrusions at its edge. (B) Podosomes (stars), consisting of actin center (red) and peripheral adhesion proteins (blue), of the fusion-initiating cell migrate from the cell interior to the pre-fusion area. (C) One of the protrusions (usually the longest) acts as a fusopod-initiating fusion and creates the fusion pore. (D) Reorganization of actin filaments expands fusion pore, allowing migration of podosomes from donor to fusion partner (Modified from Faust et al., Ref. [42]). (E) Zipper-like structures (ZLSs) at the surface of adhering MGCs formed in response to foreign materials. Membranes of adjacent cells adhere via adhesion proteins (gray ovals). Podosomes (red and blue stars) fuse into giant actin globules (red) surrounded by adhesion proteins (blue) and attached by smaller actin globules to the membrane. Actin globules are evenly spaced (resembling the zipper) along the membrane (modified from Balbyev et al., Ref. [105]). (F) Image of mouse macrophage showing podosomes (yellow). The nucleus (blue) is stained with DAPI. Actin is stained red with Rhodamine-Phalloidin; podosomes look yellow because of the high actin concentration and image overexposure. The magnification bar is equal to 10 μm.