Lamellipodia

The lamellipodium (plural lamellipodia) (from Latin , "thin sheet"; pod, "foot") is a cytoskeletal protein actin projection on the leading edge of the cell. It contains a quasi-two-dimensional actin mesh; the whole structure propels the cell across a substrate. Within the lamellipodia are ribs of actin called microspikes, which, when they spread beyond the lamellipodium frontier, are called filopodia. The lamellipodium is born of actin nucleation in the plasma membrane of the cell and is the primary area of actin incorporation or microfilament formation of the cell.

Lamellipodia are found primarily in very mobile cells, for example the keratinocytes of fish and frogs, which are involved in the quick repair of wounds, crawling at speeds of 10–20 μm / min over epithelial surfaces. A lamellipodium separated from the main part of a cell by scratching across the cell with a pipette tip can continue to crawl freely about on its own.

Lamellipodia are a characteristic feature at the front, leading edge, of motile cells. They are believed to be the actual motor which pulls the cell forward during the process of cell migration. The tip of the lamellipodium is the site where exocytosis occurs in migrating mammalian cells as part of their clathrin-mediated endocytic cycle. This, together with actin-polymerisation there, helps extend the lamella forward and thus advance the cell's front. It thus acts as a steering device for cells in the process of chemotaxis. It is also the site from which particles or aggregates attached to the cell surface migrate in a process known as cap formation.

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