Lamillipodia (singular lamillipodium) are thin, but broad (‘sheet-like’) membrane extensions of cytoplasm at the leading edge of motile cells (e.g., immune cells, neurons). They lack any major organelles, but like their growth cone companions they are composed of a dense and dynamical network of actin filaments (sometimes referred to as ‘microspikes’). Cell migration (protrusion and retraction of cells) is inextricably linked to lamillipodia, as well as with filapodia. In the absence of the later emerging filapodia, lamillipodia probe and sense the rigidity or stiffness of the extracellular matrix, in a process called ‘rigidity sensing’ or ‘mechanosensing’, which together with focal adhesions generate changes to the actin filament elements. The forces produced by these changes result in membrane protrusion and subsequent lamillipodial growth at the cell front and retraction at the rear of the cell. Protrusion is a consequence of the continuous growth of actin filaments, and retraction by the release of adhesive contacts emanating from extracellular matrix proteins.
See Actin, Adhesion molecules, Cell adhesion molecules (CAMs), Cell locomotion, Cell migration, Extracellular matrix, Filapodia, Flagella, Growth cone, Neural cell adhesion molecule (N-CAM), Organelles, Proteins