lamellipoden

Lamellipoden, also known as lamellipodia, are broad, sheet-like protrusions at the leading edge of many migrating animal cells. They are primarily composed of a dense, branched network of actin filaments and are driven by actin polymerization against the plasma membrane, enabling cells to explore their environment and generate traction for movement.

Structural features include a dense, branched actin network formed largely by the Arp2/3 complex, organized by actin-binding proteins such as the WAVE/SCAR complex. The lamellipodial network is relatively thin near the membrane and extends outward as a protrusive sheet. Filaments in lamellipodia display dynamic turnover with regulated capping and uncapping, allowing rapid remodeling in response to signals.

Regulation and dynamics are governed by signaling pathways that control actin polymerization. Activation of Rac family GTPases stimulates the WAVE/SCAR complex, which in turn activates Arp2/3 to promote new filament branches at the leading edge. Actin polymerization drives protrusion, while retrograde actin flow and the turnover of adhesion sites balance forward movement. Additional inputs from PI3K signaling, integrins, and microtubules influence directionality and persistence.

Relation to migration and cellular context: lamellipoden interact with nascent focal adhesions at the substrate, enabling traction and continuous exploration during migration. Different cell types and migratory modes exhibit variable lamellipodial activity, and some cells also deploy filopodia as supplementary protrusions. Abnormal lamellipodial dynamics can affect processes such as wound healing and cancer cell invasion.

Observations and study methods: lamellipoden are studied by fluorescence microscopy, with phalloidin staining highlighting F-actin and live imaging using GFP-tagged actin or actin-binding probes. Pharmacological disruption of actin dynamics, for example with cytochalasin D or latrunculin, rapidly diminishes lamellipodial protrusions.