Filopodia

Overview

Filopodia extending from a cell.

Filopodia are slender cytoplasmic projections that extend from the leading edge of migrating cells. They are composed of actin filaments and are involved in sensing the environment, cell movement, and cell-cell communication. Filopodia are dynamic structures that can rapidly extend and retract, allowing cells to explore their surroundings and respond to external signals.

Structure

Filopodia are primarily composed of tightly bundled parallel actin filaments. These filaments are cross-linked by actin-binding proteins such as fascin and fimbrin, which provide structural support and stability. The actin filaments in filopodia are oriented with their barbed ends pointing towards the tip, facilitating rapid polymerization and extension.

Function

Filopodia play a crucial role in various cellular processes, including:

• Cell Migration: Filopodia are essential for the directed movement of cells. They probe the extracellular matrix and guide the cell in the direction of movement.
• Environmental Sensing: Filopodia act as sensory organelles, detecting chemical and mechanical cues in the environment. This allows cells to respond to changes in their surroundings.
• Cell-Cell Communication: Filopodia can form connections with other cells, facilitating communication and the transfer of signals.

Formation

The formation of filopodia is initiated by the nucleation of actin filaments at the cell membrane. This process is regulated by small GTPases such as Cdc42, which activate downstream effectors that promote actin polymerization. The elongation of filopodia is driven by the addition of actin monomers at the barbed ends of the filaments.

Role in Development and Disease

Filopodia are involved in various developmental processes, including axon guidance and tissue morphogenesis. They are also implicated in pathological conditions such as cancer metastasis, where they contribute to the invasive behavior of cancer cells.

Related pages

• Actin
• Cell migration
• Cytoskeleton
• GTPase