2.2. Definition and characteristics of filopodia
Filopodia, in contrast to lamellipodia, exhibit a slender, finger-like
morphology characterized by the formation of tightly bundled actin
filaments. These actin bundles are organized in a parallel fashion,
providing structural stability to the protrusion. Key regulatory
proteins involved in filopodia formation include fascin and members of
the Ena/VASP family [9,23,24]. The bundling of actin filaments
imparts rigidity to filopodia, allowing them to serve as exploratory
antennae for the cell. Filopodia play a critical role in cellular
sensing and directional migration. These structures are enriched with
receptors and sensors that enable cancer cells to perceive the
surrounding microenvironment. Through interactions with the ECM and
neighboring cells, filopodia contribute to the transmission of external
signals into the cell, influencing migratory responses [25,26].
Moreover, filopodia are involved in guiding cells during directional
migration, facilitating the navigation of cancer cells through complex
tissue architectures and aiding in processes such as intravasation and
extravasation during metastasis [18].
Together, lamellipodia and filopodia contribute to the directional
motility of cancer cells by extending the cell’s leading edge and
interacting with the extracellular matrix, thus aiding in metastasis and
invasion. Lamellipodia act as a motor pulling the cell forward, while
filopodia serve sensory or exploratory functions [9].