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].