هجرة الخلايا

Cell migration occurs through three sequential steps: polarization, protrusion, and release. Polarization establishes a distinct cell front and rear, determining movement direction. Protrusion forms new adhesions at the leading edge, generating pulling forces. Release occurs at the trailing edge, where anti-adhesive signals retract focal adhesions, enabling the rear to follow forward.

Fibroblasts respond to growth factors and polarizing signals released during injury by protruding their membrane toward the signal, forming a leading edge. These protrusions adhere to the extracellular matrix through focal adhesion points, creating tensional forces that facilitate forward movement. Cyclic adhesion and release events at the trailing edge enable directional migration toward the injury site.

Collective cell migration involves groups of cells moving together while maintaining cell-cell junctions. Leader cells at the front form protrusions that pull the entire group forward. Unlike individual migration, collective migration preserves cell-to-cell connections, allowing coordinated movement of multiple cells ranging from tens to thousands, covering distances from microns to centimeters.

During wound healing, epithelial cells at the injury site follow a collective migration pattern. Cells facing the wound lead migration of rear-end cells, filling the wound in a coordinated manner while loosely held together by cell-cell junctions. This organized movement allows keratinocytes to form sheets that cover the injury site and eventually form scar tissue.

Focal adhesion points are contact sites where cell membranes adhere to the extracellular matrix. These adhesions create tensional forces that facilitate forward cell movement at the leading edge. At the trailing edge, localized anti-adhesive signals initiate focal adhesion retraction, enabling cyclic adhesion and release events that drive directional migration.

Metastatic cancer cells produce special membrane protrusions called invadopodia that enable migration away from the primary tumor location. These protrusions help cancerous cells break down tissue barriers and invade other tissues at secondary locations. In contrast, benign tumor cells lack this migration capability and proliferate only at the primary site.

Cell migration is critical for embryological development, tissue repair and regeneration, immune response, and maintaining adult tissues. During development, neural crest cells migrate to the periphery to form the peripheral nervous system. During wound healing, cells migrate to cover injury sites. Additionally, endothelial cells migrate collectively to develop new blood vessels, supporting organism viability throughout life.