Barbed ends rule

摘要

To explore their surroundings, cells use probes of various shapes. Whether the probes are broad and flat, or long and thin, seems to be regulated by proteins at the growing ends of actin filaments. Cells reach out with various structures as they crawland interact with their environment. Broad, flat protrusions called lamellipodia surge forward and adhere to surfaces, allowing cells to gain traction and move. Long, thin protrusions called filopodia extend several micrometres ahead of the cells, appearing to explore extracellular surfaces, sense guiding cues and direct the rest of the cell. Extension of both lamellipodia and filopodia is powered by polymerization of the structural protein actin into filaments. As the filaments lengthen, the fast-growing 'barbed' ends push the cell's boundary membrane outward. Lamellipodia protrude when the actin filaments at the leading edge are short and highly branched; by contrast, filopodia arise when the filaments are long, unbranched, and arranged in tight, parallel bundles. But given the similarities in the actin polymerization machinery that drives the two types of protrusion, what determines whether lamellipodia or filopodia form? Marisan Mejillano and colleagues, writing in Cell, report that the answer lies with proteins that control actin polymerization at the filament barbed ends.