In actin-based movement, what does cell crawling primarily depend on?

• A. Dynein-driven sliding of microtubules along the cortex to push the membrane forward
• B. Polymerization of microtubules at the leading edge coupled to adhesion to the substrate
• C. Passive membrane flow driven solely by osmotic water influx
• D. Polymerization of actin at the leading edge coupled to adhesion to the substrate (with myosin-based contraction aiding rear retraction)

Answer: (D)

Verified step by step guidance

1. Understand that cell crawling is a type of cell motility primarily driven by the cytoskeleton, specifically the actin filaments, rather than microtubules or passive processes.
2. Recognize that the leading edge of a crawling cell extends forward by the polymerization of actin filaments, which pushes the plasma membrane outward.
3. Note that this forward protrusion is stabilized by the formation of adhesions between the cell and the substrate, allowing the cell to gain traction.
4. Acknowledge that myosin motor proteins generate contractile forces at the rear of the cell, helping to pull the cell body forward and retract the trailing edge.
5. Combine these concepts to conclude that cell crawling primarily depends on actin polymerization at the leading edge coupled with adhesion to the substrate, with myosin-based contraction assisting in rear retraction.