How is retrograde flow of cytoplasmic actin connected to retrograde transport of attached particles?

Examples of crawling locomotion of cells:

    * wound closure and healing

    * invasiveness of cancer cells (including penetration into and out of blood vessels in metastasis)

    * (Hypothetical) Use of cell traction to realign type I collagen to form tendons, ligaments and skeletal muscles


What exerts the forces in the crawling locomotion of tissue cells?

Actin polymerizes (molecules of actin protein diffuse through the cytoplasm, and are somehow induced to polymerize ("gel?")) along some parts of the edges of each cell.

This polymerization of actin pushes forward thin stiff flat sheets of cytoplasm called "lamellipodia"

(And sometimes rod-like filopodia and small, hemispherical "blebs" or lobopodia.)

Sheets of polymerized actin get pulled rearward toward the middle of each cell.

Anything that adheres to the outer surface of the plasma membrane gets pulled rearward. (Including micron-sized particles of styrene, metal, or anything)

This is called "retrograde transport."

(Particles get pulled rearward on both the "top" and the "bottom" of crawling cells.)

video of particle transport

Cells cultured either on gels or on sheets of rubber pull rearward and distort these materials.

The force that moves the particles and distorts the gels and rubber is called "traction".
diagram of locations and directions of traction