Discussion Points Regarding the Nature Paper by Burton and Taylor:

A) What is the evidence that the length of wrinkles is linearly proportional to the strength of whatever forces produce those wrinkles?

B) Are wrinkles in the rubber substrata produced... By tension, but not by pressure?

By pressure, but not by tension?

Sometimes by tension, and sometimes by pressure?

C) What do Burton and Taylor say is the advantage of substratum wrinkles, as compared with measuring distances of movement, as a measure of forces exerted by cells? Hint, which requires more sideways displacement of a cell's surface, in order to get a measurement?

D) Did previous theories agree, or disagree, about whether the cortical cytoplasm somehow more strongly contractile at the location of the cleavage furrow, as compared with other parts of the cell cortex?

E) If opposing theories agreed about the furrow cortex being more strongly contractile, then what did they disagree about?

F) Do Burton and Taylor discuss whether the increased amounts if actin and myosin move to the furrow site:

    By diffusion as monomers through the cytoplasm, and increased polymerization at the furrow location?

    By sideways flow of (already-polymerized) fibers of actin and myosin, along the inner surface of the plasma membrane?

G) In the photograph that Nature published on its cover, which forces produced those wrinkles?

    Constriction pulling of the contractile ring, pinching the cell in two? (Tension wrinkles? Or compression wrinkles?)

    Lateral flow of actin and myosin fibers toward the cleavage furrow, carrying those contractile proteins to form the contractile ring? (Tension wrinkles? Or compression wrinkles?)

H) Could a believer in the theory of polar relaxation (as the cause of contractile ring formation) make a logical argument that the evidence in this paper is just as much consistent with polar relaxation as it is with (overlapping) polar stimulation?

I) What specific parts of the observations are most relevant to this issue?

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