Interactions between myosin and actin crosslinkers control cytokinesis contractility dynamics and mechanics.
BACKGROUND
Contractile networks are fundamental to many cellular functions, particularly cytokinesis and cell motility. Contractile networks depend on myosin-II mechanochemistry to generate sliding force on the actin polymers. However, to be contractile, the networks must also be crosslinked by crosslinking proteins, and to change the shape of the cell, the network must be linked to the plasma membrane. Discerning how this integrated network operates is essential for understanding cytokinesis contractility and shape control. Here, we analyzed the cytoskeletal network that drives furrow ingression in Dictyostelium.


RESULTS
We establish that the actin polymers are assembled into a meshwork and that myosin-II does not assemble into a discrete ring in the Dictyostelium cleavage furrow of adherent cells. We show that myosin-II generates regional mechanics by increasing cleavage furrow stiffness and slows furrow ingression during late cytokinesis as compared to myoII nulls. Actin crosslinkers dynacortin and fimbrin similarly slow furrow ingression and contribute to cell mechanics in a myosin-II-dependent manner. By using FRAP, we show that the actin crosslinkers have slower kinetics in the cleavage furrow cortex than in the pole, that their kinetics differ between wild-type and myoII null cells, and that the protein dynamics of each crosslinker correlate with its impact on cortical mechanics.


CONCLUSIONS
These observations suggest that myosin-II along with actin crosslinkers establish local cortical tension and elasticity, allowing for contractility independent of a circumferential cytoskeletal array. Furthermore, myosin-II and actin crosslinkers may influence each other as they modulate the dynamics and mechanics of cell-shape change.
Reichl
Elizabeth M
EM
Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Ren
Yixin
Y
Morphew
Mary K
MK
Delannoy
Michael
M
Effler
Janet C
JC
Girard
Kristine D
KD
Divi
Srikanth
S
Iglesias
Pablo A
PA
Kuo
Scot C
SC
Robinson
Douglas N
DN
D000199:Actins / Q000378:metabolism*; D000818:Animals; D001696:Biomechanical Phenomena; D048749:Cytokinesis / Q000502:physiology*; D004023:Dictyostelium / Q000502:physiology*; D024462:Myosin Type II / Q000502:physiology*
D000199:Actins; D024462:Myosin Type II