The interaction of actin filaments with the ATPase motor protein myosin II is known to mediate cellular motility, contraction, adhesion, and shape changes, including cytokinesis. However, questions remain about the precise mechanisms involved in these actomyosin-based processes, to include the relative contribution of myosin II’s ability to cross-link actin filaments versus perform the ATP-dependent sliding of filaments. In the present study we use the more soluble and less toxic and photosensitive derivative of the myosin II ATPase inhibitor blebbistatin –
termed para-aminoblebbistatin – to test the involvement of myosin II motor function in cytokinesis in sea urchin early embryos and centripetal flow in sea urchin coelomocytes. Our results in PAB treated embryos suggest that myosin II motor function is not required for the recruitment of myosin II to the nascent cytokinetic contractile ring (CR) but is required for the CR to contract and accomplish cell division. In coelomocytes, PAB treatment leads to a disruption of the actomyosin structural organization and an inhibition of central centripetal motility. In this study we also report the application of a new form of super-resolution microscopy termed Expansion Microscopy (ExM) to mammalian tissue culture cells and sea urchin coelomocytes. Preliminary data of ExM on coelomocytes suggest that this method of
super-resolution microscopy can be successfully applied to imaging actomyosin in these cells and therefore it offers an opportunity for inexpensive, in-house super-resolution imaging.