Cortical tension powered by myosin II is required for blebbing.

<p>(A) A cell expressing GFP-myosin II was cut, and the dynamics of myosin II in the anucleate fragments were observed under confocal microscopy. Myosin II was not observed along the leading edges of the blebs immediately after extension (arrows), and cortical myosin II remained in the basal region. (B) Kymographs of the dynamics of phase contrast and fluorescence images in the rectangles in panel A. (C) The frequency of blebbing in the anucleate fragments of wild-type (AX2), myosin II-null (HS1), and blebbistatin-treated wild-type cells. (D) A wild-type cell expressing GFP-ABD was observed under pressure applied via an agar block overlay. The cell frequently extended blebs under pressure (arrow). (E) Kymographs of the dynamics of phase contrast and fluorescence images in the rectangles shown in D. (F) Frequency (times per 5-min period) of blebbing with and without an agar overlay (n = 20). (G) After a myosin II-null cell was cut (14.1 sec), the anucleate fragment was pressed with an agar block (293.9–317.7 sec). DIC microscopy shows that the blebs extended under the pressure of the agar (arrows). Bars, 5 μm.