UC Berkeley

PtK1 cells lysed late in cell division in a medium containing the nonionic detergent Brij 58 and polyethylene glycol with continue to undergo cleavage after lysis. Maintenance of cleavage after lysis is dependent on the composition of the lysis medium; the pH must be around neutrality, MgATP must be present, and the free Ca++ concentration should be 1 microM for optimal constriction to occur. Cleavage can be stopped and reinitiated by raising and lowering the Ca++ levels in the lysis medium. Cleavage in the permeabilized cell is blocked by addition of phalloidin, cytochalasin B, and N-ethylmaleimide-modified myosin subfragment-1 to the lysis medium. This represents the first cell model system for studying cleavage since the pioneering studies of Hoffman-Berling in 1954.