3D ANALYSIS OF CELL-MOVEMENT DURING NORMAL AND MYOSIN-II-NULL CELL MORPHOGENESIS IN DICTYOSTELIUM

To gain insights into the possible guidance mechanisms used by Dictyos telium cells as they undergo morphogenesis, we have used time-lapse co mputational optical-sectioning microscopy to visualize and quantify th e three-dimensional (3D) trajectories of both normal (Ax2) and myosin- II-null cells. To accomplish this, we typically collected 30-60 time-l apse 3D images every 2-3 min at the earliest multicellular stage, the mound. These time-lapse data were used to generate 3D movies of morpho genesis and to construct 3D trajectories for individual cells. In cont rast to previous 2D time-lapse cinematography studies which revealed p redominantly spiral trajectories of Ax2 cells in the mound, we have fo und a complex assortment of motile behaviors: some cells jiggled in pl ace; others appeared to follow either linear or spiral trajectories; s ome cells reversed their directions; and others apparently converted f rom one motile behavior to another. These results suggest that a numbe r of different, potentially competing cell-guidance mechanisms are ope rative in the mound. To assess one molecular mechanism underlying this assortment of motile behaviors, we have examined cell locomotion in a mutant, namely, in myosin-II-null cells which never develop beyond th e mound. Previous studies had shown that these cells can crawl, albeit somewhat slowly, on a 2D substrate. We also found, at the earliest st ages of myosin-II-null mound formation, some directed cell locomotion. But later, as the mound condensed into a tightly packed cell conglome rate, extended cell trajectories disappeared, and instead virtually al l of the cells jiggled in place. Thus, our results suggest that myosin -II is absolutely essential for normal 3D ameboid locomotion. (C) 1995 Academic Press, Inc.