Morphogenetic Movements Contributing to Cell Aggregation in Dictyostelium Discoideum Wild-Type and Streamer F Mutants

116 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987.We investigated some cell processes which may contribute to cell aggregation patterns in the social ameba Dictyostelium discoideum. Aggregation is known to be mediated by chemotaxis up periodic extracellular cAMP gradients; however, the details of cell movement during this stage of development have not been reported. We recorded cell behavior by time-lapse cinemicroscopy and collected cell motion and cell shape data by computer-aided planimetry. Analyses of these data for wild-type strains of Dictyostelium reveals: (a) A pre-aggregation stage of synchronized cringe-chemokinesis oscillations of 5 minute period where amebae stop (speed cringe) and decrease in area (areal cringe) for about fifteen seconds, then extend pseudopods and speed up (positive orthokinesis). After about two minutes at increased speed, amebae slow down to a basal (unstimulated) velocity. (b) Aggregation stage behavior alternating between chemotaxis (for two of every six minutes) and a behavior we call quivering. In the absence of cAMP, quivering amebae extend pseudopods periodically in random directions but do not translocate. Isolated aggregation stage amebae can quiver in place for over one hour. Quivering amebae respond to artificial gradients of cAMP by accurate and rapid chemotaxis, but only for the duration of the stimulus. (c) Aggregating streamerF (stmF) mutants are defective in the intracellular degradation of cAMP-induced cGMP and exhibit periodic two minute long cessation of motililty and shape change in situ referred to as pausing. These mutants, unlike wild-type, remain elongate and oriented with respect to the previous cAMP gradient for many minutes after stimulation. We infer that elevated cGMP causes pausing and maintains elongation and orientation. (d) We report the novel observation that preaggregation stage stmF amebae exhibit autonomous, rapid oscillations (90 second, two-fold changes) in planar area, which eventually develop into synchronous, slow (5 minute) areal oscillations, corresponding to the cringe-chemokinesis oscillations in wild-type amebae.This work identified several components of Dictyostelium cell behavior which contribute to cell aggregation in this organism. The observations on stmF mutants implicate cGMP in the regulation of chemoattractant-induced cell elongation and orientation. Aggregation patterns in Dictyostelium involve morphogenetic movements of up to 10$\sp{6}$ amebae. Chemotaxis contributes to pattern formation, while quivering and stmF pausing are mechanisms for pattern stabilization and hyperstabilization, respectively, in Dictyostelium aggregation.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD