RESEARCH Albert Einstein College of Medicine Segall LAB PAGES

Dictyostelium movies

Aggregation and the Streamer F mutation

Dictyostelium demonstrates a dramatic synergy of development and cell motility when subjected to starvation. Cells begin secreting what is normally an intracellular messenger - cyclic AMP (cAMP). In addition, they begin to express G protein coupled receptors for cAMP. When these receptors bind cAMP, they stimulate chemotaxis towards higher extracellular concentrations of cAMP and also increased synthesis and secretion of cAMP. The net result is movement of the cells towards common centers, which eventually form fruiting bodies consisting of a stalk with a sorus (which contains spores) at the top.

Aggregation of XP55.(2.1 Mb)

The wild-type strain XP55 is shown aggregating on a bacterial growth plate. An aggregate of cells forms a fruiting body that protrudes upward. At the same time, a pseudoplasmodium (slug) of aggregated cells also moves into the field of view, forms a Mexican hat, and starts to form a fruiting body.

Waves during XP55 Aggregation (1.2 Mb)

In order to see the pulsatile responses of the Dictyostelium cells to the waves of cAMP that are generated, a higher time lapse interval was used. The waves are weak compared to what is seen with streamer F mutants.


Effect of the Streamer F mutation on Aggregation (2.5 Mb)

Streamer F mutants (NP368 shown here) lack the cGMP-specific phosphodiesterase that degrades the intracellular messenger cGMP that regulates (among other things) myosin heavy chain aggregation. These cells show a prolonged response to the chemoattractant cAMP, that is reflected in dramatic waves moving outward from the aggregates. In addition, the external cAMP signal appears to be propagated further through the cell mass, resulting in the extensive streams of cells moving towards the aggregates (hence the term "streamer").

Cell movement in streams of Streamer F (2.9 Mb)

A second, higher magnification of a region of the streams later in aggregation.


Chemotactic Responses to a Micropipet

Dictyostelium cells are chemotactic to a number of chemicals. During growth phase, they orient in gradients of folate, which may aid in finding food bacteria. During aggregation, they secrete cAMP(!) and, in addition, are chemotactic towards the secreted cAMP. The result of this positive feedback loop is the aggregation process that is characteristic of Dictyostelium when starved. All the movies below are of starved Dictyostelium cells responding to a micropipet filled with cAMP.

Low Magnification (1.1Mb)

Cells from the entire field of view orient towards the pipet.

Medium Magnification (1.2 Mb)

Even though cells are highly polarized, two cells show that they can reorient by producing new pseudopods from the center of the cell body.


Another Medium Magnification (1.0 Mb)

In this example, the pipet makes a cell go in a circle, showing that there can be a strong polarity for responsiveness.

High magnification (1.3 Mb)

Another example of how cells can generate pseudopods from any part of the body. At high magnification, the 3 dimensional nature of the movement of these cells is clearer - there are out of focus elements reflecting movement above the surface towards the pipet (which is somewhat above the cell).


Another High Magnification (1.5 Mb)

Note in both high magnification movies that the expanding pseudopod is phase dense but lacks visible organelles, consistent with being a concentrated filamentous actin meshwork.

Myosin Minus Cells at High Magnification (1.2 Mb)

These cells lack myosin heavy chain, yet the small cells that have been grown on a surface are clearly able to orient and move towards the micropipet. This movie was collected by one of the founders of Dictyostelium research, Dr. Guenther Gerisch.



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