Eberhard Bodenschatz, Carsten Beta, Albert Bae, and Gabriel Amselem
MPI for Dynamcis and Self-Organization, Goettingen, Germany
We report on chemotaxis and cell migration of the eukaryote Dic-
tyostelium d.(Dicty) under well-controlled spatial and temporal stimuli
in microfluidic devices. First the chemotactic response to stationary,
linear gradients of cAMP will be reported. In shallow gradients of less
than 10?-3 nM/?m, the cells showed no directional response and ex-
hibited a constant basal motility. In steeper gradients, cells moved up
the gradient on average. In very steep gradients, above 10 nM/?m, the
cells lost directionality and the motility returned to the sub-threshold
level. We found cells to be able to chemotact well even when the aver-
age difference in receptor occupancy at the front and back of the cell
is estimated to be only about 10 receptor molecules. Then we report
experiments on the intracellular response of of PH-domain proteins to
well controlled chematractant gradients. We use the photo-chemical
release of caged cAMP in microfluidic devices to expose single chemo-
tactic cells to spatio-temporally well controlled chemoattractant stim-
uli (switching time approx. 0.5 sec and arbitrarily shaped gradients).
We found that the translocation signal sets in with a finite response
only for steep gradients. At shallow gradients no translocation signal
could be measured. A theory describing polarization of the intracel-
lular signaling system will be presented. This work is in collaboration
with W. Loomis, H. Levine and W. Rappel at UCSD.