Ammonia differentially suppresses the cAMP chemotaxis of anterior-like cells and prestalk cells indictyostelium discoideum |
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Authors: | Ira N Feit Erika J Medynski Michael J Rothrock |
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Institution: | (1) Department of Biology, Franklin and Marshall College, 17603 Lancaster, PA, USA |
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Abstract: | A drop assay for chemotaxis to cAMP confirms that both anterior-like cells (ALC) and prestalk cells (pst cells) respond to
cAMP gradients. We present evidence that the chemotactic response of both ALC and pst cells is suppressed by ammonia, but
a higher concentration of ammonia is required to suppress the response in pst cells. ALC show a chemotactic response to cAMP
when moving on a substratum of prespore cells in isolated slug posteriors incubated under oxygen. ALC chemotaxis on a prespore
cell substratum is suppressed by the same concentration of ammonia that suppresses ALC chemotaxis on the agar substratum in
drop assays. Chemotaxis suppression is mediated by the unprotonated (NH3) species of ammonia. The observed suppression, by ammonia, of ALC chemotaxis to cAMP supports our earlier hypothesis that
ammonia is the tip-produced suppressor of such chemotaxis. We discuss implications of ammonia sensitivity of pst cells and
ALC with regard to the movement and localization of ALC and pst cells in the slug and to the roles played by ALC in fruiting
body formation. In addition, we suggest that a progressive decrease in sensitivity to ammonia is an important part of the
maturation of ALC into pst cells. |
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Keywords: | Ammonia anterior-like cells chemotaxis Dictyostelium |
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