A cell number-counting factor regulates group size in Dictyostelium by differentially modulating cAMP-induced cAMP and cGMP pulse sizes.
A secreted counting factor (CF), regulates the size of Dictyostelium discoideum fruiting bodies in part by regulating cell-cell adhesion. Aggregation and the expression of adhesion molecules are mediated by relayed pulses of cAMP. Cells also respond to cAMP with a short cGMP pulse. We find that CF slowly down-regulates the cAMP-induced cGMP pulse by inhibiting guanylyl cyclase activity. A 1-min exposure of cells to purified CF increases the cAMP-induced cAMP pulse. CF does not affect the cAMP receptor or its interaction with its associated G proteins or the translocation of the cytosolic regulator of adenylyl cyclase to the membrane in response to cAMP. Pulsing streaming wild-type cells with a high concentration of cAMP results in the formation of small groups, whereas reducing cAMP pulse size with exogenous cAMP phosphodiesterase during stream formation causes cells to form large groups. Altering the extracellular cAMP pulse size does not phenocopy the effects of CF on the cAMP-induced cGMP pulse size or cell-cell adhesion, indicating that CF does not regulate cGMP pulses and adhesion via CF's effects on cAMP pulses. The results suggest that regulating cell-cell adhesion, the cGMP pulse size, or the cAMP pulse size can control group size and that CF regulates all three of these independently.
Tang
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Howard Hughes Medical Institute and the Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005-1892, USA.
Ammann
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R
Gao
T
T
Gomer
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RH
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism; D000818:Animals; D001685:Biological Factors / Q000502:physiology*; D000242:Cyclic AMP / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism*; D004023:Dictyostelium / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics; D011953:Receptors, Cyclic AMP / Q000378:metabolism; D015398:Signal Transduction
D001685:Biological Factors; D015800:Protozoan Proteins; D011953:Receptors, Cyclic AMP; C101537:SmlA protein, Dictyostelium discoideum; C120918:countin protein, Dictyostelium discoideum; D000242:Cyclic AMP; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D019204:GTP-Binding Proteins; D006152:Cyclic GMP