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How can a tissue sense the percent of type A cells to regulate
its composition? If the type A cells secrete a characteristic
factor, the concentration of the factor in the tissue will be
a function of the percent of type A cells in the tissue.
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When Dictyostelium cells starve, they begin secreting a glycoprotein
called conditioned medium factor (CMF). When there is a high density
of starved cells, as indicated by a high concentration of CMF, the
cells begin expressing some of the genes involved in development and
aggregate using pulses of cAMP as a chemoattractant. CMF regulates
gene expression via a G protein-independent pathway, and simultaneously
regulates cAMP signal transduction via a G protein-dependent pathway.
 The
CMF pathway (click on image
to enlarge).
Key Papers
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A
single cell-density sensing factor stimulates distinct signal transduction
pathways through two different receptors. Deery, W.J., Gao, T.,
Ammann, R.A., and Gomer, R.H. J. Biol. Chem. 2002 277,
31972-31979.
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A
putative receptor mediating cell-density sensing in Dictyostelium.
Deery WJ, Gomer RH J Biol Chem 1999 274:34476-82
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Cell
density sensing mediated by a G protein-coupled receptor activating
phospholipase C. Brazill DT, Lindsey DF, Bishop JD,
Gomer RH. J Biol Chem 1998 273:8161-8
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The
CMF pathway (click on image
to enlarge).