Figure 1. The cartoon above indicates a tissue containing two different cell types, indicated by the blue and green ovals. How can a tissue sense the percent of the cells indicated in green to regulate its composition? If the green cells secrete a characteristic factor, the concentration of the factor in the tissue will be a function of the percent of green cells in the tissue. We found a paradigm for this sort of factor in Dictyostelium – when cells overgrow their food supply and starve, some cells starve while other cells are still finding and eating food. To let the population know how many cells are starving, the starved cells secrete a characteristic factor called CMF, and we elucidated the CMF diffusion physics and signal transduction pathway.
Figure 2. 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.
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