Abstract
Diploid budding yeast (Saccharomyces cerevisiae) can adopt one of several alternative differentiation fates in response to nutrient limitation, and each of these fates provides distinct biological functions. When different strain backgrounds are taken into account, these various fates occur in response to similar environmental cues, are regulated by the same signal transduction pathways, and share many of the same master regulators. I propose that the relationships between fate choice, environmental cues and signaling pathways are not Boolean, but involve graded levels of signals, pathway activation and master-regulator activity. In the absence of large differences between environmental cues, small differences in the concentration of cues may be reinforced by cell-to-cell signals. These signals are particularly essential for fate determination within communities, such as colonies and biofilms, where fate choice varies dramatically from one region of the community to another. The lack of Boolean relationships between cues, signaling pathways, master regulators and cell fates may allow yeast communities to respond appropriately to the wide range of environments they encounter in nature.
Highlights
A) Alternative cell fates: Biology ain’t always Boolean Most tissues contain multipotent stem cells-- i.e. cells able to differentiate into one or more cell types
These observations suggest that Boolean logic may apply to cell-fate choice—i.e. a particular fate is adopted in response to the presence or absence of a particular combination of signals
The Rgt2 /glucose induction pathway, which is activated by glucose, represses Ime2 protein stability [248, 249], the Hog1 MAPK pathway, which responds to high osmolarity, inhibits pseudohyphal differentiation [250, 251], and the cell wall integrity pathway, which responds to cell-wall stress, is required both to maintain quiescent cells [252, 253] and for pseudohyphal differentiation [254,255,256]
Summary
A) Alternative cell fates: Biology ain’t always Boolean Most tissues contain multipotent stem cells-- i.e. cells able to differentiate into one or more cell types. In the context of differentiation choices, the amount of input could reflect the concentration of a particular environmental cue or the level of activation of a given signaling pathway. C) A caveat regarding comparing laboratory and natural strains Regulation of cell differentiation by nutrient environment has been studied in many different laboratory strains of yeast.
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