During development, cells undergo transitions between states that require coordinated and often rapid changes to their transcriptomes. These transitions are considered a mechanism by which cells ‘commit’ to a particular state; however, how these rapid changes in gene expression profiles are elicited and coordinated is not clear. Now, Jonathan Chubb and colleagues investigate this question using the social amoeba Dictyostelium, which developmentally shifts from a single-cell organism to a multicellular ‘fruiting body’ in response to nutrient shortages. By performing single-cell RNA sequencing on cells sampled across this developmental gradient, the authors identify a significant ‘jump’ in global gene expression near the onset of aggregation that marks a discrete shift in cell state. They then show that the timing of this jump coincides with the onset of collective cyclic AMP (cAMP) oscillations. By imaging transcription and signalling together, and controlling cAMP pulses optogenetically, they identify particular jump genes that switch on or off during the progression of cAMP signalling, where different genes react to different oscillation frequencies. Additional temporal and spatial regulatory inputs, including starvation state of each cell, regulate these transitions and contribute to the heterogeneity within cellular states. Together, these data suggest that collective cAMP signalling coordinates rapid transcriptomic jumps during Dictyostelium development, but additional inputs may be required for full commitment.
