Timing is everything: transcription bursting in development

Differential mRNA expression is essential for driving cell type identity and cell fate transitions during tissue differentiation and organismal development. However, transcription kinetics are seemingly heterogeneous at a cell-to-cell level, occurring in a series of episodic bursts of nascent mRNA synthesis separated by refractory periods. This transcriptional bursting therefore affects both the speed and variability of developmental gene expression. Consequently, how transcription kinetics are modulated to control mRNA expression output remains an outstanding question in the field. This review examines recent literature on how these processes are modulated during differentiation and development, the theoretical models of transcription bursting, and the molecular mechanisms underlying transcription kinetics.