Cell division: once and only once Free

The basic cell cycle machinery is highly conserved across eukaryotes, and yet mitotic behaviour in developing tissues must be tightly orchestrated in time and space. How do different cell types ensure the appropriate division pattern according to their fate and position? The stomatal lineage of the plant leaf provides a valuable model for the analysis of this question. The guard cells (GCs) of the stomata derive from a single division of a guard mother cell (GMC); these in turn are generated through self-renewing divisions of meristemoids. Transcription factors (SPEECHLESS, MUTE and FAMA) have been identified that regulate the transition from self-renewing to progenitor to terminally differentiated cell, but how are these fate transitions linked to changes in cell cycle pattern? Dominique Bergmann and colleagues now identify a D-type cyclin, CYCD7;1, that is specifically expressed in the GMC and ensures it divides in a timely and restricted manner to produce a pair of GCs. CYCD7;1 has canonical cyclin activity, but its expression is controlled by the MUTE and FAMA transcription factors to ensure it is transiently active in the GMC to promote just a single round of division. This mechanism links patterns of cell division to cell fate transitions to ensure coordination between these two developmental processes.