What are possible functions of dynamic gene regulation?
Molecular time-sharing through dynamic pulsing in single cells. In collaboration with the Elowitz and Garcia-Olalvo labs, using time-lapse microscopy we found that multiple alternative sigma factors activated in ~1 hour pulses in a stochastic and repetitive fashion. Analysis of sigma factor pairs revealed that two sigma factors rarely pulse simultaneously, and some pairs are anticorrelated. These results indicate that alternative sigma factor species can effectively ‘time-share,’ or take turns utilizing, RNAP. Time-sharing provides a mechanism for cells to dynamically control the distribution of cell states within a population. Since core molecular components are limiting in many other biological systems, time-sharing may represent a common mode of regulation. See Park et al., 2018.
Fluctuations of the transcription factor ATML1 can pattern giant cells in the Arabidopsis sepal. In collaboration with Dr. Adrienne Roeder and Professor Henrik Jonsson we have examined the role of stochasticity in the expression of the transcription factor ATML1 in giant cell formation in Arabidopsis sepals. Although ATML1 is expressed in all epidermal cells, we find that ATML1 functions in a sensitive dosage dependent manner, in which high levels specify giant cells. Using modelling, live imaging, and computational image analyses we found that ATML1 fluctuates in all epidermal cells. If ATML1 levels surpass a soft threshold during the G2 phase of the cell cycle, the cell has a high probability of entering endoreduplication and becoming giant. Otherwise, the cell divides. Our results suggest a fluctuation patterning mechanism for how cellular decisions can be initiated through random processes.