Rolling dice for cell size specification in plant leaf epidermis

One of the central questions in biology is how a cell specifies its size. Because size distribution often shows a characteristically skewed pattern in a tissue, there may be some stochastic option for determining cell size. However, the underlying mechanism by which the target distribution is established by organizing a cellular coin-toss remains elusive.

Associate Professor Kensuke Kawade at Okazaki Institute for Integrative Bioscience and National Institute for Basic Biology, in collaboration with Professor Hirokazu Tsukaya at the Graduate School of Science, the University of Tokyo, discovered that endoreduplication, which promotes cellular enlargement in the epidermal tissue of Arabidopsis thaliana, occurs randomly as a Poisson process throughout cellular maturation.

This finding enabled the team to effectively reproduce experimentally measured dynamics of endoreduplication with a simple mathematical model. They then investigated whether this model was sufficient to explain cell size variation in epidermal tissue. They generated an artificial cell size distribution using the mathematical model by considering the effects of endoreduplication on cell size specification. This analysis revealed that cell size was determined by endoreduplication-dependent exponential boosting, and size heterogeneity was induced by Poissonian endoreduplication dynamics.

These results link the probabilistic property of endoreduplication dynamics to cell size distribution, providing a theoretical background to explain how size heterogeneity is established within a leaf. This work will also contribute to a quantitative understanding of how stochastic dynamics generates steady-state biological heterogeneity. The results of this research were published in PLOS ONE on September 19th, 2017.