Auxeticity in Stem Cells and Implications for the Epigenetic Landscape

Synopsis

Embryonic stem cells can differentiate into any one of the more than 220 cell types found in the adult human body. Upon differentiation,  they surrender the genomic plasticity that underlies such flexibility. This loss of plasticity is reflected in changes in the mechanical properties of the stem cell nucleus. Measurements of the elastic properties of cell nuclei in the transitional state  that intervenes between the embryonic stem cell state and the differentiation primed state of mouse stem cells, indicate that such nuclei are auxetic i.e. have a negative Poisson's ratio.  We model this unusual mechanical behaviour in terms of the coupling between chromatin compaction states and nuclear shape.  We describe several ways in which the predictions of the model can be tested, suggesting a possible biophysical interpretation of the epigenetic landscape of stem cells.