The Mechanics of Change

Abstract

Stem Cells As embryonic stem cells differentiate toward specific cell fates, shifts in the gene regulatory network accompany progression through the different states: from pluripotency, where cells are competent to differentiate into any somatic cell; to a transition state; and finally to a differentiated state where cells are irreversibly committed to a particular cell fate. Pagliara et al. used atomic force microscopy to compare the elastic stiffness of mouse cells in each of these different fates. When compressing the cytoplasm of cells in all of these states, a 5 to 10% increase in the cytoplasmic area was observed. However, only nuclei of cells in the transition state became smaller upon compression. When materials become denser with such mechanical stress, they are termed auxetic. Differences in chromatin condensation were observed by electron microscopy of the three cell states with considerably less-condensed nuclei during transition relative to the pluripotent or differentiated state. This work shows that the nucleus undergoes dynamic changes in mechanical properties and chromatin structure as cells transition toward a differentiated state. It is proposed that this auxeticity may be important for cell mechanotransduction. Nat. Mater. 10.1038/NMAT3943 (2014).