Precisely delivered nanomechanical forces induce blebbing in undifferentiated mouse embryonic stem cells

Alexandra L Hemsley1, Diana Hernandez1, Christopher Mason1, Andrew E Pelling2,3, Farlan S Veraitch11Advanced Centre for Biochemical Engineering, 2The London Centre for Nanotechnology, Centre for Nanomedicine, University College London, London, UK; 3Department of Physics, University of Ottawa, Ottawa, ON, CanadaAbstract: The aim of this study was to probe the morphological response of single mouse embryonic stem cells (mESC) to precisely delivered nanomechanical forces. Plating mESC as single cells gave rise to either round compact or flattened fibroblastic morphologies. The expression of OCT4 and Nanog was reduced in flattened cells, indicating that this population had begun to differentiate. Upon application of >5 nN of force, using atomic force microscopy and simultaneous laser scanning confocal microscopy, round cells, but not flattened cells, were capable of forming mechanically induced blebs (miBlebs). Flattened cells appeared to have a more highly developed cytoskeleton than undifferentiated stem cells as characterized by the distribution of phospho-ezrin-radixin-moesin (pERM). Higher levels of pERM and an inability to form miBlebs in flattened cells imply that the earliest stages of embryonic stem cell differentiation are associated with the development of stronger mechanical links between the plasma membrane and the cytoskeleton.Keywords: blebbing, embryonic stem cells, atomic force microscopy, cytoskeleton development, differentiation