Complex Substrate Strain Fields Reveal Anisotropic Deformation of C2C12 Cell Nuclei

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INTROExtracellular forces can result in significant nuclear deformations and may modulate transcription activity. However, the precise role of the cytoskeleton network in regulating nuclear mechanics remains poorly understood. The goal of the present study is to investigate the nuclear deformability under complex substrate strain fields to clarify the role of the microtubule and actin network on the mechanical behavior of the nucleus.METHODA custom-built cell bi-axial stretching device allowing for real time imaging of mouse myoblast (C2C12) nuclei was used. Cells were seeded on a cross-shaped silicone membrane coated with collagen I and cultured in growth medium. A live cell fluorescent nuclear stain, Hoechst-33342, was used to image the nucleus during stretching. Nocodazole and cytochalasin-D were used to depolymerize the microtubule or actin network, respectively. All cells were exposed to a stretching strain field of 23% parallel to major or minor nuclear axis.RESULTSFor all cells, substrate stretching along one nuclear axis induced stretching along this axis and compression along the orthogonal axis. Control cells displayed a higher nuclear stretching along the minor axis than the major axis with a deformation of 5% and 2% respectively. This anisotropy vanished completely in microtubule- and actin- deprived cells with a deformation of about 4% and 3.5% respectively for both axis. In concert with stretching, increased nuclear compression was observed along the minor axis compared to the major axis for all cells.CONCLUSIONThe anisotropic deformation of C2C12 cell nuclei are driven by actin and microtubule networks. It is important to understand how the cytoskeleton regulates force-induced deformation of the nucleus since they are known to alter gene expression and cell polarity. Such intrinsic mechanical behavior could also be exploited as a readout mechanism of substrate strain fields.