Interfering with the connection between the nucleus and the cytoskeleton affects nuclear rotation, mechanotransduction and myogenesis

Mechanical stress controls a broad range of cellular functions. The cytoskeleton is physically connected to the extracellular matrix via integrin receptors, and to the nuclear lamina by the LINC complex that spans both nuclear membranes. We asked here how disruption of this direct link from the cytoskeleton to nuclear chromatin affects mechanotransduction. Fibroblasts grown on flexible silicone membranes reacted to cyclic stretch by nuclear rotation. This rotation was abolished by inhibition of actomyosin contraction as well as by overexpression of dominant-negative versions of nesprin or sun proteins that form the LINC complex. In an in vitro model of muscle differentiation, cyclic strain inhibits differentiation and induces proliferation of C2C12 myoblasts. Interference with the LINC complex in these cells abrogated their stretch-induced proliferation, while stretch increased p38 MAPK and NFkappaB phosphorylation and the transcript levels of myogenic transcription factors MyoD and myogenin. We found that the physical link from the cytoskeleton to the nuclear lamina is crucial for correct mechanotransduction, and that disruption of the LINC complex perturbs the mechanical control of cell differentiation.

Pulse-shaping assisted multidimensional coherent electronic spectroscopy

Understanding nuclear and electronic dynamics of molecular systems has advanced considerably by probing their nonlinear responses with a suitable sequence of pulses. Moreover, the ability to control crucial parameters of the excitation pulses, such as duration, sequence, frequency, polarization, slowly varying envelope, or carrier phase, has led to a variety of advanced time-resolved spectroscopic methodologies. Recently, two-dimensional electronic spectroscopy with ultrashort pulses has become a more and more popular tool since it allows to obtain information on energy and coherence transfer phenomena, line broadening mechanisms, or the presence of quantum coherences in molecular complexes. Here, we present a high fidelity two-dimensional electronic spectroscopy setup designed for molecular systems in solution. It incorporates the versatility of pulse-shaping methods to achieve full control on the amplitude and phase of the individual exciting and probing pulses. Selective and precise amplitude- and phase-modulation is shown and applied to investigate electronic dynamics in several reference molecular systems.