Yuki Yahiro

Estimation of the mechanical connection between apical stress fibers and the nucleus in vascular smooth muscle cells cultured on a substrate

Actin stress fibers (SFs) generate intercellular tension and play important roles in cellular mechanotransduction processes and the regulation of various cellular functions. We recently found, in vascular smooth muscle cells (SMCs) cultured on a substrate, that the apical SFs running across the top surface of the nucleus have a mechanical connection with the cell nucleus and that their internal tension is transmitted directly to the nucleus. However, the effects of the connecting conditions and binding forces between SFs and the nucleus on force transmission processes are unclear at this stage. Here, we estimated the mechanical connection between apical SFs and the nucleus in SMCs, taking into account differences in the contractility of individual SFs, using experimental and numerical approaches. First, we classified apical SFs in SMCs according to their morphological characteristics: one subset appeared pressed onto the apical surface of the nucleus (pressed SFs), and the other appeared to be smoothly attached to the nuclear surface (attached SFs). We then dissected these SFs by laser irradiation to release the pretension, observed the dynamic behavior of the dissected SFs and the nucleus, and estimated the pretension of the SFs and the connection strength between the SFs and the nucleus by using a simple viscoelastic model. We found that pressed SFs generated greater contractile force and were more firmly connected to the nuclear surface than were attached SFs. We also observed line-like concentration of the nuclear membrane protein nesprin 1 and perinuclear DNA that was significantly located along the pressed SFs. These results indicate that the internal tension of pressed SFs is transmitted to the nucleus more efficiently than that of attached SFs, and that pressed SFs have significant roles in the regulation of the nuclear morphology and rearrangement of intranuclear DNA.

Stress fibers stabilize the position of intranuclear DNA through mechanical connection with the nucleus in vascular smooth muscle cells.

Actin stress fibers (SFs) running across the top surface of the nucleus in vascular smooth muscle cells were dissected using laser nano‐dissection technique to release its pretension, and the dynamic behavior of SFs, nucleus, and intranuclear DNA were investigated. SFs shortened across the top surface of the nuclei after their dissection. The nuclei moved in the direction of SF retraction, and showed marked local deformation, indicating that SFs firmly connected to the nuclear surface. Intranuclear DNA located near and around the dissected SFs disappeared and their distribution changed markedly. These findings suggest that SFs stabilize the position of intranuclear chromatin through mechanical connection with the nucleus. The tension of SFs may be transmitted mechanically to the nucleus inducing conformational changes of intranuclear chromatin.

In Situ Observation of Nuclear Behavior During Laser Nano-Dissection of Actin Stress Fibers: Mechanical Interaction Between Actin Stress Fibers and Nucleus

In order to elucidate the mechanotransduction mechanism of adherent cells, it is crucial to clarify how forces applied to cells are transmitted through intracellular components. Actin stress fibers (SFs) play important roles in various cellular events including cell proliferation [1], differentiation [2] and gene expression [3]. SFs generate internal forces and contribute to physical interactions between cells and extracellular matrices [4]. It has recently been suggested that cytoskeletons have the potential to interact with nuclei via certain nuclear membrane proteins [5, 6]. However, it remains unclear at this stage whether SFs are involved in a mechanical interaction with the cell nucleus and their internal forces are transmitted directly to the nucleus.Copyright

On the Roles of Actin Stress Fibers on the Mechanical Regulation of Nucleus in Adherent Cells

Actin stress fibers (SFs) play important roles in cellular mechanotransduction and regulation of various cellular functions. SFs generate internal tension and contribute to physical interactions between cells and extracellular matrices. It has recently been suggested that cytoskeletons have the potential to interact with the nuclei via nuclear membrane proteins. However, it remains unclear at this stage whether SFs are involved in a mechanical interaction with the nucleus, and their internal forces are transmitted directly to the nucleus and influence the intranuclear DNA.