Sculpting rupture-free nuclear shapes in fibrous environments

Abstract

Cytoskeleton-mediated force transmission regulates nucleus morphology. How nuclei shaping occurs in fibrous in vivo environments remains poorly understood. Here a suspended nanofiber assay of precisely-tunable (nm-μm) diameters is used to quantify nucleus plasticity in fibrous environments mimicking the natural extracellular matrix. In contrast to the apical cap over the nucleus in cells on 2-dimensional surfaces, the cellular cytoskeleton of cells on fibers displays a uniform actin network caging the nucleus. The role of contractility-driven caging in sculpting nuclear shapes is investigated as cells spread on aligned single fibers, doublets, and multiple fibers of varying diameters. Cell contractility increases with fiber diameter due to increased focal adhesion clustering and density of actin stress fibers, which correlates with increased mechanosensitive transcription factor YAP translocation to the nucleus. Unexpectedly, large- and small-diameter fiber combinations lead to teardrop-shaped nuclei due to stress-fiber anisotropy across the cell. As cells spread on fibers, diameter-dependent invaginations that run the nucleus’s length are formed at contact sites. The deepest and sharpest invaginations are insufficient to trigger nucleus rupture, often observed in 2D or confined systems. Overall, we describe the unknown adaptability of nuclei to fibrous environments and resultant sculpting of the nucleus shapes, with pathophysiological implications.

Deep Learning Enabled Label-free Cell Force Computation in Deformable Fibrous Environments

“…We observe line tensions in the range 5-25 mN/m, which over a representative adhesion patch on fibers of 10 μm results in 50-250 nN force, in agreement with forces reported by our parallel-fiber network based Nanonet Force Microscopy 45 . The typical force per adhesion patch is measured to be in a similar range using soft gels (2-50 nN 46,47 ), fibrous networks (100-400 nN 31,45 ), and micropost arrays (1-80 nN 46,48,49 ). To visualize the spatial organization of cellular contractility, we developed force polarity maps that show the contractility 𝐶𝐶 𝜃𝜃 at an angle 𝜃𝜃 to the x-axis in a polar plot (Fig.…”

Dynamic Heterochromatin States in Anisotropic Nuclei of Cells on Aligned Nanofibers

“…We used suspended nanofibers that mimic the loose interstitial network found in vivo with large and small pore sizes to the extent that cells make contact with only single fibers. 52 We have recently shown that nuclei may lack apicobasal polarity, which causes a uniform distribution of proteins, including lamins, actin, and cytoskeleton, 53 which causes compression of the nuclei from all sides of the nanofiber. Thus, the nuclei of the cells attached to suspended nanofibers show considerable differences from the other in vitro systems with constrained apicobasal polarity, a potential reason for the difference in heterochromatin organization and dynamics.…”

Actin filaments couple the protrusive tips to the nucleus through the I-BAR domain protein IRSp53 for migration of elongated cells on 1D fibers

“…Motivated by these results on two fiber systems, we enquired if there were any differences in the nucleus shape for cells migrating on single fibers. Confocal imaging revealed invaginations in the nuclear envelope at fiber-specific sites [46] . We examined the shape of local invaginations and found a remarkable difference between the WT and KO cells ( Fig.…”