Correlating nuclear morphology and external force with combined atomic force microscopy and light sheet imaging separates roles of chromatin and lamin A/C in nuclear mechanics

Abstract

Nuclei are constantly under external stressbe it during migration through tight constrictions or compressive pressure by the actin capand the mechanical properties of nuclei govern their subsequent deformations. Both altered mechanical properties of nuclei and abnormal nuclear morphologies are hallmarks of a variety of disease states. Little work, however, has been done to link specific changes in nuclear shape to external forces. Here, we utilize a combined atomic force microscope and light sheet microscope (AFM-LS) to show SKOV3 nuclei exhibit a two-regime force response that correlates with changes in nuclear volume and surface area, allowing us to develop an empirical model of nuclear deformation. Our technique further decouples the roles of chromatin and lamin A/C in compression, showing they separately resist changes in nuclear volume and surface area respectively; this insight was not previously accessible by Hertzian analysis. A two-material finite element model supports our conclusions. We also observed that chromatin decompaction leads to lower nuclear curvature under compression, which is important for maintaining nuclear compartmentalization and function. The demonstrated link between specific types of nuclear morphological change and applied force will allow researchers to better understand the stress on nuclei throughout various biological processes.

Integer topological defects organize stresses driving tissue morphogenesis

“…To test our theory (Fig3E,F), we characterized the nuclear volume and cell density, as internal rulers for external mechanical pressure( 37 ). In asters, as expected, nuclear volume decreased towards the center (Fig.3G,H), and cell density increased (Fig.3G,I).…”

Modeling of Cell Nuclear Mechanics: Classes, Components, and Applications

“…Exact solutions to physical problems characteristic of these models typically require idealized conditions and sweeping assumptions that almost certainly do not hold true for biophysical problems. Cell nuclei have been shown to be anisotropic [ 11 ], heterogeneous [ 12 ], and strain stiffening in both compression [ 7 ] and extension [ 8 ]; this directly invalidates these key assumptions. One must then be cautious in interpreting the absolute magnitude of the mechanical properties determined by such schematic models as their assumptions are often not met.…”

“…However, computationally solving CM models through means such as finite element analysis (FEA) allows investigators to circumvent some of assumptions of analytically-solved CM models at the cost of computational intensity. For example, computationally solved CM models of AFM have allowed investigators to move beyond the Hertz model and study the separate roles of lamins and chromatin, more accurate nuclear geometries, and viscous contributions [ 7 , 16 , 17 , 18 ]. The first benefit of this approach is in the flexibility of the geometry of the system.…”

“…Lamins’ storied role in nuclear mechanics has led to its inclusion in most mechanical models. Most commonly (and simply), the nuclear lamina has been modeled as a linear elastic shell, either infinitely thin [ 7 ] or with some finite thickness [ 16 , 18 , 20 , 35 , 36 , 38 ]. This serves primarily to capture the mechanical resistance from stretching of the nuclear lamina, but may oversimplify key experimental findings.…”

Nanomechanical properties of enucleated cells: contribution of the nucleus to the passive cell mechanics

“…While quite often the nucleus is considered to be the stiffest organelle in the cell [1,[9][10][11][12], other studies have shown that the nucleus is relatively soft, at least softer than the cytoskeletal structures [6,[13][14][15]. The recent studies have established that the mechanical behavior of the nucleus is quite complex, and different properties are expected in different deformation ranges and modes [3,16,17]. The mechanical properties of the nucleus were shown to be determined by chromatin at low deformations, and by lamina (a meshwork of intermediate filaments under the nuclear envelope) at high deformations [16,17].…”