Atomic Force Microscopy micro-rheology reveals large structural inhomogeneities in single cell-nuclei

Abstract

During growth, differentiation and migration of cells, the nucleus changes size and shape, while encountering forces generated by the cell itself and its environment. Although there is increasing evidence that such mechanical signals are employed to control gene expression, it remains unclear how mechanical forces are transduced through the nucleus. To this end, we have measured the compliance of nuclei by applying oscillatory strains between 1 and 700 Hz to individual nuclei of multiple mammalian cell-lines that were compressed between two plates. The quantitative response varied with more than one order of magnitude and scaled with the size of the nucleus. Surprisingly, the qualitative behaviour was conserved among different cell-lines: all nuclei showed a softer and more viscous response towards the periphery, suggesting a reduced degree of crosslinking of the chromatin. This may be an important feature to regulate transcription via mechano-transduction in this most active and dynamic region of the nucleus.

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

“…Previous work, however, has modeled the nucleus as having a strain-dependent elastic modulus (Lherbette et al 2017), which could provide an alternate explanation of the origin of the two-regime phenomenon we have observed. To differentiate the two explanations, we examined the transition point as a function of ΔNP.…”

“…While Hertzian analysis has brought to light many novel insights, it is limited by its ability to decouple contributions of specific structures. More intricate computational models have given direct insight into many mechanical techniques, including constricted migration (Cao et al 2016), micropipette aspiration (Vaziri and Mofrad 2007), magnetic bead twisting (Karcher et al 2003), plate compression (Caille et al 2002), micromanipulation Stephens et al 2017), and atomic force microscopy (Lherbette et al 2017); however, their specificity inhibits extrapolation of their conclusions. There exists a need for an intermediate understanding of nuclear deformation that informs both the relative contributions of the various nuclear mechanical constituents as well as their roles in protecting against specific deformations to nuclear morphology.…”

Image-based elastography of heterochromatin and euchromatin domains in the deforming cell nucleus

“…The significant effort in this line have been pursued by the intranuclear rheology 22,23 which tracks the passive movement of fiduciary markers such as beads but such approach has a few limitations -(1) the characterization of the mechanical properties under active mechanical loading is not possible, (2) inserting beads in the nucleus is technically difficult, specifically in several primary cells and for cells in situ or in vivo, (3) bead insertion can be a highly invasive method which compromises the cell viability. Atomic force microscopy (AFM) can also potentially probe the nuclear elasticity distribution [24][25][26][27] , but that is also technically challenging specifically because -(1) the insertion of AFM probe inside the nucleus after crossing cell and tissue barrier is difficult, (2) this technique is invasive for the cell, and therefore it can significantly disrupt the cell physiology.…”

High throughput mechanobiology: Force modulation of ensemble biochemical and cell-based assays

“…In this manner, physical forces provide a mechanism to propagate signals within and between cells (Mohammed et al, 2019). Specialized single molecule force measurements (such as atomic force microscopy, optical traps and magnetic tweezers) have been advancing rapidly over the past two decades and have revealed how force is used in biological systems, from individual proteins to complexes and from individual organelles to cells (Elosegui-Artola et al, 2017, Seo et al, 2016, Yao et al, 2016, Lherbette et al, 2017. More recently, these techniques have been combined with highresolution single molecule fluorescence approaches and cell imaging to visualise dynamic systems under the controlled application of force (Cordova et al, 2014, Madariaga-Marcos et al, 2018, Newton et al, 2019, Swoboda et al, 2014.…”