Image texture-based elastography of the intranuclear space
Tutor / director / evaluatorNeu, Corey P.
CovenanteeUniversity of Colorado Boulder
Document typeMaster thesis
Rights accessRestricted access - author's decision
Specific interest has emerged in exploring the fascinating area of nuclear mechanobiology, a field which has seen unprecedented growth in the recent years1–7. The cell nucleus is known to contain, maintain, and interpret the genomic information. The chromatin in the nucleus is a highly organized structure that organizes for efficient DNA replication and transcription. The heterochromatin is a compact region with high DNA density, while the euchromatin is a less compacted region that is believed to contain most transcriptionally-active genes. The relative mechanical role of the euchromatin and heterochromatin regions can reveal the mechanobiological function of the chromatin, specifically in mechanically active tissues such as heart. However, intranuclear mechanics (e.g. stiffness of subnuclear domains) is not well understood, in part due to technical challenges of measurement inside the subcellular organelle. We propose a noninvasive image texture-based elastography technique that can elucidate relative stiffness of euchromatin and heterochromatin regions. Cardiomyocytes (CM) were derived from embryonic H2b-eGFP mice heart and were seeded on two groups of silicon substrates with soft (15 kPa) and stiff (400 kPa) elastic properties to mimic normal and fibrotic cardiac environments. The histone tag present in all nucleosome complexes rendered the image texture. During spontaneous CM beating, the deforming nuclei were imaged using an epifluorescenece microscope. Further, deformation microscopy, a technique developed in the lab of Professor Corey P Neu, was applied to the reference undeformed and deformed images to quantify the spatial intranuclear displacement map. The technique relies on image texture and registers a warped undeformed image template to images of the deformed nucleus. We further segmented and defined euchromatin and heterochromatin regions of interest that were assumed to have uniform stiffness. We solved an inverse problem to quantify the relative stiffness of the two intranuclear regions, with known displacements defined as boundary conditions, by minimization of nodal displacements obtained from finite element forward simulation and the deformation microscopy. A linear elastic material model was used to calculate the Young’s Modulus with known Poison’s ratio 0.35. The reported technique can be applied to broader application areas on any images that have inherent texture with an assumption that the image intensity is a function of the stiffness.
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