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SUMMARY:Polymer physics of metabolically active isolated nuclei - Paul Jan
 mey (University of Pennsylvania)
DTSTART:20230703T090000Z
DTEND:20230703T100000Z
UID:TALK201076@talks.cam.ac.uk
DESCRIPTION:Nuclei are generally the stiffest organelle in the cell\, and 
 their large elastic modulus is thought to be due to a combination of polym
 er networks formed by chromatin and the 2D lamin network underlying the nu
 clear membrane. Direct measurement of nuclear stiffness within the cell is
  complicated by the surrounding cytoskeleton\, and isolating nuclei by dis
 rupting the cell results in diffusion of solutes through the nuclear pores
 \, loss of ATP-dependent active processes\, and osmotic dysregulation that
  might affect nuclear mechanics. &nbsp\;Therefore\, metabolically active i
 solated nuclei were produced from live cells by a centrifugation process t
 hat enucleates the cell. This process leaves behind a cytoplast and produc
 es a nucleus that is wrapped by a plasma membrane and a thin layer of cyto
 sol (a karyoplast)\, but no discernible cytoskeleton\, endoplasmic reticul
 um\, ribosomes or other large organelles. The metabolic activity within th
 is membrane-wrapped nucleus remains intact for at least 12 hours after iso
 lation. Force-indentation curves measured by atomic force microscopy show 
 that the apparent Young's modulus of these nuclei is on the order of 5 to 
 8 kilopascal. This large Young's modulus contrasts with the <1 kPa elastic
  modulus of crosslinked DNA gels at the same concentration either made fro
 m purified DNA or within bacterial biofilms. The large Young&rsquo\;s modu
 lus inferred from force-indentation curves assumes a purely elastic object
 \, but comparison of the force-indentation and force-retraction curves fro
 m AFM studies shows that most of the work of nuclear indentation is dissip
 ated.&nbsp\; Repeated deformations show little or no weakening of the nucl
 eus and very little rate dependence\, suggesting that the material is not 
 a passive viscoelastic body.&nbsp\; In contrast\, treatment with a glycoly
 sis inhibitor nearly eliminates the dissipation\, suggesting that it depen
 ds on active processes within the nucleus.\n&nbsp\;
LOCATION:Seminar Room 1\, Newton Institute
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