First published online April 16, 2004
doi: 10.1242/10.1242/jcs.01073
Journal of Cell Science 117, 2159-2167 (2004)
Published by The Company of Biologists 2004
Micro-organization and visco-elasticity of the interphase nucleus revealed by particle nanotracking
Yiider Tseng1,
Jerry S. H. Lee1,
Thomas P. Kole1,
Ingjye Jiang1 and
Denis Wirtz1,2,3,*
1 Department of Chemical and Biomolecular Engineering, The Johns Hopkins University, Baltimore, 3400 N. Charles Street, MD 21218, USA
2 Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore, 3400 N. Charles Street, MD 21218, USA
3 Graduate Program in Molecular Biophysics, The Johns Hopkins University, Baltimore, 3400 N. Charles Street, MD 21218, USA
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Fig. 1. Nuclei of cells under shear flow do not deform. (A) Four phase-contrast micrographs of Swiss 3T3 cells subject to a shear flow (wall shear stress=9.4 dyn/cm2) taken over 23 minutes. Vertical and horizontal lines are guides to the eye. Cells were sheared for 27 minutes; arrows indicate the direction of flow. Three nucleoli are indicated. (B) Examples of relative surface areas of contact of two sheared cells with their substratum (dashed lines) and (apparent) surface areas of nuclei (solid lines) of the same sheared cells as a function of shearing time. The initial values of nucleus and cell surface areas are, respectively, 5100 µm2 and 710 µm2 for the cell shown in A (black lines; see movie M.2, http://jcs.biologists.org/supplemental/) and 4810 µm2 and 350 µm2 for the cell shown in movie M.3 (red lines). Surface areas were measured by morphometric analysis of phase-contrast micrographs of the cells under shear. Same colors correspond to the same cell. (Inset) Displacements of the centroids of sheared cells. Arrow indicates flow direction. This figure shows how cells can either move in the flow direction (black line) or counter-current (red line) (corresponding to cell shown in A). The starting point is where the two trajectories meet in the middle. (C) Typical movements of nucleoli centroids and nucleus centroid of a sheared cell (cell shown in A). In this particular case, nucleoli 1-3 and nucleus move from left to right (compare micrographs in A), and therefore move counter-current. The time lapse between symbols is 1 minute. 1-3 and 1'-3', respectively, indicate start and end points of the trajectories. (D) Time-dependent distances between nucleoli centroids and the nucleus centroid (red lines) of a cell under shear and distance between cell centroid and nucleus centroid (black line) of the same sheared cell.
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Fig. 2. Localization of microinjected probe nanospheres within the cell. Superposition of a phase-contrast micrograph of a cell and a fluorescent micrograph of DAPI-stained DNA (blue) and nanospheres (red) embedded in: (A) the intranuclear region (nanospheres 1-3) and (B) cytoplasm (nanospheres a-c). B was taken at a lower plane of focus than A. (C) Subcellular localization of nuclear (blue) and cytoplasmic (gray) nanospheres shown in A and B. Images represent composite images obtained by superimposing phase-contrast micrographs of the cell with fluorescent micrographs of the nanospheres and nuclear DAPI-stained DNA taken at different planes of focus. (D) Overall shape of the plasma membrane (phase contrast) and nucleus (blue DAPI stain) of the cells used in A-C.
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Fig. 3. Spontaneous movements of probe nanospheres embedded in the cytoplasm and the intranuclear region of the same cell. Typical trajectories of nanospheres embedded: (A) and (B) intranuclear region, (C) cytoplasm. (A'), (B') and (C') Associated MSDs,  .
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Fig. 5. Viscoelastic properties of the intranuclear region and the cytoplasm. (A) Mean frequency-dependent elastic [G'( )] and viscous [G''()] moduli of the intranuclear region (black lines) and cytoplasm (red lines). Open symbols: G'; closed symbols: G''. (Inset) Frequency-dependent phase-angle for cytoplasm (black line) and intranuclear region (red line),  ()=tan—1[G'' ()/G'()]. Examplary angles for liquids (e.g., glycerol), =90° and elastic solids (e.g. concrete), =0°. Mean moduli G' () and G'' () were calculated from the ensemble-averaged MSD,  , as described (Mason et al., 1997 ). Distribution of (B) elastic and (C) viscous moduli, G' and G'', respectively, in the intranuclear region measured at a frequency of 1 Hz. (D) Distribution of shear viscosity  s [which is approximately the product of the plateau modulus G'p (inset in B)] and the relaxation time  R (inset), s=G'pR (see text for details). For panels B-D, n=84; 1 Poise (P) = 1 Pascal second (Pa.s); 1 dyn/cm2 = 0.1 Pa = 0.1 N/m2.
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© The Company of Biologists Ltd 2004
obtained by the sum of all MSDs and divided by the number of MSDs (n=84). (C) Size distribution of nuclear microdomains probed by particle nanotracking. The mean diameter is 290±50 nm (mean±s.d., n=84). (D) Mean diffusion coefficient, 
, of the nanospheres in the intranuclear region (n=84). At early time-points, D decreases with time, a sign for elastic trapping, whereas at later time-points, D becomes independent of time, a sign for viscous diffusion, albeit at a much slower pace than predicted by using the low interstitial viscosity measured by FRAP (see Discussion). The diffusion coefficient of the same nanospheres in water is constant and equals to 4.53 µm2/second.