Figure 2
Chromatin folds into packing domains that have similar mass scaling behavior. (A) STEM HAADF image of a 150 nm section of a BJ cell nucleus for tomography reconstruction. Scale bar: 2 µm. (B) A magnified view of the chromatin and the nuclear periphery of the same cell in (A) with gold fiducial markers (white). The intensity variation of the image shows that the chromatin packs at different densities throughout. Scale bar: 200 nm. (C) A virtual 2D slice of the chromatin of a BJ cell after tomography reconstruction. Scale bar: 100 nm. The mass scaling analysis was performed on the gray scale tomograms (D, E) The average mass scaling (MS) curves from the analysis of four A549 cells in (D) 3D and (E) Ring, 2D, and 3D. The mass scaling was conducted for the entire grayscale tomogram and the average mass scaling curves weighted by the chromatin density values were computed. 3D mass scaling curve exhibits power-law behavior with a single scaling exponent up to r = 60 nm. Two regimes of mass scaling with different packing scaling D can be identified. In the 2D cases, the MS curve starts with a packing scaling with Dlog < 3 (blue dashed line) and smoothly transitions to values close to Dlog = 3 (red dashed line).
