Figure 2. Analysis of TERRA distribution.

(a) Live-cell imaging of TERRA molecules. Fluorescence images were obtained using a representative U2OS cell expressing iRFP-TRF1 (left), TERRA probe (middle), and a single-particle reconstruction of TERRA from the middle image (right, movie S1 and S2). The white broken line in the left panel outlines the nucleus. Each Gaussian spot in the right image is reconstructed as a spot with 200 nm diameter. Scale bar, 2.0 μm. (b) Overlaid images of fluorescent spots representing telomeres (left) and TERRA (right) in movie S1. Time-integrated images were constructed to show the spatial distributions of telomeres and TERRA foci. The TERRA density is shown in pseudo-color. Scale bars, 4.0 μm. (c) Schematic of the radial distribution function, ρ(r). ρ(r) is the number of TERRA spots divided by the observation time and area within the region between r − 0.25 and r (μm) (blue) from the center of a reference telomere (magenta). (d) Averaged ρ(r) of the TERRA spots for all the telomeres in the cell shown in Fig. 2A (±s.e.m., n = 26). ρ(r = 0.25 μm) and ρ(r = 1.00 μm) exceed ρ(r > 3.00 μm) (Student’s t-test, p < 0.05). (e) Plots of ρ(r) against r for the four individual telomeres shown in Fig. 2b. The dotted line represents the threshold for the peak (ρ(r) = 1.9).