Fig. 3. Synchronization of HeLa cells in G₁ and late S-G₂ phases and nuclear volume measurements.

(A) Cell cycle progression. The nuclear volume (gray circle) increases as the cell cycle progresses from G₁ to G₂, with accompanying genomic DNA doubling. (B) Cellular DNA contents in indicated HeLa cell populations measured by flow cytometry. 2 N and 4 N show genomic DNA amount. “W thymidine block” means “double thymidine block.” Each histogram represents more than 16,000 cells. (C) Quantification from data in (B). (D) Top: Low-magnification images of 4′,6-diamidino-2-phenylindole (DAPI)–stained HeLa nuclei with the indicated conditions. Bottom: Reconstructed three-dimensional (3D) images of HeLa nuclei with the indicated conditions. (E) Quantitative data of nuclear volume (means ± SE) of the indicated HeLa cell populations. Mean volumes: lanes 1 (658 μm³, n = 32 cells), 2 (510 μm³, n = 36 cells), and 3 (1263 μm³, n = 37 cells). ***P < 0.0001 (P = 2.3 × 10⁻²¹) by Wilcoxon rank sum test.