Figure 7. Oxygen levels affect mechanics and organization of subcellular structures in PSCs.

(A) In low oxygen, nuclei become longer and lamins (red) appear smoothed at the nuclear periphery and interact with actin (green; dashed circle). Cytoskeleton depolymerization causes nuclear collapse and “wrinkling” of the nuclear lamina, suggesting that the intact cytoskeleton had been producing outward stress on the nucleus. Scale is 25 µm. (B) Quantification of nuclear morphology shows that PSC nuclei are more elongated than in MSCs, and low oxygen enhances this difference (ANOVA p < 0.001), (C) While PSCs are normally less deformable than MSCs (as in Figure 2), culture in low oxygen shows higher deformability (t-test p < 0.005 – line). The three values for A (Pa⁻¹) are statistically distinct (ANOVA p < 0.04). (D) Changes in nuclear area with depolymerization of the cytoskeleton are related to how deformed the nucleus is inside the cell by mechanoactive structures. Projected nuclear area is larger in cells cultured at 6% O₂ than at 21% O₂, but nuclei dramatically retract with cytoskeletal disruption. Nuclear area in cells cultured at 21% O₂ show no statistical change with cytoskeletal disruption. Dashed lines are p < 0.001 (t-test between samples). Errors are SEM.