Mouse embryo nuclei soften as their own genes switch on
Mouse embryos briefly soften their cell nuclei at the two-cell stage, when their own genes become active. Peer-reviewed experiments traced the change to removal of a structural protein from the nuclear envelope. Artificially stiffening nuclei disrupted gene activity and early development, identifying a physical contribution to this transition in mice alongside biochemical regulation.
Science··Midday
The two-cell stage brings a softer nucleus
Cell nuclei in mouse embryos briefly soften as the embryo's own genes become active. The peer-reviewed experiments connect this temporary mechanical change with early development. Researchers followed embryos through the one-cell, two-cell and four-cell stages.[1], [2]
A narrow mechanical probe measured deformation, alongside live imaging and protein labelling. Nuclear stiffness fell from about 5.0 nanonewtons per micrometre at the one-cell stage to 2.0 at the two-cell stage, then rose to 4.6 at four cells. The softening was temporary rather than a continuous decline as cells divided.[1]
Removing a structural protein changes flexibility
Lamin B1, a protein supporting the nuclear envelope, declined around the nucleus during the two-cell stage. Its peripheral amount fell by about 70 percent roughly 21–24 hours after insemination. A cellular clearance process contributed to its removal. Researchers interfered with this process to alter the nucleus's mechanical properties.[1]
A separate intervention used artificial links between membrane proteins to stiffen nuclei without the same lamin manipulation. Stiffness approximately doubled. Measurements of ribonucleic acid, or RNA, identified 634 genes whose activity declined. Gene positions near the nuclear periphery were also reorganized as gene activity changed.[1]
Stiffened embryos develop differently
All 66 embryos whose nuclei softened normally reached the blastocyst stage, an early developmental stage. Seven of fifteen embryos in a stiffened group failed to reach it. Some lamin interventions also involved damage to deoxyribonucleic acid, or DNA, so their effects cannot all be assigned to stiffness alone. The experiments establish a physical contribution in mice; pregnancy outcomes and infertility treatment in people were not investigated.[1]
