Intermediate filaments promote nuclear mechanical constraints during somatic cell nuclear transfer in the mouse.

The somatic cell nuclear transfer (SCNT) procedure requires nuclear remodeling to return differentiated somatic nuclei to the totipotent undifferentiated stage. We hypothesize that mechanical constraints might occur upon SCNT and thereby affect nuclear remodeling. Therefore, we analyzed the nuclear structures upon SCNT using as donors either wild-type fibroblasts with a dense vimentin network or vimentin-deprived cells [embryonic stem cells (ESCs) and fibroblasts invalidated for vimetin]. We demonstrated that following nuclear transfer of wild-type fibroblasts, vimentin intermediate filaments (IFs) persisted around the transplanted nuclei and 88% of them presented severe distortions. We also showed that the presence of vimentin filaments in the reconstructed embryos was correlated with DNA damage, as evidenced by γH2A.X foci. On the other hand, when ESCs or vimentin-null (Vim(-/-)) fibroblasts devoid of IFs were used as nuclear donors, no nuclear distortion and less DNA damage were observed. Altogether we believe that the introduction of vimentin into recipient oocytes during SCNT induces a mechanical constraint on the transplanted nucleus that is responsible for nuclear distortions and DNA damage. This could lead to incomplete reprogramming that would be detrimental to further embryonic development.