The expression of nuclear lamin A and C epitopes is regulated by the developmental stage of the cytoplasm in mouse oocytes or embryos.

The cytoplasmic regulation of changes of nuclear lamin antigens was examined by transferring 16-cell stage blastomeres into mouse oocytes. Sixteen-cell stage blastomeres were transferred to either pronuclear eggs, enucleated pronuclear eggs or metaphase II oocytes, which were subsequently activated. Pronuclei react with a monoclonal antibody to A/C lamins (J9), whereas nuclei from 16-cell stage blastomeres do not react with J9. However, after transfer of 16-cell stage nuclei to activated metaphase II oocytes, the transferred nuclei acquire the antigen. This is in contrast to 16-cell nuclei that were transferred to intact or enucleated pronuclear eggs; i.e., the nuclei only faintly acquired the A/C epitope. These results suggest that the developmental stage of the cytoplasm regulates the exposure of nuclear lamina epitopes, perhaps by limiting the supply of lamin A/C in the oocyte or because nuclear lamina assembly can only occur at the telophase transition. Furthermore, it appears that there is some exchange of the A/C epitope between (pro)nuclei within the same cell but that the majority of the A/C lamin epitope can be removed from a cell with (pro)nuclear removal.