Epigenetic reprogramming and chromatin dynamics tin the course of mammalian oocyte development and fertilization

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We tried to determine whether the replacement of somatic linker histones with H1foo occurs during the process of mouse nuclear transfer. H1foo was detected in the donor nucleus soon after transplantation. Thereafter, H1foo was restricted to the chromatin in up to two-cell stage embryos. After fusion of an oocyte with a cell expressing GFP (green fluorescent protein)-tagged somatic linker histone H1c, immediate release of H1c in the donor nucleus was observed. In addition, we found that H1foo is more mobile than H1c in living cells using fluorescence recovery after photobleaching (FRAP). The greater mobility of H1foo may contribute to its rapid replacement and the less stability of an embryonic chromatin structure. These results suggest that rapid replacement of H1c with H1foo may play a significant role in nuclear remodeling. Finally, we identified human H1foo using direct RT-nested PCR of a single human oocyte.Taken together, we conclude that the replacement of oocyte specific linker histones in the donor or sperm nucleus leads to the less stable assembly of chromatin, and thus it might contribute to the assembly of embryonic chromatin structures that are more easily replicated and transcribed when zygotic gene activation occurs.