PARENT SESSION

(W294) GENOME REPROGRAMMING INVOLVES ERASING CELL MEMORY DURING MEIOSIS.

Akiyama, Tomohiko¹, Liu, Honglin¹, Kim, Jin-Moon¹, Nagata, Masao¹, Aoki, Fugaku¹, ¹ University of Tokyo, Kashiwa, Japan

ABSTRACT- During meiosis and/or fertilization, gene expression in differentiated gametes is reprogrammed to allow the totipotent zygotes of the next generation to start the new program. Recent success in the reprogramming of gene expression in differentiated somatic cells by nuclear transfer into enucleated oocytes at metaphase II of meiosis has demonstrated that the cytoplasm of oocytes has an ability to reprogram gene expression. However, the molecular mechanism of the reprogramming is unknown. During mitosis in somatic cells, an epigenetic mechanism maintains a lineage-specific program of gene expression to propagate the gene expression pattern in the daughter cells. This mechanism is called cell memory, and many epigenetic modifications have been suggested as the marker of cell memory. In this study, we examined the changes in three candidates for cell memory markers, TBP binding, S1 nuclease sensitive state, and histone variant H3.3 replacement, in the chromosomes of somatic nuclei transferred into enucleated mouse oocytes. The results showed that all three candidate markers were lost in the oocytes. When the nuclei of NIH 3T3 cells expressing TBP-GFP or H3.3-GFP were transferred into enucleated unfertilized oocytes, the GFP fluorescence decreased to a faint level accompanying the occurrence of premature chromosome condensation. Although S1 nuclease sensitivity is higher in the M phase chromosome than in the interphase nucleus during the mitotic cell cycle, the nuclei of NIH 3T3 cells transferred into enucleated oocytes had decreased S1 nuclease sensitivity in the prematurely condensed chromosome. These findings suggest that the cytoplasm of oocytes can initialize the program of gene expression by erasing the cell memory.

KEY WORDS: genome reprogramming, cell memory, oocyte, meiosis