Functional analysis of a novel gene, Oogenesin, which localizes to the nucleus at the time of ZGA

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In the present study, we performed functional analysis of oocyte-specific gene, Oogenesin (Oog1). We recently demonstrated that Oog1 translocates to the nucleus at the late 1-cell to early 2-cell stage in mouse embryos. The periods coincide with the time of the first gene expression during early preimplantation development that has been termed 'zygotic gene activation (ZGA).' The time of ZGA depends on species ; however, the precise mechanism of ZGA remains unknown. We speculate that Oog1 has some role in ZGA because Oog1 disappears suddenly after ZGA. First of all, to identify the interacting protein with Oog1, we performed yeast two-hybrid experiment. As a result, we identified RalGDS and Chchd6 protein that interact with Oog1. These proteins are also maternally derived products and express specifically in oocyte and preimplantation embryos during early development. Since RalGDS is one of the Ras signaling proteins, Oog1 may function under stream of Ras signaling. RalGDS and Chchd6 have nuclear localization signal suggesting that nuclear localization of Oog1 depend on these proteins. A novel protein Chchd6 has CHCH domain that is essential for the interaction with Oog1. The expression pattern of RalGDS and Chchd6 is quite similar with that of Oog1, suggesting the function of these protein in early embryogenesis. In addition, Oog1 interact with Importin b and Ran in GTP dependent manner, suggesting the involvement of G-protein in Oog1 function.