Embryo development is characterized by lack of cell cycle check-points and overexpression of core circadian oscillators. On previous report we have identified several genes over-and under-detected at human embryo blastomeres. In this study, we investigated the expression profile of Kcnh5, KIFC1 and miRNA-302 genes at three pre-implantation stages of mouse embryo development. Material and methods: Total RNA was extracted from mouse embyos at 8-cell, morula and blastocyst stage. The expression

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... file of Kcnh5, KIFC1 and miRNA-302 was assessed by RT-PCR and the results were normalized with G6pdh expression levels. Results: Kcnh5 showed absence of expression at all stages, indicating novel mechanisms of cell cycle control during blastomeres divisions. KIFC1 showed positive expression at all stages, with decreasing levels as the embryogenesis progresses. This finding indicates that KIFC1 may have more important role at early events. miRNA-302 showed increased levels of expression at all stages, with morula having the highest levels. Therefore, miRNA-302 might play an important role at the events that happen during morula stage such as compaction. Conclusions: Cell cycle control of blastomeres at early embryogenesis might be based on different mechanisms compared to somatic cells and more research is needed in order to reveal crucial cycling elements.