The early stages of embryonic development are maternally driven. As development proceeds, maternally inherited informational molecules decay, and embryogenesis becomes dependent on de novo synthesized RNAs of embryonic genome. The aim of the present study is to investigate the role of de novo transcription in the development of embryos during embryonic genome activation. Autoradiography for detection of transcriptional activity and transmission electron microscopy were applied in in vitro produced bovine embryos cultured to the late 8-cell stage with or without (control group) a-amanitin, specific inhibitor of RNA-polymerases II and III transcription. The a-amanitin (AA) groups presented three sets of embryos cultivated with AA in different time intervals (6, 9 and 12 h). In control group, nucleoplasm and nucleolar structures displayed strong autoradiographic labeling and showed initial development of fibrillo-granular nucleoli. In a-amanitin groups, lack of autoradiographic labeling and disintegrated nucleolus precursor bodies (NPBs) stage were observed. Inhibition of RNA polymerase II (RNA pol II) already in the early phases of embryonic genome activation has detrimental effect on nucleolar formation and embryo survival, what was shown for the first time.