SUMMARY
In vivo nucleologenesis was studied in bovine embryos by electron microscopic immunogold labelling of DNA, RNA, protein C23 and protein B23. According to Kopecny et al. (1989b) and Kopecny (1990) we have considered four stages of nucleologenesis: compact nucleolar
precursor body (NPB), monovacuolated NPB, NPB containing secondary vacuoles and fully reticulated nucleolus. These different features of early bovine embryo nucleologenesis were observed during the eight-cell stage. From the first stage of nucleolar development, the
association of compact NPB with DNA structures were observed. DNA was also labelled in some small secondary vacuoles appearing during third developmental stage. From the second stage of nucleologenesis when a single NPB-vacuole appeared, the labelling of protein C23
was observed in dense fibrillar component (DFC). Protein B23 was labelled in the same substructure from the third stage when secondary nucleolar vacuoles were developing. RNA labelling was observed in NPB containing secondary vacuoles (third stage) for the first time. RNA labelling was observed in the peripheral region of DFCs as well as in close contact with the vacuoles.
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