Cell cycle; DAPI; Synchronization; Zygotic genome activation

Detailed knowledge of early embryo development is a prerequisite for implementation of reproductive biotechnologies. We described the timing of mid-blastula transition in the sturgeon Acipenser ruthenus and hybrid of A. ruthenus and Acipenser gueldenstaedtii. To identify mitotic changes during cell division, the nuclei of embryo blastomeres were sampled every 30 min from 4 to 25 h post-fertilization and stained with 5 mg/ml 4'-6-diaminido-2phenylindole. We observed embryos of hybrids to lose synchrony after the eighth cell division, one cycle earlier than in purebred sterlet embryos. To reveal the timing of zygotic gene activation, developing embryos were dechorionated and injected with 10, 50, 100, 250, or 500 mu g/ml a-Amanitin. Termination of development in embryos was recorded throughout the period from the 1000 cell stage until gastrulation, showing the process of transition from maternal to zygotic gene transcription in sterlet to be of extended duration and not directly linked to mid-blastula transition.