Interphase-arrested Drosophila embryos activate zygotic gene expression and initiate mid-blastula transition events at a low nuclear-cytoplasmic ratio

摘要: Externally deposited eggs begin development with an immense cytoplasm and a single overwhelmed nucleus. Rapid mitotic cycles restore normality as the ratio of nuclei to (N/C) increases. A threshold N/C has been widely proposed activate zygotic genome transcription onset morphogenesis at mid-blastula transition (MBT). To test whether is required for these events, we blocked increase by down-regulating cyclin/Cdk1 arrest early cell in Drosophila. Embryos that were arrested two prior normal MBT activated widespread including genes previously described dependent. Zygotic largely retained features their regulation space time. Furthermore, zygotically regulated post-MBT events such cellularization gastrulation movements occurred cycle-arrested embryos. These results are not compatible models suggesting directly coupled N/C. Cyclin/Cdk1 activity normally declines tight association increasing By experimentally promoting decrease cyclin/Cdk1, uncoupled from increase, arguing N/C-guided down-regulation sufficient activation MBT.