Minor zygotic gene activation is essential for mouse preimplantation development

Significance Results presented in this report demonstrate that minor zygotic gene activation (ZGA) must precede major ZGA to execute successfully the maternal-to-zygotic transition, and that the timely occurrence of minor ZGA is crucial for preimplantation development to continue beyond the two-cell stage. In addition, the results show that the gene-expression program proceeds in a step-by-step fashion, and at least initially, is not regulated by a “zygotic clock” (e.g., compaction) or cell cycle progression (e.g., major ZGA that occurs during the two-cell stage).