Role of Maternal MCM4 in Zygotic DNA Replication and Oocyte-to-Embryo Transition

Faithful DNA replication is essential for genome integrity and successful embryonic development. During the first mitotic division of the mammalian zygote, genome duplication is exclusively dependent on maternal replication factors deposited during oogenesis. The MCM2-7 helicase complex plays a central role in DNA replication licensing, but the function of maternal MCM components during the oocyte-to-zygote transition remains untested in vivo. We have generated the first oocyte-specific conditional knockout (cKO) of MCM4, a core component of the MCM2-7 complex. Strikingly, Mcm4 cKO zygotes (Mcm4 cKO eggs fertilized by wild-type sperm) fail to incorporate EdU, indicating a complete absence of DNA replication, yet over half of them still enter mitosis and cleave into 2-cell embryos, displaying fragmentation and abnormal chromatin structures. This suggests that the mitotic program can proceed without genome duplication, raising critical questions about cell cycle regulation, checkpoint bypass, and chromatin remodeling under replication-deficient conditions. This project aims to define how maternal MCM4 governs zygotic replication and mitotic fidelity and to uncover the epigenetic and transcriptional consequences resulting from loss of maternal MCM4. We will use live imaging, immunofluorescence, and RNA-seq to investigate mitotic progression, chromatin dynamics, and zygotic genome activation in Mcm4 cKO embryos. These studies will fill a major gap in our understanding of maternal control during early development and may offer new insights into the origins of developmental arrest, infertility, and early embryonic loss. Project Number: 1R03HD121842-01 | Fiscal Year: 2026 | NIH Institute/Center: Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) | Principal Investigator: Wei Cui | Institution: UNIVERSITY OF MASSACHUSETTS AMHERST, HADLEY, MA | Award Amount: $157,427 | Activity Code: R03 | Study Section: Special Emphasis Panel[ZRG1 EMS-C (02)] View on NIH RePORTER: https://reporter.nih.gov/project-details/11353358