Understanding the mechanism of pre- to naïve- to formative- pluripotency transitions

Understanding the mechanism of pre- to naïve- to formative-pluripotency transitions Abstract Pregnancy loss affects about 15% of couples globally. Of which, over 50% are due to developmental abnormalities at peri-implantation. Peri-implantation represents a specific developmental window during which the inner cell mass (ICM) goes through a number of differentiations and pluripotent transitions to prepare for gastrulation. Understanding the molecular, cellular, and epigenetic events that occur during peri-implantation is critical for determining how this process goes awry. However, the limited number of mammalian peri-implantation embryos, as well as the technical complexity in handling these cells, has been a major constraint in progressing research. Central to peri-implantation development is the pluripotency transitions of epiblast (Epi) cells from pre- pluripotency (E3.5 ICM cells that co-express Oct4, Nanog, and Gata6) to naïve, formative and primed pluripotent states with distinct developmental potentials. To overcome the technical difficulties in working with peri- implantation embryos, in vitro ESC culture systems have been developed to mimic the various in vivo pluripotent states, which have largely contributed to our current understanding of the pluripotency transition. However, several factors shown to be important for pluripotency transition in vitro failed to generate the expected phenotype, or even no phenotype in mouse knockouts, indicating that studies using peri-implantation embryos are urgently needed. Thus, understanding how the various pluripotency transitions take place in vivo is critical not only for understanding peri-implantation development, but also for understanding peri-implantation-related diseases and infertility. To be able to work with limited peri-implantation embryos, we have established innovative techniques to overcome the technical hurdles. With our state-of-art tools and unique mouse models, we have established the following three aims: 1) Identifying key TFs and dissecting the mechanisms of ICM to epiblast transition 2) Identifying key TFs and dissecting the mechanism of naïve to formative transition 3) Understanding how DNA methylation regulates naïve to formative transition Completion of the proposed studies will not only reveal the mechanisms of pluripotent transitions, but may also reveal targets for therapeutic intervention of the peri-implantation-related diseases.