RESEARCH ARTICLE Position- and Hippo signaling-dependent plasticity during lineage segregation in the early mouse embryo Eszter Posfai1, Sophie Petropoulos2,3,4, Flavia Regina Oliveira de Barros1, John Paul Schell2,4, Igor Jurisica5,6,7, Rickard Sandberg3,8, Fredrik Lanner2,4, Janet Rossant1,9* 1Program in Developmental and Stem Cell Biology, Hospital for Sick Children, Toronto, Canada; 2Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, Sweden; 3Ludwig Institute for Cancer Research, Karolinska Institutet, Stockholm, Sweden; 4Division of Obstetrics and Gynecology, Karolinska Universitetssjukhuset, Stockholm, Sweden; 5Princess Margaret Cancer Centre, University Health Network, University of Toronto, Toronto, Canada; 6Departments of Medical Biophysics and Computer Science, University of Toronto, Toronto, Canada; 7Institute of Neuroimmunology, Slovak Academy of Sciences, Bratislava, Slovakia; 8Department of Cell and Molecular Biology, Karolinska Institutet, Stockholm, Sweden; 9Department of Molecular Genetics, University of Toronto, Toronto, Canada Abstract The segregation of the trophectoderm (TE) from the inner cell mass (ICM) in the mouse blastocyst is determined by position-dependent Hippo signaling. However, the window of responsiveness to Hippo signaling, the exact timing of lineage commitment and the overall relationship between cell commitment and global gene expression changes are still unclear. Single- cell RNA sequencing during lineage segregation revealed that the TE transcriptional profile *For correspondence: janet. stabilizes earlier than the ICM and prior to blastocyst formation. Using quantitative Cdx2-eGFP
[email protected] expression as a readout of Hippo signaling activity, we assessed the experimental potential of individual blastomeres based on their level of Cdx2-eGFP expression and correlated potential with Competing interests: The gene expression dynamics. We find that TE specification and commitment coincide and occur at authors declare that no competing interests exist.