Project Summary / Abstract A major shortcoming of most efforts to understand the 4D nucleome is that they have mainly focused on in vitro cell lines, rather than on dynamic, in vivo systems. Arguably, the most important in vivo system, which also happens to be the most dynamic, is development itself, wherein the nucleome both shapes and is shaped by the initial emergence of the myriad mammalian cell types. While these in vivo dynamics are presently poorly documented and understood, recently emerged technologies offer a path forward. Here we propose to establish the University of Washington 4-Dimensional Genomic Nuclear Organization of Mammalian Embryogenesis Center (UW 4D GENOME Center), which will address these massive gaps in our understanding by generating systematic datasets on nuclear morphology and associated molecular measurements in mammalian tissues and cell types. These datasets will be generated in the context of the leading model organism for mammalian development, the mouse. Our approach focuses on following nuclear structure, chromatin and gene expression changes at a “whole organism” scale, using a combination of scalable single cell profiling and “visual cell sorting” (VCS) methods, all well-established and mostly developed in our own labs. Our goal is to generate a high- resolution 4DN atlas of mouse embryogenesis for the community. The different types of data will be integrated, including cross-species imputation to integrate with human data, as well as models and navigable maps applied to pathways relevant to mammalian development.