PROJECT SUMMARY / ABSTRACT A fundamental challenge in developmental biology is to dissect how one multipotent cell differentiates into a specific cell type. Most studies are limited to 1-dimensional genomic data that measure transcription level (RNA- seq), protein binding intensity (ChIP-seq), and chromatin accessibility (ATAC-seq). These datasets lack direct evidence of communication between various regulatory elements that accommodate gene regulation and differentiation. To solve this problem, we will leverage cutting-edge 3D genome technologies, ChIA-PET and ChIA-Drop. By enriching for specific protein factors CCCTC binding factor (CTCF) and RNA Polymerase II (RNAPII), one can interrogate chromatin architecture and gene regulation in aggregated bulk cells (ChIA-PET) and in a single molecule (ChIA-Drop). We will exploit the highly dissimilar genomes in F1 hybrid mouse strains derived from mating a laboratory mouse and a wild mouse to assign high-throughput sequencing reads to parental origin, thereby unraveling the allele-specific gene expression and chromatin interactions. We propose to: (i) determine whether allele-specific interactions between regulatory elements and methylation status in mouse embryonic stem cells (mESCs) drive allele-specific gene expression, (ii) quantify cell-to-cell heterogeneity of multiplex chromatin interactions. We will subsequently differentiate mESCs into three lineage-specific precursors ectoderm, mesoderm, and endoderm in vitro. By performing ChIA-PET, we can identify which, if any, of the pre-established interactions among enhancers, promoters, and CTCF persist or vanish after this process. ChIA-Drop data will potentially capture the dynamics therein. Throughout the K99 and R00 phases, we will continue to develop computational algorithms that can: (i) quantitatively assess reproducibility of replicate experiments, (ii) identify statistically significant differential interactions, and (iii) trace and quantify single- molecule dynamics and heterogeneity of allele-specific multiplex interactions. To succeed in these aims, the investigator will expand her knowledge domain to developmental biology and receive additional hands-on experimental training in 3D genome mapping technologies and mouse embryonic stem cell culture, harvest, and differentiation techniques. Together, these genome-wide communication links between regulatory elements and architectural protein will provide insights into gene regulation and genomic imprinting mechanisms during gastrulation.

PROJECT NARRATIVE / RELEVANCE TO PUBLIC HEALTH The genetic program by which one multipotent cell gives rise to multiple cell types—skin, brain, liver, etc.—is largely unknown. To identify the molecular mechanisms by which genes are precisely controlled to successfully differentiate into specific cell types, we will leverage 3-dimensional genome technologies that can probe which loci are closely interacting in nuclei. A combination of hybrid mouse models, advanced experimental techniques, and new algorithms will likely reveal a new paradigm of dynamic gene regulation during development.