PROJECT SUMMARY Human physiology depends on precise cellular responses to environmental signals. Specificity in responding to environmental signals is achieved through specific proteomic, transcriptomic, epigenomic, and non-genetic cell states. In physiological states, healthy cells function in harmony with their surrounding tissues, performing specific functions in response to environmental stimuli. In disease, dysregulation of cell state can prevent cells from producing necessary responses and lead to proliferation independent of physiological context. Understanding how cell state drives cell function is essential for understanding tissue function in health and disease, and is required for engineering cell therapies capable of specific behaviors encoded by their target environments. Despite decades of research into single cell biology, we still don't understand the fundamental principles that connect cell state with specificity in cellular responses to their environment In my proposed research, I will use synthetic biology tools to quantitatively probe the connection between cell state and signaling specificity. My proposed work will provide insight into how cells of different types achieve unique responses to their environments and will generate computational models that can be used to engineer cellular behavior. To investigate how cells of different types uniquely respond to the same signal, I will use optogenetics to perturb the model signal cAMP in candidate cell types of the early mouse embryo and in an unbiased screen in developing zebrafish. My studies in mouse embryonic stem cells will serve as a proof of principle for controlling cell type through intracellular signaling and for rewiring cellular responses with genetic expression programs. My work in zebrafish will result in a predictive model that can be used to infer a given cell's unique response to a stimulus using only transcriptional data from that cell. Throughout this work, I will focus on generating interpretable computational models that can be used in the future to engineer cellular behavior. I will achieve the above work through synthesizing my previous training in neuroscience, cell signaling, and applied synthetic biology with proposed training in developmental biology, genomics, quantitative modeling of cellular processes, and cellular engineering. I will also supplement my previous training and experience in teaching and mentorship with new training in advocacy to best position myself to mentor my future trainees and further justice, diversity, equity, and inclusion throughout the scientific enterprise. Through my proposed research and training, I will be well positioned to transition to an independent position where I can achieve my scientific and advocacy goals.