Research summary: Monoatomic ions (Na+, K+, Ca2+, Cl-, etc.) are some of the simplest and most abundant chemical species in the biological milieu, but the regulation of their distribution is complex: the human genome contains up to 2000 genes thought to encode components of ion channels and transporters. We aim to map flows of intracellular and extracellular ions, and determine how these can direct cellular decisions on growth, motion, and differentiation. We study these behaviors in the context of embryonic development, where naïve tissues must alter their ion physiology along stereotyped trajectories to form specialized organs such as the heart, brain, and kidney. To do so, we use and develop biosensors and optogenetic tools to nondestructively measure and control these processes, along with other molecular, genetic, and computational modeling approaches. We use the zebrafish embryo as a model to understand cellular computation in a natural context and to observe emergent tissue-level phenomena, and cultured cells as a model to get simplified access to the underlying biochemistry and subcellular biophysics.