PROJECT SUMMARY Embryogenesis from a fertilized egg into an individual is a precisely controlled process. One of the critical aspects of embryogenesis is developmental patterning, which determines organ size and shape by orchestrating many developmental and cellular events. Any abnormality from this patterning process will lead to congenital diseases in humans. However, understanding the mechanisms that pattern embryos remains a central challenge in developmental biology. The status quo of embryonic developmental patterning centers on the conceptual framework that development is governed predominantly by morphogenetic proteins that activate transcription factor networks in responding cells. The roles of bioelectricity in regulating embryonic developmental patterning have just started to be recognized as a new mechanism of cellular signaling. Given many ion channels and solute carriers are frequently involved in human congenital diseases, there is a critical need to understand ion channel-mediated bioelectricity in developmental patterning. The lack of information about this bioelectric patterning mechanism is a significant obstacle to understanding fundamental biological sciences and developing therapeutic strategies for many human congenital diseases. To address the demanding need, we will investigate the embryonic patterning mechanism of bioelectricity in the zebrafish model using newly developed technologies for neuroscience, such as chemogenetic tools and genetically encoded voltage indicators. Aim1. To elucidate the roles of bioelectricity in regulating zebrafish fin patterning. Aim 2. To reveal the roles of bioelectricity in pigment cell patterning. With this long-studied pigment system, we will further demonstrate bioelectricity as a general patterning mechanism in vertebrate embryogenesis. The expected outcomes will elucidate a less recognized developmental patterning mechanism by bioelectricity in both zebrafish fin and skin pigment. This knowledge will establish a new concept for patterning in developmental biology, provide the foundation for understanding vertebrate morphological diversity in evolution, and principles for developing prevention or therapeutic strategies for congenital diseases.