PROJECT SUMMARY Some animals have very robust regenerative capacities while others, like humans, have more limited ones. The severity of the injury, as well as the type of the tissue damaged and the animal age, can all impact the regeneration outcomes. Sensory organs are of particular interest to regenerative medicine, as they play a fundamental role in collecting information from our surrounding environment, are composed of multiple cell types, some of these highly specialized, and are directly connected to the central nervous system. Because of this complexity and the scarcity of animals that can robustly regenerate them as adults, we did not have the systems and tools to answer several core questions on this topic. To uncover the molecular mechanisms driving the complete regeneration of sensory organs, we use a freshwater apple snail, Pomacea canaliculata, that has the extraordinary ability to fully regenerate its complex eyes and its cephalic tentacles in only a few weeks. After sequencing the P. canaliculata genome, I developed methods to assess their gene function through CRISPR/Cas9 mutagenesis and mRNA overexpression and collected transcriptomic datasets during the regeneration of the eyes. The proposed project focuses on the mechanisms regulating cell fate specification during the complete regeneration of different complex sensory organs in adult animals. To achieve this, we will take advantage of the possibility to compare the regeneration of two different sensory organs in apple snails: the cephalic tentacles and the eyes. We will take a two-pronged approach: (1) We will establish at what stage the regeneration programs of the two injury paradigms diverge by identifying similarities and differences in the transcriptional responses following eye and tentacle amputation. This will allow us to distinguish between a general regeneration program and organ-specific ones. (2) We will determine the regulatory regions that orchestrate the regeneration of complex