From yeast to humans, actin – a protein best known for its role in forming cytoskeletal filaments that give cells their shape and allow them to move – also localizes to and functions inside the nucleus. This nuclear localization of actin was controversial initially, so the functions of nuclear actin are only just now being uncovered. This project will define functions of nuclear actin within the nucleolus, a subcompartment of the nucleus. The nucleolus is a non-membrane bound organelle that is the site of ribosomal RNA (rRNA) synthesis and, so, mediates ribosome formation; ribosomes produce proteins, the factors that mediate cellular functions. Thus, too little or too much nucleolar activity has deleterious outcomes, from cell dysfunction to cell or organism death. The project will use Drosophila, a robust genetic system, and the non-essential tissues of oogenesis (egg development) to advance understanding of how nuclear actin tightly controls nucleolar functions, providing insights into normal cellular function and development, as well as into how misregulation can contribute to diseases. This project will also train the next generation of biologists by developing undergraduate laboratory course modules that bring this research into the classroom and by mentoring trainees in the research lab. The functions of actin in both the cytoplasm and the nucleus depend on the form of actin – monomers, polymers, filaments, and networks of filaments. The objective of this proposal