The broad goal of the proposed research is to understand how organellar trafficking is regulated temporally and spatially during development. The developing Drosophila eye will be used as a model system and a gene called marbles (marb) will be used as a starting point. The marb gene product is required for particular nuclear migrations specific to differentiating cells in the developing eye; in eyes of flies with mutations in the marb gene, differentiating cells fail to undergo a stereotypical pattern of nuclear migrations, resulting in inappropriate cell shapes in the adult eye. There is evidence that MARB may be a cell type-specific component of a motor protein complex that facilitates nuclear migration. Many independent marb mutations have been generated and the marb gene has been molecularly cloned. These materials will be used to achieve three specific goals, using a combination of molecular biology histology, genetics, and biochemistry. First, using an antibody to the MARB protein, the expression pattern and subcellular localization of MARB protein in the developing eye will be determined. Second, genetic screens will be employed to identify Drosophila genes that interact with marb genetically. Finally, biochemical assays will be performed in order to test MARB protein for physical interactions with particular cytoskeletal proteins and the products of appropriate genes identified in the genetic screens. The identification of the marb gene provides the opportunity to study two critical cell biological problems from a unique starting point and in an ideal genetic system. First, active regulation of nuclear migration is a key feature of many important biological processes in vertebrates. For example, nuclear migration is required for cell migration in early human brain development; some brain disorders, like lissencephaly, result from defects in nuclear migration. Second, how molecular motor proteins attach to specific cargo is largely unknown. MARB protein may function as an adaptor protein that links the nucleus, either directly or indirectly, to a molecular motor. Almost without exception, every gene and biochemical pathway with an important role in Drosophila development exists and plays a similar role in human development.
