Researchers have proposed that a malfunction during brain development when neurons are growing and forming connections with other nerve cells is an underlying cause of autism. In particular, there appears to be impairments in the growth of dendrites—branch-like protrusions the neurons use to form connections with other nerve cells. Defects in dendrite development can lead to abnormal neural connectivity, which reduces the nervous system's ability to function properly. Although a leading theory of autism, this hypothesis needs to be tested at the cellular, molecular and genetic level. Dr. Jan and post-doctoral fellow Quan Yuan plan to study dendrite development in Drosophila—the common fruit fly. Drosophila is a useful system for studying brain development and function because of its simplicity. In fact, researchers can attach molecular markers onto the dendrites of specific neurons and monitor their growth during development. Drs. Jan and Quan will examine the regulation of dendrite development and how abnormal development affects brain function and fly behavior. To do this, they will screen large numbers of Drosophila to find fly mutants with defects in various aspects of dendrite development. They will then use these mutants and state-of-the art genetic techniques to examine the functional consequence of abnormal dendrite development at defined development stages and in specific tissues. Genes identified in these studies could in turn be used to screen for candidate genes for autism in humans. Implications: Findings from this research will demonstrate how defects in the ability of neurons to form connections can influence brain function as well as behavior. It will also establish a vital animal model for studying the brain defects in autism and will help identify underlying genetic components of autism spectrum disorders.