Most eukaryotic cells are asymmetric or polar; this polarity is essential for normal function. Cellular polarity is established via a number of mechanisms, including the regulated subcellular localization of specific messenger RNAs (mRNAs). Localized mRNA leads to local protein synthesis and use; this is extremely important for normal development of many cells and for synaptic plasticity in neurons. The goal of this research is to deepen our understanding of the basic processes underlying mRNA localization in all cells and, particularly, in neurons. The first aims of the project are to adapt an in vivo technique for use in a particular model organism, the nematode Caenorhabditis elegans. C. elegans is ideally suited for studies of basic cellular processes in neurons for a variety of reasons. The animal is translucent and has a very simple and well described body plan, so individual marked neurons can readily be observed in vivo. It has a completely sequenced and well characterized genome. Finally, it is easy to make transgenic animals and to rapidly isolate mutants. The first part of the project will be to generate transgenic C. elegans that carry fluorescently tagged mRNAs that are non-uniformly distributed within individual identified neurons. After these transgenics have been generated, they will be used in mutageneses and screens to isolate mutants that have abnormal mRNA localization in neurons. Using the tools available in C. elegans, the isolation of mutants will readily lead to the identification of some of the genes involved in this process. Two or more of these genes will be cloned and initial characterization of their expression and protein products will begin before the end of the two year period covered by this grant. The information on these genes and on mRNA localization in C. elegans in vivo will increase our understanding of basic processes that lead to cell polarity and function.