The generation of neuronal diversity in the nervous system is a complex process involving the specification and differentiation of a multitude of cellular lineages. Successive developmental programs control the determination and proliferation of individual neuronal types, cell migration, axon extension, and ultimately the formation of functional synaptic connections. Most of these steps are controlled by specific gene expression programs, such as cell fate decisions that lead to the generation of neuronal precursors. The genetic programs underlying the differentiation of mature neurons from their progenitors remain largely unknown, however, in part because of the difficulty in studying neuronal stem cells in their native environments. In the vertebrate olfactory system, primary sensory neurons are continuously regenerated throughout adult life via the proliferation and differentiation of neural progenitor cells. This feature makes the olfactory system particularly amenable for studies on the properties of neuronal stem cells. While some stages of this lineage have been identified with a limited set of molecular markers, the genetic programs that both define and regulate olfactory neurogenesis remain largely unknown. The enormous complexity inherent in this biolo,qical _roblem demands a .qlobal view of .qene expression in order to fully understand the ,qenetic networks Jnderlyin.q neural function and development in this developmental system. In this application we propose a suite of DNA microarray-based techniques to identify - on a ,qlobal scale - patterns of .qene expression correspondin.q to distinct sta.qes of the olfactory neuron linea,qe. We propose (1) to perform temporal profiling of gene expression in olfactory epithelium during embryonic development and lesion-induced regeneration to identify the genes and gene expression programs associated with distinct stages of this lineage, including the earliest multipotent progenitor stage;and (2) to refine this analysis by comparing gene expression patterns in mutants known to disrupt olfactory neurogenesis, and to validate the microarray-based predictions by RNA in situ hybridizations. Our approach is expected to yield highly detailed information about the molecules and pathways responsible for the genesis of olfactory sensory neurons from their progenitor cells. In addition, a broader panel of molecular markers will be generated for distinct stages of olfactory neurogenesis. The elucidation of these ,qenetic pro,qrams at the ,qenome-wide level will provide valuable insi.qhts into the properties of pro,qenitor stem cells from a variety of neural and non-neural systems.
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