SUBCELLULAR LOCALIZATION OF MRNAS IN MAMMALIAN NEURONS

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DESCRIPTION (Investigator's Abstract): Neuronal development has been studied by examining process pathfinding and responses to modulators of process outgrowth. In both the developing and mature neuron the functioning of neuronal processes is critical to the plasticity capacity of the cells. Neuronal processes are specialized cellular structures which function such that neuronal polarity is established with information from presynaptic cells arriving via dendrites while output to post-synaptic cells generally occurs via functioning of the axon. Characterization of proteins in these neuronal structures has been an area of intense study yielding information showing that particular cellular proteins are enriched in the processes. This enrichment likely results in the specialized functioning of these cellular structures. Over the last decade a handful of mRNAs have likewise been localized to the dendritic class of processes and a few mRNAs have been shown to be present in axons of specialized neuronal cell types. With the discovery of these mRNAs and the ultrastructural localization of ribosomes to dendrites it was reasonable to assume that local protein synthesis may contribute to the functioning of dendrites. Recently, these investigators have proven that protein synthesis does indeed occur in individual dendrites and growth cones of hippocampal neurons. As part of their preliminary survey of mRNAs which are present in this subcellular site, they unexpectedly found that the mRNA encoding cAMP responsive element binding protein (CREB) is present in developing dendrites. They have further shown that this CREB mRNA is translated into CREB protein, that this CREB can bind to DNA and that fluorescent CREB which is diffused into these processes moves to the cell nucleus. These data suggest a critical role for CREB and other transcription factors which may be made in neuronal processes, in a developmental process called nuclear imprinting which facilitates the direct communication of dendritic environment with the nucleus of the cell. In this revised grant application, they propose to characterize the biochemistry of CREB in neuronal processes and its potential role in nuclear imprinting by determining whether the translation and post- transnational processing of the CREB that is localized in the neuronal process is altered by synaptic signaling. Because of the potential importance of this observation, they further propose to extend the concept of nuclear imprinting to determine the molecular participants in this regulatory process by doing a detailed expression profile of dendritic growth cones during "development" using the single cell aRNA amplification technology and the DNA chip (screening for 14,000 different mRNAs simultaneously) as well as a novel differential display protocol they have recently developed.