The discovery of transcription factor protein and mRNA in neuronal dendrites led to an elaboration of the """"""""dendritic imprinting"""""""" hypothesis which suggests that transcription factors that are synthesized in the dendrite move to the nucleus to elicit a transcriptional response. The biological rationale for dendritic synthesis of a transcription factor that functions in the nucleus may be that the dendritic transcription factor would produce a transcriptional response distinct from that that would be generated through the normal convergence of stimulus-induced second messenger system signaling that modulates nuclearly localized transcription factors. Such distinct functioning may be associated with a unique dendritically-induced post-translational modification of the transcription factor. To examine the viability of this hypothesis, dendrites were screened for the presence of mRNAs that encode transcription factors. Among the dendritically localized transcription factors that we found, Elk-1 mRNA was particularly intriguing given that preliminary data shows selective dendritic translation of Elk-1 protein causes neuronal cell death. This discovery was enabled by our development of a novel photoporation technique that permits the introduction of small amounts of RNA into any subregion of a live neuron. The ability of a dendritically translated protein to elicit cell death was unexpected. The mechanism(s) by which dendritically synthesized Elk-1 protein causes cell death will be assessed through three Specific Aims.
These Aims are to 1) Define the neuronal morphological parameters associated with the ability of dendritically synthesized Elk-1 to elicit cell death, 2) Characterize the post-translational modifications of dendritically synthesized Elk-1 that permit it to associate with mitochondria and to move into the nucleus to elicit cell death and 3) Determine the genes that are modulated by dendritically synthesized Elk-1 protein versus that made in the cell soma. The ability of the genes whose abundances are altered selectively by dendritic Elk-1 to recapitulate cell death will be assessed using a novel """"""""global mixed RNA pool"""""""" functional screen. Upon completion of these studies we anticipate that the data will inform our understanding of the role of dendrites in modulating cell viability and may provide insight into the neurodegenerative processes associated with selected human diseases. The biological consequences of the localization of transcription factor mRNA and local synthesis in neuronal dendrites will be assessed. A combination of standard and novel cell biological, anatomical and molecular approaches will be used in this determination.
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