PRESENCE AND PHOSPHORYLATION OF TRANSCRIPTION FACTORS IN DEVELOPING DENDRITES

In screening amplified poly(A) mRNA from hippocampal dendrites and gro wth cones in culture to determine candidates for local translation, we found that select transcription factor mRNAs were present, We hypothe sized that synthesis of transcription factor proteins within dendrites would provide a direct signaling pathway between the distal dendrite and the nucleus resulting in modulation of gene expression important f or neuronal differentiation. To evaluate this possibility, radiolabell ed amplified antisense RNA was used to probe slot blots of transcripti on factor cDNAs as well as arrayed blots of zinc finger transcription factors, The mRNAs encoding the cAMP response element binding protein (CREB), zif 268, and one putative transcription factor were detected, We expanded upon these results showing that CREB protein is present in dendrites, that translation of CREB mRNA in isolated dendrites is fea sible and that CREB protein found in dendrites can interact with the c is-acting cyclic AMP response element DNA sequence by using an in situ Southwestern assay. Further, CREB protein in dendrites is not transpo rted to this site from the cell body because fluorescently tagged CREB microperfused into the soma did not diffuse into the dendrites, In ad dition, CREB protein microperfused into dendrites was rapidly transpor ted to the nucleus, its likely site of bioactivity, Lastly, by using t he isolated dendrite system we show that phosphorylation of Ser-133 on CREB protein can occur in isolated dendrites independent of the nucle us, These data provide a regulatory pathway in which transcription fac tors synthesized and posttranslationally modified in dendrites directl y alter gene expression bypassing the integration of signal transducti on pathways that converge on the nucleus.