Transcription Factors in Dendrites: Dendritic Imprinting of the Cellular Nucleus

With the advent of new mRNA amplification technologies and improvement in the sensitivity of older methods, an ever-increasing number of mRNAs have been identified in neuronal dendrites. Initially, in situ hybridization was used to localize CamKII (Burgin et al. 1990) and MAP2 (Garner et al. 1988) mRNAs to neuronal dendrites. These experiments were performed by incorporating radioactive nucleotides into cDNA or cRNA probes followed by in situ hybridization and emulsion dipping. Exposure times of a few weeks to a few months were often required to visualize the signal. Because of the limitations of this methodology, only a handful of mRNAs have been identified in dendrites. By combining mRNA amplification methodologies with single dendrite analysis, we have been able to characterize a much larger fraction of the dendritic mRNA population (Miyashiro et al. 1994; Crino and Eberwine 1996). These mRNA amplification methods include aRNA amplification, a linear amplification procedure, which preserves the relative abundances of the amplified mRNAs compared with their original abundances (Van Gelder et al. 1990; Eberwine et al. 1992); and the polymerase chain reaction, which is an exponential amplification procedure (Saikai et al. 1986). Using the aRNA procedure, dendrite cDNA libraries have been made from single dendrites. A photomicrograph of the single dendrite isolation procedure is shown in Fig. 1.