Takaaki Tamura

Molecular cloning and characterization of neural activity-related RING finger protein (NARF): a new member of the RBCC family is a candidate for the partner of myosin V

Activity‐dependent synaptic plasticity has been thought to be a cellular basis of memory and learning. The late phase of long‐term potentiation (L‐LTP), distinct from the early phase, lasts for up to 6u2003h and requires de novo synthesis of mRNA and protein. Many LTP‐related genes are enhanced in the hippocampus during pentyrenetetrazol (PTZ)‐ and kainate (KA)‐mediated neural activation. In this study, mice were administered intraperitoneal injections of PTZ 10 times, once every 48u2003h, and showed an increase in seizure indexes. Genes related to plasticity were efficiently induced in the mouse hippocampus. We used a PCR‐based cDNA subtraction method to isolate genes that are expressed in the hippocampus of repeatedly PTZ‐treated mice. One of these genes, neural activity‐related RING finger protein (NARF), encodes a new protein containing a RING finger, B‐box zinc finger, coiled‐coil (RBCC domain) and β‐propeller (NHL) domain, and is predominantly expressed in the brain, especially in the hippocampus. In addition, KA up‐regulated the expression of NARF mRNA in the hippocampus. This increase correlated with the activity of the NMDA receptor. By analysis using GFP‐fused NARF, the protein was found to localize in the cytoplasm. Enhanced green fluorescent protein‐fused NARF was also localized in the neurites and growth cones in neuronal differentiated P19 cells. The C‐terminal β‐propeller domain of NARF interacts with myosinu2003V, which is one of the most abundant myosin isoforms in neurons. The NARF protein increases in hippocampal and cerebellar neurons after PTZ‐induced seizure. These observations indicated that NARF expression is enhanced by seizure‐related neural activities, and NARF may contribute to the alteration of neural cellular mechanisms along with myosinu2003V.

Transcriptional regulation of mouse type 1 inositol 1,4,5-trisphosphate receptor gene by NeuroD-related factor.

Abstract: The type 1 inositol 1,4,5‐trisphosphate receptor (IP3R1) is a Ca2+ channel protein that is expressed abundantly in the CNS, such as in the cerebellar Purkinje cells and hippocampus. We previously demonstrated that the box‐I element, which is located —334 relative to the transcription initiation site of the mouse IP3R1 gene and includes an E‐box consensus sequence, is involved in the up‐regulation of such IP3R1 gene expression. Furthermore, the previous study also indicated that some CNS‐related basic helix‐loop‐helix (bHLH) factors bind to the box‐I and activate IP3R1 gene expression. In this study, we demonstrated that one of the CNS‐related bHLH factors, neuronal differentiation factor (NeuroD)‐related factor (NDRF), specifically bound to the box‐I sequence with a ubiquitously expressed bHLH protein, E47, and activated IP3R1 gene expression. In situ hybridization of adult mouse brain revealed that IP3R1 and NDRF mRNA were co‐expressed in many subsets of neurons, highly in Purkinje cells and hippocampus and moderately in cerebral cortex, olfactory bulb, and caudate putamen. Furthermore, the spatiotemporal expression patterns of these two genes resembled one another throughout postnatal development of the mouse CNS. From these results, we suggest that NDRF is involved in the tissue‐specific regulation of IP3R1 gene expression in the CNS.

MECHANISMS OF TRANSCRIPTIONAL REGULATION AND NEURAL GENE EXPRESSION

Gene transcription is governed by a set of basal transcription machineries and gene-specific factors. Eukaryotic RNA polymerases alone can not direct specific transcription, but need associated factors, namely general transcription factors (GTFs). The basal transcription machineries composed of RNA polymerase and GTFs bind to a promoter and govern efficient and correct transcription for constitutive gene expression. Protein-coding genes are transcribed by RNA polymerase (Pol) II whereas Pol I and Pol III synthesize ribosomal RNA and various small RNAs, respectively. Enhancer is another class of cis-element for Pol II to which transcription regulatory factors bind. Those factors are involved in inducible, repressive, and tissue-specific gene expressions via binding to their target sequences. Regulatory factors have multiple structural motifs and interact with basal machineries directly or indirectly (using mediators) in addition to DNA. Many transcription factors are known to regulate nervous system-specific gene expression, which include bHTH, bHLH, basic leucine zipper, and zinc finger factors and prorine-rich activators. These factors, some of which belong to a neural silencer factor, play roles in neural development, establishment of memory and learning, and expression of nervous system-specific proteins.