[New in situ hybridization technique with non-radio-labeled probe--detection of choline-acetyltransferase gene expression in rat spinal cord].

We have established a new in situ hybridization method utilizing non-radiolabeled probes. Using this technique, we have attempted to detect the choline-acetyltransferase (ChAT) gene expression in rat spinal cord. It was revealed that the ChAT gene was expressed mainly in the cytoplasm of motor neurons and para-central cells. On the other hand, ChAT protein has already been reported to exhibit a diffused distribution in the cholinergic fibers. Comparing the localization of the ChAT gene with that of the ChAT protein, the ChAT gene was shown to exist only in the cytoplasm surrounding the nuclei. However, the ChAT gene was not expressed in axon terminals where ChAT protein synthesized acetylcholine. This result indicates that the ChAT gene is translated into protein around the nuclei and is thereafter transported toward the action site. We now think that there are two different patterns of neurotransmitter gene distribution. After mRNA is translated into protein, this protein is carried to the action site. On the other hand, mRNA itself is delivered to the action site and translated into protein. After the translation, this protein form exerts its own function. The ChAT gene is suspected as belonging to the first category of gene distribution. In Alzheimer disease, not only the acetylcholine system but also its biosynthetic enzyme, ChAT, system are supposedly destroyed by an unknown factor. If we can clarify the regulatory mechanism of the ChAT gene, this will lead us to the molecular pathogenesis of Alzheimer disease. Additionally, this new in situ hybridization technique should shed some light on the complex brain networks.