Gene expression and localization of diacylglycerol kinase isozymes in the rat spinal cord and dorsal root ganglia

The dorsal root ganglion (DRG) and dorsal horn of the spinal cord are areas through which primary afferent information passes enroute to the brain. Previous studies have reported that, during normal neuronal activity, the regional distribution of a second messenger, diacylglycerol (DG), which is derived from phosphoinositide turnover, is diverse in these areas. However, the way that DG is regulated in these organs remains unknown. The present study was performed to investigate mRNA expression and protein localization of DG kinase (DGK) isozymes, which play a central role in DG metabolism. Gene expression for DGK isozymes was detected with variable regional distributions and intensities in the spinal cord. Among the isozymes, most intense signals were found for DGK zeta and DGK iota in the DRG. By immunohistochemical analysis, DGK iota immunoreactivity was detected heterogeneously in the nucleus and cytoplasm of small DRG neurons with variable levels of distribution, whereas it was detected exclusively in the cytoplasm of large neurons. On the other hand, DGK iota immunoreactivity was distributed solely in the cytoplasm of most of the DRG neurons. Double-immunofluorescent imaging of these isozymes showed that they coexisted in a large population of DRG neurons at distinct subcellular sites, i.e., DGK zeta in the nucleus and DGK iota in the cytoplasm. Thus, DGK isozymes may have different functional roles at distinct subcellular sites. Furthermore, the heterogeneous subcellular localization of DGK zeta between the nucleus and cytoplasm implies the possible translocation of this isozyme in small DRG neurons under various conditions.