Selective localization of diacylglycerol kinase (DGK)ζ in the terminal tubule cells in the submandibular glands of early postnatal mice

The present immunohistochemical study was attempted to localize in the submandibular glands of mice at various postnatal stages a diacylglycerol kinase (DGK) isoform termed DGKζ which is characterized by a nuclear localization signal and a nuclear export signal. This attempt was based on following facts: the continuous postnatal differentiation of glandular cells in the rodent submandibular gland, the regulatory role of DGK in the activity of protein kinase C (PKC) through attenuation of diacylglycerol (DAG), and the possible involvement of PKC in various cellular activities including the saliva secretion as well as the cell differentiation. As a result, a selective localization of immunoreactivity for DGKζ was detected in terminal tubule (TT) cells which comprise a majority of the newborn acinar structure and differentiate into the intercalated duct cells and/or the acinar cells. The immunoreactivity was deposited in portions of the cytoplasm lateral and basal to the nucleus, but not in the nuclei themselves. Although the immunoreactive TT cells remained until later stages in female specimen than in male, they eventually disappeared in both sexes by young adult stages. The present finding suggests that the regulatory involvement of DGKζ in PKC functions via control of DAG is exerted in the differentiation of the TT cells. In addition, another possible involvement of DGKζ in the regulation of secretion of the TT cells as well as its functional significance of its nuclear localization in the submandibular ganglion cells was also discussed.