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β-actin, a cytoskeletal protein, is the most widely used housekeeping gene. Although housekeeping genes are expressed in all tissues, the β-actin gene is expressed in certain cell types because of differential binding of transcriptional factors to the regulatory elements of the gene. The expression and localization of β-actin protein in the submandibular glands (SMG) of mice were investigated in this study, using Western blot analysis and immunohistochemistry. In ICR and C57BL/6J mice, the levels of β-actin protein in the SMG of females are significantly higher than those in the SMG of males. β-actin protein is majorly distributed in acinar cells of SMG. There is no significant difference in the expression level of β-actin protein between females and castrated males. After castrated male ICR mice are treated with 10 mg/kg/day testosterone propionate (TP) for 3 weeks, the levels of β-actin protein in SMG decrease. The numbers of duct per unit area increase, whereas the numbers of acinus per unit area decrease after TP administration. These data suggest that β-actin protein is mainly distributed in acinar cells of SMG and results in a marked sexual dimorphism in mice.

The effect of ligation of the main excretory duct (MED) of the mouse submandibular gland (SMG) on the expression of Sca-1, a stem cell antigen, was examined by Western blotting and immunohistochemistry. By Western blotting, the expression of Sca-1 with a molecular weight of 18 kDa was identified in the normal gland. At 1 day post-ligation, the expression level of Sca-1 was strongly increased in the experimental gland and weakly in the contralateral gland, and such expression in both glands decreased at 6 days. By immunohistochemistry, Sca-1 was detected weakly in the apical membrane of excretory duct (ED) cells of the SMG under the normal condition. By duct ligation, Sca-1 became expressed strongly in most cells of the two major duct systems, i.e., the striated duct (SD) and granular convoluted tubules (GCT), but was not detected in the acinar (Ac) cells. By fluorescence-activated cell sorter (FACS) analysis, the number of side population (SP) cells in this gland was found to be increased by ligation. These results imply that Sca-1-positive cells may have a role in the duct cell proliferation in the regeneration step elicited by MED ligation-induced injury.

Background: The submandibular gland (SMG) is a major salivary gland, which plays an important role in maintenance the oral health. In this study, we intended to explore the role of the SMG's defense system of the animals in which experimental inflammation is induced. Methods: The levels of mRNAs for inflammation cytokines and acute phase proteins were detected by reverse transcriptase-polymerase chain reaction (RT-PCR). Results: The mRNAs for acute phase proteins were found to be increased in the SMG and extraorbital and intraorbital lacrimal gland (ELG and ILG) of rats at 24 h after subcutaneous injection of turpentine oil. The induction of mRNA for these inflammatory proteins by turpentine oil was preceded by a transient increase in the level of mRNAs for IL-1β, IL-6 and TNF-α at 6 h after subcutaneous injection of the oil. Such cytokine induction was similarly seen by lipopolysaccharide (LPS) injection, and involvement of Toll-like receptor 4 (TLR4) was strongly suggested from experiment using C3H/HeJ mice, a TLR4-deficient mutant strain. Conclusion: The up-regulation of acute phase proteins and inflammation cytokines in the SMG, ELG and ILG by experimental inflammation suggests the existence of a strict defense system via the innate immune system in the SMG and other exocrine gland.