Distinct hormonal regulation of two types of sexual dimorphism in submandibular gland of mice.

The submandibular gland (SMG) of mice exhibits prominent sexual dimorphism in two aspects: the preferential development of granular convoluted tubule (GCT) cells and the earlier disappearance of granular intercalated duct (GID) cells in males after puberty. The former is dependent on androgens and thyroid hormones, whereas the hormonal dependence of the latter remains obscure. In the present study, we examined the effects of the postnatal administration of androgens and thyroid hormones to wild-type (WT) and androgen-receptor-knockout (ARKO) mice on these two types of sexual dimorphism by counting the numbers of GCT and GID cells labeled with nerve growth factor and submandibular gland protein C, respectively, as immunohistochemical markers. WT females and ARKO males and females exhibited a lower number of GCT cells and higher number of GID cells at 5 and 11 weeks postpartum than WT males. The administration of dihydrotestosterone for 1-2 weeks prior to these ages caused an increase in GCT cells and decrease in GID cells in WT females to similar levels as those in WT males, whereas it had no effects in ARKO, indicating that both types of sexual dimorphism are androgen-dependent. In contrast, the administration of thyroxine caused an increase in GCT cells but did not cause a decrease in GID cells in WT females or ARKO, indicating that the former is dependent on thyroid hormones, whereas the latter is not. The present results suggest that the two types of sexual dimorphism in the mouse SMG undergo distinct forms of hormonal regulation and, therefore, have different mechanisms.

Synthesis, localization and possible function of serine (or cysteine) peptidase inhibitor, clade B, member 6a (Serpinb6a) in mouse submandibular gland.

The granular convoluted tubule (GCT) in the duct system of the submandibular gland (SMG) develops preferentially in male mice and produces a number of bioactive peptides including proteases such as renin and kallikrein. We examine the synthesis and localization of the serine (or cysteine) peptidase inhibitor, clade B, member 6a (Serpinb6a), the mouse ortholog of the human intracellular serine protease inhibitor SERPINB6, in the mouse SMG by using reverse transcription plus the polymerase chain reaction, in situ hybridization, immunoblotting and immunohistochemistry. Serpinb6a mRNA expression was more abundant in the male than in the female SMG and in the GCT than in other duct portions or acini. Within GCT cells, immunoreactivity for Serpinb6a was localized in the nucleus and cytosol but was absent in the secretory granules. The binding target of Serpinb6a in the SMG was investigated by using a mass spectrometric analysis of immunoprecipitation products and kallikrein-1-related peptidase b26 (Klk1b26), a serine protease, was identified. These results raise the possibility that Serpinb6a functions in the protection of GCT cells from intracellular kallikreins that may leak from secretory granules.