Expression and localization of receptor protein tyrosine phosphatase β and its ligand pleiotrophin in the submandibular gland of mice.

OBJECTIVES The family of receptor protein tyrosine phosphatase β (RPTPβ) is composed of 4 splice variants and thought to play roles in the neural migration and outgrowth. Several ligands including the growth factor pleiotrophin (PTN) bind to RPTPβ and inhibit its phosphatase activity, thereby activating cellular signalling pathways. We examined the expression and localization of RPTPβ and its ligands in the submandibular gland (SMG) of mice, which is known for a prominent sexual dimorphism in the duct system. DESIGN The homogenates and tissue sections of male and female mouse SMG were analysed with RT-PCR, Western blotting, and immunohistochemistry. RESULTS The short receptor type of RPTPβ (RPTPβ-S) was dominantly expressed in the SMG, and the male gland had significantly higher levels of RPTPβ-S expression than the female gland. In the male, RPTPβ-S was localized predominantly in intercalated duct (ID) cells, but was not found in granular convoluted tubule (GCT) cells or acinar cells. In the female, weaker reactivity was demonstrated in both ID and striated duct (SD) cells. Of the known ligands for RPTPβ, PTN was expressed in the SMG, without sexual difference in levels. In the male, PTN was localized in ID cells as well as in cells located in the distal ends of GCT that are in close vicinity to the ID, whereas in the female PTN was colocalized with RPTPβ-S throughout ID and SD cells. CONCLUSIONS These results indicated that the distribution of RPTPβ-S and its ligand PTN has a close relation to the sexual dimorphism in the duct system of mouse SMG.