Expression with early postnatal peak and female-dominant sexual dimorphism of phospholipase D (PLD) 2 in submandibular gland ducts in situ of mice

In the present study, expression and localization of PLD2 were examined in mouse submandibular glands in situ in comparison with those of PLD1 previously reported by the present authors. In immunoblots, PLD2-expression was high at postnatal 0 week (P0W) and P2W, and at P4W decreased considerably with the decrease of the male gland more marked, and at P8W it was undetectable in the male gland, but remained faint in the female. In the male gland at P8W after castration at P6W, PLD2-expression reappeared faintly. In the female glands with daily injections of testosterone started at P6W, at P8W the expression was undetectable. In immunohistochemistry, PLD2 was localized throughout immature duct epithelia without distinct regional differences in its intensity at P0W and P2W. PLD2-localization was weak and diffuse in granular convoluted tubules at P4W and negligible there at P8W in the female gland, while it was at negligible levels in the tubules at P4W and at undetectable levels there at P8W in the male gland. The expression changes detected in immunoblots after castration or testosterone injection were duplicated in granular convoluted tubules in immunohistochemistry. The present findings suggest that PLD2 is dominantly involved in proliferation/differentiation/apoptosis of most immature ductal cells at early postnatal and at least perinatal stages, different from PLD1. This also indicates that the female-dominant sexual dimorphism of PLD2-expression occurs in synchrony of differentiation of granular convoluted tubules at puberty and at young adulthood, similar to PLD1 though at much lower levels.