Acidic β-galactosidase in the developing mouse submandibular gland

Acidic β-galactosidase (β-gal) is expressed at high concentrations in the salivary glands, where its function is unknown but probably related to lysosomal catabolism of glycolipids or glycoproteins such as mucin. Here, the developmental pattern of the enzyme activity in the submandibular gland of B10A/SGSNJ mice was investigated in relation to the expression of mucin. Biochemical studies indicated that the activity of acidic β-gal increases significantly from birth to 3 weeks of age (P<0.05). Histochemical staining of the submandibular glands of embryonic day 15 (E15), E18, 3-week-old and adult mice showed a trend of increasing staining intensity accompanied by a change in the cellular distribution of enzyme activity from E15 to adulthood. Acidic β-gal activity was first evident at E18, around the time mucin production starts, primarily in terminal-bud epithelial cells. The spatial and temporal coordination between the appearance of β-gal and embryonic mucin in the terminal buds of acinar cells might be related to a role of this enzyme in lysosomal degradation of embryonic mucin. In contrast, in adult mice, β-gal activity was primarily found in granular-duct cells. The function of β-gal in duct cells is unclear, but the change in the cellular distribution of β-gal in the mouse submandibular gland could reflect a change in the substrate specificity of this enzyme between E18 and adulthood.