Two gene products for beta-galactosidase are differentially expressed in the mouse salivary glands

The specific activity of GM1 ganglioside beta-galactosidase, also known as lysosomal or acidic beta-galactosidase, and the neutral beta-galactosidase were determined in the mouse three major salivary glands and compared to other tissues. Our data indicate that at pH 4.4, lysosomal beta-galactosidase activity in the submandibular gland and the sublingual gland of the mature male is the higher than in the parotid gland, kidney, and skeletal muscle. At pH 7.3, neutral beta-galactosidase activity is overall much lower and is higher in the submandibular gland compared to the sublingual and the parotid glands, kidney, and muscle. En bloc histochemical staining of tissues using x-gal as a substrate at pH 4.4 demonstrates high beta-galactosidase activity in all three salivary glands in comparison to skeletal muscle. At pH 7.3, the submandibular gland demonstrates higher activity, whereas the parotid appears negative and the sublingual gland demonstrates intermediate activity levels. En bloc staining using x-fucose (another substrate of lysosomal beta-galactosidase) demonstrates high activity in all three glands at pH 4.4, and no activity in any of the glands at pH 7.3. Microscopic histochemistry indicates that beta-galactosidase activity is localized to parenchymal cells. Thus, the two gene products for beta-galactosidase are differentially expressed in the salivary glands. These novel findings question the previous use of the bacterial beta-galactosidase (lacZ) as a reporter gene in the salivary glands. Endogenous beta-galactosidase activity in the salivary glands is probably related to glycoprotein metabolism, processing glycoconjugates containing a terminal beta-galactosidic linkage. Further studies of beta-galactosidase function and differential regulation in these tissues are needed.