Electron Microscopic Immunogold Localization of Salivary Mucins MG1 and MG2 in Human Submandibular and Sublingual Glands

Abstract

S U M M A R YThe human salivary mucins MG1 and MG2 are well characterized biochemically and functionally. However, there is disagreement regarding their cellular and glandular sources. The aim of this study was to define the localization and distribution of these two mucins in human salivary glands using a postembedding immunogold labeling method. Normal salivary glands obtained at surgery were fixed in 3% paraformaldehyde-0.1% glutaraldehyde and embedded in Lowicryl K4M or LR Gold resin. Thin sections were labeled with rabbit antibodies to MG1 or to an N-terminal synthetic peptide of MG2, followed by gold-labeled goat anti-rabbit IgG. The granules of all mucous cells of the submandibular and sublingual glands were intensely reactive with anti-MG1. No reaction was detected in serous cells. With anti-MG2, the granules of both mucous and serous cells showed reactivity. The labeling was variable in both cell types, with mucous cells exhibiting a stronger reaction in some glands and serous cells in others. In serous granules, the electron-lucent regions were more reactive than the dense cores. Intercalated duct cells near the acini displayed both MG1 and MG2 reactivity in their apical granules. In addition, the basal and lateral membranes of intercalated duct cells were labeled with anti-MG2. These results confirm those of earlier studies on MG1 localization in mucous cells and suggest that MG2 is produced by both mucous and serous cells. They also indicate differences in protein expression patterns among salivary serous cells.

An unusual glycoform of human salivary mucin MG2

“…Alternatively, the split MG2 bands could arise by expression of different glycoforms in mucous or serous acini. This is consistent with immunogold electron microscopy experiments showing that both mucous and serous acini produce MG2 [9].…”

“…Immunochemical and in situ hybridization studies have localized MG2 to serous acini in submandibular, sublingual, and minor salivary glands [5,6] whereas another group using the same procedures localized MG2 to a subset of mucous acini in submandibular and labial salivary glands [7,8]. On the other hand, by using immunogold electron microscopy, we found that MG2 could be localized in both mucous and serous acini of submandibular and sublingual glands, but not in parotid glands [9]. Together, the information above indicates that the MUC7 gene for MG2 has complex expression patterns in the major salivary glands.…”

Expression Analysis of Human Salivary Glands by Laser Microdissection: Differences Between Submandibular and Labial Glands

“…One group localized MUC7 to serous acini in SMGs and LGs using immunohistochemistry and in situ hybridization [40,41]; whereas two other groups clearly defined mucous acini as the expression sites using the same techniques [42,43]. Furthermore, electron microscopic immunogold localization detected MUC7 in both serous and mucous cells with varying intensities [44]. Thus, the results presented here (Fig.…”

Respiratory Tract Mucin Genes and Mucin Glycoproteins in Health and Disease

“…Interestingly, MUC7 mucin, which is well-expressed in mucosal and serosal cells in salivary glands (205), is typically localized to a subset of serous cells in SMG, but only in 15-20% of airway tissue from normal individuals (245). Studies on MUC gene expression in tissues from patients with airway diseases are limited in number and overviewed in section II. Mucin expression in the in vitro NHBE and NHNE model cell systems has also been evaluated in cells derived from healthy airway tissues (19).…”