Prominin-1 Expression in Developing Submandibular Gland

Objectives: The tube structure of mammalian salivary glands results from lumen formation in a solid mass of epithelial cells during embryonic development. Although the epithelial lumen formation is closely associated with the de novo establishment of apical-basal polarity in cells, how the apical or luminal surfaces of cells are established are largely unknown partly because a molecule expressed on the forming apical cell membranes is unidentified. Here we report that the transmembrane protein prominin-1 is expressed on the apical cell surfaces from the onset of lumen formation in the developing mouse SMG.

Methods: Submandibular gland (SMG) rudiments were isolated from embryos of ddY strain mice. For DNA microarray analysis, total RNA was extracted from embryonic day (E)13 and E17 SMG rudiments, amplified and hybridized on DNA chips (Agilent's Mouse Whole genome4 X 44K). For immunofluorescence microscopy, frozen tissue sections of SMG rudiments taken from embryonic and postnatal mice were incubated with primary antibodies against prominin-1, claudins, ZO-1, and acuaporin-5, followed by incubation with fluorescein-conjugated secondary antibodies and observation with a fluorescence microscope.

Results: To compare gene expression profiles before and after lumen formation in the developing mouse SMG, DNA microarray analysis was performed using E13 and E17 SMG rudiments. The expression level of mRNAs for several transmembrane proteins was found several-fold higher at E17 than E13, one of which was the stem and progenitor cell marker prominin-1. Immunofluorescence microscopy revealed that prominin-1 was expressed in the epithelial but not mesenchymal tissue and detectable at the apical side of cells from the onset of lumen formation. Prominin-1 was localized at more apical side of cells tight junction proteins.

Conclusions: Prominin-1 may be a useful marker for clarifying mechanisms of lumen formation and apical differentiation of polarizing cells in developing salivary glands.