Cytosolic distribution of villin in M cells from mouse Peyer's patches correlates with the absence of a brush border.

Abstract

The follicle-associated epithelium (FAE) of Peyer's patches mainly consists of two cell types: absorptive enterocytes with a brush border and M cells without this apical specialization. To study the controversial ontogeny of M cells (mesenchymal vs. epithelial origin), the expression pattern of tissue-specific cytoskeletal proteins, markers of cell origin that play a crucial role in the specific shape of epithelial cells and brush border assembly, was investigated. The localization of cytokeratins, vimentin, and villin was determined on mouse FAE using immunocytochemistry and electron microscopy. Epithelial-specific cytokeratins were expressed in both absorptive enterocytes and M cells, whereas vimentin was not detected in mouse FAE. Villin, a tissue-specific, actin-binding protein of the brush border, was expressed in the two cell types. This protein had an unusual cytoplasmic distribution in FAE cells lacking a brush border and in cells having an intraepithelial pocket filled with lymphocytes. The presence of villin and the absence of vimentin in M cells support the intestinal origin of M cells. The cytoplasmic distribution of villin provides a new identification criteria for M cells and reflects the reorganization of the F-actin network, which correlates with the inability of M cells to assemble a brush border.