Marian L. Miller

Image of an intraepithelial lymphocyte (IEL) from a CLIC5 mutant mouse small intestine. The CLIC (Chloride Intracellular Channel) family of proteins is expressed in a wide variety of cell types, and several isoforms are known to cycle between soluble and membranebound forms. As well as being widely expressed, the CLICs are involved in diverse functions, including tubulogenesis, immune cell activation, apoptosis and calcium handling. CLIC5 has been shown to associate with cytoskeletal proteins in placental microvilli and inner ear cells, and is required for proper maintenence of hair cell steriocilia. It has also been localized to the cytosol of human intestinal epithelial cells, though its function there remains unclear. The study in which this particular “IEL” was found, involved a search to see what function CLIC5 played in the modulation of tubulovesicles and microvillar apical membranes in the process of acid secretion. In particular, the relative amounts and structural characteristics of these two membrane types was quantified in parietal cells.

Gingival overgrowth is a common health problem caused by genetic and environmental risk factors. Animal models for quantitative histological studies are needed to uncover genetic predisposition and dose‐response data that might put individuals at increased risk for gingival disease. Gingival height, thickness, inflammation, and the degree of encroachment of gingiva over the tooth, are clinical measures of overgrowth; most of these parameters can be measured histologically, but in order to quantify gingival coverage of the tooth, the image of the crown must be present. Tooth and bone typically require decalcification for histology; thus, the tooth crown, a critical landmark, is lost. We describe a method for imaging the crown histologically, using impression materials applied to dissected mouse mandibles. Four dental alginates, three polyvinyl siloxanes, and one polyether and gelatin were used. The impression‐material/mandibular tissue blocks were processed routinely. Polyvinyl siloxanes were incompatible with embedding resin; alginates, polyether and gelatin could be fixed, decalcified, embedded, and sectioned. Alginates and gelatin could be stained. Success in imaging the tooth crown varied with the preparation, but the alginates, polyether, and gelatin permitted a useful degree of measurement of exposed crown and enamel thickness, along with other morphometric parameters such as thickness of the dentin, lateral mandibular ramus, rete pegs, height of the gingiva, and volume density of vessels and inflammatory cells in the lamina propria. In conclusion, this new application for impression materials allows gingival coverage of tooth crown, as well as numerous other parameters to be measured for comparison with clinical data. Microsc. Res. Tech. 60:528–536, 2003.

Ion transporters play a central role in gastric acid secretion. To determine whether some of these transporters are necessary for the normal ultrastructure of secretory membranes in gastric parietal cells, mice lacking transporters for H⁺, K⁺, Cl^–, and Na⁺ were examined for alterations in volume density (Vd) of basolateral, apical, tubulovesicular and canalicular membranes, microvillar dimensions, membrane flexibility, and ultrastructure. In mice lacking Na⁺/H⁺ exchanger 1 (NHE1) or the Na⁺-K⁺-2Cl^– cotransporter (NKCC1), the ultrastructure and Vd of secretory membranes and the secretory canalicular to tubulovesicular membrane ratio (SC/TV), a morphological correlate of secretory activity, were similar to those of wild-type mice. In mice lacking Na⁺/H⁺ exchanger 2 (NHE2) or gastric H⁺, K⁺-ATPase α- or β-subunits, the SC/TV ratio and Vd of secretory membranes were decreased, though canaliculi were often dilated. In H⁺, K⁺-ATPase-deficient parietal cells, canalicular folds were decreased, normally abundant tubulovesicles were replaced with a few rigid round vesicles, and microvilli were sparse, stiff and short, in contrast to the long and flexible microvilli in wild-type cells. In addition, microvilli of the H⁺, K⁺-ATPase-deficient parietal cells had centrally bundled F-actin filaments, unlike the microvilli of wild-type cells, in which actin filaments were peripherally positioned concentric to the plasmalemma. Data showed that the absence of H⁺, K⁺-ATPase produced fundamental changes in parietal cell membrane ultrastructure, suggesting that the pump provides an essential link between the membranes and F-actin, critical to the gross architecture and suppleness of the secretory membranes.