In contrast to H&E (Fig. 5.26a), the periodic acid–Schiff (PAS) staining technique (Fig. 5.26b) results in a positive reaction at the site of the basement membrane. It appears as a thin, well-defined magenta layer between the epithelium and the connective tissue. The stain reacts with the sugar moieties of proteoglycans, accumulating in sufficient amounts and density to make the basement membrane visible in the light microscope. Techniques involving the chapter 5 Epithelial Tissue TH E BASAL DOMAI N AN D ITS SPECIALIZATIONS TABLE Summary of Junctional Features 5.4 Associated Major Intracellular Link Extracellular Cytoskeleton Attachment Classification Proteins Ligands Components Proteins Functions Zonula Occludins, Occludins, Actin ZO-1, ZO-2, Seals adjacent occludens claudins, claudins, flaments ZO-3, AF6, cells together, (tight junction) JAMs JAMs in cingulin controls adjacent cell symplectin passage of ASIP/Povr 3 molecules Rab 36, 13, 8 between them Sec 4, 6, 8 (permeability), defnes apical domain of plasma membrane, involved in cell signaling Zonula E-cadherin-E-cadherin-Actin -Actinin, Couples the adherens catenin catenin flaments vinculin actin cytoske-complex complex in leton to the adjacent cell plasma mem-brane at regi-ons of cell-cell adhesion Macula Cadherins (e.g., Desmogleins, Intermediate Desmoplakins, Couples the adherens desmogleins, desmocollins flaments plakoglobins intermediate (desmosome) desmocollins) in adjacent flaments to cell the plasma membrane at regions of cell-cell adhesion Focal Integrins Extracellular Actin Vinculin, talin, Anchors the adhesion matrix flaments -actinin, actin cytoske-proteins (e.g., paxillin leton to the fbronectin) extracellular matrix, detects and transdu-ces signals from outside the cell Hemides-Integrins Extracellular Intermediate Desmoplakin-Anchors the mosome (64 matrix protein flaments like proteins, intermediate integrin), (e.g., (possible microtu-BP 230 flaments to collagen laminin-5, bules and actin plectin, the extrace-XVII collagen-IV) flaments via inter-erbin llular matrix action with plectin) Gap junction Connexin Connexin in None Not Known Creates a (nexus) adjacent cell conduct between two adjacent cells for passage of small ions and informational micro-molecules Occluding Junction(cell-to-cell) Anchoring Junctions(cell-to-cell) Communicating Junction (cell-to-cell) Anchoring Junctions(cell-to–extracellular matrix) hhhh
FIGURE 5.24 • Lateral interdigitations. This electron micrograph shows infoldings or interdigitations at the lateral surfaces of two adjoining intestinal absorptive cells. 25,000.
reduction of silver salts by the sugars blacken the basement membrane and are also used to demonstrate this structure. Although the basement membrane is classically described as exclusively associated with epithelia, similar PAS-positive and silver-reactive sites can be demonstrated surrounding peripheral nerve supporting cells, adipocytes, and muscle cells (Fig. 5.27); this helps to delineate them from the surrounding connective tissue in histologic sections. Connective tissue cells other than adipocytes do not show a similar PAS-positive or silver reaction. That most connective tissue cells are not surrounded by basement membrane material is consistent with their lack of adhesion to the connective tissue fibers. In fact, they must migrate within the tissue under appropriate stimuli to function.