A morphometric study of alterations in rough endoplasmic reticulum during differentiation in stratified squamous epithelium.

Stereological techniques were applied to investigate several structural parameters characterising the rough endoplasmic reticulum (RER) during differentiation in hamster cheek-pouch epithelium. Mucosal samples from five Syrian golden hamsters were obtained and processed for electron microscopy. Following a strict sampling regime, micrographs were obtained from defined basal, spinous and granular layers, and subjected to stereological point and intersection counting procedures. This enabled volume and surface densities, and volume-to-surface ratios of RER to be determined for each cellular layer. From previous estimates of the mean cytoplasmic volume of the "average" basal, spinous and granular cell in this tissue, it was possible to calculate the absolute volume and surface area of RER present in these average cells. Both volume and surface densities of RER decreased between basal and granular layers, whereas the total volume and surface area present in the average spinous and granular cell were both higher than in the average basal cell. These data suggest that RER is being synthesised during epithelial differentiation. In view of the role of the RER in the production of exportable proteins, it is possible that increased amounts of this organelle are required to synthesise the enzymes and glycoproteins found in membrane-coating granules, since these are also seen with increasing frequency in successively higher strata.