To understand the changes undergone by squamous epithelial cells during terminal differentiation, it is important to determine distributions of key proteins at successive stages. As a complement to immuno-cytochemistry, we have performed EM-based elemental mapping of sulfur and nitrogen in newborn mouse epidermis and forestomach. Energy-filtered transmission electron microscopy (EFTEM) images reveal high sulfur concentrations in round cytoplasmic granules and in the cornified cell envelope (CE), correlating with loricrin (about 6% cysteine). Electron energy-loss spectroscopy (EELS) analysis confirms these observations, supporting the inferred precursor-product relationship between L-granules and the CE. Other deposits near the epidermal CE have a similar sulfur content, but do not label with antiloricrin antibodies, thus suggesting the presence of another S-rich protein.
