Keratohyalin-like granules in lizard epidermis: Evidence from cytochemical, autoradiographic, and microanalytic studies

Epidermal sloughing in lizards is determined by the formation of an intraep ithelial shedding complex in which keratohyalin-like granules are formed. T he chemical nature of these granules is unknown, as is their role in kerati nization. The goal of this study was to test whether they contain some amin o acids similar to those found in mammalian keratohyalin. The embryonic and regenerating epidermis of lizards are useful systems to study the formatio n of these granules. Histochemically keratohyalin-like granules react to hi stidine and contain some sulfhydryl groups (cysteine). X-ray microanalysis shows that these granules contain sulfur and often phosphorus, two elements also present in the mature clear, oberhautchen, and beta layer. Instead th e mesos, alpha, and lacunar layers contain only sulfur. Most sulfur is prob ably in a disulfide-bonded form, particularly in mature cells of the sheddi ng complex, in large keratohyalin-like granules, and in the beta-keratin la yer. Early differentiating beta-keratin cells have the maximal incorporatio n of tritiated proline, whereas tritiated arginine is slightly more concent rated in the basal layer of the epidermis. A high uptake of tritiated histi dine is observed mainly in keratohyalin-like granules of the clear layer, b ut also in the oberhautchen layer and forming the alpha-lacunar layer. Immu nogold electron microscopy shows that keratohyalin-like granules do not loc alize keratin but are embedded within a keratin network. These results sugg est that keratohyalin-like granules of lizards, like mammalian keratohyalin , contain some sulfur-rich and histidine-rich proteins. These granules part icipate in the process of hardening of the clear layer that molds the spinu lae of the deeper oberhautchen to form the superficial microornamentation. (C) 2001 Wiley-Liss, Inc.