Immunocytochemistry and Keratinization in the Epidermis of Crocodilians

Lorenzo Alibardi (2003) Immunocytochemistry and keratinization in the epidermis of crocodilians. Zoological Studies 42(2): 346-356. The distributions of alpha and beta keratins, filaggrin and loricrine are described in crocodilian epidermis by immunocytochemistry and electron microscopy. Many layers of beta keratin cells are produced in the outer surface of the scutes, but in the hinge region between scales they are reduced to thin cells of alpha keratin. Alpha keratins are expressed mainly in the basal and a few suprabasal layers, but disappear in the upper spinosus, prekeratinized and keratinized layers. The production of beta keratin, as studied using an antibody against a chicken scale beta keratin, decreases in hinge regions where alpha keratin, including weak keratin-AE2, filaggrin-like, and loricrin-like immunoreactivities are seen. These immunoreactivities are probably associated with a common, unknown antigen. Beta keratin is deposited on bundles of tonofilaments and desmosomes in cells of the upper part of the stratum spinosus which are turned into electron-pale beta keratin packets with the typical 3-4-nm keratin pattern. Some desmosome remnants are present among beta cells of the stratum corneum. Lipid material is also deposited in early beta-keratinizing cells, especially in the hinge regions where beta keratin is replaced by alpha keratin and thin alpha keratinocytes are produced like in the apteric epidermis of birds. Melanosomes derived from epidermal melanocytes are incorporated in maturing keratinocytes from the lowermost level of the stratum spinosus into the stratum corneum, and this produces the skin pigmentation. Although beta keratinization is similar in both neck (softer scales) and tail verticils (harder scales) a heavier condensation of pale beta packets is present in the larger and spinulated beta cells of the tail epidermis. http://www.sinica.edu.tw/zool/zoolstud/42.2/346.pdf