Ultrastructure and immunohistochemistry of apteric skin in ratites and its epidermal soft cornification

An electron microscopy and immunohistochemistry study has been conducted to acquire comparative information on the structure of apteric skin in ratites, ostrich and emu. The epidermis is thin in the neck of both species and thicker in the dorsal region where acidic and neutral keratins are present in the viable epidermis and stratum corneum. The dermis in both species is mostly occupied by collagen fibrils that form large bundles, often organized in alternated layers in the deeper part of the dermis. Numerous collagen fibrils contact the basement membrane of the epidermis. Sparse tactile Meissner or Krause sensilli are present among the thick collagen bundles. The ostrich epidermis in the dorsal skin is thicker than in the neck, with a columnar basal layer, 3-5 intermediate suprabasal layers and a thick corneous layer. The epidermis of the neck in emu is very thin, featuring two-three narrow cell layers above a flat basal layer and a relatively thick corneous layer. Basal and suprabasal keratinocytes contain lipid droplets and small keratin bundles but no keratohyalin accumulates in pre-corneous cells. The thin corneocytes form a multilayered corneous layer. Loricrine is present in pre-corneous and corneous layers while CBPs, formerly indicated as beta-keratins, are absent in apteric epidermis.