Immunolocalization of Scaffoldin, a Trichohyalin‐Like Protein, in the Epidermis of the Chicken Embryo

ABSTRACT Recent comparative genomic studies have identified a chicken gene that codes for a trichohyalin‐like protein rich in arginine and glutamic acid termed scaffoldin. Immunocytochemistry and immunoelectron microscopy show that this protein is predominantly localized in periderm granules, subcellular structures present in the periderm of the embryonic epidermis of chick scales, beak, claw, and in the sheath of developing and regenerating feathers. This suggests that scaffoldin contributes to the formation of periderm granules and to the soft cornification of the embryonic epidermis before the definitive epidermis is formed. Scaffoldin is absent from the definitive and adult epidermis generated underneath the periderm in scales and in inter‐follicular regions. Scaffoldin mixes with corneous beta‐proteins (beta‐keratins) synthesized in keratinocytes of the transitional layers formed beneath the periderm in the subunguis of the developing claws. Immunoreactivity for scaffoldin is absent in keratinocytes that accumulate corneous beta‐proteins such as those of scales, claws, and barbule‐barb cells of feathers. Corneous beta‐proteins represent the prevalent type of proteins present in adult epidermis of claws, scales, and feathers. These observations indicate that scaffoldin is a protein of transitional epidermal cells of the avian integument and might represent an important component of periderm granules. Anat Rec, 298:479–487, 2015. © 2014 Wiley Periodicals, Inc.