Ultrastructural Visualization of Cross-Linked Protein Features in Epidermal Appendages

The study investigated the structural integrity of mammalian hair, bird feathers, and hagfish horny teeth after extraction with ionic detergent under reducing conditions. Despite the removal of solubilizable components like disulfide-bonded keratins, the structures remained largely intact due to ε-(γ-glutamyl)lysine cross-linked proteins. In hair, cell envelopes and intracellular deposits were preserved, while feathers retained barb structures but not the rachis. Hagfish teeth maintained visible cellular organization. The study identified four types of cross-linked features, highlighting the role of transglutaminases and substrate proteins in maintaining the function of epidermal appendages. These findings suggested potential diagnostic applications for assessing structural perturbations in these tissues.