Structural Features and Sites of Expression of a New Murine 65 kD and 48 kD Hair-Related Keratin Pair, Associated with a Special Type of Parakeratotic Epithelial Differentiation

The study identified a new pair of murine keratins, 65 kD and 48 kD, expressed in specific epithelial sites such as the suprabasal cells of adult mouse tail scale epidermis and the posterior unit of the filiform papillae of the mouse tongue. These keratins were associated with a unique type of parakeratotic epithelial differentiation, characterized by the absence of a granular layer and a compact stratum corneum. Their expression was suppressed during retinoic acid-induced orthokeratotic conversion. Structurally, these keratins resembled "hard" α keratins, with non α-helical domains rich in cysteine and proline, and they evolved alongside hair keratins, forming an independent branch within the keratin multigene family. Their expression was adapted to anatomical sites where a balance between softness and rigidity was functionally necessary.