Distribution of Keratin and Associated Proteins in the Epidermis of Monotreme, Marsupial, and Placental Mammals

The study examined the distribution of keratin and associated proteins in the epidermis of monotreme and marsupial mammals, comparing them to eutherian mammals. It found significant interspecific variation in keratohyalin granules (KHGs) size and distribution, particularly in hairless or low-density hair regions. Monotreme and marsupial epidermis showed similarities to eutherians in the distribution of acidic and basic proteins, but differences in the cross-reactivity of antibodies against certain proteins like involucrin and trichohyalin, suggesting species-specific molecular structures. Loricrin distribution in monotremes resembled that in reptiles and birds, indicating a primitive pattern of amniote α-keratogenesis. The study suggested that the presence of loricrin-like proteins in amniote corneous tissues is a primitive feature, and the redistribution mechanism in monotreme keratinocytes might be less specialized than in therian mammals.