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 that while the distribution of acidic and basic keratins in monotreme and marsupial epidermis was similar to eutherians, there were significant differences in the presence and cross-reactivity of other proteins like filaggrin, loricrin, involucrin, and trichohyalin. Notably, loricrin showed a weak to intense cross-reactivity in monotremes and marsupials, suggesting a primitive feature of amniote α-keratogenesis. The study highlighted that the mechanism of protein redistribution during keratinocyte maturation in monotremes might be more primitive compared to therian mammals.