Embryonic Keratinization in Vertebrates in Relation to Land Colonization

The study examined the embryogenesis and cytology of the epidermis in vertebrates, highlighting the formation of a stratum corneum, which was crucial for land colonization. This process involved keratinocytes composed of cross-linked keratins, proteins, and lipids, forming an effective barrier against water loss, mechanical and chemical stress, and microbial penetration. The epidermis transitioned from an aquatic to a terrestrial type during embryogenesis, preparing for terrestrial life at hatching or birth. The study detailed the development of glycine-rich alpha-keratins and the formation of cornified cell membranes, essential for adult epidermis in reptiles, birds, and mammals. The evolution of keratin-associated proteins was linked to the development of hard skin derivatives like claws and beaks.