Molecular evolution of skin appendages

The evolution of cornified skin appendages, such as claws and hair, was critical for the evolution of land-dwelling vertebrates. Hair, which is the best characterized type of skin appendage, depends on its main protein components, the hair keratins, and on Hoxc13, a regulator of keratin gene expression. The molecular control of other skin appendages and their evolutionary relationships are not well understood. The aim of the present project is to gain insights into the evolutionary origin of the genetic program which controls the growth and protein composition of cornified skin appendages. We hypothesize that hair keratin-like proteins and their regulation by Hoxc13 have originated already during the water-to-land transition of early tetrapods. Accordingly, they are predicted to play critical roles not only in hair but also in cornified skin appendages of amphibians. To test these hypotheses, we will determine the protein composition of claws and the effect of Hoxc13 deletion in a model species, the western clawed frog. The genetic control of claws will be compared among representative species from all main clades of tetrapods. This project will inform about key steps in the evolution of cornified skin appendages in terrestrial vertebrates.