Skin appendage development: from local molecular signalling to tissue-scale mechanics

Vertebrate skin appendages are a diverse group of micro-organs, including feathers, hair, and scales, that have enabled vertebrates to adapt to distinct modes of life. These structures provide crucial models for investigating how developmental patterning and morphogenesis generate intricate and complex biological forms. Classically, these processes have been attributed to chemical (i.e., molecular) systems driven by the interactions of (effectively) diffusing morphogens. However, mechanical processes, driven by the growth and material properties of embryonic tissues, also play a key role in shaping embryonic form. For example, compressive folding that arises from constrained growth of the skin, frustrated by its attachment to underlying tissues, can explain the formation of crocodile head scales. My research investigates both the chemical and mechanical processes governing skin appendage patterning and morphogenesis in diverse vertebrate models, including the embryonic shark, crocodile, tortoise, and chicken. Collectively, I show that, in addition to paradigmatic chemical signalling processes, mechanically-dominated mechanisms also mediate the development and evolution of vertebrate skin appendage diversity.