The evolution and development of mechanochemical patterning systems mediating integumentary appendage emergence

Biological patterning involves the spatial organisation of cells and tissues from homogenous states into complex forms, and therefore underlies the development of all living systems. Classical research has focused upon chemical (including molecular) patterning processes, such as Turing reaction-diffusion (RD). In such RD systems, interactions of diffusing activatory and inhibitory morphogens produce stable patterns which dictate the spatial organisation of biological structures. Recent work has shown that mechanochemical processes, in which mechanical cues are integrated with chemical signalling, also contribute to patterning. For example, the mechanical contraction of dermal cells triggers chemical RD patterning of feathers in the chicken. The discovery of mechanochemical processes has constituted a paradigm shift in our knowledge of pattern formation. However, to go beyond the state-of-the-art and obtain a comprehensive evolutionary and developmental understanding of mechanochemical patterning, we must examine these systems in evolutionarily diverse species. MechChem will examine the mechanochemical patterning of denticles (or scales) in the embryonic shark. As sharks belong to an early-diverging vertebrate lineage (the cartilaginous fishes), they occupy the sister lineage of bony vertebrates. Previously, I revealed broad conservation of chemical RD dynamics between both denticle and feather patterning. However, integrated mechanochemical systems in the shark remain unexplored. Using state-of-the-art techniques in fluorescent imaging and biophysical analysis, MechChem will characterise and manipulate mechanical elements of denticle development, to elucidate the roles of mechanochemical patterning. Results will be compared to published work regarding feather patterning and new data concerning avian scale patterning, yielding important evolutionary conclusions regarding the role of mechanochemical systems in mediating biological patterning across the vertebrates.