Are periodic tissue patterns produced by Turing reaction-diffusion?
In plain words
In 1952 Turing showed that two diffusing chemicals, one activating and one inhibiting, can make spots and stripes from a uniform start. Whether real fingers, hair follicles and feather buds form this way, or by cells pulling on each other, is settled for few systems.
Precise statement
For a periodic pattern (vertebrate digits, hair follicles, feather buds, fish skin stripes), determine whether reaction-diffusion of the identified molecules, with measured diffusion constants and reaction rates, satisfies the Turing instability conditions and predicts the wavelength and its change with tissue size, or whether a mechanochemical instability driven by cell traction sets the pattern. Answer: a classification per system with the measured parameters.
What would settle it
In vivo measurement of diffusion and reaction rates of the candidate molecules plus perturbations of diffusion or traction that shift the wavelength as one model predicts.
Status in the literature
A Bmp-Sox9-Wnt Turing network was proposed for digit patterning (Raspopovic and co-workers, Science 2014, doi 10.1126/science.1252960), while mechanical patterning was reported for feather follicles (Shyer and co-workers, 2017).