Nick Monk
(University of Sheffield)
From Turing to Wolpert, and Back Again

The concept of a morphogen was introduced by Turing to capture the idea that biologically active chemicals could play an active role in generating form and pattern. The active nature of morphogens is prominent during spontaneous pattern formation in Turing reaction-diffusion systems, and has played an important conceptual role in thinking about the nature of developmental biology. In the late 1960s, a more restricted use of the term morphogen was prompted by Lewis Wolpert's concept of positional information. In Wolpert's approach (and in subsequent work), morphogens became identified with diffusible chemicals that could do little more than passively provide cells with information on their position within a developmental field. This notion of morphogen was much more restricted than Turing's original conception, but had strong support from experimental data. Recent studies on seemingly 'flagship' examples of Wolpertian morphogens has shown, however, that these morphogens actually participate actively in regulatory feedbacks involving tight integration across the whole field being patterned. This extended view of Wolpert's morphogens returns to them the active status that they had in Turing's original concept, and provides new opportunities for exploring Turing's ideas in the context of concrete biological data.