Page 1 of 32 Developmental Dynamics Positional Information – a concept underpinning our understanding of developmental biology Neil Vargesson Author for correspondence: Prof Neil Vargesson. School of Medicine, Medical Sciences and Nutrition. Institute of Medical Sciences. University of Aberdeen. Foresterhill. Aberdeen. AB25 2ZD. Email:
[email protected];
[email protected]. Tel: 01224 437374. Key words: Lewis Wolpert, Hydra, Sea Urchin, Chick limb development, French flag model, Progress Zone, Morphogen gradient, Positional value, Pattern formation. 1 John Wiley & Sons, Inc. Developmental Dynamics Page 2 of 32 Abstract It is now 50 years since Lewis Wolpert published the paper in which he set out the concept of Positional Information to explain how spatial patterns of cellular differentiation are generated. This concept has provided a universal model for pattern formation in embryonic development and regeneration and become part of the fabric of the field of developmental biology. Here I outline how Wolpert devised the concept of Positional Information and describe landmark studies from his lab investigating how Positional Information is specified in the developing chick limb. 2 John Wiley & Sons, Inc. Page 3 of 32 Developmental Dynamics Origins of the concept of Positional Information – sea urchins, Hydra and the ‘French Flag Problem’ How a fertilised egg produces a fully patterned embryo and ultimately an independent organism, has fascinated generations of biologists for centuries. Over more than a century ago, some elegant experiments by the German embryologist Hans Driesch (reviewed in Driesch, 1908) on sea urchin embryos began to shed light on this. Driesch separated the two-cell stage embryo into single cells and found that each cell made a complete and perfect embryo but was half the normal size.