Understanding form is probably the biggest problem in biology. OK, many would argue that the brain is the one. But let’s not quibble. If we can just about understand how single-celled life evolved, working out how we acquire our limbs, eye, noses, mouths is a way beyond that in terms of complexity. But we know a lot. Why do pretty well all higher creatures have 5 digits? A gene called sonic hedgehog is largely responsible. But it used to be thought that the gene operates on the basis of a concentration gradient. It runs from thumb to little finger then runs out of steam (polydactyl though is sometimes seen).
But a report in Science back in December (only just arrived in the British Library after supply problems) shows that Alan Turing’s reaction–diffusion process may be involved. This was proposed in 1952, a year before DNA let alone genome biology and for a long time was regarded with suspicion by biologists. But it is very much back in the frame now. Turing’s mechanism was originally devised to explain stripes and spots but if you think about it, digits are stripes: digit, no digit, digit, no digit . . . It has long been known that the hand begins as a one-piece and between the digits cells have to die to create the famous five. Now it seems that hox genes control the expression of sonic hedgehog. In mice, knocking them out causes a progressive increase in digits – 14 being the maximum attained so far. The researchers interpret the extra digits in terms of Turing’s theory: the wavelength of the reaction–diffusion patterns has been changed by the hox genes, resulting in more toes in the same space. There’s lets more to learn about this but new insights into form such as this are coming thick and fast now.
Science, 2012, 338, pp. 1406 and 1476.
But a report in Science back in December (only just arrived in the British Library after supply problems) shows that Alan Turing’s reaction–diffusion process may be involved. This was proposed in 1952, a year before DNA let alone genome biology and for a long time was regarded with suspicion by biologists. But it is very much back in the frame now. Turing’s mechanism was originally devised to explain stripes and spots but if you think about it, digits are stripes: digit, no digit, digit, no digit . . . It has long been known that the hand begins as a one-piece and between the digits cells have to die to create the famous five. Now it seems that hox genes control the expression of sonic hedgehog. In mice, knocking them out causes a progressive increase in digits – 14 being the maximum attained so far. The researchers interpret the extra digits in terms of Turing’s theory: the wavelength of the reaction–diffusion patterns has been changed by the hox genes, resulting in more toes in the same space. There’s lets more to learn about this but new insights into form such as this are coming thick and fast now.
Science, 2012, 338, pp. 1406 and 1476.
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