Diet and the evolution of human amylase gene copy number variation

Diet and the - LETTERS 2007 Nature Publishing Group http/www.nature.com/naturegenetics Diet and the evolution of human amylase gene copy number

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Diet and the evolution of human amylase gene copy number variation George H Perry 1,2 , Nathaniel J Dominy 3 , Katrina G Claw 1,4 , Arthur S Lee 2 , Heike Fiegler 5 , Richard Redon 5 , John Werner 4 , Fernando A Villanea 3 , Joanna L Mountain 6 , Rajeev Misra 4 , Nigel P Carter 5 , Charles Lee 2,7,8 & Anne C Stone 1,8 Starch consumption is a prominent characteristic of agricultural societies and hunter-gatherers in arid environments. In contrast, rainforest and circum-arctic hunter- gatherers and some pastoralists consume much less starch 1–3 . This behavioral variation raises the possibility that different selective pressures have acted on amylase, the enzyme responsible for starch hydrolysis 4 . We found that copy number of the salivary amylase gene ( AMY1 ) is correlated positively with salivary amylase protein level and that individuals from populations with high-starch diets have, on average, more AMY1 copies than those with traditionally low-starch diets. Comparisons with other loci in a subset of these populations suggest that the extent of AMY1 copy number differentiation is highly unusual. This example of positive selection on a copy number–variable gene is, to our knowledge, one of the Frst discovered in the human genome. Higher AMY1 copy numbers and protein levels probably improve the digestion of starchy foods and may buffer against the Ftness-reducing effects of intestinal disease. Hominin evolution is characterized by signiFcant dietary shifts, facilitated in part by the development of stone tool technology, the control of Fre and, most recently, the domestication of plants and animals 5–7 . Starch, for instance, has become an increasingly prominent component of the human diet, particularly among agricultural societies 8 . It stands to reason, therefore, that studies of the evolution of amylase in humans and our close primate relatives may provide insight into our ecological history. Because the human salivary amylase gene ( AMY1 ) shows extensive variation in copy number 9,10 , we Frst assessed whether a functional relationship exists between AMY1 copy number and the amount of amylase protein in saliva. We then determined if AMY1 copy number differs among modern human populations with contrasting amounts of dietary starch. We estimated diploid AMY1 gene copy number for 50 European Americans using an AMY1 -speciFc real-time quantitative PCR (qPCR) assay. We observed extensive variation in AMY1 copy number in this population sample ( Fig. 1a and Supplementary Table 1 online), consistent with previous studies 10,11 . Next, we performed protein blot experiments with saliva samples from the same indivi- duals in order to estimate salivary amylase protein levels ( Fig. 1b ). These experiments showed a signiFcant positive correlation between salivary amylase gene copy number and protein expression ( P o 0.001; Fig. 1c ).
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This note was uploaded on 01/06/2010 for the course NS 1150 taught by Professor Levitsky during the Fall '05 term at Cornell University (Engineering School).

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Diet and the - LETTERS 2007 Nature Publishing Group http/www.nature.com/naturegenetics Diet and the evolution of human amylase gene copy number

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