Tuesday, November 7, 2006

Pecking Ordered

drj writes "Darwin found on the Galapagos Islands 14 species of finches with different beak shapes. He proposed that their different beaks allowed them to exploit different foods – short and wide for cracking seeds vs. long and narrow for reaching into flowers. Abzhanov et al. now show that expression of the bone morphogenic protein 4 gene (Bmp4) is higher in the upper beak epithelium of embryonic chicks growing shorter, stronger beaks, suggesting that BMP4 shapes beaks. Expression of Bmp2 and Bmp4 message, in contrast, correlated with the size of the beak. Surprisingly, expression of Bmp4 in the lower beak epithelium does not vary despite shape differences that are comparable to those in the upper beak. Infection with a virus expressing BMP4 protein produced shorter, wider beaks whereas infection with a virus expressing Noggin, which antagonizes BMP2/4/7 activity, produced longer, narrower beaks. The authors are also “tempted to speculate” that Sonic hedgehog (shh) and Fibroblast growth factor 8 (fgf8) are the nuclear factors driving expression of bmp4. The accompanying article by Wu et al. also concludes that BMP4 shapes beaks. Who regulates the regulators (ssh, fgf8)?
PubMed Bmp4 and Morphological Variation of Beaks in Darwin’s Finches Arhat Abzhanov, Meredith Protas, B. Rosemary Grant, Peter R. Grant, Clifford J. Tabin. Science 305:1462, September 3, 2004

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