Science-2011-Heinrich

Science-2011-Heinrich - PERSPECTIVES formed; excess RA can...

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www.sciencemag.org SCIENCE VOL 332 27 MAY 2011 1039 PERSPECTIVES formed; excess RA can reprogram a “distal” amputation blastema (the site of progenitors for regeneration) to produce more proximal in addition to distal structures ( 9 ). Signal- ing by WNT and FGF plays an essential role in appendage regeneration in several differ- ent systems ( 10 , 11 ), and WNTs may pro- long regeneration in species that normally lose this capacity at metamorphosis ( 10 ). Whether this occurs through the maintenance of progenitors by WNT and FGF, as seen in the chick limb bud, remains to be seen. The nding that embryonic limb progenitor cells can be manipulated to maintain or extend their plasticity opens a new door to analyzing how these progenitors become committed to particular fates, whether and to what extent this process can be reversed, and the degree to which such programming is shared between limb development and regeneration. References 1. C. Tabin, L. Wolpert, Genes Dev. 21 , 1433 (2007). 2. J. L. Galloway et al ., Nature 460 , 400 (2009). 3. K. L. Cooper et al ., Science 332 , 1083 (2011). 4. A. Roselló-Díez et al ., Science 332 , 1086 (2011). 5. D. ten Berge et al ., Development 135 , 3247 (2008). 6. X. Zhao et al ., Curr. Biol. 19 , 1050 (2009). 7. J. Schlueter, T. Brand, Cytogenet. Genome Res. 117 , 256 (2007). 8. F. V. Mariani et al ., Nature 453 , 401 (2008). 9. M. Maden, Nature 295 , 672 (1982). 10. Y. Kawakami et al ., Genes Dev. 20 , 3232 (2006). 11. G. Lin, J. M. Slack, Dev. Biol. 316 , 323 (2008). 10.1126/science.1207554 A Logical Use for Atoms PHYSICS Andreas Heinrich and Sebastian Loth The coupled spins of individual atoms can be used to demonstrate basic logic function. ±I t is increasingly more diffi cult and costly to continue to shrink silicon chip com- ponents. Moore’s law, which describes such progress, is running into serious trouble. Technologists have been seeking out alterna- tive architectures for computation. Some have even pondered the possibility of shrinking the components to the ultimate end of any road- map—to the scale of atoms. On page 1062 of this issue, Khajetoorians et al . pre sent such a radical leap forward ( 1 ) by demonstrating spin-based logic operation in chains of mag- netic atoms on a surface. Spintronics promises to add functionality to semiconductor devices by making use of the spin—the magnetic degree of freedom— of electrons that are fl owing through devices. But can logic operations be performed with- out pushing electrons (spin-polarized or not) through wires? Indeed, several schemes have been proposed to do just that. One example is magnetic domain wall logic ( 2 ). Another relies on the dipolar coupling between mag- netic nanodots. Cascades of such dots can meet at intersections where it was shown that logic operations could be performed ( 3 , 4 ). About 10 years ago (
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Science-2011-Heinrich - PERSPECTIVES formed; excess RA can...

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