Catálogo de publicaciones - revistas

<jats:p>Phenotypic variation is ubiquitous in biology and is often traceable to underlying genetic and environmental variation. However, even genetically identical cells in identical environments display variable phenotypes. Stochastic gene expression, or gene expression “noise,” has been suggested as a major source of this variability, and its physiological consequences have been topics of intense research for the last decade. Several recent studies have measured variability in protein and messenger RNA levels, and they have discovered strong connections between noise and gene regulation mechanisms. When integrated with discrete stochastic models, measurements of cell-to-cell variability provide a sensitive “fingerprint” with which to explore fundamental questions of gene regulation. In this review, we highlight several studies that used gene expression variability to develop a quantitative understanding of the mechanisms and dynamics of gene regulation.</jats:p>

<jats:p>Computational approaches are breaking new ground in understanding how embryos form. Here, we discuss recent studies that couple precise measurements in the embryo with appropriately matched modeling and computational methods to investigate classic embryonic patterning strategies. We include signaling gradients, activator-inhibitor systems, and coupled oscillators, as well as emerging paradigms such as tissue deformation. Parallel progress in theory and experiment will play an increasingly central role in deciphering developmental patterning.</jats:p>

<jats:title>Going Ape Over Genetic Maps</jats:title> <jats:p> Recombination is an important process in generating diversity and producing selectively advantageous genetic combinations. Thus, changes in recombination hotspots may influence speciation. To investigate the variation in recombination processes in humans and their closest existing relatives, <jats:bold> Auton <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="193" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1216872">193</jats:related-article> , published online 15 March) prepared a fine-scale genetic map of the Western chimpanzee and compared it with that of humans. While rates of recombination are comparable between humans and chimpanzees, the locations and genetic motifs associated with recombination differ between the species. </jats:p>

<jats:title>Harnessing the Magnetoelectric Effect</jats:title> <jats:p> Some multiferroic materials exhibit the so-called magnetoelectric effect, in which an external magnetic field can cause electric polarization and an electric field can cause magnetic order. This is important because the manipulation of magnetic structures by electric means is technologically highly desirable. <jats:bold> Seki <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="198" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1214143">198</jats:related-article> ) discovered spin whirlpools called skyrmions in the multiferroic material Cu <jats:sub>2</jats:sub> OSeO <jats:sub>3</jats:sub> and observed a magnetoelectric coupling exerted by the skyrmions. The existence of skyrmions in an insulating magnetoelectric material holds promise for their future manipulation. </jats:p>

<jats:title>Entangling Qubits</jats:title> <jats:p> The basic building block of a quantum computer, a qubit, has been realized in many physical settings, each of which has its advantages and drawbacks. Solid-state spin qubits interact weakly with their environment and each other, leading not only to long coherence times but also to difficulties in performing multiqubit operations. <jats:bold> Shulman <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="202" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1217692">202</jats:related-article> ) used a double quantum dot to produce a singlet-triplet qubit, where the two quantum states available are a singlet and a triplet formed by two spin-1/2 electrons. Two such qubits are then entangled by electrical gating, which affects the charge configuration of one qubit and that, in turn, influences the electric field experienced by the other. This type of two-qubit entanglement is essential for further development of quantum computing in these systems. </jats:p>

<jats:title>Manipulating Optical Topology</jats:title> <jats:p> Phase transitions in solid-state systems are often associated with a drastic change in the properties of that system. For example, metal-to-insulator transition or magnetic-to-nonmagnetic states find wide application in memory storage technology. An exotic electronic phase transition is the Lifshitz transition, whereby the Fermi surface undergoes a change in topology and a drastic change in the electronic density of states. <jats:bold> Krishnamoorthy <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="205" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1219171">205</jats:related-article> ) now show that the notion of such a phase transition can be carried over to the optical regime by the suitable design of a metamaterial structure. This effect could be used to control the interaction between light and matter. </jats:p>

<jats:title>Finessing Ferroelectric Liquid Crystals</jats:title> <jats:p> For a material to show a ferroelectric response, it needs to have segments that can be polarized, with a net polarization that remains when the applied field is removed. However, the fluidity that allows liquid crystal molecules to easily move under an applied force also makes it hard to create a ferroelectric response. <jats:bold> Miyajima <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="209" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1217954">209</jats:related-article> ) show that a set of columnar liquid crystal molecules, with polar cyano groups tethered to amide-capped nonpolar chains, can assemble into an umbrella-shaped core–shell architecture, in which hydrogen bonding among the amides keeps the cyano groups confined. With only subtle variations in the tether chemistry, the assemblies can be tuned from having a para-electric to a ferroelectric response, which requires only a small coercive field. </jats:p>

<jats:title>Mercury Inside and Out</jats:title> <jats:p> The MESSENGER spacecraft orbiting Mercury has been in a ∼12-hour eccentric, near-polar orbit since 18 March 2011 (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6078" page="162" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1220825">McKinnon</jats:related-article> </jats:bold> ). <jats:bold> Smith <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="214" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218809">214</jats:related-article> , published online 21 March) present the most recent determination of Mercury's gravity field, based on radio tracking of the MESSENGER spacecraft between 18 March and 23 August 2011. The results point to an interior structure that differs from those of the other terrestrial planets: the density of the planet's solid outer shell suggests the existence of a deep reservoir of high-density material, possibly an Fe-S layer. <jats:bold> Zuber <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="217" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218805">217</jats:related-article> , published online 21 March) used data obtained by the MESSENGER laser altimeter through to 24 October 2011 to build a topographic map of Mercury's northern hemisphere. The map shows less variation in elevation, compared with Mars or the Moon, and its features add to the body of evidence that Mercury has sustained geophysical activity for much of its history. </jats:p>

<jats:title>Mercury Inside and Out</jats:title> <jats:p> The MESSENGER spacecraft orbiting Mercury has been in a ∼12-hour eccentric, near-polar orbit since 18 March 2011 (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6078" page="162" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1220825">McKinnon</jats:related-article> </jats:bold> ). <jats:bold> Smith <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="214" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218809">214</jats:related-article> , published online 21 March) present the most recent determination of Mercury's gravity field, based on radio tracking of the MESSENGER spacecraft between 18 March and 23 August 2011. The results point to an interior structure that differs from those of the other terrestrial planets: the density of the planet's solid outer shell suggests the existence of a deep reservoir of high-density material, possibly an Fe-S layer. <jats:bold> Zuber <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="217" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1218805">217</jats:related-article> , published online 21 March) used data obtained by the MESSENGER laser altimeter through to 24 October 2011 to build a topographic map of Mercury's northern hemisphere. The map shows less variation in elevation, compared with Mars or the Moon, and its features add to the body of evidence that Mercury has sustained geophysical activity for much of its history. </jats:p>

<jats:title>To Cut or Not to Cut</jats:title> <jats:p> During animal cell division, the final separation of daughter cells requires ESCRT-III (endosomal sorting complex required for transport III), the core membrane scission machinery. <jats:bold> Carlton <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="220" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1217180">220</jats:related-article> , published online 15 March; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6078" page="166" related-article-type="in-this-issue" vol="336" xlink:href="10.1126/science.1221832"> <jats:bold>Petronczki and Uhlmann</jats:bold> </jats:related-article> ) report that ESCRT-III modulates abscission timing through one of its subunits, CHMP4C. Depletion of CHMP4C results in faster resolution of the midbody, the cytoplasmic bridge that connects the daughter cells at the end of cytokinesis. This phenotype correlates with a differential spatiotemporal distribution of CHMP4C at the midbody. As CHMP4C is essential for activating the Aurora B–mediated abscission checkpoint, consequently, depletion of CHMP4C results in the accumulation of genetic damage. Thus, the ESCRT machinery protects the cell against genetic damage by coordinating its cytokinetic activity with the abscission checkpoint. </jats:p>