Catálogo de publicaciones - revistas

<jats:title>Damage, Signal, Maneuver</jats:title> <jats:p> Cellular processes, such as transcription and DNA repair, require modification and manipulation of chromosomally associated proteins by a diverse set of chromatin remodeling complexes. The mechanisms by which cells regulate chromatin remodeling are not completely understood. During the response elicited by DNA damage, the addition of poly(ADP-ribose) to chromatin is associated with chromatin decondensation, which is thought to promote efficient DNA repair. <jats:bold> Ahel <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1240" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1177321">1240</jats:related-article> , published online 30 July 2009) have identified a chromatin remodeling enzyme as a DNA damage-response protein, which binds poly(ADP-ribose). </jats:p>

<jats:title>Adaptive Limits</jats:title> <jats:p> Species adapt to a changing environment as a result of selection acting on current genetic variation. However, the degree of variation underlying traits that can respond to selection is unclear. <jats:bold> Kellermann <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1244" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1175443">1244</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1212" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1179326">Merilä</jats:related-article> ) investigated the degree of genetic variation available to fruit flies for cold and desiccation tolerance. Species from the tropics tended to have low variability for these traits, while flies from more temperate climates showed higher levels of variation. However, overall genetic variability did not differ, suggesting that the tropical species lacked the alleles that confer tolerance to these environmental extremes and restrict their potential range. </jats:p>

<jats:title>Tissue-Specific Control</jats:title> <jats:p> The effect of genetic variation on gene expression and phenotype among individuals is largely unknown. <jats:bold> Dimas <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1246" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174148">1246</jats:related-article> , published online 30 July 2009) show that in humans there are several genes whose allelic expression varies in a tissue-specific manner and are apparently controlled by cis elements. Up to 80% of variants seem to have tissue-specific functions when compared in fibroblasts, as well as B cells and T cells. This variation among regulatory variants correlated with transcript complexity, which suggests that some of the observed regulatory variation is due to genotype-specific use of transcripts and transcription start sites. </jats:p>

<jats:title>Fascin-Actin Rab Bristles</jats:title> <jats:p> Rab proteins have diverse functions in directing intracellular traffic and may also affect development. <jats:bold> Zhang <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1250" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174921">1250</jats:related-article> ) show that during <jats:italic>Drosophila</jats:italic> development Rab35 influences the development of bristles, neurosensory structures built upon bundled actin. Rab35 also caused massive actin-rich filopodia protrusions from cultured cells. Activated Rab35 interacted directly with fascin, an actin filament bundling protein, to colocalize near the plasma membrane. When Rab35 was engineered to interact with the surface of mitochondria, it stimulated localized actin assembly in a fascin-dependent manner. Thus, fascin is a Rab35 effector protein that links membrane trafficking regulation to cytoskeleton assembly during development. </jats:p>

<jats:title>Epigenetic Signals</jats:title> <jats:p> The lipid sphingosine-1-phosphate (S1P) is a signaling molecule that binds to receptors on the cell surface to initiate biochemical changes that control a range of biological processes from growth and survival to immune reactions. <jats:bold> Hait <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="1254" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1176709">1254</jats:related-article> ) report that S1P can also function by direct binding to the nuclear enzymes, histone deacetylases (HDACs) 1 and 2. The enzyme that generates S1P, sphingosine kinase 2 (ShpK2) is present in the nucleus in complexes with HDAC1 and HDAC2. Generation of S1P and its binding to HDACs inhibited deacetylation of histone. Such histone modification is an epigenetic mechanism that controls gene transcription. Thus, generation of S1P in the nucleus appears to be a signaling mechanism by which cells can control gene expression in response to various stimuli. </jats:p>

<jats:title>Adult Fears</jats:title> <jats:p> Why are fear memories almost impossible to get rid of—even with extensive extinction training? Animal studies have shown that the efficacy of extinction learning depends on age. Fear memories in young animals can be permanently erased, but in adults they can be easily recovered after extinction training. Perineuronal nets, the highly organized form of extracellular matrix around inhibitory neurons, mediate the shift from juvenile to adult forms of learning in sensory systems. <jats:bold> Gogolla <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1258" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174146">1258</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1214" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1179697">Pizzorusso</jats:related-article> </jats:bold> ) have discovered that the formation of perineuronal nets in the amygdala coincides with the developmental shift in the ability to erase fear memories by extinction. Removal of perineuronal nets in adult animals re-enabled the erasure of fear memories. Thus, in adults it appears that fear memories are actively protected from erasure by the perineuronal nets. </jats:p>

<jats:title>Reigning In Tumor Suppression</jats:title> <jats:p> Mitogenic signaling through phosphoinositide-3 kinase generates the lipid second messenger phosphatidyl inositol 3,4,5-trisphosphate (PIP3). The tumor suppressor gene product and lipid phosphatase PTEN (phosphatase and tensin homolog on chromosome 10) opposes such mitogenic signaling by dephosphorylating PIP3. In a screen for proteins that interact with PTEN, <jats:bold> Fine <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1261" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1173569">1261</jats:related-article> ) identified P-REX2a, a guanine nucleotide exchange factor (GEF) for the RAC small guanosine triphosphatase. Endogenous P-REX2a and PTEN interacted in human embryonic kidney 293 cells, and P-REX2a inhibited catalytic activity of PTEN. Thus, like that of many protein phosphatases, the activity of PTEN is kept in check by an interacting protein inhibitor. P-REX2a thus provides a mechanism through which tumor cells may inactivate PTEN. </jats:p>

<jats:title>Preparation for Cell Wars</jats:title> <jats:p> When T cells encounter an infection, they proliferate to create a larger army to fight the invader. The overall magnitude of the T cell response depends on the severity of infection and is determined by the number of T cells of a particular antigen specificity that are initially recruited, as well as the magnitude of the proliferative response. The extent to which these two components contribute to the response is unknown. By using DNA barcoding to track the responses of individual T cells, <jats:bold> van Heijst <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1265" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1175455">1265</jats:related-article> ) showed that the recruitment of T cells of a particular antigen specificity is similar and nearly complete, but that the extent of the proliferative response differed, and this determined the overall magnitude of the T cell response. </jats:p>

<jats:title>Boxing Clever?</jats:title> <jats:p> Piaget showed that 10-month-old infants will persist in looking for a toy in box A, where it has been placed several times, even after having been shown that it has been moved to box B, whereas 12-month-old infants do not. This phenomenon marks a developmental milestone in human infant cognition that <jats:bold> Topál <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1269" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1176960">1269</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1213" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1179670">Tomasello and Kaminski</jats:related-article> </jats:bold> and the news story by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1194" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.2009.325.5945.325_1194">Pennisi</jats:related-article> </jats:bold> ) explored in a remarkable series of comparative tests. The results support the view that infants and adult dogs will both persevere in searching erroneously in box A because they regard the placement of the toy by a human experimenter as a social teaching event. By contrast, wolves rapidly learn correctly to search box B. They also observed that infants are able to generalize and thus still persevere when one experimenter places the toy in box A and a second then places the toy in box B. Dogs, however, display episodic learning, and a second experimenter reduces their searching choice to chance. </jats:p>

<jats:title>Carrots Are Better Than Sticks</jats:title> <jats:p> The challenge of dealing with freeloaders—who benefit from a common good but refuse to pay their “fair share” of the costs—has often been met in theoretical and laboratory studies by sanctioning costly punishment, in which contributors pay a portion of their benefit so that freeloaders lose theirs. <jats:bold> Rand <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1272" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1177418">1272</jats:related-article> ; see the news story by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5945" page="1196" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.2009.325.5945.325_1196"> <jats:bold>Pennisi</jats:bold> </jats:related-article> and the cover) added a private interaction session after each round of the public goods game during which participants were allowed to reward or punish other members of their group. The outcome showed that reward was as effective as punishment in maintaining a cooperative mindset, and doing so via rewarding interactions allowed the entire group to prosper because less is lost to the costs of punishing. </jats:p>