Catálogo de publicaciones - revistas

<jats:title>Interrogating Growing Nanoparticles</jats:title> <jats:p> Several methods can be used to follow the mechanistic steps of a chemical reaction, but the growth of a nanoparticle from a small seed crystal is more difficult to follow. <jats:bold> Langille <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="954" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1225653">954</jats:related-article> ) used plasmonic gold nanocrystals of different shapes (cubes and octahedral) as seeds for the growth of larger silver nanoparticles. Electron microscopy was used to track the formation of several different particle shapes and internal structures during the growth process. </jats:p>

<jats:title>A Family of Languages</jats:title><jats:p>English is part of the large Indo-European language family, which includes Celtic, Germanic, Italic, Balto-Slavic, and Indo-Iranian languages. The origin of this family is hotly debated: one hypothesis places the origin north of the Caspian Sea in the Pontic steppes, from where it was disseminated by Kurgan semi-nomadic pastoralists; a second suggests that Anatolia, in modern-day Turkey, is the source, and the language radiated with the spread of agriculture.<jats:bold>Bouckaert<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="957" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1219669">957</jats:related-article>) used phylogenetic methods and modeling to assess the geographical spread of the Indo-European language group. The findings support the suggestion that the origin of the language family was indeed Anatolia 7 to 10 thousand years ago—contemporaneous with the spread of agriculture.</jats:p>

<jats:title>Making Arabidopyrones</jats:title> <jats:p> Plants possess specialized metabolic systems that rapidly explore new chemical space as a means to adapt to their environments. <jats:bold> Weng <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="960" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1221614">960</jats:related-article> ) describe the evolutionary trajectory underlying the emergence of a class of α-pyrone-bearing metabolites—arabidopyrones—in the model plant <jats:italic>Arabidopsis</jats:italic> . The first step of the arabidopyrone synthesis pathway is catalyzed by a cytochrome P450 enzyme neofunctionalized following a recent gene duplication event. This development led to the synthesis of a catechol-substituted substrate, which became a new substrate for a highly conserved extradiol ring-cleavage dioxygenase. Thus, plants can rapidly assemble a specialized metabolic pathway by substituting a new biological activity into an existing catalytic framework. </jats:p>

<jats:title>BMP Signaling and Transcription</jats:title> <jats:p> Bone morphogenetic protein signaling (BMP) is widely used for dorsoventral axis determination in animal embryos, which involves specific interactions between BMPs and their antagonists. In the genomes of many animals, the gene <jats:italic>Pinhead</jats:italic> is encoded as a neighbor of one of the BMP ligand genes, <jats:italic>Admp</jats:italic> (antidorsalizing morphogenetic protein). Working in ascidian tailbud-stage embryos, <jats:bold> Imai <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="964" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1222488">964</jats:related-article> ) now show that <jats:italic>Pinhead</jats:italic> is an antagonist of ADMP and is important for the establishment of the sharp boundary of the ventral epidermis. Transcription of <jats:italic>Pinhead</jats:italic> disturbs transcription of <jats:italic>Admp</jats:italic> by a <jats:italic>cis</jats:italic> -acting mechanism, which may explain the mutually exclusive expression of these two functionally opposed genes. </jats:p>

<jats:title>Movement in the Cancer Genome</jats:title> <jats:p> Transposable elements are genetic sequences that can replicate and move within the genome. The factors that make an element mobile are unknown but are generally considered rare in mammals. <jats:bold> Lee <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="967" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1222077">967</jats:related-article> , published online 28 June) analyzed five cancer types occurring among several individuals and found that three types of epithelial tumors exhibited high rates of element movement relative to brain and blood cancers. Furthermore, these somatically acquired, tumor-specific elements targeted genes in colorectal cancer that, when disrupted, impact gene expression and thus may be a factor in the progression of the cancers. </jats:p>

<jats:title>Maintaining Repression</jats:title> <jats:p> The Polycomb Repressive Complex 2 (PRC2) plays a critical role in gene silencing in metazoans, methylating histone H3 on lysine 27 (H3K27) to generate a repressive chromatin mark. The catalytic subunit E(z)/Ezh2 requires the presence of two other subunits—ESC/EED and Su(z)12—for enzyme activity. <jats:bold> Yuan <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="971" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1225237">971</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="6097" page="919" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1227684">Pirrotta</jats:related-article> </jats:bold> ) show that both a fragment of the histone H3 N-terminal tail, and histone H1 stimulated PRC2 enzyme activity on poor, low-density chromatin substrates, indicating that that PRC2 is regulated by the density and compaction states of chromatin. The histone H3 fragment binds to the Su(z)12 subunit of PRC2 to stimulate E(z)/Ezh2. Local chromatin compaction preceded establishment of histone H3K27 methylation indicating how PRC2 might maintain the repressed state. </jats:p>

<jats:title>Metabolic Sensor</jats:title> <jats:p> The enzyme O-GlcNAc transferase (OGT) catalyzes the transfer of <jats:italic>N</jats:italic> -acetylglucosamine from uridine diphospho- <jats:italic>N</jats:italic> -acetylglucosamine (UDP-GlcNAc) to serine or threonine residues of intracellular proteins and responds to the metabolic status of the cell. <jats:bold> Yi <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="975" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1222278">975</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="6097" page="925" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1227513">Mattaini and Vander Heiden</jats:related-article> </jats:bold> ) show that O-GlcNAcylation of phosphofructokinase 1 (PFK1) reduces its activity, thus influencing rates of glycolysis within cells. O-GlcNAcylation of PFK1 was increased in cells exposed to hypoxia, and was increased in several cell lines derived from human tumors. Thus, metabolic changes mediated by O-GlcNAcylation may benefit anabolism and growth of cancer cells. However, glycosylation of PFK1 was not detected in rapidly proliferating normal cells. </jats:p>

<jats:title>Keep on Neurexin</jats:title> <jats:p> Mutations altering neurexin and neuroligin have been linked to several psychiatric disorders, including autism and schizophrenia. However, it remains uncertain how these mutations alter neural circuit development and function. Working in the nematode <jats:italic>Caenorhabditis elegans</jats:italic> , <jats:bold> Hu <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="980" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1224896">980</jats:related-article> , published online 2 August) found that neurexin and neuroligin function downstream of a muscle microRNA (miR-1), mediating a retrograde synaptic signal that inhibits neurotransmitter release. This retrograde signal inhibited transmission by adjusting the rate and duration of synaptic vesicle release. </jats:p>

<jats:title>Coding Complex Movements</jats:title> <jats:p> The dorsal premotor cortex is a critical area for planning reaching movements. <jats:bold>Pearce and Moran</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="984" related-article-type="in-this-issue" vol="337" xlink:href="10.1126/science.1220642">984</jats:related-article> , published online 19 July) trained two macaques to reach around randomly placed objects in a virtual reality task while simultaneously recording neuronal activity in the premotor cortex. Neurons in the premotor cortex coded for the direction of the hand movement and at the same time also coded other variables, including the position of the hand and the final location of the target. Population vector analyses were able to decode multiple kinematic variables from the neural activity. In one monkey, the population vector was first directed to the target but when the obstacle appeared the population vector rotated. However, the other monkey waited until the obstacle appeared. The differences in the neural planning between these two monkeys suggest different optimization strategies. </jats:p>

<jats:p>The show includes mapping the history of Indo-European languages, the origins of a supernova, the Guppy Project, and more.</jats:p>