Catálogo de publicaciones - revistas

<jats:title>Sleeping Around the Clock</jats:title> <jats:p> Fruit flies do not sleep all night like humans, but they do manage to spend about half of their day in bouts of inactivity that have similarity to sleep in other species. <jats:bold>Rogulja and Young</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1617" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1212476">1617</jats:related-article> ) searched for genes in neurons whose products regulated sleep. Depletion of the protein regulator of cyclin A1 (Rca1) caused the flies to be slow to go to sleep and to get less total sleep in a day because their sleep episodes were shorter. The mechanism by which Rca1 influences sleep is not yet clear. It appears not to disrupt circadian rhythms. However, the neurons that express Rca1 in the fly brain are located near the neurons that make up the circadian clock, potentially allowing for coordination of circadian behavior with sleep regulation. </jats:p>

<jats:title>Making the CoTC</jats:title> <jats:p> In eukaryotes, cotranscriptional cleavage (CoTC) of nascent RNA transcripts at the polyadenylation (polyA) site is involved in transcription termination of RNA polymerase II genes. The Dicer endoribonucleases, on the other hand, are generally associated with gene silencing through the generation of small RNAs from double-stranded RNA. Now, <jats:bold> Liu <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="1621" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1214402">1621</jats:related-article> ) show that transcriptional read-through of the <jats:italic>Arabidopsis FCA</jats:italic> gene is regulated by <jats:italic>DICER-LIKE 4</jats:italic> ( <jats:italic>DCL4</jats:italic> ). DCL4 associated with the <jats:italic>FCA</jats:italic> gene downstream of the polyA site and repressed transcriptional read-through. The C terminus of DCL4 has a similar domain structure to the yeast endoribonuclease Rnt1, involved in CoTC, which suggests that DCL4 is involved in repressing read-through of endogenous <jats:italic>FCA</jats:italic> by prompting cotranscriptional cleavage. </jats:p>

<jats:title>Spreading the Excitation</jats:title> <jats:p> Inhibitory interneurons balance network excitation, control spike-time precision of principal neurons, and control synchrony within and across brain regions. <jats:bold> Vervaeke <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="1624" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215101">1624</jats:related-article> , published online 8 March) combined electrophysiology, immunohistology, and numerical simulation to investigate the properties of Golgi cells, the main inhibitory interneurons in the input layer of the cerebellar cortex. The dendrites of these neurons were truly passive and acted as linear cables. Gap junctions were distributed nonuniformly on the Golgi cell surface, with a higher density on distal dendrites. Thus, gap junction-mediated lateral excitation preferentially enhanced the distal inputs, enabling distal synapses to drive network activity more effectively. </jats:p>

<jats:title>Building the Brain</jats:title> <jats:p> Brain connectivity is often described as a network of discrete independent cables analogous to a switchboard, but how is the physical structure of the brain constructed (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6076" page="1582" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1221366">Zilles and Amunts</jats:related-article> </jats:bold> )? <jats:bold> Wedeen <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="1628" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215280">1628</jats:related-article> ) used high-resolution diffusion tensor imaging in humans and four species of nonhuman primates to identify and compare the geometric structure of large fiber tracts in the brain. Fiber tracts followed a highly constrained and regular geometry, which may provide an efficient solution for pathfinding during ontogenetic development. Much of development occurs through elaboration and assembly of semiautonomous building blocks. <jats:bold> Chen <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="1634" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215330">1634</jats:related-article> ) applied statistical analysis to the form of the human cortex in brain-imaging studies that compared more than 400 di- and mono-zygotic twins. The findings suggest that the structure of the human cortex is defined by genetics. </jats:p>

<jats:title>Building the Brain</jats:title> <jats:p> Brain connectivity is often described as a network of discrete independent cables analogous to a switchboard, but how is the physical structure of the brain constructed (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6076" page="1582" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1221366">Zilles and Amunts</jats:related-article> </jats:bold> )? <jats:bold> Wedeen <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="1628" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215280">1628</jats:related-article> ) used high-resolution diffusion tensor imaging in humans and four species of nonhuman primates to identify and compare the geometric structure of large fiber tracts in the brain. Fiber tracts followed a highly constrained and regular geometry, which may provide an efficient solution for pathfinding during ontogenetic development. Much of development occurs through elaboration and assembly of semiautonomous building blocks. <jats:bold> Chen <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="1634" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215330">1634</jats:related-article> ) applied statistical analysis to the form of the human cortex in brain-imaging studies that compared more than 400 di- and mono-zygotic twins. The findings suggest that the structure of the human cortex is defined by genetics. </jats:p>

<jats:title>Cost-Benefit Analysis</jats:title> <jats:p> Mounting resistance to infection is costly, requires energetic input, and may thus compromise fecundity. <jats:bold> Duffy <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="1636" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215429">1636</jats:related-article> ; see the cover) tested the relationships between productivity, predation, and mortality in a combination of observations of a natural lake and an experimental replica of a clonal zooplankton-parasitic yeast population. In the wild, epidemics of the yeast could exceed 60% and cause significant host mortality. In this situation, the clonal zooplankton host faces the physiological dilemma of either increasing resistance to deal with infection or of safeguarding fecundity. Zooplankton that feed quickly can reproduce quickly, but also end up ingesting more yeast spores. However, because fish tend to cull infected hosts, fish predation counters infection. Ultimately, both wild and model systems showed that lakes with high productivity (more nitrogen) and/or few fish supported greater epidemics of yeast and more resistant hosts, whereas less productive lakes, or those with more fish, had smaller epidemics and hosts with higher susceptibility to the yeast. </jats:p>

<jats:title>Dissecting Rapamycin Responses</jats:title> <jats:p> Long-term treatment of mice and other organisms with the drug rapamycin extends life span. But, at the same time, the drug disrupts metabolic regulation and the action of the hormone insulin. <jats:bold> Lamming <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="1638" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215135">1638</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="6076" page="1578" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1221365">Hughes and Kennedy</jats:related-article> </jats:bold> ) dissected the action of rapamycin in genetically modified mice and found, encouragingly, that these two actions of rapamycin can be separated. Rapamycin inhibits a protein kinase complex known as mTORC1, and this appears to provide most of the life-lengthening effects of the drug. However, rapamycin also acts on a related complex known as mTORC2, and it is the disruption of mTORC2 action that produces the diabetic-like symptoms of decreased glucose tolerance and insensitivity to insulin. </jats:p>

<jats:title>Choosing the Right Path</jats:title> <jats:p> RNA molecules are synthesized in the cell nucleus, yet many have to be moved to the cytoplasm to be processed and/or to effect their function. Different classes of RNA are transported from the nucleus by different transport systems. Messenger RNAs (mRNAs) and uridine-rich small nuclear RNAs (U snRNAs) are transcribed by RNA polymerase II and are capped and bound by the cap-binding machinery in the nucleus but are exported by different protein complexes. The feature that distinguishes the two classes of RNA is their length: U snRNAs are short and mRNAs are long. Using an in vitro system and human tissue culture cells, <jats:bold> McCloskey <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="1643" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1218469">1643</jats:related-article> ) show that the length of the RNAs is measured by the heterogeneous nuclear ribonicleoprotein (hnRNP) C tetrameric protein complex. The hnRNP C cannot bind to the short U snRNAs, allowing the U snRNA-specific export adaptor protein, PHAX, to bind and mediate export. Longer mRNAs are bound by hnRNP C, which prevents the binding of PHAX, thus identifying these RNAs for export from the nucleus via the mRNA pathway. </jats:p>

<jats:p>A weekly roundup of information on newly offered instrumentation, apparatus, and laboratory materials of potential interest to researchers.</jats:p>

<jats:p>The show includes uranium age-dating, the brain's geometry, data replication, and more.</jats:p>