Catálogo de publicaciones - revistas

<jats:title>Seeing Double</jats:title> <jats:p> A particular set of ubiquitous small (nucleolar) ribonucleoproteins are important for optimal ribosome function and protein synthesis. <jats:bold> Bleichert <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="1384" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1176099">1384</jats:related-article> ) used electron microscopy and single-particle analysis to investigate the structure of an archaeal version that contains the small RNA (sRNA) and all the associated core proteins. Unexpectedly, this ribonucleoprotein is a homodimer, formed of two sRNAs and four copies of each of the core proteins. This dimer is likely to be the enzymatically active form, as mutations disrupting di-sRNP formation inhibited activity. </jats:p>

<jats:title>Making Mother of Pearl</jats:title> <jats:p> Nacre is an iridescent layer of calcium carbonate lining the inside of shells of marine mollusks and is commonly known as “mother of pearl.” It is composed of layers of uniformly oriented crystals of aragonite (a metastable form of calcium carbonate) separated by layers of organic matrix. How the ordered structure of aragonite layers is achieved has been unclear. <jats:bold> Suzuki <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="1388" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1173793">1388</jats:related-article> , published online 13 August 2009; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="5946" page="1351" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1177055">Kröger</jats:related-article> </jats:bold> ) identified two acidic matrix proteins (Pif 97 and Pif 80) that regulate nacre formation in the Japanese pearl oyster. The proteins appear to form a complex in which Pif 80 binds to aragonite and Pif 97 binds to other macromolecules in the organic matrix. </jats:p>

<jats:title>MITE-y Jumps</jats:title> <jats:p> Tranposable elements are genetic elements ubiquitous to most genomes, and their expansion, loss, and potential movement are major components of genome evolution. A type of noncoding transposable element in plants, known as a MITE (minature inverted repeat transposable element), shows evidence of recent expansion within specific rice genomes. However, these elements lack the necessary transposase to help them move. <jats:bold> Yang <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="1391" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1175688">1391</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="5946" page="1352" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1179556">González and Petrov</jats:related-article> </jats:bold> ) found that the expansion of MITEs occurs because they exploit the activity of other, unrelated, transposons and consequently identified the molecular determinants that allowed mobilization. Surprisingly, the element coding for the transposase repressed its own movement unless the MITE was present. These findings may explain why some genetic elements can replicate within the genome and reach high copy numbers while others do not. </jats:p>

<jats:title>Maintaining Germline Stem Cells</jats:title> <jats:p> Spermatogonial stem cell pools in postnatal testes have to be maintained to continuously generate spermatozoa. It has been difficult to identify these stem cells in vivo, because of their small numbers and lack of appropriate molecular markers, but now <jats:bold> Sada <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="1394" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1172645">1394</jats:related-article> ) show that the RNA-binding protein NANOS2 is expressed in a small subset of spermatogonia that behave as self-renewing stem cells in intact testes. By a combinatorial use of loss- and gain-of-function studies, NANOS2 was found to be essential for the maintenance of the immature state of spermatogonial stem cells by supporting their self-renewing properties and by suppressing differentiation. </jats:p>

<jats:title>Crystal Clear</jats:title> <jats:p> Guanine nucleotide exchange factors stimulate exchange of guanine diphosphate (GDP) for guanine triphosphate (GTP) and activate small guanosine triphosphatases (GTPases) required for the regulation of many biological processes. <jats:bold> Yang <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="1398" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174468">1398</jats:related-article> ) provide a detailed picture of the complete catalytic cycle by which a guanine nucleotide exchange factor, DOCK9, activates the small GTPase, Cdc42. A small region of DOCK9 appears to sense whether GTP or GDP is bound to Cdc42 in a mechanism that is distinct from that observed for other GTPases. </jats:p>

<jats:title>Making Myelin</jats:title> <jats:p> The myelin sheath insulates neurons and facilitates rapid axonal conduction, and its disruption is characteristic of some neurological disorders, such as multiple sclerosis. Axonal signals stimulate Schwann cells to form myelin in peripheral nerves, but the mechanism is not completely known. By characterizing a mutation identified in zebrafish, <jats:bold> Monk <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="1402" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1173474">1402</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="5946" page="1353" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1180103">Meijer</jats:related-article> </jats:bold> ) show that Gpr126, a member of the G protein–coupled receptor superfamily, is essential for myelin formation. It appears that Gpr126 acts as a receptor for axonal signals to elevate cAMP levels in Schwann cells and trigger myelination. </jats:p>

<jats:title>Minimizing Brain Energy Consumption</jats:title> <jats:p> How much energy is actually required to generate neuronal activity and information processing? By combining direct recordings at physiological temperatures from mossy fiber axons in rat brain slices with modeling and simulation approaches, <jats:bold> Alle <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="1405" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1174331">1405</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="5946" page="1349" related-article-type="in-this-issue" vol="325" xlink:href="10.1126/science.1180102">Magistretti</jats:related-article> </jats:bold> ) found that the regenerative action potentials in nonmyelinated axons of mammalian hippocampus are remarkably energy efficient. The data indicate a surprisingly minor contribution of action potentials to the entire energy expenditure of neural information processing. </jats:p>

<jats:p>The show includes the transmissibility of swine-origin influenza, the genetic complexity underlying beach mouse adaptation, and more.</jats:p>

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