Catálogo de publicaciones - revistas

<jats:title>Small-Molecule Protease Activator</jats:title> <jats:p> Human proteases regulate numerous biological processes. Most are stored as inactive proenzymes that are activated either by upstream processes or by self-proteolysis. <jats:bold> Wolan <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="853" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1177585">853</jats:related-article> ) have identified a small molecule that activates the apoptotic procaspases-3 and -6. These caspases are homodimers, and the compound probably competitively inhibits one active site, but stabilizes an on-state conformation that promotes self-cleavage by the unoccupied site. It may thus be possible to find other small-molecule activators for other proenzymes that should facilitate functional and mechanistic studies. </jats:p>

<jats:title>Shivering Viromes</jats:title> <jats:p> Despite its icy reputation, freshwater ponds and lakes do occur in Antarctica, and open freshwater can be found for a few brief weeks during the austral summer. The ecology of these lakes is, as expected, rather specialized to cope with the extreme seasonal conditions. In a metagenomic study, <jats:bold> López-Bueno <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="858" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1179287">858</jats:related-article> ) inspected the virus community of Lake Limnopolar on Livingston Island and found an unexpectedly rich genetic diversity. A dominant group of previously unidentified single-stranded DNA viruses was found, and a striking shift after ice-melt in spring from single-stranded to double-stranded DNA viruses was observed, probably as their algal hosts started to bloom with increasing daylight hours. The diverse viruses may donate specialized genes that host organisms can also exploit to aid their survival under winter extremes of heat and light deprivation. </jats:p>

<jats:title>The Death of Cocco</jats:title> <jats:p> <jats:italic>Emiliania huxleyi</jats:italic> is a coccolithophore, a class of unicellular phytoplankton that forms vast blooms mediating the oceanic carbon cycle through shedding of its calcium carbonate scales. <jats:italic>E. huxleyi</jats:italic> is routinely infected and killed by lytic viruses that can abruptly halt a bloom. <jats:bold> Vardi <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="861" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1177322">861</jats:related-article> ) have found that in <jats:italic>E. huxleyi</jats:italic> strains that are sensitive or resistant to infection, a sphingolipid-based “arms race” appears to regulate cell fate during host-virus interactions. The lipid also serves as a biomarker for active infection that may help to quantify the role and activity of viruses and virus-mediated processes in the oceans. This information will help in assessing the biogeochemical impact of these plankton species. </jats:p>

<jats:title>A Horse Is a Horse, of Course</jats:title> <jats:p> The history of horse domestication is closely tied to the history of the human society. <jats:bold> Wade <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="865" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1178158">865</jats:related-article> ) report on the sequencing and provide a single nucleotide polymorphism map of the horse ( <jats:italic>Equus caballus</jats:italic> ) genome. Horses are a member of the order perissodactyla (odd-toed animals with hooves). The analysis reveals an evolutionarily new centromere on equine chromosome 11 that displays properties of an immature but fully functioning centromere and is devoid of centromeric satellite sequence. The findings clarify the nature of genetic diversity within and across horse breeds and suggest that the horse was domesticated from a relatively large number of females, but few males. </jats:p>

<jats:title>Self-Renewing Macrophages</jats:title> <jats:p> The capacity for self-renewal is associated with progenitor cell populations and is lost upon differentiation. <jats:bold> Aziz <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="867" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1176056">867</jats:related-article> ) discovered an exception to this rule when mouse monocytes and macrophages deficient in the transcription factors MafB and c-Maf were cultured in the presence of the growth factor, macrophage colony-stimulating factor (M-CSF). Under these conditions, MafB/c-Maf–deficient cells were able to divide continuously while maintaining the phenotype and function of mature cells. Unexpectedly, when these in vitro–cultured cells were transferred into mice, they did not induce tumors, despite continuing to divide, but rather incorporated themselves into tissues and adopted normal macrophage functions. Suppression of two genes involved in the self-renewal capacity of inducible pluripotent stem cells, KLF4 and c-Myc, inhibited the ability of MafB/c-Maf–deficient macrophages to self-renew. Such long-term propagation of a differentiated cell population that does not result in transformation when reintroduced in vivo has exciting therapeutic potential. </jats:p>

<jats:title>Goldilocks Immunology</jats:title> <jats:p> T cells are carefully calibrated in the thymus to react to invading pathogens and to ignore the self. This occurs through interactions between the T cell receptor and major histocompatibility complexes (MHCs) expressing self-peptides. A Goldilocks-like selection process is carried out whereby T cells that do not react or react too strongly to self-peptide MHCs are deleted, whereas those with interactions that are “just right” are allowed to survive. The result is T cells highly specific for a particular foreign peptide-MHC complex. Receipt of survival signals from “just-right” interactions (positive selection) and deletion of cells that are too reactive (negative selection) are spatially and temporally segregated in the thymus, and it is unclear at which stage T cells acquire their high degree of peptide-MHC specificity. By using mice expressing a single peptide-MHC complex, <jats:bold> Wang <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="871" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1177627">871</jats:related-article> ) now show that this single complex is sufficient for selection of a CD8 <jats:sup>+</jats:sup> T cell repertoire with a broad range of specificity. Importantly, recognition of peptide MHC by these cells was highly specific, demonstrating that peptide-MHC specificity is acquired during positive selection in the thymus. </jats:p>

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

<jats:p> This issue of <jats:italic>Science</jats:italic> includes the program of the 2010 AAAS Annual Meeting. The theme of the AAAS Annual Meeting in San Diego, 18 to 22 February 2010, is "Bridging Science and Society," and calls on all scientists and engineers to make their work both beneficial and understandable. </jats:p> <jats:p> A <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://www.sciencemag.org/cgi/reprint/326/5954/876.pdf">PDF</jats:ext-link> of the program as it appears in this issue is available here; for more information on the meeting (including registration forms and information on accommodations), please visit <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="www.aaas.org/meetings/">www.aaas.org/meetings/</jats:ext-link> . </jats:p>