Catálogo de publicaciones - revistas

<jats:p>Stem cell tourism is criticized on grounds of consumer fraud, blatant lack of scientific justification, and patient safety. However, the issues are complex because they invoke questions concerning the limits of acceptable medical innovation and medical travel. Here we discuss these issues and articulate conditions under which “unproven” therapies may be offered to patients outside of regular clinical trials.</jats:p>

<jats:p>The process of wound repair in epithelium-lined organs of mammals is complex and is influenced by numerous secreted factors including cytokines, growth factors, and chemokines. However, the cellular organizers of this process are still not understood. Recent studies of tissue regeneration in organisms with simpler development have uncovered details about the activity of stem cells in the mesenchyme (the blastema) during this process. These blastemal cells are well positioned to interpret cues from the environment and to execute decisions about the direction of wound repair. In mammalian wounds, stromal stem cells appear to be positioned to perform functions similar to those of blastemal cells, including communication with both the overlying epithelium and the inflammatory cells in the mesenchyme.</jats:p>

<jats:p>The investigation and study of cancer stem cells (CSCs) have received enormous attention over the past 5 to 10 years but remain topics of considerable controversy. Opinions about the validity of the CSC hypothesis, the biological properties of CSCs, and the relevance of CSCs to cancer therapy differ widely. In the following commentary, we discuss the nature of the debate, the parameters by which CSCs can or cannot be defined, and the identification of new potential therapeutic targets elucidated by considering cancer as a problem in stem cell biology.</jats:p>

<jats:p>Stem cell fate is influenced by a number of factors and interactions that require robust control for safe and effective regeneration of functional tissue. Coordinated interactions with soluble factors, other cells, and extracellular matrices define a local biochemical and mechanical niche with complex and dynamic regulation that stem cells sense. Decellularized tissue matrices and synthetic polymer niches are being used in the clinic, and they are also beginning to clarify fundamental aspects of how stem cells contribute to homeostasis and repair, for example, at sites of fibrosis. Multifaceted technologies are increasingly required to produce and interrogate cells ex vivo, to build predictive models, and, ultimately, to enhance stem cell integration in vivo for therapeutic benefit.</jats:p>

<jats:title>Winner Takes All?</jats:title> <jats:p> Competition between individual cells plays a role in normal animal development and cell homeostasis. <jats:bold>Johnston</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1679" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1163862">1679</jats:related-article> ) reviews two situations of cell competition in <jats:italic>Drosophila</jats:italic> , one involving epithelial cells in the wing and another involving germline or somatic stem cells. “Loss” in cell competition is evidenced by the “weaker” cell's death or displacement. On the other hand, winners may engulf the loser or display enhanced proliferation. Competitive interactions allow cells to sense and eliminate poor-quality cells during development. </jats:p>

<jats:p>Acidification of the oceans may have unexpected effects on the development of bony structures in fish larvae.</jats:p>

<jats:title>Flower Functionalization</jats:title> <jats:p> The development of the specialized cells that make up the female reproductive unit in flowering plants, the gametophyte, requires the hormone auxin. However, auxin's function and movement to and within these cells are unclear. <jats:bold> Pagnussat <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="1684" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1167324">1684</jats:related-article> , published online 4 June; see the Perspective <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1652" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1176526">Friedman</jats:related-article> </jats:bold> ) provide evidence that auxin is synthesized at specific positions within the female gametophyte and exerts a positional effect and that a gradient of auxin controls patterning of these specialized cells. </jats:p>

<jats:title>Cuprate Analysis</jats:title> <jats:p> Despite more than 20 years of intensive effort, the mechanism providing superconductivity in the cuprates remains elusive and contentious, partly because the cuprates are inhomogeneous. Scanning tunneling spectroscopy (STS) and high-resolution, angle-resolved photoemission spectroscopy provide energy and momentum information about the excitations in the high-temperature cuprate superconductors. <jats:bold> Pushp <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="1689" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1174338">1689</jats:related-article> , published online 4 June) provide a STS study of the cuprate Bi <jats:sub>2</jats:sub> Sr <jats:sub>2</jats:sub> CaCu <jats:sub>2</jats:sub> O <jats:sub>8+δ</jats:sub> over a range of doping levels and temperatures. This methodology for analyzing the spectra takes into account the inhomogeneity and may provide insight into how a superconducting pairing mechanism evolves from the parent insulating state. </jats:p>

<jats:title>NMR Under Stormy Conditions</jats:title> <jats:p> Nuclear magnetic resonance spectroscopy is immensely useful for molecular characterization. However, the resolution necessary for making fine structural distinctions relies on sample isolation in a surrounding magnetic field that exhibits minimal variation in space and time over the course of the measurement; this requirement limits the range of materials that can be easily probed. <jats:bold> Pelupessy <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="1693" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1175102">1693</jats:related-article> ) present an approach that circumvents the need for spatiotemporal field homogeneity by detecting coherence transfer among coupled spins. Whereas prior methods have compensated for heterogeneity by applying corrective magnetic fields, this technique relies on the inherent insensitivity of the measured coherences to changes in the local magnetic environment and thus can be applied without prior knowledge of the field variation profile. </jats:p>

<jats:title>Molecular Fire Quencher</jats:title> <jats:p> Cage-shaped molecular assemblies can regulate the reactivity of smaller molecules trapped within them. <jats:bold> Mal <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="1697" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1175313">1697</jats:related-article> ) extend this approach to enable the protection of elemental white phosphorus (P <jats:sub>4</jats:sub> ), a substance that rapidly ignites on contact with oxygen. The tetrahedral cages self-assemble in aqueous solution through coordination of six ligands to four iron ions, and efficiently capture phosphorus from a suspension. The water-soluble host-guest constructs were stable in air for at least 4 months, but released intact P <jats:sub>4</jats:sub> rapidly on displacement by added benzene. </jats:p>