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<jats:title>P Granule Conundrum</jats:title> <jats:p> In many organisms, the presumptive germ cells can be distinguished from somatic cells by the presence of distinctive cytoplasmic granules. In <jats:italic>Caenorhabditis elegans</jats:italic> , these P granules are more or less uniformly distributed in the oocyte and one-cell stage of the fertilized egg. By the end of the first cleavage, however, the anterior cell is essentially free of P granules, whereas the posterior cell still displays a prominent population of granules. Exactly how this process occurs and whether it involves directed migration of the granules is unclear. Now <jats:bold> Brangwynne <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="1729" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1172046">1729</jats:related-article> , published online 21 May; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="1654" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1176523"> <jats:bold>Le Goff and Lecuit</jats:bold> </jats:related-article> ) provide evidence that localization occurs by a quite different mechanism, controlled dissolution and condensation of granule components. This type of cytoplasmic remodeling by physicochemical mechanisms can now be looked for in other cellular and developmental systems. </jats:p>

<jats:title>BDNF and Drug Dependence</jats:title> <jats:p> Brain-derived neurotrophic factor (BDNF) is a growth factor involved in neuronal plasticity that is expressed after chronic administration of drugs of abuse and may play a crucial role in chronic opiate effects. <jats:bold> Vargas-Perez <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="1732" related-article-type="in-this-issue" vol="324" xlink:href="10.1126/science.1168501">1732</jats:related-article> , published online 28 May) found that BDNF was directly involved in the switching mechanism in the ventral tegmental area, from an opiate-naïve, dopamine-independent drug reward substrate to an opiate-dependent, dopamine-dependent motivational substrate. In the ventral tegmental area, BDNF changed the action of GABA-A receptors from inhibitory to excitatory. This change led to behavioral changes that defined a neurobiological boundary between the acute phase of drug-taking and addiction. </jats:p>

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<jats:p> The show includes new draft NIH guidelines for human stem cell research, investigating the neural basis of memory, your Letters to <jats:italic>Science</jats:italic> , and more. </jats:p>