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<jats:title>Optogenetic Insights</jats:title> <jats:p> Mapping functional neural circuits for many behaviors has been almost impossible, so <jats:bold> Vogelstein <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="386" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1250298">386</jats:related-article> , published online 27 March; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="372" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1253853"> <jats:bold>O'Leary and Marder</jats:bold> </jats:related-article> ) developed a broadly applicable optogenetic method for neuron-behavior mapping and used it to phenotype larval <jats:italic>Drosophila</jats:italic> and thus developed a reference atlas. As optogenetic experiments become routine in certain fields of neuroscience research, creating even more specialized tools is imperative (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="369" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1253616">Hayashi</jats:related-article> </jats:bold> ). By engineering channelrhodopsin, <jats:bold> Wietek <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="409" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1249375">409</jats:related-article> , published online 27 March) and <jats:bold> Berndt <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="420" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1252367">420</jats:related-article> ) created two different light-gated anion channels to block action potential generation during synaptic stimulation or depolarizing current injections. These new tools not only improve understanding of channelrhodopsins but also provide a way to silence cells. </jats:p>

<jats:title>A Dual Approach to 2 + 2</jats:title> <jats:p> Asymmetric catalysis generally accelerates the pathway to one specific product geometry that can be manipulated by reducing the temperature to slow down competing reactions. It is more difficult to be selective in photochemical reactions, but in the [2 + 2] coupling of olefins to make four-membered rings, <jats:bold> Du <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="392" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1251511">392</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="6182" page="368" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1252965">Neier</jats:related-article> </jats:bold> ) used a ruthenium catalyst that absorbs visible light to activate the substrates below the frequency threshold where they absorb intrinsically. Then a second—a chiral Lewis acid—catalyst directs the product stereochemistry. A major advantage of the dual reactions is that each catalyst can be tuned independently. </jats:p>

<jats:title>Magnified Flare-Up</jats:title> <jats:p> The rise and fall of the luminosity of a supernova detected in 2010 was typical for its class, but its apparent brightness was 30 times greater than similar events. <jats:bold> Quimby <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="396" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1250903">396</jats:related-article> ) compared spectra from the time of peak brightness and after the supernova faded, from which they concluded that something was interfering with our line of sight to the supernova. A previously unknown foreground galaxy turned out to be acting as a lens, bending and magnifying the light from the supernova. Potentially, spacetime warping like this could allow direct testing of cosmic expansion. </jats:p>

<jats:title>Wetted Apatite</jats:title> <jats:p> The long-running story of the dry Moon was rewritten a few years ago when hydrogen-bearing glass spherules were discovered. The highest water contents are found in lunar apatite, at levels suspiciously comparable to the water content of Earth apatites. <jats:bold> Boyce <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="400" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1250398">400</jats:related-article> , published online 20 March; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="365" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1253266">Anand</jats:related-article> </jats:bold> ) now show that the water content of lunar apatite is not a reliable indicator of the abundance of water in mare basalts. The existence of apatite with high water content is an almost inevitable consequence of the loss of tiny amounts of fluorine-rich apatite from a melt and replacement by hydrogen and is thus no indication of a “wet” Moon. </jats:p>

<jats:title>Deep Freeze</jats:title> <jats:p> Geologists usually consider glaciers and ice sheets to be gigantic abrasives, scouring the ground beneath them and carving out relief on the underlying landscapes. <jats:bold> Bierman <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="402" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1249047">402</jats:related-article> , published online 17 April) show that this is not always the case. They found that the silt at the very bottom of the Greenland Ice Sheet Project 2 core contained significant amounts of beryllium-10, an isotope produced in the atmosphere by cosmic rays and which adheres to soils when it is deposited on them. Hence, the dust at the bottom of the ice sheet indicates the persistence of a landscape under 3000 meters of glacial ice that is millions of years old. </jats:p>

<jats:title>Understanding N Loss</jats:title> <jats:p> Biologically available nitrogen (N) is essential for marine plants, and shortage of N limits photosynthesis. Marine N can be removed by denitrification and anaerobic ammonia oxidation (anammox) processes, but what controls the balance between these two pathways? <jats:bold> Babbin <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="406" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1248364">406</jats:related-article> , published online 10 April) tested the effects of stoichiometry on N removal in the lab and found that the balance of N loss processes depends on the stoichiometry of the source organic material. </jats:p>

<jats:title>Optogenetic Insights</jats:title> <jats:p> Mapping functional neural circuits for many behaviors has been almost impossible, so <jats:bold> Vogelstein <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="386" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1250298">386</jats:related-article> , published online 27 March; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="372" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1253853"> <jats:bold>O'Leary and Marder</jats:bold> </jats:related-article> ) developed a broadly applicable optogenetic method for neuron-behavior mapping and used it to phenotype larval <jats:italic>Drosophila</jats:italic> and thus developed a reference atlas. As optogenetic experiments become routine in certain fields of neuroscience research, creating even more specialized tools is imperative (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="369" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1253616">Hayashi</jats:related-article> </jats:bold> ). By engineering channelrhodopsin, <jats:bold> Wietek <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="409" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1249375">409</jats:related-article> , published online 27 March) and <jats:bold> Berndt <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="420" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1252367">420</jats:related-article> ) created two different light-gated anion channels to block action potential generation during synaptic stimulation or depolarizing current injections. These new tools not only improve understanding of channelrhodopsins but also provide a way to silence cells. </jats:p>

<jats:title>RNA Heteroplasmy</jats:title> <jats:p> Like nuclear DNA, the mitochondrial genome has to be posttranscriptionally modified to function properly; however, among individuals, mitochondrial RNA (mtRNA) transcripts vary in ways that are poorly understood. <jats:bold> Hodgkinson <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="413" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1251110">413</jats:related-article> ) looked at mtRNA editing events and posttranscriptional methylation in more than 700 individuals. Interestingly, variation at the ninth position within transfer RNAs showed a high frequency of variation that, in some cases, is genetically attributable. </jats:p>

<jats:title>Cyanobacterial Diversity</jats:title> <jats:p> What does it mean to be a global species? The marine cyanobacterium <jats:italic>Prochlorococcus</jats:italic> is ubiquitous and, arguably, the most abundant and productive of all living organisms. Although to our eyes the seas look uniform, to a bacterium the ocean's bulk is a plethora of microhabitats, and by large-scale single-cell genomic analysis of uncultured cells, <jats:bold> Kashtan <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="416" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1248575">416</jats:related-article> ; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="366" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1253817"> <jats:bold>Bowler and Scanlan</jats:bold> </jats:related-article> ) reveal that <jats:italic>Prochlorococcus</jats:italic> has diversified to match. This “species” constitutes a mass of subpopulations—each with million-year ancestry—that vary seasonally in abundance. The subpopulations in turn have clades nested within that show covariation between sets of core alleles and variable gene content, indicating flexibility of responses to rapid environmental changes. Large sets of coexisting populations could be a general feature of other free-living bacterial species living in highly mixed habitats. </jats:p>

<jats:title>Optogenetic Insights</jats:title> <jats:p> Mapping functional neural circuits for many behaviors has been almost impossible, so <jats:bold> Vogelstein <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="386" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1250298">386</jats:related-article> , published online 27 March; see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="372" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1253853"> <jats:bold>O'Leary and Marder</jats:bold> </jats:related-article> ) developed a broadly applicable optogenetic method for neuron-behavior mapping and used it to phenotype larval <jats:italic>Drosophila</jats:italic> and thus developed a reference atlas. As optogenetic experiments become routine in certain fields of neuroscience research, creating even more specialized tools is imperative (see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="369" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1253616">Hayashi</jats:related-article> </jats:bold> ). By engineering channelrhodopsin, <jats:bold> Wietek <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="409" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1249375">409</jats:related-article> , published online 27 March) and <jats:bold> Berndt <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6182" page="420" related-article-type="in-this-issue" vol="344" xlink:href="10.1126/science.1252367">420</jats:related-article> ) created two different light-gated anion channels to block action potential generation during synaptic stimulation or depolarizing current injections. These new tools not only improve understanding of channelrhodopsins but also provide a way to silence cells. </jats:p>