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<jats:title>Lineage tracing in mouse using CRISPR</jats:title> <jats:p> A homing guide RNA (hgRNA) that directs CRISPR-Cas9 to its own DNA locus can diversify its sequence and act as an expressed genetic barcode. Kalhor <jats:italic>et al.</jats:italic> engineered a mouse line carrying 60 independent loci of hgRNAs, thus generating a large number of unique barcodes in various embryonic and extraembryonic tissues in fully developed mice. This method demonstrates lineage tracing from the very first branches of the development tree up to organogenesis events and was used to elucidate embryonic brain patterning. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" related-article-type="in-this-issue" xlink:href="10.1126/science.aat9804">eaat9804</jats:related-article> </jats:p>

<jats:p> Reich <jats:italic>et al</jats:italic> . (Reports, 20 April 2018, p. 317) reported that elevated carbon dioxide (eCO <jats:sub>2</jats:sub> ) switched its effect from promoting C <jats:sub>3</jats:sub> grasses to favoring C <jats:sub>4</jats:sub> grasses in a long-term experiment. We argue that the authors did not appropriately elucidate the interannual climate variation as a potential mechanism for the reversal of C <jats:sub>4</jats:sub> -C <jats:sub>3</jats:sub> biomass in response to eCO <jats:sub>2</jats:sub> . </jats:p>

<jats:p> Editors at <jats:italic>Science</jats:italic> requested our input on the above discussion (comment by Best <jats:italic>et al</jats:italic> . and response by Riback <jats:italic>et al</jats:italic> .) because both sets of authors use our data from Fuertes <jats:italic>et al</jats:italic> . (2017) to support their arguments. The topic of discussion pertains to the discrepant inferences drawn from SAXS versus FRET measurements regarding the dimensions of intrinsically disordered proteins (IDPs) in aqueous solvents. Using SAXS measurements on labeled and unlabeled proteins, we ruled out the labels used for FRET measurements as the cause of discrepant inferences between the two methods. Instead, we propose that FRET and SAXS provide complementary readouts because of a decoupling of size and shape fluctuations that is intrinsic to finite-sized, heteropolymeric IDPs. Accounting for this decoupling resolves the discrepant inferences between the two methods, thus making a case for the utility of both methods. </jats:p>

<jats:p> In this issue of <jats:italic>Science</jats:italic> , we present reviews of four technologies whose power and rapid growth across biological research communities make them revolutionary (see page 864). New technology is one of the most powerful drivers of scientific progress. For example, the earliest microscopes magnified images only 50-fold at most. When the Dutch fabric merchant and amateur scientist Antonie van Leeuwenhoek developed microscopes with more than 200-fold magnifications (likely to examine cloth), he used them to study many items, including pond water and plaque from teeth. His observations of “animalcules” led to fundamental discoveries in microbiology and cell biology, and spurred the elaboration of improved microscopes. Today, various light microscopes remain prime tools in modern biology. This example embodies two characteristics of a revolutionary technology: a capability for addressing questions better than extant technologies, and the possibility of being utilized and adapted by many other investigators. </jats:p>

<jats:p>A roundup of weekly science policy and related news.</jats:p>

<jats:p>Researchers seek permit to release American chestnut engineered to resist a deadly blight.</jats:p>

<jats:p>By slowing action or targeting different receptors, altered opioids or alternatives aim to sidestep abuse.</jats:p>

<jats:p>Genomic study helps explain how schistosomiasis gained a foothold in Europe.</jats:p>

<jats:p>Agency reminds applicants to report all grant sources, warns against violating confidentiality of peer review.</jats:p>

<jats:p>Treatment repairs gene in beagles by further mutating it, but human trials are far off.</jats:p>