Catálogo de publicaciones - revistas

<jats:title>Building the cell wall is flipping difficult</jats:title> <jats:p> The cell wall of bacteria is constructed from a polysaccharide called peptidoglycan (PG). It forms a matrix that surrounds cells and is essential for the integrity of the cytoplasmic membrane. Many of our most successful antibiotics target PG synthesis. The synthetic pathway involves the assembly of sugar building blocks on a lipid carrier at the inner face of the cytoplasmic membrane. The reactions that produce this so-called lipid II precursor and the enzymes that catalyze them have been known for decades. However, the identity of the flippase enzyme that “flips” lipid II in the membrane to expose the sugar building blocks on the cell surface for polymerization has remained highly controversial. Sham <jats:italic>et al.</jats:italic> now show that the essential protein MurJ is the long sought-after flippase responsible for the translocation of lipid-linked cell wall precursors across the bacterial cytoplasmic membrane (see the Perspective by Young). The work completes the cell wall biogenesis pathway and defines the function of an attractive target for new antibiotics. </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" issue="6193" page="220" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1254522">220</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6193" page="139" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1256585">139</jats:related-article> </jats:p>

<jats:title>Observing an embryonic Doppler effect</jats:title> <jats:p> The sound of an oncoming train changes as it passes you, a phenomenon termed the Doppler effect. Soroldoni <jats:italic>et al.</jats:italic> propose a similar event during the formation of vertebrate embryo body segments. It is generally thought that the internal timing of a genetic oscillator called the “segmentation clock” sets the rhythm of body segments called somites. However, time-lapse microscopy of the spatial waves of oscillations and the timing of body segment formation showed segments forming faster than spatial genetic oscillations. This “Doppler effect” occurs because the end of the oscillating tissue moves steadily into the oncoming waves. Thus, the rhythm of sequential body segmentation is a function of genetic oscillations, their changing wave pattern, and tissue shortening. </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" issue="6193" page="222" related-article-type="in-this-issue" vol="345" xlink:href="10.1126/science.1253089">222</jats:related-article> </jats:p>

<jats:p>Microbiomes–the distinct microbial populations that colonize an array of bodily and environmental niches–are rapidly gaining prominence in numerous fields of research. Increasing understanding of the composition and characteristics of these microbial communities is providing substantial insight into the function, and dysfunction, of a broad range of processes in the host organisms. Recent discoveries indicate a role of the microbiome in specific physical conditions and disease states; these discoveries suggest considerable potential for the development of microbiome-based diagnostic and therapeutic tools. While the microbiota of the human gut has drawn much attention to date, microbiome research is by no means limited to the study of the intestinal populations, or even to the study of humans. Efforts in environmental and agricultural research, for example, reflect a growing interest in the relevance of nonhuman microbiomes.</jats:p>

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

<jats:p>On this week's show: A sea of plastic bits and a roundup of stories from our daily news site.</jats:p>

<jats:p> Allohexaploid bread wheat ( <jats:italic>Triticum aestivum</jats:italic> L.) provides approximately 20% of calories consumed by humans. Lack of genome sequence for the three homeologous and highly similar bread wheat genomes (A, B, and D) has impeded expression analysis of the grain transcriptome. We used previously unknown genome information to analyze the cell type–specific expression of homeologous genes in the developing wheat grain and identified distinct co-expression clusters reflecting the spatiotemporal progression during endosperm development. We observed no global but cell type– and stage-dependent genome dominance, organization of the wheat genome into transcriptionally active chromosomal regions, and asymmetric expression in gene families related to baking quality. Our findings give insight into the transcriptional dynamics and genome interplay among individual grain cell types in a polyploid cereal genome. </jats:p>

<jats:title>The making of bodies part by part</jats:title> <jats:p>Mention of organoids—organlike structure growing in a Petri dish—might conjure up images of science fiction. However, the generation of organoids is very real, as is the increased understanding of organ form and function that comes from studying them. Lancaster and Knoblich review organoids as structures that include more than one cell type of an organ that exhibit structural and functional features of the natural counterpart. Knowledge of normal organ developmental pathways guides the formation of these structures. Organoids show great promise for modeling human development and disease and for biomedical research and regenerative medicine.</jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue <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.1247125">10.1126/science.1247125</jats:related-article> </jats:p>

<jats:p>We produced a reference sequence of the 1-gigabase chromosome 3B of hexaploid bread wheat. By sequencing 8452 bacterial artificial chromosomes in pools, we assembled a sequence of 774 megabases carrying 5326 protein-coding genes, 1938 pseudogenes, and 85% of transposable elements. The distribution of structural and functional features along the chromosome revealed partitioning correlated with meiotic recombination. Comparative analyses indicated high wheat-specific inter- and intrachromosomal gene duplication activities that are potential sources of variability for adaption. In addition to providing a better understanding of the organization, function, and evolution of a large and polyploid genome, the availability of a high-quality sequence anchored to genetic maps will accelerate the identification of genes underlying important agronomic traits.</jats:p>

<jats:p> An ordered draft sequence of the 17-gigabase hexaploid bread wheat ( <jats:italic>Triticum aestivum</jats:italic> ) genome has been produced by sequencing isolated chromosome arms. We have annotated 124,201 gene loci distributed nearly evenly across the homeologous chromosomes and subgenomes. Comparative gene analysis of wheat subgenomes and extant diploid and tetraploid wheat relatives showed that high sequence similarity and structural conservation are retained, with limited gene loss, after polyploidization. However, across the genomes there was evidence of dynamic gene gain, loss, and duplication since the divergence of the wheat lineages. A high degree of transcriptional autonomy and no global dominance was found for the subgenomes. These insights into the genome biology of a polyploid crop provide a springboard for faster gene isolation, rapid genetic marker development, and precise breeding to meet the needs of increasing food demand worldwide. </jats:p>