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[Research highlight] Transcription in action

In a work just published at Nature, Churchman and Weissman (2011) describe a new method for directly capturing and sequencing elongating, or nascent, RNA transcripts. The authors then use this method to provide a detailed look at the transcriptional process in action, revealing a histone modification-dependent mechanism that constrains genome-wide antisense transcription, and pervasive transcriptional pausing and backtracking throughout genes.  Read more

[Research highlight] modENCODE releases extensive functional investigation of fly and worm genomes

Recently, a series of publications by members of the modENCODE consortium were released online at Science, Nature, and Genome Research. These works collectively describe a massive effort to functionally characterize and annotate the Drosophila melanogaster and Caenorhabditis elegans genomes, including in-depth analyses of genes and transcripts, epigenetic marks, transcription factor binding, and replication timing, across a range of developmental and tissue sources.  Read more

[Research highlight] Multicellular computers

Elaborate computation tasks can be performed by distributing the work across interconnected elementary information processing units. This principle underlies not only the operation of integrated electronic circuits, but also of many biological processes including development and, of course, the activity of the brain.  Read more

The role of neutral mutations in the evolution of phenotypes

The role of neutral mutations in the evolution of phenotypes

In a recent opinion piece, Andreas Wagner tries to reconcile the tension between proponents of neutral evolution and selectionism (Wagner 2008). He argues that “neutral mutations prepare the ground for later evolutionary innovation”. Wagner illustrates this point using a network model of genotype-phenotype relationships (Wagner 2005). In a so-called ‘neutral network’, nodes correspond to distinct genotypes associated with the same phenotype and are connected by an edge if the respective genotypes differ only by a single mutation event (eg point mutation). Examples of neutral networks include different genotypes coding for RNA or protein structures. In this representation, highly connected networks correspond to robust phenotypes that are not very sensitive to changes in genotype. Wagner notes the zinc finger fold as an impressive example of a highly connected neutral network as its structure remains essentially the same even after mutating all but seven of its 26 residues to alanine.  Read more

Rewiring E. coli transcriptional network

Rewiring E. coli transcriptional network

Gene duplications and mutations are central driving forces in the evolution of genomes. Genomes must be robust to such changes in order to be evolvable, and many studies have probed genome robustness using systematic gene knockouts or overexpression experiments. In a recent paper, Isalan et al. (2008) took a new approach to test the robustness of Escherichia coli gene circuitry by reconstructing gene duplication events by shuffling the promoter-ORF pairs for about 300 transcription factors and introducing 598 recombined pairs one-by-one into E. coli to rewire its transcriptional network. Surprisingly, ~95% of such additions are robustly tolerated, and some networks even exhibit greater fitness under various selection pressures. Moreover, the study shows that, in contrast to naive expectations, the introduction of positive or negative feedback loops has little effect on the protein expression levels of regulated ORFs.  Read more

A refreshing model: peppermint terpenoids

A refreshing model: peppermint terpenoids

Living cells are typically asymmetric, having tens of thousands different biopolymers (proteins and polynucleotides), but merely <1000 types of small molecules, such as amino acids and lipids. An exception is certain plant cells that harbor members of ~40,000 strong group of low molecular weight terpenoids, often displaying a complex compositional balance essential for plant growth and survival (Aharoni et al, 2005). Understanding the intricacies of biosynthesis and interconversion of such unusual cellular components appears to require the full power of Systems Biology. In a recent paper, Rios-Estepa et al (2008) harness a systems approach, including iterative cycles of mathematical modeling and experimental testing, to help elucidate the metabolic dynamics of the terpenoid universe.  Read more

EGFR and c-Met core signaling network

EGFR and c-Met core signaling network

Targeting receptor tyrosine kinases (RTKs) is currently thought to be a promising anti-cancer strategy (Baselga, 2006). However, clinical trials with RTK inhibitors demonstrated that some solid tumors are sensitive to these drugs while others are not. For instance, only a subset of non small cell lung cancer (NSCLC) tumors with EGFR-activating mutations seems to respond to EGFR inhibitors (Lynch et al, 2004).  Read more

Transcription paused and poised for regulation

Transcription paused and poised for regulation

For eukaryotes, it is widely thought that transcription is primarily regulated through recruitment of the essential machinery to transcription start-sites. Previous hints challenging this paradigm have been confirmed by recent analyses showing that transcription regulation of a large number of genes actually occurs after recruitment. Mechanistically, such studies have gone furthest in Drosophila melanogaster (Muse et al, 2007; Zeitlinger et al, 2007). Here, conservative estimates indicate that more than 10% of genes are regulated through promoter-proximal pausing. On such genes, RNA polymerase II is recruited and initiates transcription, but then pauses around 50 bp downstream of the transcription start-site where it awaits further signals to resume elongation and complete transcription proper.  Read more