Hot off the presses! Jun 24 Cell

The Jun 24 issue of the Cell is now up on Pubget (About Cell): if you're at a subscribing institution, just click the link in the latest link at the home page. (Note you'll only be able to get all the PDFs in the issue if your institution subscribes to Pubget.)

Latest Articles Include:

• In This Issue
  - Cell 145(7):995, 997 (2011)
  
• Cardiac Damage and Its Repair
  - Cell 145(7):999, 1001 (2011)
  Cardiomyocytes are the body's ultimate endurance specialists. Recent advances provide insight into how cardiomyocytes respond to injury and stress and reveal pathways that control cardiac growth in development and disease. These findings point to new potential therapies for heart disease, including a surprising intervention that wakes up dormant cardiomyocyte precursors after ischemic injury.
• p63 and Epithelial Metaplasia: A Gutsy Choice
  - Cell 145(7):1003-1005 (2011)
  Barrett's esophagus is an epithelial metaplasia associated with an increased risk for cancer, but its underlying mechanisms have been debated. Now Wang et al. (2011) suggest an intriguing explanation for this puzzle: a population of residual embryonic cells, lacking the transcription factor p63, migrates and repopulates a normal tissue damaged by inflammation or gastroesophageal reflux.
• Stress Signaling Etches Heritable Marks on Chromatin
  - Cell 145(7):1005-1007 (2011)
  Transgenerational inheritance of epigenetic states allows organisms to pass on adaptive responses to the environment to their offspring. Seong et al. (2011) now reveal how stress-induced signaling through dATF-2 disrupts heterochromatin and leaves heritable marks that influence patterns of gene expression in subsequent generations.
• Stuck in the Middle: Drugging the Ubiquitin System at the E2 Step
  - Cell 145(7):1007-1009 (2011)
  The discovery of a small-molecule allosteric inhibitor of the CDC34 ubiquitin-conjugating enzyme (E2) by Ceccarelli et al. raises the possibility that it will be generally feasible to selectively inhibit ubiquitin transfer at this central step in the ubiquitin pathway.
• The Pessimist's and Optimist's Views of Adult Neurogenesis
  - Cell 145(7):1009-1011 (2011)
  The reports by Bonaguidi et al. (in this issue of Cell) and Encinas et al. (in Cell Stem Cell) come to differing conclusions about whether and how the proliferation of radial glia-like stem cells of the adult hippocampus impacts their long-term potential for neurogenesis.
• Life at the Leading Edge
  - Cell 145(7):1012-1022 (2011)
  Cell migration requires sustained forward movement of the plasma membrane at the cell's front or "leading edge." To date, researchers have uncovered four distinct ways of extending the membrane at the leading edge. In lamellipodia and filopodia, actin polymerization directly pushes the plasma membrane forward, whereas in invadopodia, actin polymerization couples with the extracellular delivery of matrix-degrading metalloproteases to clear a path for cells through the extracellular matrix. Membrane blebs drive the plasma membrane forward using a combination of actomyosin-based contractility and reversible detachment of the membrane from the cortical actin cytoskeleton. Each protrusion type requires the coordination of a wide spectrum of signaling molecules and regulators of cytoskeletal dynamics. In addition, these different protrusion methods likely act in concert to move cells through complex environments in vivo.
• Residual Embryonic Cells as Precursors of a Barrett's-like Metaplasia
  - Cell 145(7):1023-1035 (2011)
  Barrett's esophagus is an intestine-like metaplasia and precursor of esophageal adenocarcinoma. Triggered by gastroesophageal reflux disease, the origin of this metaplasia remains unknown. p63-deficient mice, which lack squamous epithelia, may model acid-reflux damage. We show here that p63 null embryos rapidly develop intestine-like metaplasia with gene expression profiles similar to Barrett's metaplasia. We track its source to a unique embryonic epithelium that is normally undermined and replaced by p63-expressing cells. Significantly, we show that a discrete population of these embryonic cells persists in adult mice and humans at the squamocolumnar junction, the source of Barrett's metaplasia. We show that upon programmed damage to the squamous epithelium, these embryonic cells migrate toward adjacent, specialized squamous cells in a process that may recapitulate early Barrett's. Our findings suggest that certain precancerous lesions, such as Barrett's, initiate not! from genetic alterations but from competitive interactions between cell lineages driven by opportunity. PaperClip To listen to this audio, enable JavaScript on your browser. However, you can download and play the audio by clicking on the icon below Download this Audio (6787 K)
• Exome Sequencing of Ion Channel Genes Reveals Complex Profiles Confounding Personal Risk Assessment in Epilepsy
  - Cell 145(7):1036-1048 (2011)
  Ion channel mutations are an important cause of rare Mendelian disorders affecting brain, heart, and other tissues. We performed parallel exome sequencing of 237 channel genes in a well-characterized human sample, comparing variant profiles of unaffected individuals to those with the most common neuronal excitability disorder, sporadic idiopathic epilepsy. Rare missense variation in known Mendelian disease genes is prevalent in both groups at similar complexity, revealing that even deleterious ion channel mutations confer uncertain risk to an individual depending on the other variants with which they are combined. Our findings indicate that variant discovery via large scale sequencing efforts is only a first step in illuminating the complex allelic architecture underlying personal disease risk. We propose that in silico modeling of channel variation in realistic cell and network models will be crucial to future strategies assessing mutation profile pathogenicity and dr! ug response in individuals with a broad spectrum of excitability disorders.
• Inheritance of Stress-Induced, ATF-2-Dependent Epigenetic Change
  - Cell 145(7):1049-1061 (2011)
  Atf1, the fission yeast homolog of activation transcription factor-2 (ATF-2), contributes to heterochromatin formation. However, the role of ATF-2 in chromatin assembly in higher organisms remains unknown. This study reveals that Drosophila ATF-2 (dATF-2) is required for heterochromatin assembly, whereas the stress-induced phosphorylation of dATF-2, via Mekk1-p38, disrupts heterochromatin. The dATF-2 protein colocalized with HP1, not only on heterochromatin but also at specific loci in euchromatin. Heat shock or osmotic stress induced phosphorylation of dATF-2 and resulted in its release from heterochromatin. This heterochromatic disruption was an epigenetic event that was transmitted to the next generation in a non-Mendelian fashion. When embryos were exposed to heat stress over multiple generations, the defective chromatin state was maintained over multiple successive generations, though it gradually returned to the normal state. The results suggest a mechanism by wh! ich the effects of stress are inherited epigenetically via the regulation of a tight chromatin structure.
• Insights into the Micromechanical Properties of the Metaphase Spindle
  - Cell 145(7):1062-1074 (2011)
  The microtubule-based metaphase spindle is subjected to forces that act in diverse orientations and over a wide range of timescales. Currently, we cannot explain how this dynamic structure generates and responds to forces while maintaining overall stability, as we have a poor understanding of its micromechanical properties. Here, we combine the use of force-calibrated needles, high-resolution microscopy, and biochemical perturbations to analyze the vertebrate metaphase spindle's timescale- and orientation-dependent viscoelastic properties. We find that spindle viscosity depends on microtubule crosslinking and density. Spindle elasticity can be linked to kinetochore and nonkinetochore microtubule rigidity, and also to spindle pole organization by kinesin-5 and dynein. These data suggest a quantitative model for the micromechanics of this cytoskeletal architecture and provide insight into how structural and functional stability is maintained in the face of forces, such a! s those that control spindle size and position, and can result from deformations associated with chromosome movement. PaperFlick To view the video inline, enable JavaScript on your browser. However, you can download and view the video by clicking on the icon below Download this Video (11573 K)
• An Allosteric Inhibitor of the Human Cdc34 Ubiquitin-Conjugating Enzyme
  - Cell 145(7):1075-1087 (2011)
  In the ubiquitin-proteasome system (UPS), E2 enzymes mediate the conjugation of ubiquitin to substrates and thereby control protein stability and interactions. The E2 enzyme hCdc34 catalyzes the ubiquitination of hundreds of proteins in conjunction with the cullin-RING (CRL) superfamily of E3 enzymes. We identified a small molecule termed CC0651 that selectively inhibits hCdc34. Structure determination revealed that CC0651 inserts into a cryptic binding pocket on hCdc34 distant from the catalytic site, causing subtle but wholesale displacement of E2 secondary structural elements. CC0651 analogs inhibited proliferation of human cancer cell lines and caused accumulation of the SCFSkp2 substrate p27Kip1. CC0651 does not affect hCdc34 interactions with E1 or E3 enzymes or the formation of the ubiquitin thioester but instead interferes with the discharge of ubiquitin to acceptor lysine residues. E2 enzymes are thus susceptible to noncatalytic site inhibition and may represe! nt a viable class of drug target in the UPS.
• The INAD Scaffold Is a Dynamic, Redox-Regulated Modulator of Signaling in the Drosophila Eye
  - Cell 145(7):1088-1101 (2011)
  INAD is a scaffolding protein that regulates signaling in Drosophila photoreceptors. One of its PDZ domains, PDZ5, cycles between reduced and oxidized forms in response to light, but it is unclear how light affects its redox potential. Through biochemical and structural studies, we show that the redox potential of PDZ5 is allosterically regulated by its interaction with another INAD domain, PDZ4. Whereas isolated PDZ5 is stable in the oxidized state, formation of a PDZ45 "supramodule" locks PDZ5 in the reduced state by raising the redox potential of its Cys606/Cys645 disulfide bond by 330 mV. Acidification, potentially mediated via light and PLCβ-mediated hydrolysis of PIP2, disrupts the interaction between PDZ4 and PDZ5, leading to PDZ5 oxidation and dissociation from the TRP Ca2+ channel, a key component of fly visual signaling. These results show that scaffolding proteins can actively modulate the intrinsic redox potentials of their disulfide bonds to exert reg! ulatory roles in signaling.
• Golgi Export of the Kir2.1 Channel Is Driven by a Trafficking Signal Located within Its Tertiary Structure
  - Cell 145(7):1102-1115 (2011)
  Mechanisms that are responsible for sorting newly synthesized proteins for traffic to the cell surface from the Golgi are poorly understood. Here, we show that the potassium channel Kir2.1, mutations in which are associated with Andersen-Tawil syndrome, is selected as cargo into Golgi export carriers in an unusual signal-dependent manner. Unlike conventional trafficking signals, which are typically comprised of short linear peptide sequences, Golgi exit of Kir2.1 is dictated by residues that are embedded within the confluence of two separate domains. This signal patch forms a recognition site for interaction with the AP1 adaptor complex, thereby marking Kir2.1 for incorporation into clathrin-coated vesicles at the trans-Golgi. The identification of a trafficking signal in the tertiary structure of Kir2.1 reveals a quality control step that couples protein conformation to Golgi export and provides molecular insight into how mutations in Kir2.1 arrest the channels at the! Golgi.
• A Phosphorylation Cycle Shapes Gradients of the DYRK Family Kinase Pom1 at the Plasma Membrane
  - Cell 145(7):1116-1128 (2011)
  Concentration gradients regulate many cell biological and developmental processes. In rod-shaped fission yeast cells, polar cortical gradients of the DYRK family kinase Pom1 couple cell length with mitotic commitment by inhibiting a mitotic inducer positioned at midcell. However, how Pom1 gradients are established is unknown. Here, we show that Tea4, which is normally deposited at cell tips by microtubules, is both necessary and, upon ectopic cortical localization, sufficient to recruit Pom1 to the cell cortex. Pom1 then moves laterally at the plasma membrane, which it binds through a basic region exhibiting direct lipid interaction. Pom1 autophosphorylates in this region to lower lipid affinity and promote membrane release. Tea4 triggers Pom1 plasma membrane association by promoting its dephosphorylation through the protein phosphatase 1 Dis2. We propose that local dephosphorylation induces Pom1 membrane association and nucleates a gradient shaped by the opposing acti! ons of lateral diffusion and autophosphorylation-dependent membrane detachment.
• A Role for the Primary Cilium in Notch Signaling and Epidermal Differentiation during Skin Development
  - Cell 145(7):1129-1141 (2011)
  Ciliogenesis precedes lineage-determining signaling in skin development. To understand why, we performed shRNA-mediated knockdown of seven intraflagellar transport proteins (IFTs) and conditional ablation of Ift-88 and Kif3a during embryogenesis. In both cultured keratinocytes and embryonic epidermis, all of these eliminated cilia, and many (not Kif3a) caused hyperproliferation. Surprisingly and independent of proliferation, ciliary mutants displayed defects in Notch signaling and commitment of progenitors to differentiate. Notch receptors and Notch-processing enzymes colocalized with cilia in wild-type epidermal cells. Moreover, differentiation defects in ciliary mutants were cell autonomous and rescued by activated Notch (NICD). By contrast, Shh signaling was neither operative nor required for epidermal ciliogenesis, Notch signaling, or differentiation. Rather, Shh signaling defects in ciliary mutants occurred later, arresting hair follicle morphogenesis in the skin.! These findings unveil temporally and spatially distinct functions for primary cilia at the nexus of signaling, proliferation, and differentiation.
• In Vivo Clonal Analysis Reveals Self-Renewing and Multipotent Adult Neural Stem Cell Characteristics
  - Cell 145(7):1142-1155 (2011)
  Neurogenesis and gliogenesis continue in discrete regions of the adult mammalian brain. A fundamental question remains whether cell genesis occurs from distinct lineage-restricted progenitors or from self-renewing and multipotent neural stem cells in the adult brain. Here, we developed a genetic marking strategy for lineage tracing of individual, quiescent, and nestin-expressing radial glia-like (RGL) precursors in the adult mouse dentate gyrus. Clonal analysis identified multiple modes of RGL activation, including asymmetric and symmetric self-renewal. Long-term lineage tracing in vivo revealed a significant percentage of clones that contained RGL(s), neurons, and astrocytes, indicating capacity of individual RGLs for both self-renewal and multilineage differentiation. Furthermore, conditional Pten deletion in RGLs initially promotes their activation and symmetric self-renewal but ultimately leads to terminal astrocytic differentiation and RGL depletion in the adult h! ippocampus. Our study identifies RGLs as self-renewing and multipotent neural stem cells and provides novel insights into in vivo properties of adult neural stem cells.
• A Rapid, Extensive, and Transient Transcriptional Response to Estrogen Signaling in Breast Cancer Cells
  - Cell 145(7):1156 (2011)
  
• SnapShot: Mitochondrial Dynamics
  - Cell 145(7):1158-1158.e1 (2011)