bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlling the efficiency of an artificial light-harvesting complex
Authors: Savolainen Janne , Fanciulli Riccardo , Dijkhuizen Niels , Moore Ana L. , Hauer Jürgen , Buckup Tiago , Motzkus Marcus , Herek Jennifer L.
Published: May 2008

Adaptive femtosecond pulse shaping in an evolutionary learning loop is applied to a bioinspired dyad molecule that closely mimics the early-time photophysics of the light-harvesting complex 2 (LH2) photosynthetic antenna complex. Control over the branching ratio between the two competing pathways for energy flow, internal conversion (IC) and energy transfer (ET), is realized. We show that by pulse shaping it is possible to increase independently the relative yield of both channels, ET and IC. The optimization results are analyzed by using Fourier analysis, which gives direct insight to the mechanism featuring quantum interference of a low-frequency mode. The results from the closed-loop experiments are repeatable and robust and demonstrate the power of coherent control experiments as a spectroscopic tool (i.e., quantum-control spectroscopy) capable of revealing functionally relevant molecular properties that are hidden from conventional techniques.
Immunity to a salivary protein of a sand fly vector protects against the fatal outcome of visceral leishmaniasis in a hamster model
Authors: Gomes Regis , Teixeira Clarissa , Teixeira Maria Jânia , Oliveira Fabiano , Menezes Maria José , Silva Claire , de Oliveira Camila I. , Miranda Jose C. , Elnaiem Dia-Eldin , Kamhawi Shaden , Valenzuela Jesus G. , Brodskyn Cláudia I.
Published: May 2008

Visceral leishmaniasis (VL) is a fatal disease for humans, and no vaccine is currently available. Sand fly salivary proteins have been associated with protection against cutaneous leishmaniasis. To test whether vector salivary proteins can protect against VL, a hamster model was developed involving intradermal inoculation in the ears of 100,000Leishmania infantum chagasiparasites together withLutzomyia longipalpissaliva to mimic natural transmission by sand flies. Hamsters developed classical signs of VL rapidly, culminating in a fatal outcome 5–6 months postinfection. Saliva had no effect on the course of infection in this model. Immunization with 16 DNA plasmids coding for salivary proteins ofLu. longipalpisresulted in the identification of LJM19, a novel 11-kDa protein, that protected hamsters against the fatal outcome of VL. LJM19-immunized hamsters maintained a low parasite load that correlated with an overall high IFN-γ/TGF-β ratio and inducible NOS expression in the spleen and liver up to 5 months postinfection. Importantly, a delayed-type hypersensitivity response with high expression of IFN-γ was also noted in the skin of LJM19-immunized hamsters 48 h after exposure to uninfected sand fly bites. Induction of IFN-γ at the site of bite could partly explain the protection observed in the viscera of LJM19-immunized hamsters through direct parasite killing and/or priming of anti-Leishmaniaimmunity. We have shown that immunity to a defined salivary protein (LJM19) confers powerful protection against the fatal outcome of a parasitic disease, which reinforces the concept of using components of arthropod saliva in vaccine strategies against vector-borne diseases.
Load-dependent ADP binding to myosins V and VI: Implications for subunit coordination and function
Authors: Oguchi Yusuke , Mikhailenko Sergey V. , Ohki Takashi , Olivares Adrian O. , De La Cruz Enrique M. , Ishiwata Shin'ichi
Published: May 2008

Dimeric myosins V and VI travel long distances in opposite directions along actin filaments in cells, taking multiple steps in a “hand-over-hand” fashion. The catalytic cycles of both myosins are limited by ADP dissociation, which is considered a key step in the walking mechanism of these motors. Here, we demonstrate that external loads applied to individual actomyosin V or VI bonds asymmetrically affect ADP affinity, such that ADP binds weaker under loads assisting motility. Model-based analysis reveals that forward and backward loads modulate the kinetics of ADP binding to both myosins, although the effect is less pronounced for myosin VI. ADP dissociation is modestly accelerated by forward loads and inhibited by backward loads. Loads applied in either direction slow ADP binding to myosin V but accelerate binding to myosin VI. We calculate that the intramolecular load generated during processive stepping is ≈2 pN for both myosin V and myosin VI. The distinct load dependence of ADP binding allows these motors to perform different cellular functions.
Electrostatic basis for the unidirectionality of the primary proton transfer in cytochrome
c
oxidase
Authors: Pisliakov Andrei V. , Sharma Pankaz K. , Chu Zhen T. , Haranczyk Maciej , Warshel Arieh
Published: May 2008

Gaining detailed understanding of the energetics of the proton-pumping process in cytochrome
c
oxidase (CcO) is one of the challenges of modern biophysics. Despite promising mechanistic proposals, most works have not related the activation barriers of the different assumed steps to the protein structure, and there has not been a physically consistent model that reproduced the barriers needed to create a working pump. This work reevaluates the activation barriers for the primary proton transfer (PT) steps by calculations that reflect all relevant free energy contributions, including the electrostatic energies of the generated charges, the energies of water insertion, and large structural rearrangements of the donor and acceptor. The calculations have reproduced barriers that account for the directionality and sequence of events in the primary PT in CcO. It has also been found that the PT from Glu-286 (E) to the propionate of heme a
3
(Prd) provides a gate for an initial back leakage from the high pH side of the membrane. Interestingly, the rotation of E that brings it closer to Prd appears to provide a way for blocking competing pathways in the primary PT. Our study elucidates and quantifies the nature of the control of the directionality in the primary PT in CcO and provides instructive insight into the role of the water molecules in biological PT, showing that “bridges” of several water molecules in hydrophobic regions present a problem (rather than a solution) that is minimized in the primary PT.
Cidea is associated with lipid droplets and insulin sensitivity in humans
Authors: Puri Vishwajeet , Ranjit Srijana , Konda Silvana , Nicoloro Sarah M. C. , Straubhaar Juerg , Chawla Anil , Chouinard My , Lin Chenyi , Burkart Alison , Corvera Silvia , Perugini Richard A. , Czech Michael P.
Published: May 2008

Storage of energy as triglyceride in large adipose-specific lipid droplets is a fundamental need in all mammals. Efficient sequestration of fat in adipocytes also prevents fatty acid overload in skeletal muscle and liver, which can impair insulin signaling. Here we report that the Cide domain-containing protein Cidea, previously thought to be a mitochondrial protein, colocalizes around lipid droplets with perilipin, a regulator of lipolysis. Cidea-GFP greatly enhances lipid droplet size when ectopically expressed in preadipocytes or COS cells. These results explain previous findings showing that depletion of Cidea with RNAi markedly elevates lipolysis in human adipocytes. Like perilipin, Cidea and the related lipid droplet protein Cidec/FSP27 are controlled by peroxisome proliferator-activated receptor γ (PPARγ). Treatment of lean or obese mice with the PPARγ agonist rosiglitazone markedly up-regulates Cidea expression in white adipose tissue (WAT), increasing lipid deposition. Strikingly, in both omental and s.c. WAT from BMI-matched obese humans, expression of Cidea, Cidec/FSP27, and perilipin correlates positively with insulin sensitivity (HOMA-IR index). Thus, Cidea and other lipid droplet proteins define a novel, highly regulated pathway of triglyceride deposition in human WAT. The data support a model whereby failure of this pathway results in ectopic lipid accumulation, insulin resistance, and its associated comorbidities in humans.
Control of endothelial cell proliferation and migration by VEGF signaling to histone deacetylase 7
Authors: Wang Shusheng , Li Xiumin , Parra Maribel , Verdin Eric , Bassel-Duby Rhonda , Olson Eric N.
Published: May 2008

VEGF has been shown to regulate endothelial cell (EC) proliferation and migration. However, the nuclear mediators of the actions of VEGF in ECs have not been fully defined. We show that VEGF induces the phosphorylation of three conserved serine residues in histone deacetylase 7 (HDAC7) via protein kinase D, which promotes nuclear export of HDAC7 and activation of VEGF-responsive genes in ECs. Expression of a signal-resistant HDAC7 mutant protein in ECs inhibits proliferation and migration in response to VEGF. These results demonstrate that phosphorylation of HDAC7 serves as a molecular switch to mediate VEGF signaling and endothelial function.
LRP6 transduces a canonical Wnt signal independently of Axin degradation by inhibiting GSK3's phosphorylation of β-catenin
Authors: Cselenyi Christopher S. , Jernigan Kristin K. , Tahinci Emilios , Thorne Curtis A. , Lee Laura A. , Lee Ethan
Published: May 2008

Wnt/β-catenin signaling controls various cell fates in metazoan development and is misregulated in several cancers and developmental disorders. Binding of a Wnt ligand to its transmembrane coreceptors inhibits phosphorylation and degradation of the transcriptional coactivator β-catenin, which then translocates to the nucleus to regulate target gene expression. To understand how Wnt signaling prevents β-catenin degradation, we focused on the Wnt coreceptor low-density lipoprotein receptor-related protein 6 (LRP6), which is required for signal transduction and is sufficient to activate Wnt signaling when overexpressed. LRP6 has been proposed to stabilize β-catenin by stimulating degradation of Axin, a scaffold protein required for β-catenin degradation. In certain systems, however, Wnt-mediated Axin turnover is not detected until after β-catenin has been stabilized. Thus, LRP6 may also signal through a mechanism distinct from Axin degradation. To establish a biochemically tractable system to test this hypothesis, we expressed and purified the LRP6 intracellular domain from bacteria and show that it promotes β-catenin stabilization and Axin degradation in
Xenopus
egg extract. Using an Axin mutant that does not degrade in response to LRP6, we demonstrate that LRP6 can stabilize β-catenin in the absence of Axin turnover. Through experiments in egg extract and reconstitution with purified proteins, we identify a mechanism whereby LRP6 stabilizes β-catenin independently of Axin degradation by directly inhibiting GSK3's phosphorylation of β-catenin.
A latitudinal diversity gradient in planktonic marine bacteria
Authors: Fuhrman Jed A. , Steele Joshua A. , Hewson Ian , Schwalbach Michael S. , Brown Mark V. , Green Jessica L. , Brown James H.
Published: May 2008

For two centuries, biologists have documented a gradient of animal and plant biodiversity from the tropics to the poles but have been unable to agree whether it is controlled primarily by productivity, temperature, or historical factors. Recent reports that find latitudinal diversity gradients to be reduced or absent in some unicellular organisms and attribute this to their high abundance and dispersal capabilities would suggest that bacteria, the smallest and most abundant organisms, should exhibit no latitudinal pattern of diversity. We used amplified ribosomal intergenic spacer analysis (ARISA) whole-assemblage genetic fingerprinting to quantify species richness in 103 near-surface samples of marine bacterial plankton, taken from tropical to polar in both hemispheres. We found a significant latitudinal gradient in richness. The data can help to evaluate hypotheses about the cause of the gradient. The correlations of richness with latitude and temperature were similarly strong, whereas correlations with parameters relating to productivity (chlorophyll, annual primary productivity, bacterial abundance) and other variables (salinity and distance to shore) were much weaker. Despite the high abundance and potentially high dispersal of bacteria, they exhibit geographic patterns of species diversity that are similar to those seen in other organisms. The latitudinal gradient in marine bacteria supports the hypothesis that the kinetics of metabolism, setting the pace for life, has strong influence on diversity.
Dimeric subunit stoichiometry of the human voltage-dependent proton channel Hv1
Authors: Lee Seok-Yong , Letts James A. , MacKinnon Roderick
Published: May 2008

In voltage-gated Na
+
, K
+
, and Ca
2+
channels, four voltage-sensor domains operate on a central pore domain in response to membrane voltage. In contrast, the voltage-gated proton channel (Hv) contains only a voltage-sensor domain, lacking a separate pore domain. The subunit stoichiometry and organization of Hv has been unknown. Here, we show that human Hv1 forms a dimer in the membrane and define regions that are close to the dimer interface by using cysteine cross-linking. Two dimeric interfaces appear to exist in Hv1, one mediated by S1 and the adjacent extracellular loop, and the other mediated by a putative intracellular coiled-coil domain. It may be significant that Hv1 uses for its dimer interface a surface that corresponds to the interface between the voltage sensor and pore in Kv channels.
DHHC2 Affects Palmitoylation, Stability, and Functions of Tetraspanins CD9 and CD151
Authors: Sharma Chandan , Yang Xiuwei H. , Hemler Martin E.
Published: May 2008

Although palmitoylation markedly affects tetraspanin protein biochemistry and functions, relevant palmitoylating enzymes were not known. There are 23 mammalian “DHHC” (Asp-His-His-Cys) proteins, which presumably palmitoylate different sets of protein substrates. Among DHHC proteins tested, DHHC2 best stimulated palmitoylation of tetraspanins CD9 and CD151, whereas inactive DHHC2 (containing DH→AA or C→S mutations within the DHHC motif) failed to promote palmitoylation. Furthermore, DHHC2 associated with CD9 and CD151, but not other cell surface proteins, and DHHC2 knockdown diminished CD9 and CD151 palmitoylation. Knockdown of six other Golgi-resident DHHC proteins (DHHC3, -4, -8, -17, -18, and -21) had no effect on CD9 or CD151. DHHC2 selectively affected tetraspanin palmitoylation, but not the palmitoylations of integrin β4 subunit and bulk proteins visible in [3H]palmitate-labeled whole cell lysates. DHHC2-dependent palmitoylation also had multiple functional effects. First, it promoted physical associations between CD9 and CD151, and between α3 integrin and other proteins. Second, it protected CD151 and CD9 from lysosomal degradation. Third, the presence of DHHC2, but not other DHHC proteins, shifted cells away from a dispersed state and toward increased cell–cell contacts.
Xenopus TACC3/Maskin Is Not Required for Microtubule Stability but Is Required for Anchoring Microtubules at the Centrosome
Authors: Albee Alison J. , Wiese Christiane
Published: May 2008

Members of the transforming acidic coiled coil (TACC) protein family are emerging as important mitotic spindle assembly proteins in a variety of organisms. The molecular details of how TACC proteins function are unknown, but TACC proteins have been proposed to recruit microtubule-stabilizing proteins of the tumor overexpressed gene (TOG) family to the centrosome and to facilitate their loading onto newly emerging microtubules. Using Xenopus egg extracts and in vitro assays, we show that the Xenopus TACC protein maskin is required for centrosome function beyond recruiting the Xenopus TOG protein XMAP215. The conserved C-terminal TACC domain of maskin is both necessary and sufficient to restore centrosome function in maskin-depleted extracts, and we provide evidence that the N terminus of maskin inhibits the function of the TACC domain. Time-lapse video microscopy reveals that microtubule dynamics in Xenopus egg extracts are unaffected by maskin depletion. Our results provide direct experimental evidence of a role for maskin in centrosome function and suggest that maskin is required for microtubule anchoring at the centrosome.
Saccharomyces cerevisiaeRot1 Is an Essential Molecular Chaperone in the Endoplasmic Reticulum
Authors: Takeuchi Masato , Kimata Yukio , Kohno Kenji
Published: May 2008

Molecular chaperones prevent aggregation of denatured proteins in vitro and are thought to support folding of diverse proteins in vivo. Chaperones may have some selectivity for their substrate proteins, but knowledge of particular in vivo substrates is still poor. We here show that yeast Rot1, an essential, type-I ER membrane protein functions as a chaperone. Recombinant Rot1 exhibited antiaggregation activity in vitro, which was partly impaired by a temperature-sensitive rot1-2 mutation. In vivo, the rot1-2 mutation caused accelerated degradation of five proteins in the secretory pathway via ER-associated degradation, resulting in a decrease in their cellular levels. Furthermore, we demonstrate a physical and probably transient interaction of Rot1 with four of these proteins. Collectively, these results indicate that Rot1 functions as a chaperone in vivo supporting the folding of those proteins. Their folding also requires BiP, and one of these proteins was simultaneously associated with both Rot1 and BiP, suggesting that they can cooperate to facilitate protein folding. The Rot1-dependent proteins include a soluble, type I and II, and polytopic membrane proteins, and they do not share structural similarities. In addition, their dependency on Rot1 appeared different. We therefore propose that Rot1 is a general chaperone with some substrate specificity.
A Role for Soluble N-Ethylmaleimide-sensitive Factor Attachment Protein Receptor Complex Dimerization during Neurosecretion
Authors: Fdez Elena , Jowitt Thomas A. , Wang Ming-Chuan , Rajebhosale Manisha , Foster Keith , Bella Jordi , Baldock Clair , Woodman Philip G. , Hilfiker Sabine
Published: May 2008

The interactions underlying the cooperativity of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes during neurotransmission are not known. Here, we provide a molecular characterization of a dimer formed between the cytoplasmic portions of neuronal SNARE complexes. Dimerization generates a two-winged structure in which the C termini of cytosolic SNARE complexes are in apposition, and it involves residues from the vesicle-associated SNARE synaptobrevin 2 that lie close to the cytosol–membrane interface within the full-length protein. Mutation of these residues reduces stability of dimers formed between SNARE complexes, without affecting the stability of each individual SNARE complex. These mutations also cause a corresponding decrease in the ability of botulinum toxin-resistant synaptobrevin 2 to rescue regulated exocytosis in toxin-treated neuroendocrine cells. Moreover, such synaptobrevin 2 mutants give rise to a dominant-negative inhibition of exocytosis. These data are consistent with an important role for SNARE complex dimers in neurosecretion.
Differences in Regulation ofDrosophilaand Vertebrate Integrin Affinity by Talin
Authors: Helsten Teresa L. , Bunch Thomas A. , Kato Hisashi , Yamanouchi Jun , Choi Sharon H. , Jannuzi Alison L. , Féral Chloe C. , Ginsberg Mark H. , Brower Danny L. , Shattil Sanford J.
Published: May 2008

Integrin-mediated cell adhesion is essential for development of multicellular organisms. In worms, flies, and vertebrates, talin forms a physical link between integrin cytoplasmic domains and the actin cytoskeleton. Loss of either integrins or talin leads to similar phenotypes. In vertebrates, talin is also a key regulator of integrin affinity. We used a ligand-mimetic Fab fragment, TWOW-1, to assess talin's role in regulating Drosophila αPS2βPS affinity. Depletion of cellular metabolic energy reduced TWOW-1 binding, suggesting αPS2βPS affinity is an active process as it is for vertebrate integrins. In contrast to vertebrate integrins, neither talin knockdown by RNA interference nor talin head overexpression had a significant effect on TWOW-1 binding. Furthermore, replacement of the transmembrane or talin-binding cytoplasmic domains of αPS2βPS with those of human αIIbβ3 failed to enable talin regulation of TWOW-1 binding. However, substitution of the extracellular and transmembrane domains of αPS2βPS with those of αIIbβ3 resulted in a constitutively active integrin whose affinity was reduced by talin knockdown. Furthermore, wild-type αIIbβ3 was activated by overexpression of Drosophila talin head domain. Thus, despite evolutionary conservation of talin's integrin/cytoskeleton linkage function, talin is not sufficient to regulate Drosophila αPS2βPS affinity because of structural features inherent in the αPS2βPS extracellular and/or transmembrane domains.
Retrotranslocation of Prion Proteins from the Endoplasmic Reticulum by Preventing GPI Signal Transamidation
Authors: Ashok Aarthi , Hegde Ramanujan S.
Published: May 2008

Neurodegeneration in diseases caused by altered metabolism of mammalian prion protein (PrP) can be averted by reducing PrP expression. To identify novel pathways for PrP down-regulation, we analyzed cells that had adapted to the negative selection pressure of stable overexpression of a disease-causing PrP mutant. A mutant cell line was isolated that selectively and quantitatively routes wild-type and various mutant PrPs for ER retrotranslocation and proteasomal degradation. Biochemical analyses of the mutant cells revealed that a defect in glycosylphosphatidylinositol (GPI) anchor synthesis leads to an unprocessed GPI-anchoring signal sequence that directs both ER retention and efficient retrotranslocation of PrP. An unprocessed GPI signal was sufficient to impart ER retention, but not retrotranslocation, to a heterologous protein, revealing an unexpected role for the mature domain in the metabolism of misprocessed GPI-anchored proteins. Our results provide new insights into the quality control pathways for unprocessed GPI-anchored proteins and identify transamidation of the GPI signal sequence as a step in PrP biosynthesis that is absolutely required for its surface expression. As each GPI signal sequence is unique, these results also identify signal recognition by the GPI-transamidase as a potential step for selective small molecule perturbation of PrP expression.
MicroRNA-21 Targets Sprouty2 and Promotes Cellular Outgrowths
Authors: Sayed Danish , Rane Shweta , Lypowy Jacqueline , He Minzhen , Chen Ieng-Yi , Vashistha Himanshu , Yan Lin , Malhotra Ashwani , Vatner Dorothy , Abdellatif Maha
Published: May 2008

The posttranscriptional regulator, microRNA-21 (miR-21), is up-regulated in many forms of cancer, as well as during cardiac hypertrophic growth. To understand its role, we overexpressed it in cardiocytes where it revealed a unique type of cell-to-cell “linker” in the form of long slender outgrowths and branches. We subsequently confirmed that miR-21 directly targets and down-regulates the expression of Sprouty2 (SPRY2), an inhibitor of branching morphogenesis and neurite outgrowths. We found that β-adrenergic receptor (βAR) stimulation induces up-regulation of miR-21 and down-regulation of SPRY2 and is, likewise, associated with connecting cell branches. Knockdown of SPRY2 reproduced the branching morphology in cardiocytes, and vice versa, knockdown of miR-21 using a specific ‘miRNA eraser’ or overexpression of SPRY2 inhibited βAR-induced cellular outgrowths. These structures enclose sarcomeres and connect adjacent cardiocytes through functional gap junctions. To determine how this aspect of miR-21 function translates in cancer cells, we knocked it down in colon cancer SW480 cells. This resulted in disappearance of their microvillus-like protrusions accompanied by SPRY2-dependent inhibition of cell migration. Thus, we propose that an increase in miR-21 enhances the formation of various types of cellular protrusions through directly targeting and down-regulating SPRY2.
A Novel Juxtamembrane Domain in Tumor Necrosis Factor Receptor Superfamily Molecules Activates Rac1 and Controls Neurite Growth
Authors: Ruan Wenjing , Lee Christopher T. , Desbarats Julie
Published: May 2008

Members of the tumor necrosis factor receptor (TNFR) superfamily control cell fate determination, including cell death and differentiation. Fas (CD95) is the prototypical “death receptor” of the TNFR superfamily and signals apoptosis through well established pathways. In the adult nervous system, Fas induces apoptosis in the context of neuropathology such as stroke or amyotrophic lateral sclerosis. However, during nervous system development, Fas promotes neurite growth and branching. The molecular mechanisms underlying Fas-induced process formation and branching have remained unknown to date. Here, we define the molecular pathway linking Fas to process growth and branching in cell lines and in developing neurons. We describe a new cytoplasmic membrane proximal domain (MPD) that is essential for Fas-induced process growth and that is conserved in members of the TNFR superfamily. We show that the Fas MPD recruits ezrin, a molecule that links transmembrane proteins to the cytoskeleton, and activates the small GTPase Rac1. Deletion of the MPD, but not the death domain, abolished Rac1 activation and process growth. Furthermore, an ezrin-derived inhibitory peptide prevented Fas-induced neurite growth in primary neurons. Our results define a new domain, topologically and functionally distinct from the death domain, which regulates neuritogenesis via recruitment of ezrin and activation of Rac1.
DNA-Ligase IV and DNA-Protein Kinase Play a Critical Role in Deficient Caspases Activation in Apoptosis-resistant Cancer Cells by Using Doxorubicin
Authors: Friesen Claudia , Uhl Miriam , Pannicke Ulrich , Schwarz Klaus , Miltner Erich , Debatin Klaus-Michael
Published: May 2008

Resistance toward cytotoxic drugs is one of the primary causes for therapeutic failure in cancer therapy. DNA repair mechanisms as well as deficient caspases activation play a critical role in apoptosis resistance of tumor cells toward anticancer drug treatment. Here, we discovered that deficient caspases activation in apoptosis-resistant cancer cells depends on DNA-ligase IV and DNA-protein kinase (DNA-PK), playing crucial roles in the nonhomologous end joining (NHEJ) pathway, which is the predominant pathway for DNA double-strand break repair (DNA-DSB-repair) in mammalian cells. DNA-PK(+/+) as well as DNA-ligase IV (+/+) cancer cells were apoptosis resistant and deficient in activation of caspase-3, caspase-9, and caspase-8 and in cleavage of poly(ADP-ribose) polymerase after doxorubicin treatment. Inhibition of NHEJ by knocking out DNA-PK or DNA-ligase IV restored caspases activation and apoptosis sensitivity after doxorubicin treatment. In addition, inhibition of caspases activation prevented doxorubicin-induced apoptosis but could not prevent doxorubicin-induced DNA damage, indicating that induction of DNA damage is independent of caspases activation. However, caspases activation depends on induction of DNA damage left unrepaired by NHEJ-DNA-DSB-repair. We conclude that DNA damage left unrepaired by DNA-ligase IV or DNA-PK might be the initiator for caspases activation by doxorubicin in cancer cells. Failure in caspases activation using doxorubicin depends on loss of DNA damage and is due to higher rates of NHEJ-DNA-DBS-repair.
Successful same-sex pairing in Laysan albatross
Authors: Young Lindsay C , Zaun Brenda J , VanderWerf Eric A
Published: May 2008

Unrelated same-sex individuals pairing together and cooperating to raise offspring over many years is a rare occurrence in the animal kingdom. Cooperative breeding, in which animals help raise offspring that are not their own, is often attributed to kin selection when individuals are related, or altruism when individuals are unrelated. Here we document long-term pairing of unrelated female Laysan albatross (
Phoebastria immutabilis
) and show how cooperation may have arisen as a result of a skewed sex ratio in this species. Thirty-one per cent of Laysan albatross pairs on Oahu were female–female, and the overall sex ratio was 59% females as a result of female-biased immigration. Female–female pairs fledged fewer offspring than male–female pairs, but this was a better alternative than not breeding. In most female–female pairs that raised a chick in more than 1 year, at least one offspring was genetically related to each female, indicating that both females had opportunities to reproduce. These results demonstrate how changes in the sex ratio of a population can shift the social structure and cause cooperative behaviour to arise in a monogamous species, and they also underscore the importance of genetically sexing monomorphic species.
Sex differences in responsiveness to begging in a cooperative mammal
Authors: English Sinead , Kunc Hansjoerg P , Madden Joah R , Clutton-Brock Tim H
Published: May 2008

In species where young are provisioned by both parents, males commonly contribute less to parental care than females, and are less responsive to variation in begging rates. Similar differences in the care of young occur among adults in cooperative breeders, but fewer studies have investigated whether these are associated with differences in responsiveness. Here, we present results from a playback experiment investigating responsiveness to begging in the meerkat (
Suricata suricatta
), a cooperatively breeding mammal. Although increased begging rate raised the feeding rate of adults of both sexes, there was no consistent tendency for females to be more responsive than males. However, when we examined changes in the proportion of food items found that were fed to pups (generosity), we found that females were more responsive than males to increased begging rate. These results can be explained in terms of sex differences in dispersal: in meerkats, females are philopatric and receive considerable benefits from investing in young, both directly, by increasing group size, and indirectly, by recruiting helpers if they inherit the breeding position. In addition, they emphasize that generosity provides a more sensitive measure of responsiveness to begging than feeding rate, as it accounts for variation in foraging success.
Concealed weapons: erectile claws in African frogs
Authors: Blackburn David C , Hanken James , Jenkins Farish A
Published: May 2008

Vertebrate claws are used in a variety of important behaviours and are typically composed of a keratinous sheath overlying the terminal phalanx of a digit. Keratinous claws, however, are rare in living amphibians; their microstructure and other features indicate that they probably originated independently from those in amniotes. Here we show that certain African frogs have a different type of claw, used in defence, that is unique in design among living vertebrates and lacks a keratinous covering. These frogs have sectorial terminal phalanges on their hind feet that become functional by cutting through the skin. In the resting state, the phalanx is subdermal and attached to a distal bony nodule, a neomorphic skeletal element, via collagen-rich connective tissue. When erected, the claw breaks free from the nodule and pierces the ventral skin. The nodule, suspended by a sheath attached to the terminal phalanx and supported by collagenous connections to the dermis, remains fixed in place. While superficially resembling the shape of claws in other tetrapods, these are the only vertebrate claws known to pierce their way to functionality.
The origin and evolution of a unisexual hybrid:Poecilia formosa
Authors: Lampert K.P , Schartl M
Published: May 2008

Clonal reproduction in vertebrates can always be traced back to hybridization events as all known unisexual vertebrates are hybrids between recognized species or genetically defined races. Interestingly, clonal vertebrates often also rely on interspecific matings for their reproduction because gynogenesis (sperm-dependent parthenogenesis) and hybridogenesis are common modes of propagation. While in most cases these hybridization events leave no hereditary traces in the offspring, occasionally the genome exclusion mechanism fails and either small parts of male genetic material remain inside the oocyte in the form of microchromosomes, or fusion of the sperm nucleus with the oocyte nucleus leads to polyploid individuals. In this review, we highlight the important role of hybridization for the origin and evolution of a unisexual hybrid: the Amazon molly,Poecilia formosa.
Spatial, environmental and anthropogenic effects on the taxon composition of hybridizingDaphnia
Authors: Keller Barbara , Wolinska Justyna , Manca Marina , Spaak Piet
Published: May 2008

The competitive ability of hybrids, compared with their parental taxa, can cover a wide fitness range from poor to superior. For example communities of theDaphnia galeata–hyalina–cucullataspecies complex often show hybrid dominance. We tested whether taxa composition of 43 European lakes inhabited by this species complex can be explained by habitat characteristics (e.g. size descriptors, trophy level) or geography. We found thatD. galeataoccurs more frequently south of the Alps, whereasD. hyalinaandD. cucullataare found more in the north. Lakes withD. galeatadominance had higher temperatures whereasD. hyalinadominance could be attributed to low phosphorus loads. The dominance of F1-hybrids, however, was not explainable with current environmental variables. In a subset of 28 lakes, we studied the impact of eutrophication history on F1-hybrid success. Lakes with the highest trophic state in the past tended to be dominated by F1-hybrids. Our data demonstrate that human-mediated habitat disturbance (eutrophication) has facilitated hybrid success and altered theDaphniataxon composition across lakes. At the same time, specific habitat conditions might provide a refuge from hybridization for native genotypes.
Male territorial vocalizations and responses are decoupled in an avian hybrid zone
Authors: den Hartog Paula M , Slabbekoorn Hans , ten Cate Carel
Published: May 2008

A core area of speciation research concerns the coevolution of species-specific signals and the selective sensitivity to such signals. Signals and responses to them should be tuned to each other, to be effective in intraspecific communication. Hybrid zones are ideal to study the presence of such ‘behavioural coupling’ and the mechanisms governing it, and this has rarely been done. Our study examines acoustic signals of males and their response to them in the context of territorial interactions in a natural hybrid zone between two dove species,
Streptopelia vinacea
and
Streptopelia capicola
. Male signals are important in hybrid zone dynamics as they are essential for territory establishment, which is crucial for successful reproduction. We tested whether the response of individual male hybrids is linked to how similar their own signal is to the playback signal. We did not find evidence for behavioural coupling. The combined evidence from the low level of response to hybrid and heterospecific signals outside the hybrid zone and a lack of coupling within the hybrid zone suggests that perceptual learning may explain our results. Learning to respond to locally abundant signals may be the best individual strategy and is likely to contribute to the maintenance of a hybrid zone.
Fission and fusion of Darwin's finches populations
Authors: Grant B.Rosemary , Grant Peter R
Published: May 2008

This study addresses the causes and evolutionary consequences of introgressive hybridization in the sympatric species of Darwin's ground finches (Geospiza) on the small island of Daphne Major in the Galápagos archipelago. Hybridization occurs rarely (less than 2% of breeding pairs) but persistently across years, usually as a result of imprinting on the song of another species. Hybrids survive well under some ecological conditions, but not others. Hybrids mate according to song type. The resulting introgression increases phenotypic and genetic variation in the backcrossed populations. Effects of introgression on beak shape are determined by the underlying developmental genetic pathways. Introgressive hybridization has been widespread throughout the archipelago in the recent past, and may have been a persistent feature throughout the early history of the radiation, episodically affecting both the speed and direction of evolution. We discuss how fission through selection and fusion through introgression in contemporary Darwin's finch populations may be a reflection of processes occurring in other young radiations. We propose that introgression has the largest effect on the evolution of interbreeding species after they have diverged in morphology, but before the point is reached when genetic incompatibilities incur a severe fitness cost.
Making it on their own: sperm-dependent hybrid fishes (Cobitis) switch the sexual hosts and expand beyond the ranges of their original sperm donors
Authors: Choleva Lukáš , Apostolou Apostolos , Ráb Petr , Janko Karel
Published: May 2008

Interspecific hybridization may result in asexual hybrid lineages that reproduce via parthenogenesis. Contrary to true parthenogens, sperm-dependent asexuals (gynogens and hybridogens) are restricted to the range of bisexual species, generally the parental taxa, by their need for a sperm donor. It has been documented that asexual lineages may rarely use sperm from a non-parental species or even switch a host. The available literature reports do not allow distinguishing, between whether such host switches arise by the expansion of asexuals out of their parental's range (and into that of another's) or by the local extinction of a parental population followed by a host switch. The present study combines new and previously collected data on the distribution and history of gynogenetic spined loaches (Cobitis) of hybrid origin. We identified at least three clonal lineages that have independently switched their sperm dependency to different non-parentalCobitisspecies, and in cases incorporated their genomes. Our current knowledge of EuropeanCobitisspecies and their hybrids suggests that this pattern most probably results from the expansion of gynogenetic lineages into new areas. Such expansion was independent of the original parental species. This suggests that sperm dependence is not as restrictive to geographical expansion when compared with true parthenogenesis as previously thought.
Training with inedible food in Aplysia causes expression of C/EBP in the buccal but not cerebral ganglion
Authors: Levitan David , Lyons Lisa C. , Perelman Alexander , Green Charity L. , Motro Benny , Eskin Arnold , Susswein Abraham J.
Published: May 2008

Training with inedible food in Aplysia increased expression of the transcription factor C/EBP in the buccal ganglia, which primarily have a motor function, but not in the cerebral or pleural ganglia. C/EBP mRNA increased immediately after training, as well as 1–2 h later. The increased expression of C/EBP protein lagged the increase in mRNA. Stimulating the lips and inducing feeding responses do not lead to long-term memory and did not cause increased C/EBP expression. Blocking polyADP-ribosylation, a process necessary for long-term memory after training, did not affect the increased C/EBP mRNA expression in the buccal ganglia.
Reactivation-dependent amnesia for appetitive memories is determined by the contingency of stimulus presentation
Authors: Lee Jonathan L.C. , Everitt Barry J.
Published: May 2008

Previously acquired aversive and appetitive memories are not stable and permanent. The reactivation of such memories by re-exposure to training stimuli renders them vulnerable to disruption by amnestic agents such as the noncompetitive N-methyl-D-aspartate receptor antagonist (+)-5-methyl-10,11-dihydro-SH-dibenzo{a,d}cyclohepten-5,10imine maleate (MK-801). However, relatively little is known about the parameters that influence the reactivation process. Here, we show that the method of stimulus presentation during memory reactivation is of great importance. Male Lister Hooded rats were trained to acquire a lever press response that delivered a sucrose reward paired with a light conditioned stimulus (CS). The CS–sucrose association was then reactivated through re-exposure to the CS, either contingently upon the lever press response, or noncontingently in the absence of instrumental responding. Systemic administration of MK-801 (0.1 mg/kg) at the time of memory reactivation resulted in amnesia, and hence a reduction in subsequent sucrose seeking induced by, and dependent upon, presentation of the CS, only when the memory was reactivated contingently. Therefore, stimuli may have to be presented in the same manner at memory reactivation as during learning in order to render a previously acquired memory vulnerable to disruption. These results have important implications for the potential translational use of glutamatergic treatments in conjunction with targeted memory reactivation.
Sequence Analysis of Bacterial Artificial Chromosome Clones from the Apospory-Specific Genomic Region ofPennisetumandCenchrus
Authors: Conner Joann A. , Goel Shailendra , Gunawan Gunawati , Cordonnier-Pratt Marie-Michele , Johnson Virgil Ed , Liang Chun , Wang Haiming , Pratt Lee H. , Mullet John E. , DeBarry Jeremy , Yang Lixing , Bennetzen Jeffrey L. , Klein Patricia E. , Ozias-Akins Peggy
Published: May 2008

Apomixis, asexual reproduction through seed, is widespread among angiosperm families. Gametophytic apomixis in Pennisetum squamulatum and Cenchrus ciliaris is controlled by the apospory-specific genomic region (ASGR), which is highly conserved and macrosyntenic between these species. Thirty-two ASGR bacterial artificial chromosomes (BACs) isolated from both species and one ASGR-recombining BAC from P. squamulatum, which together cover approximately 2.7 Mb of DNA, were used to investigate the genomic structure of this region. Phrap assembly of 4,521 high-quality reads generated 1,341 contiguous sequences (contigs; 730 from the ASGR and 30 from the ASGR-recombining BAC in P. squamulatum, plus 580 from the C. ciliaris ASGR). Contigs containing putative protein-coding regions unrelated to transposable elements were identified based on protein similarity after Basic Local Alignment Search Tool X analysis. These putative coding regions were further analyzed in silico with reference to the rice (Oryza sativa) and sorghum (Sorghum bicolor) genomes using the resources at Gramene (www.gramene.org) and Phytozome (www.phytozome.net) and by hybridization against sorghum BAC filters. The ASGR sequences reveal that the ASGR (1) contains both gene-rich and gene-poor segments, (2) contains several genes that may play a role in apomictic development, (3) has many classes of transposable elements, and (4) does not exhibit large-scale synteny with either rice or sorghum genomes but does contain multiple regions of microsynteny with these species.
SCAMPs Highlight the Developing Cell Plate during Cytokinesis in Tobacco BY-2 Cells
Authors: Lam Sheung Kwan , Cai Yi , Hillmer Stefan , Robinson David G. , Jiang Liwen
Published: May 2008

We previously demonstrated that rice (Oryza sativa) SECRETORY CARRIER MEMBRANE PROTEIN1 (OsSCAMP1)-yellow fluorescent protein in transgenic tobacco (Nicotiana tabacum) Bright Yellow-2 cells locates to the plasma membrane and to motile punctate structures, which represent the trans-Golgi network/early endosome and are tubular-vesicular in nature. Here, we now show that SCAMPs are diverted to the cell plate during cytokinesis dividing Bright Yellow-2 cells. As cells progress from metaphase to cytokinesis, punctate OsSCAMP1-labeled structures begin to collect in the future division plane. Together with the internalized endosomal marker FM4-64, they then become incorporated into the cell plate as it forms and expands. This was confirmed by immunogold electron microscopy. We also monitored for the Golgi apparatus and the prevacuolar compartment (PVC)/multivesicular body. Golgi stacks tend to accumulate in the vicinity of the division plane, but the signals are clearly separate to the cell plate. The situation with the PVC (labeled by green fluorescent protein-BP-80) is not so clear. Punctate BP-80 signals are seen at the advancing periphery of the cell plate, which was confirmed by immunogold electron microscopy. Specific but weak labeling was observed in the cell plate, but no evidence for a fusion of the PVC/multivesicular body with the cell plate could be obtained. Our data, therefore, support the notion that cell plate formation is mainly a secretory process involving mass incorporation of domains of the trans-Golgi network/early endosome membrane. We regard the involvement of multivesicular late endosomes in this process to be equivocal.
Case ascertainment and estimated incidence of drug‐induced long‐QT syndrome: study in Southwest France
Authors: Molokhia Mariam , Pathak Atul , Lapeyre‐Mestre Maryse , Caturla Laetitia , Montastruc Jean Louis ,   L'Association Française des Centres Régionaux de Pharmacovigilance (CRPV), McKeigue Paul
Published: May 2008

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Drug‐induced long‐QT syndrome (LQTS) is a potentially fatal condition that has led to a number of postmarketing withdrawals in recent years.

• However, many cases may not survive long enough to reach hospital, and only a small proportion are reported to pharmacovigilance agencies.

• The extent to which genetic determinants of susceptibility to LQTS are specific to particular drugs, or common to several classes of drug, remains to be determined.

WHAT THIS STUDY ADDS

• We estimated population prevalence of drug‐induced LQTS in the Midi‐Pyrenees region, southwest France, using five different institutions and assessed feasibility of tracing potential cases (in addition to pharmacovigilance data), using hospital data and rigorous case definition.

• These methods can be adapted to a wider region, used to augment pharmacovigilance reporting, and offer researchers the opportunity to study genetic susceptibility to drug‐induced LQTS.

AIMS

The aim of this study was to investigate the incidence and reporting rate of drug‐induced long‐QT syndrome (LQTS) in France [defined by evidence of torsades de pointes (TdP), QT prolongation and exposure to a relevant drug] and to assess feasibility of case collection for drug‐induced LQTS.

METHODS

A retrospective population‐based study was carried out in Southwest France in five institutions: three main hospitals, one private clinic and one cardiac emergency unit, searched from 1 January 1999 to 1 January 2005 (population coverage of 614 000). The study population consisted of 861 cases with International Classification of Diseases‐10 diagnostic codes for ventricular tachycardia (I147.2), ventricular fibrillation (I149.0) and sudden cardiac death (I146.1) from hospital discharge summaries, supplemented by cases reported to national or regional pharmacovigilance systems, and voluntary reporting by physicians, validated according to internationally defined criteria for drug‐induced LQTS.

RESULTS

Of 861 patients coded with arrhythmias or sudden cardiac death, there were 40 confirmed surviving acquired cases of drug‐induced LQTS. We estimated that the incidence of those who survive to reach hospital drug‐induced LQTS is approximately 10.9 per million annually in France (95% confidence interval 7.8, 14.8).

CONCLUSIONS

Many cases of drug‐induced LQTS may not survive before they reach hospital, as the reporting rate for drug‐induced LQTS identified through the cardiology records and also reported to pharmacovigilance systems for the Midi‐Pyrenees area is 3/40 (7.5%). Using the methods outlined it is possible to assemble cases to study genetic susceptibility to drug‐induced LQTS and adapt these methods more widely.