bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Inoculation Methods to Reproduce Sunflower Premature Ripening Caused byPhoma macdonaldii
Authors: Seassau C. , Debaeke P. , Mestries E. , Dechamp-Guillaume G.
Published: August 2010

Three inoculation methods were evaluated for effectiveness to cause sunflower premature ripening (PR). Evaluations were conducted on a sunflower (Helianthus annuus) cultivar susceptible to PR in replicated, multilocation experiments under greenhouse conditions. Plants were inoculated with Phoma macdonaldii, either with mycelium, conidia, or infected residues at the stem base or with buried residues. Disease severity (DS) was measured by percent girdling necrosis at the stem base and percent final PR; the infection spread was assessed using the area under the disease progress curve (AUDPC). Inoculation with mycelia or 1 × 106spores/ml caused significantly more DS and PR than lower spore concentrations or infected residues (P < 0.05). Amending soil with residues induced root necrosis but no PR. P. macdonaldii was mainly isolated at the stem base and above but rarely on root systems. Microscopic evaluations showed that hyphae colonized mainly the cortex and vascular stem tissues. The overall results demonstrated a clear role of aerial infection in PR compared with soilborne inoculum, and that inoculation at the stem base with a spore suspension could be used for screening genotypes for resistance to PR.
First Report of Neofusicoccum vitifusiforme Causing Blueberry Blight of Blueberry in China
Authors: Kong C. S. , Qiu X. L. , Yi K. S. , Yu X. F. , Yu L.
Published: August 2010

In May 2008, symptoms of blueberry blight were observed on half-high blueberry (Vaccinium corymbosum L.) in a plant nursery in Anning, Yunnan Province. Symptoms included dieback and bud and branch blight. Symptomatic plant samples were washed with running tap water, disinfected with 2% sodium hypochlorite and then 70% alcohol, rinsed in sterile distilled water, plated on potato dextrose agar (PDA), and incubated at 26°C. Conidia forming on PDA were hyaline, granular, fusoid to ellipsoid, widest in the upper third with an obtuse apex and flattened, subtruncate base, and 18 to 21 × 4.5 to 8 μm. The pathogen was also identified to the species level by sequencing the ribosomal internal transcribed spacer regions 1 and 2 (ITSI-5.8S-ITS2) and the translation elongation factor 1-alpha (EF1-α). BLAST searches at GenBank showed the highest nucleotide sequence identity with Neofusicoccum vitifusiforme reference sequence (ITS: >98%, EF638785; EF1-α: 100%, EF638744 and AY343343). Representative sequences of isolates from both regions were deposited in GenBank (ITS: Accession No. HM131604; EF1-α: Accession No. HM454277). Pathogenicity tests were conducted on 2-year-old blueberry seedlings (half-high blueberry). Mycelial plugs (3 mm in diameter) of N. vitifusiforme from actively growing colonies (PDA) were applied to same-size bark wounds in the center of the stems. Inoculation wounds were wrapped with Parafilm. Control seedlings received sterile PDA plugs. Inoculated and control seedlings (five each) were kept in a greenhouse and watered as needed. After 2 weeks, all of the inoculated but none of the control blueberry seedlings showed dark vascular stem tissue. N. vitifusiforme was reisolated from symptomatic tissues, thus fulfilling Koch's postulates. N. vitifusiforme has been reported as a pathogen of olive (2), plum, peach (1), and grapevine (3). To our knowledge, this is the first report of N. vitifusiforme on blueberry in China as well as worldwide.

References: (1) U. Damm et al. Mycologia 99:664, 2007. (2) C. Lazzizera et al. Plant Pathol. 57:948, 2008. (3) J. M. van Niekerk et al. Mycologia 96:781, 2004.
Sexual Reproduction and Gene Flow in the Pine Pathogen Dothistroma septosporum in British Columbia
Authors: Dale A. L. , Lewis K. J. , Murray B. W.
Published: August 2010

Dothistroma septosporum has caused a serious needle blight epidemic in the lodgepole pine forests in northwest British Columbia over the past several years. Although ascocarps had been observed in British Columbia, nothing was known about the contribution of sexual reproduction, gene flow and long-distance dispersal to the epidemic. Amplified fragment length polymorphism and mating-type markers in 19 sites were used to generate population and reproductive data. Overall, evidence suggests a mixed mode of reproduction. Haplotypic diversity was high, with 79 unique and 56 shared haplotypes (possible clones) identified from 192 fungal isolates. Overall, mating-type segregation did not differ significantly from 1:1; however, random mating was rejected in most populations in the index of association and parsimony tree-length permutation analyses using the full data set and, when using clone-corrected data sets, more of the smaller populations showed random mating. Two of the smaller populations consistently showed random mating for both tests using both clone-corrected and noncorrected data. High gene flow is suggested by no differentiation between 14 of the 19 sites, several of which came from young plantations where the pathogen was not likely present prior to the current outbreak. The remaining five sites showed some level of divergence, possibly due to historic separation and endemic pathogen populations. Results indicate a high evolutionary potential and long-distance dispersal in this pathogen, important to consider in future forest management.
Predator diversity stabilizes and strengthens trophic control of a keystone grazer
Authors: Griffin John N. , Silliman Brian R.
Published: August 2010

Despite the global vulnerability of predators to extinction, and the critical functional role they play in many ecosystems, there have been few realistic tests of the consequences of predator species deletion (conversely, predator diversity) in natural ecosystems. We performed a four-month field experiment in a southeastern United States salt marsh to test the role of predatory crab diversity in regulating populations of a keystone grazer that can decimate marsh vegetation at high densities. Our results revealed that a combination of this system's two resident predator species, in comparison to individual species, both stabilize and strengthen predation rates on the potent grazer. Monthly monitoring of predation rates from intense, hot summer months into the cooler autumn indicate this diversity benefit arises from predators responding differentially to changing environmental conditions across seasons. This study provides some of the first experimental field support for the insurance hypothesis from marine ecosystems, suggests that predator temporal complementarity may be more common than currently perceived, and argues for conservation of predator diversity to ensure reliable and effective control of potentially habitat-destroying grazers.
Anthony David Bradshaw. 17 January 1926 — 21 August 2008
Authors: Fitter A. H.
Published: August 2010

Tony Bradshaw successfully straddled the divide between fundamental and applied science at a time when few achieved the feat. He made major contributions to our understanding of evolution in plant populations and of the significance of phenotypic plasticity, and then exploited those advances to develop new, science-based techniques for the restoration of degraded ecosystems. His discovery of the speed and local scale of evolution in grass populations remains one of the finest demonstrations of evolution in action, and he was one of the founders of the new discipline of restoration ecology.
Three-dimensional secondary instability of a spatially developing von Kármán vortex street in a far wake
Authors: Liu J. T. C. , Yu X.
Published: August 2010

This paper presents studies of a three-dimensional secondary instability of a spatially developing von Kármán vortex street. It develops owing to the nonlinear interaction between a two-dimensional mean far-wake flow and its most unstable disturbances. This forms a nonlinear primary wake flow. Sections of this flow are selected to perform a temporal secondary stability study under the assumption of parallel flow. The eigenvalue characteristics of the secondary instability are compared with the results from the use of a linear primary flow comprising unmodified mean wake flow coexisting with a linear primary fundamental disturbance with an empirical amplitude as a parameter, resulting in a simpler Floquet analysis. The maximum amplification rates occur at about the same spanwise wavenumber for both the nonlinear and linear primary flows, in qualitative agreement. But the amplification rate versus the spanwise wavenumber spectrum are both qualitatively and quantitatively different, the nonlinear primary flow results in a lower magnitude of the amplification rates. Some interpretations of controlled experiments are made, and it is concluded that the two- and three-dimensional disturbances so obtained appeared to be from the primary instability, where the amplification mechanisms come from the unmodified mean flow. A general discussion of the nonlinear interaction between the primary two-dimensional flow and the three-dimensional secondary instability is given, which may well form the basis for further nonlinear studies.
A fully nonlinear, dynamically consistent numerical model for solid-body ship motion. I. Ship motion with fixed heading
Authors: Lin Ray-Qing , Kuang Weijia
Published: August 2010

In this paper, we describe the details of our numerical model for simulating ship solid-body motion in a given environment. In this model, the fully nonlinear dynamical equations governing the time-varying solid-body ship motion under the forces arising from ship–wave interactions are solved with given initial conditions. The net force and moment (torque) on the ship body are directly calculated via integration of the hydrodynamic pressure over the wetted surface and the buoyancy effect from the underwater volume of the actual ship hull with a hybrid finite-difference/finite-element method. Neither empirical nor free parametrization is introduced in this model, i.e. no
a priori
experimental data are needed for modelling. This model is benchmarked with many experiments of various ship hulls for heave, roll and pitch motion. In addition to the benchmark cases, numerical experiments are also carried out for strongly nonlinear ship motion with a fixed heading. These new cases demonstrate clearly the importance of nonlinearities in ship motion modelling.
Insulin signalling regulates remating in femaleDrosophila
Authors: Wigby Stuart , Slack Cathy , Grönke Sebastian , Martinez Pedro , Calboli Federico C. F. , Chapman Tracey , Partridge Linda
Published: August 2010

Mating rate is a major determinant of female lifespan and fitness, and is predicted to optimize at an intermediate level, beyond which superfluous matings are costly. In femaleDrosophila melanogaster, nutrition is a key regulator of mating rate but the underlying mechanism is unknown. The evolutionarily conserved insulin/insulin-like growth factor-like signalling (IIS) pathway is responsive to nutrition, and regulates development, metabolism, stress resistance, fecundity and lifespan. Here we show that inhibition of IIS, by ablation ofDrosophilainsulin-like peptide (DILP)-producing median neurosecretory cells, knockout ofdilp2,dilp3ordilp5genes, expression of a dominant-negative DILP-receptor (InR) transgene or knockout ofLnk, results in reduced female remating rates. IIS-mediated regulation of female remating can occur independent of virgin receptivity, developmental defects, reduced body size or fecundity, and the receipt of the female receptivity-inhibiting male sex peptide. Our results provide a likely mechanism by which females match remating rates to the perceived nutritional environment. The findings suggest that longevity-mediating genes could often have pleiotropic effects on remating rate. However, overexpression of the IIS-regulated transcription factor dFOXO in the fat body—which extends lifespan—does not affect remating rate. Thus, long life and reduced remating are not obligatorily coupled.
Nutritional state and collective motion: from individuals to mass migration
Authors: Bazazi Sepideh , Romanczuk Pawel , Thomas Sian , Schimansky-Geier Lutz , Hale Joseph J. , Miller Gabriel A. , Sword Gregory A. , Simpson Stephen J. , Couzin Iain D.
Published: August 2010

In order to move effectively in unpredictable or heterogeneous environments animals must make appropriate decisions in response to internal and external cues. Identifying the link between these components remains a challenge for movement ecology and is important in understanding the mechanisms driving both individual and collective motion. One accessible way of examining how internal state influences an individual's motion is to consider the nutritional state of an animal. Our experimental results reveal that nutritional state exerts a relatively minor influence on the motion of isolated individuals, but large group-level differences emerge from diet affecting inter-individual interactions. This supports the idea that mass movement in locusts may be driven by cannibalism. To estimate how these findings are likely to impact collective migration of locust hopper bands, we create an experimentally parametrized model of locust interactions and motion. Our model supports our hypothesis that nutrient-dependent social interactions can lead to the collective motion seen in our experiments and predicts a transition in the mean speed and the degree of coordination of bands with increasing insect density. Furthermore, increasing the interaction strength (representing greater protein deprivation) dramatically reduces the critical density at which this transition occurs, demonstrating that individuals' nutritional state could have a major impact on large-scale migration.
Trade-offs limiting the evolution of coloniality: ecological displacement rates used to measure small costs
Authors: Yokota Kiyoko , Sterner Robert W.
Published: August 2010

Multicellular organisms that benefit from division of labour are presumably descended from colonial species that initially derived benefits from larger colony size, before the evolution of specialization. Life in a colony can have costs as well as benefits, but these can be hard to measure. We measured physiological costs to life in a colony using a novel method based on population dynamics, comparing growth rates of unicells and kairomone-induced colonies of a green algaDesmodesmus subspicatusagainst a reference co-occurring species. Coloniality negatively affected growth during the initial log growth phase, while no adverse effect was detected under nutrient-limited competitive conditions. The results point to costs associated with traits involved in rapid growth rather than those associated with efficient growth under resource scarcity. Some benefits of coloniality (e.g. defence from herbivory) may be different from when this trait evolved, but our approach shows how costs would have depended on conditions.
Are exports a monotonic function of exchange rate volatility? Evidence from disaggregated pork exports
Authors: Bonroy Olivier , Gervais Jean‐Philippe , Larue Bruno
Published: August 2010

Abstract.  Production and marketing lags in agri‐food supply chains often force agricultural producers and food processors to commit to output targets before prices and exchange rates are realized. A theoretical model illustrates how the processor's degree of risk aversion and domestic sales may cause the relationship between volatility of the exchange rate and exports to be non‐monotonic. The relationship between exchange rate volatility and Quebec pork exports to the United States and Japan is investigated using linear and non‐linear estimation methods. The results support the hypothesis that the relationship between exports and volatility is non‐monotonic.
Competition and the location of overseas assembly
Authors: Swenson Deborah L.
Published: August 2010

Abstract.  How does international competition affect overseas outsourcing? To address this question, this paper studies production decisions in the U.S.'s overseas assembly program (OAP). In this setting, a number of regularities emerge. First, prior participation is highly correlated with current participation, which suggests that sunk costs influence outsourcing choices. Second, increases in own‐country costs and declines in competitor‐country costs reduce participation probabilities. In addition, these persistence and cost effects are much larger for outsourcing in developing countries. Finally, outsourcing responses appear to reflect differences in 'market thickness,’ as cost sensitivity generally rises with competitor presence.
Optimal supervision intensity, collusion, and the organization of work
Authors: Bac Mehmet
Published: August 2010

Abstract.  The intensity of supervision, defined as the proportion of supervisors to bottom‐rank productive workers, differs widely across organizations and nations. Analysing three monitoring systems that differ in their supervision intensity, I show that the possibility of collective shirking arrangements can impose a system‐dependent limit on the range of implementable performances. This brings about a tradeoff in the choice of the monitoring system: the system that economizes on incentive costs may implement an inferior range of performances. Applications of the model generate work‐disutility‐, ethics‐ and job‐characteristics‐based explanations for variations in the intensity of supervision.
Ethnic enclaves and immigrant earnings growth
Authors: Warman Casey
Published: August 2010

Abstract.  The impact of living in an ethnic enclave on earnings growth of immigrants in Canada is examined using the 1981–2001 Censuses. Consistent with U.S. findings, enclaves are found to have a negative impact on the earnings growth of male immigrants. A negative impact is also found for female immigrants. Living in an enclave was found to be particularly harmful for individuals immigrating as adults, especially for females, but did not affect immigrants who arrived at a young age. Enclaves had a more negative impact on high‐skilled male immigrants, especially if they had received the bulk of their education outside Canada. Enclaves were also found to hinder language skills.
Which workers gain upon adopting a computer?
Authors: Zoghi Cindy , Pabilonia Sabrina Wulff
Published: August 2010

Abstract.  Using the Canadian Workplace and Employee Survey and controlling for individual and establishment fixed‐effects, we find that within a year of adopting a computer, the average worker earns a 3.6% higher wage than a worker who did not use a computer. Returns are even larger for managers and professionals, highly educated workers, and those with significant prior computer experience. Employees who adopt computers for use with applications that require high cognitive skills earn the highest returns.
Market structure and communicable diseases
Authors: Mechoulan Stéphane
Published: August 2010

Abstract.  Communicable diseases pose a formidable challenge for public policy. Using numerical simulations, we show under which scenarios a monopolist's price and prevalence paths converge to a non‐zero steady state. In contrast, a planner typically eradicates the disease. If eradication is impossible, the planner subsidizes treatments as long as the prevalence can be controlled. Drug resistance exacerbates the welfare difference between monopoly and first best outcomes. Nevertheless, because the negative externalities from resistance compete with the positive externalities of treatment, a mixed competition/monopoly regime may perform better than competition alone. This result has important implications for the design of many drug patents.
Trend‐cycle correlation, drift break and the estimation of trend and cycle in Canadian GDP
Authors: Basistha Arabinda
Published: August 2010

Abstract.  Univariate correlated trend cycle models are highly sensitive to the specifications of breaks in the data. This paper argues, using Monte Carlo experiments, that a bivariate correlated unobserved components (UC) framework with breaks delivers substantially more accurate results for the trend‐cycle parameters than the corresponding univariate frameworks in a finite sample size. The paper estimates stochastic trend and cyclical fluctuations in Canada from a bivariate UC model. Results show a fairly volatile stochastic trend after the drift break and the negative trend‐cycle shock correlation are accounted for. The estimated cyclical component is large, persistent, and consistent with ECRI denoted Canadian recessions.
Fiscal leadership and central bank design
Authors: Hallett Andrew Hughes , Weymark Diana N.
Published: August 2010

Abstract.  This article investigates the impact, on economic performance, of the timing of moves in a policy game between the government and the central bank for a government that has both redistributional and stabilization objectives. It is shown that both inflation and income inequality are reduced without sacrificing output growth if the government assumes a leadership role compared with a regime in which monetary and fiscal policy are determined simultaneously. Further, it is shown that government leadership benefits both the fiscal and monetary authorities through the enhanced coordination that this arrangement implies.
Economic liberalization and price response of aggregate private investment: time series evidence from India
Authors: Shahe Emran M. , Shilpi Forhad , Alam M. Imam
Published: August 2010

Abstract.  This paper presents evidence on the effects of economic liberalization of 1991 on the price responsiveness of aggregate private investment in India. The wide ranging reforms are expected to increase the price response of private investment due to (i) the Le Chatelier effect, (ii) a higher price elasticity of demand for final goods, and (iii) possible relaxation of the credit constraint. The empirical results, based on alternative specifications, estimation methods, and sample periods, show a dramatic increase in the price response; the elasticity of investment with respect to the relative cost of capital has increased five times after the dismantling of the ‘Licence Raj.’
Tariffs and the adoption of clean technology under asymmetric information
Authors: Ludema Rodney D. , Takeno Taizo
Published: August 2010

Abstract.  This paper examines the effect of a tariff on the decision of a foreign monopolist to adopt ‘clean’ technology, which reduces the flow of a negative cross‐border externality. The clean technology increases the marginal cost of production relative to the dirty technology, but only the firm knows the extent of the increase. Under complete information, despite its protectionist motivation, the importing country's optimal tariff induces the firm to adopt the clean technology if and only if it is globally efficient to do so. Under incomplete information, this efficiency property is disrupted, and the firm biases its choice in favour of dirty technology. JEL classification: F13, F18
Envy, leisure, and restrictions on working hours
Authors: Alvarez‐Cuadrado Francisco
Published: August 2010

Abstract.  We present a simple model of capital accumulation where agents care about their consumption relative to the consumption of other members of society, ‘envy,’ In this context we quantify the extent of the distortions and welfare costs associated with envy. Under conservative estimates of envy we find that the implied welfare losses are substantial. We explore the implications of alternative policy arrangements designed to minimize the effects of the consumption externality. Our results suggest that if the optimal tax policy is not politically feasible, restrictions on working hours provide an alternative tool to induce a market outcome that resembles the efficient allocation achieved under a benevolent central planner. JEL classification: D62, H21
Viewpoint: Estimating the equity premium
Authors: Campbell John Y.
Published: August 2010

Abstract.  Finance theory restricts the time‐series behaviour of valuation ratios and links the cross‐section of stock prices to the level of the equity premium. This can be used to strengthen the evidence for predictability in stock returns. Steady‐state valuation models are useful predictors of stock returns, given the persistence in valuation ratios. A steady‐state approach suggests that the world geometric average equity premium fell considerably in the late twentieth century, rose modestly in the early years of the twenty‐first century, and was almost 4% at the end of March 2007.
The optimal choice of monetary policy instruments in a small open economy
Authors: Singh Rajesh , Subramanian Chetan
Published: August 2010

Abstract.  This paper studies how the nature of shocks affects the optimal choice of monetary policy instruments in a small open economy. Three classic rules, fixed exchange rates, monetary targeting, and inflation targeting are studied and ranked by comparing with the optimal monetary policy under commitment. We find that the ranking of the simple rules can be mapped to the terms‐of‐trade variability that the rule allows relative to what a particular shock optimally calls for. It turns out that inflation targeting dominates the other two rules under productivity or velocity shocks, whereas monetary targeting is the best performer under fiscal shocks.
Forecasting Canadian time series with the New Keynesian model
Authors: Dib Ali , Gammoudi Mohamed , Moran Kevin
Published: August 2010

Abstract.  This paper assesses the out‐of‐sample forecasting accuracy of the New Keynesian Model for Canada. We estimate a variant of the model on a series of rolling subsamples, computing out‐of‐sample forecasts one to eight quarters ahead at each step. We compare these forecasts with those arising from vector autoregression (VAR) models, using econometric tests of forecasting accuracy. We show that the forecasting accuracy of the New Keynesian Model compares favourably with that of the benchmarks, particularly as the forecasting horizon increases. These results suggest that the model could become a useful forecasting tool for Canadian time series.
Agglomeration and fair wages
Authors: Egger Peter , Seidel Tobias
Published: August 2010

Abstract.  This paper implements a fair wage constraint into an analytically tractable core‐periphery agglomeration model. This enables us to study the role of imperfect labour markets for the pattern of agglomeration. In the short run, a marginal increase in fair wage preferences leads to an unambiguous compression of the national factor price differential between skilled and unskilled labour, involving an increase in the unemployment rate of unskilled workers. In the long run, this mechanism renders full dispersion of an unstable equilibrium already at higher trade costs than in perfect labour markets. There is a tendency for fair wage preferences to enforce agglomeration.
Rising trade costs? Agglomeration and trade with endogenous transaction costs
Authors: Duranton Gilles , Storper Michael
Published: August 2010

Abstract.  While transport costs have fallen, the empirical evidence also points at rising total trade costs. In a model of industry location with endogenous transaction costs that seeks to replicate features from the machinery industry, we show how and under which conditions a decline in transport costs can lead to an increase in the total cost of trade. The subtle relationship between (endogenous) transport costs and the sensitivity of trade to distance is also explored.
What you don't see can't hurt you: an economic analysis of morality laws
Authors: Curry Philip A. , Mongrain Steeve
Published: August 2010

Abstract.  This paper provides an efficiency explanation for regulation of sex, drugs, and gambling. We propose that these ‘morality laws’ can be explained by considering some activities to impose a negative externality when the activity is observed. Efficiency requires discretion by the individual who engages in such activities. When discretion is difficult to regulate directly, the activities can instead be proscribed, thereby giving individuals incentive to hide their actions from others. We find conditions for the first‐best levels of consumption and hiding to be implementable. Since some level of activity is efficient, the optimal sanctions are not maximal.
Functional regeneration of the olfactory bulb requires reconnection to the olfactory nerve in Xenopus larvae
Authors: Yoshino Jun , Tochinai Shin
Published: August 2010

Larvae of the South African clawed frog (Xenopus laevis) can regenerate the telencephalon, which consists of the olfactory bulb and the cerebrum, after it has been partially removed. Some authors have argued that the telencephalon, once removed, must be reconnected to the olfactory nerve in order to regenerate. However, considerable regeneration has been observed before reconnection. Therefore, we have conducted several experiments to learn whether or not reconnection is a prerequisite for regeneration. We found that the olfactory bulb did not regenerate without reconnection, while the cerebrum regenerated by itself. On the other hand, when the brain was reconnected by the olfactory nerve, both the cerebrum and the olfactory bulb regenerated. Morphological and histological investigation showed that the regenerated telencephalon was identical to the intact one in morphology, types and distributions of cells, and connections between neurons. Froglets with a regenerated telencephalon also recovered olfaction, the primary function of the frog telencephalon. These results suggest that the Xenopus larva requires reconnection of the regenerating brain to the olfactory nerve in order to regenerate the olfactory bulb, and thus the regenerated brain functions, in order to process olfactory information.
Dan is required for normal morphogenesis and patterning in the developing chick inner ear
Authors: Yamanishi Takahiro , Katsu Kenjiro , Funahashi Jun‐ichi , Yumoto Eiji , Yokouchi Yuji
Published: August 2010

During vertebrate inner ear development, compartmentalization of the auditory and vestibular apparatuses along two axes depends on the patterning of transcription factors expressed in a region‐specific manner. Although most of the patterning is regulated by extrinsic signals, it is not known how Nkx5.1 and Msx1 are patterned. We focus on Dan, the founding member of the Cerberus/Dan gene family that encodes BMP antagonists, and describe its function in morphogenesis and patterning. First, we confirmed that Dan is expressed in the dorso‐medial region of the otic vesicle that corresponds to the presumptive endolymphatic duct and sac (ed/es). Second, we used siRNA knockdown to demonstrate that depletion of Dan induced both a severe reduction in the size of the ed/es and moderate deformities of the semicircular canals and cochlear duct. Depletion of Dan also caused suppression of Nkx5.1 in the dorso‐lateral region, suppression of Msx1 in the dorso‐medial region, and ectopic induction of Nkx5.1 and Msx1 in the ventro‐medial region. Most of these phenotypes also appeared following misexpression of the constitutively active form of BMP receptor type Ib. Thus, Dan is required for the normal morphogenesis of the inner ear and, by inhibiting BMP signaling, for the patterning of the transcription factors Nkx5.1 and Msx1.
Microarray analysis of zygotic expression of transcription factor genes and cell signaling molecule genes in early Ciona intestinalis embryos
Authors: Hamaguchi Makoto , Fujie Manabu , Noda Takeshi , Satoh Nori
Published: August 2010

In ascidians, specification of embryonic cells takes place very early at the 16‐, 32‐ and 64‐cell stages, and this developmental event involves zygotic expression of various genes, some encoding transcription factors and some encoding cell signaling molecules. Previous studies have demonstrated that approximately 50 transcription factor genes and 25 signaling molecule genes commence their zygotic expression by the 64‐cell stage of Ciona intestinalis embryos. With the aid of oligonucleotide‐based microarray, we examined the zygotic expression profiles of developmental genes in early Ciona embryos. Although the microarray method had a tendency to barely detect zygotic expression of genes that are expressed maternally, the present results confirmed the results of previous studies. In addition, the present analysis demonstrated the zygotic expression of four genes that were not identified in previous studies, and this result was confirmed by whole‐mount in situ hybridization. Our results therefore provide further information on the developmental genes that are zygotically expressed in early Ciona embryos, and demonstrate that the microarray is a powerful tool for future studies of the gene regulatory network in Ciona, a basal chordate with a body plan similar to that of vertebrates.
Quantitation of the male and female types of mitochondrial DNA in a blue mussel, Mytilus galloprovincialis, using real‐time polymerase chain reaction assay
Authors: Sano Natsumi , Obata Mayu , Komaru Akira
Published: August 2010

The system termed doubly uniparental inheritance (DUI) of mitochondrial transmission to progeny has been reported in Mytilus. Under DUI, it has been thought that males have both paternally (M type) and maternally (F type) transmitted mitochondrial DNA (mtDNA), and females have only F type. However, the presence of M type in females has been reported. To clarify the ratio of M type to F type mtDNA in female and male tissues to further our understanding of mitochondrial transmission, we developed a procedure to measure the copy numbers of the two types of mtDNA in Mytilus galloprovincialis using a real‐time polymerase chain reaction assay. The following results were obtained by this method. In females, the copy numbers of M type mtDNA detected in adductor muscle, gonad and eggs were approximately 10 000‐fold lower than those of F type. In males, F type dominated in adductor muscle, as in the female tissue. However, copy numbers of M type mtDNA were approximately 1000‐fold higher than those of F type in gonad and 100 000‐fold higher than those of F type in sperm. We examined the quantity relationship between the two types of mtDNA and the transmission mechanism of mtDNA in M. galloprovincialis.
Improved method for visualizing cells revealed dynamic morphological changes of ventral neuroblasts during ventral cleft closure of Caenorhabditis elegans
Authors: Liu Zhicen , Nukazuka Akira , Takagi Shin
Published: August 2010

The formation of intricate and functional biological structures depends on the dynamic changes of cellular morphology. Confocal laser scanning microscopy (CLSM) is a widely used method to reveal the three‐dimensional (3‐D) structure of cells during the development of Caenorhabditis elegans (C. elegans) and other model organisms. Improving the efficiency and image quality of CLSM would benefit studies using this method. We found that CED‐10::GFP::CED‐10, a green fluorescent protein (GFP) marker, is intensely expressed beneath the cell surface, facilitating visualization of cellular morphology in C. elegans embryos. By combining the unique properties of this marker, and with the help of direct 3‐D rendering of images obtained by CLSM, we developed a simple but powerful method for investigating cellular morphology in developing embryos. Using this method we, for the first time, document the dynamic changes in the morphology of ventral neuroblasts in vivo during ventral cleft closure.
Hair cycle‐dependent changes of alkaline phosphatase activity in the mesenchyme and epithelium in mouse vibrissal follicles
Authors: Iida Machiko , Ihara Setsunosuke , Matsuzaki Takashi
Published: August 2010

Alkaline phosphatase (ALP) activity was detected in the restricted mesenchymal and epithelial regions in mouse vibrissal follicles. Its localization and strength dramatically changed during the hair cycle. Activity in the dermal papilla (DP) was moderate in very early anagen, reached a maximal level in early anagen, decreased at the proximal region of DP after mid anagen, and was kept at a low level during catagen. The bulbar dermal sheath showed intense ALP activity only in early anagen. Although most bulbar epithelium did not show ALP activity, germinative epidermal cells that were adjacent to the ALP‐negative DP cells became ALP‐positive in mid anagen and rearranged in a single layer so as to encapsulate the DP in mid catagen. During catagen, the outermost layer of bulbar epithelium became ALP‐positive, which could be follicular epithelial precursors migrating from the bulge. Before the initiation of hair formation, ALP activity in the bulbar epithelium rapidly decreased and that in DP increased. These dynamic changes of ALP expression might be related to DP's functions in hair induction and also to reconstruction of the bulbar structure during the hair cycle.
Regeneration of the amphibian retina: Role of tissue interaction and related signaling molecules on RPE transdifferentiation
Authors: Araki Masasuke
Published: August 2010

Regeneration of eye tissue is one of the classic subjects in developmental biology and it is now being vigorously studied to reveal the cellular and molecular mechanisms involved. Although many experimental animal models have been studied, there may be a common basic mechanism that governs retinal regeneration. This can also control ocular development, suggesting the existence of a common principle between the development and regeneration of eye tissues. This notion is now becoming more widely accepted by recent studies on the genetic regulation of ocular development. Retinal regeneration can take place in a variety of vertebrates including fish, amphibians and birds. The newt, however, has been considered to be the sole animal that can regenerate the whole retina after the complete removal of the retina. We recently discovered that the anuran amphibian also retains a similar ability in the mature stage, suggesting the possibility that such a potential could be found in other animal species. In the present review article, retinal regeneration of amphibians (the newt andXenopus laevis) and avian embryos are described, with a particular focus on transdifferentiation of retinal pigmented epithelium. One of the recent progresses in this field is the availability of tissue culture methods to analyze the initial process of transdifferentiation, and this enables us to compare the proliferation and neural differentiation of retinal pigmented epithelial cells from various animal species under the same conditions. It was revealed that tissue interactions between the retinal pigmented epithelium and underlying connective tissues (the choroid) play a substantial role in transdifferentiation and that this is mediated by a diffusible signal such as fibroblast growth factor 2. We propose that tissue interaction, particularly mesenchyme–neuroepithelial interaction, is considered to play a fundamental role both in retinal development and regeneration.
Cardiomyocytes re‐enter the cell cycle and contribute to heart development after differentiation from cardiac progenitors expressing Isl1 in chick embryo
Authors: Hayashi Shinichi , Inoue Akio
Published: August 2010

Cardiomyocytes are generated from the precardiac mesoderm and the size of the heart increases dramatically during embryogenesis. However, it is unclear how differentiation and proliferation correlate in the cardiac cell line during development. Here, we show that cardiomyocytes re‐entered into a proliferative state after differentiation with a concomitant cell cycle arrest in chick embryo. The cells in the course of differentiation from Isl1‐positive cardiac precursors to cardiomyocytes did not proliferate, but differentiated cardiomyocytes proliferated even after the acquisition of contractile function. After differentiation, cardiomyocytes developed a proliferative potential to contribute to the increase in cell numbers during heart development. Almost all differentiated cardiomyocytes (82.8%) incorporated bromodeoxyuridine (BrdU) in vitro, indicating the ability of DNA replication. Furthermore, mitotic chromosomes were observed in the cardiomyocytes in which a sarcomeric structure was sustained in the cytoplasm. We conclude that the sequential events of the differentiation to contractile myocytes and the re‐entry into the cell cycle are strictly regulated during cardiac cell maturation. These results provide an insight into the maturation mechanism of the cardiac cell line.
Distinct hemogenic potential of endothelial cells and CD41+ cells in mouse embryos
Authors: Hashimoto Kazuaki , Fujimoto Tetsuhiro , Shimoda Yuri , Huang Xin , Sakamoto Hiroshi , Ogawa Minetaro
Published: August 2010

Definitive hematopoietic progenitor cells have been thought to develop from the vascular endothelium located in the aorta‐gonad‐mesonephros region of the mouse embryo. However, several recent findings have suggested that most hematopoietic progenitors are derived from non‐endothelial precursor cells expressing CD41. We characterized two distinct precursor populations of definitive hematopoietic cell lineages, vascular endothelial (VE)‐cadherin+ CD41− CD45− endothelial cells and CD41+ CD45− non‐endothelial progenitors, both of which are derived from lateral mesoderm. VE‐cadherin+ endothelial cells obtained from cultures of differentiating embryonic stem cells possessed hematopoietic potential encompassing erythroid, myeloid and B lymphoid lineages, whereas CD41+ progenitors lacked the B lymphopoietic potential. VE‐cadherin+ endothelial cells in the lower trunk of the embryo proper showed a significant potential for initiating B lymphopoiesis in cultures, while endothelial cells in the yolk sac appeared to have a bias for myeloerythropoietic differentiation. CD41+ progenitors isolated from yolk sac and embryo proper were capable of generating multiple hematopoietic lineages, although mast cell precursors were exclusively enriched in CD41+ progenitors in the yolk sac. These results suggest that hemogenic endothelial cells and CD41+ progenitors possess distinct hematopoietic potential depending on the tissues in which they reside.
How to make a zone of polarizing activity: Insights into limb development via the abnormality preaxial polydactyly
Authors: Hill Robert E.
Published: August 2010

Early in vertebrate limb development, a program initiates that polarizes the limb along the antero‐posterior axis. The mesenchyme at the posterior margin is ultimately responsible for the asymmetry due to a region called the zone of polarizing activity (ZPA). The ZPA produces and secretes the molecule SHH, which coordinates the patterning of the resulting digits. Preaxial polydactyly (PPD) is a commonly occurring limb abnormality; investigating the genetic basis of this defect has provided insights into our understanding of digit patterning. PPD disrupts limb asymmetry by producing an ectopic ZPA at the opposite margin of the limb bud. Mutations in the long‐range, limb‐specific regulatory element of the Shh gene are responsible for the defect. Genetic analysis of this limb abnormality provides an important approach in understanding the mechanisms that control digit patterning.
Ectopic germline cells in embryos of Xenopus laevis
Authors: Ikenishi Kohji , Ohno Takeshi , Komiya Tohru
Published: August 2010

Whether all descendants of germline founder cells inheriting the germ plasm can migrate correctly to the genital ridges and differentiate into primordial germ cells (PGCs) at tadpole stage has not been elucidated in Xenopus. We investigated precisely the location of descendant cells, presumptive primordial germ cells (pPGCs) and PGCs, in embryos at stages 23–48 by whole‐mount in situ hybridization with the antisense probe for Xpat RNA specific to pPGCs and whole‐mount immunostaining with the 2L‐13 antibody specific to Xenopus Vasa protein in PGCs. Small numbers of pPGCs and PGCs, which were positively stained with the probe and the antibody, respectively, were observed in ectopic locations in a significant number of embryos at those stages. A few of the ectopic PGCs in tadpoles at stages 44–47 were positive in TdT‐mediated dUTP digoxigenin nick end labeling (TUNEL) staining. By contrast, pPGCs in the embryos until stage 40, irrespective of their location and PGCs in the genital ridges of the tadpoles at stages 43–48 were negative in TUNEL staining. Therefore, it is evident that a portion of the descendants of germline founder cells cannot migrate correctly to the genital ridges, and that a few ectopic PGCs are eliminated by apoptosis or necrosis at tadpole stages.
The short toes mutation of the axolotl
Authors: Sato Kazuna , Chernoff Ellen A. G.
Published: August 2010

The axolotl mutant strain, short toes (s/s), can regenerate spinal cord and tail, but not limbs. This makes s/s potentially very useful for limb regeneration studies. This mutant merits a new examination that integrates the original description of the mutant, existing experimental studies, new data and current thinking about stem cells and regeneration. There are still major gaps in information about this mutant; the gene(s) causing the defects has not yet been discovered, and even the histological description is incomplete, especially regarding muscle abnormalities. In the short toes limb, MyHC (myosin heavy chain)‐1, MyHC‐2b and pax7 are down‐regulated. In particular, all three MyHC genes and pax7 are highly expressed in the normal limb, but almost lost in the s/s limb. MyHC genes are one of the main components of skeletal muscle, and Pax7 is the skeletal muscle satellite cell marker. Histological experiments confirm that severe s/s has lost most skeletal muscle and myosin. These results suggest that skeletal muscle, which includes satellite cells, could play an important role in axolotl limb regeneration.
Embryologic, cytobiologic and genetic interpretations of DDK syndrome in mice
Authors: Wakasugi Noboru
Published: August 2010

DDK syndrome is known as embryonic death at the morula‐blastocyst stage in female mice of the DDK strain mated with males from other strains (alien males). The embryonic death is interpreted to be caused by incompatibility between oocyte factors and the product from male pronucleus, both of which are under the control of alleles at the same locus on Chromosome 11. This review explains the hypothesis proposing that the embryonic death may be caused primarily by failure in de novo regeneration of centrosomes containing centrioles in the trophectodermal cells. Centrioles disintegrate during gametogenesis in mice, and new centrioles are formed after the cleavage stage during which cell division proceeds with the microtubule organizing center having no centrioles. The failure in de novo regeneration of the centrosomes may arrest cell division and consequently result in embryonic death. Another aspect of DDK syndrome is distortion of the second polar body extrusion in the semi‐incompatible cross. In the heterozygous (DDK/alien) oocytes fertilized with alien spermatozoa, DDK allele is more frequently retained in the oocyte nucleus, and alien allele tends to be carried into the polar body. This distortion may possibly be caused by derangement in the spindle system. Therefore, both aspects of DDK syndrome can be regarded as being derived from the abnormality in the centrosome‐spindle system according to this hypothesis.