Combining "real effort" with induced effort costs: the ball-catching task

We introduce the "ball-catching task", a novel computerized task, which combines a tangible action ("catching balls") with induced material cost of effort. The central feature of the ball-catching task is that it allows researchers to manipulate the cost of effort function as well as the production function, which permits quantitative predictions on effort provision. In an experiment with piece-rate incentives we find that the comparative static and the point predictions on effort provision are remarkably accurate. We also present experimental findings from three classic experiments, namely, team production, gift exchange and tournament, using the task. All of the results are closely in line with the stylized facts from experiments using purely induced values. We conclude that the ball-catching task combines the advantages of real effort tasks with the use of induced values, which is useful for theory-testing purposes as well as for applications.

Risk-taking in social settings: Group and peer effects

We investigate experimentally the effect of consultation (unincentivized advice) on choices under risk in an incentivized investment task. We compare consultation to two benchmark treatments: one with isolated individual choices, and a second with group choice after communication. Our benchmark treatments replicate findings that groups take more risk than individuals in the investment task; content analysis of group discussions reveals that higher risk-taking in groups is positively correlated with mentions of expected value. In our consultation treatments, we find evidence of peer effects: decisions within the peer group are significantly correlated. However, average risk-taking after consultation is not significantly different from isolated individual choices. We also find that risk-taking after consultation is not affected by adding a feedback stage in which subjects see the choices of their consultation peers.

Peer Effects in Pro-Social Behavior: Social Norms or Social Preferences?

We compare social preference and social norm based explanations for peer effects in a three-person gift-exchange experiment. In the experiment a principal pays a wage to each of two agents, who then make effort choices sequentially. In our baseline treatment we observe that the second agent's effort is influenced by the effort choice of the first agent, even though there are no material spillovers between agents. This peer effect is predicted by the Fehr-Schmidt (1999) model of social preferences. As we show from a norms-elicitation experiment, it is also consistent with social norms compliance. A conditional logit investigation of the explanatory power of payoff inequality and elicited norms finds that the second agent's effort is best explained by the social preferences model. In further experiments we find that the peer effects change as predicted by the social preferences model. Again, a conditional logit analysis favors an explanation based on social preferences, rather than social norms. Our results suggest that, in our context, the social preferences model provides a parsimonious explanation for the observed peer effect.

Quantitative analysis of polymeric procyanidins (Tannins) from grape (Vitis vinifera) seeds by reverse phase high-performance liquid chromatography

A reverse phase C(18) HPLC method with potential for high automated throughput has been developed for the quantitative analysis of polymeric procyanidins (tannins) in grape seed extracts. Chromatography gave rise to 13 distinct UV-absorbing peaks with good baseline separation. The UV-absorbing peak eluting last is distinct and therefore easily quantified. Biochemical analyses including ultrafiltration, protein precipitation, and Sephadex LH20 chromatography combined with electrospray mass spectrometric analyses establish that this peak predominantly contains polymeric procyanidins. The polymers, which appear to be galloylated to various degrees and seem to fragment in a characteristic manner during electrospray mass spectrometry, are well separated from catechins and procyanidin oligomers of up to 4 units. The recovery of polymeric grape seed tannins with this HPLC method was 86%, which is similar to the 89% recovery achieved with commercial quebracho tannins. The concentration of tannins in seeds from ripe Vitis vinifera cv. Shiraz grapes ranged from 1360 to 2830 mg/kg of berries.

Expression of the G protein-coupled receptor kinase 2 during early mouse embryogenesis

Whilst several G protein-coupled receptors (GPCRs) have been shown to play important roles during development, little study has been carried out on the G protein-coupled receptor kinases (GRKs) that modulate their activity in embryos. Here, we have analyzed the expression of GRK2, the predominant GRK expressed during embryogenesis. We show that at early stages, the expression of GRK2 is restricted to populations of cells that are undifferentiated, multipotent and in many cases, migratory. As such, GRK2 transcripts were found in the early mesoderm and neural crest as they migrate from the primitive streak and the neural tube, respectively. In the limb bud, GRK2 transcripts were observed in cells of the progress zone and in the interdigital areas. At later stages, the expression in the heart is compatible with the phenotype observed in the GRK2 deficient mice.

Exploring redundancy in the yeast genome: an improved strategy for use of the cre-loxP system

Gene families having more than three members are a common phenomenon in the Saccharomyces cerevisiae genome. As yeast research enters the post-genome era, the development of existing deletion strategies is crucial for tackling this apparent redundancy, hence a method for performing rapid multiple gene disruptions in this organism has been developed. We constructed three replacement cassettes in which different selectable markers were placed between two loxP loci. Multiple deletions (of members of a gene family) were generated, in one strain, using sequential integration of different replacement markers (kanMX, LYS2, KlURA3 and SpHIS5). Their excision from the genome was performed simultaneously, as the final step, using a new cre recombinase vector, which carries the cycloheximide-resistance gene from Candida maltosa as a selectable marker. Our multiple gene deletion system significantly accelerates and facilitates the functional analysis process and is particularly useful for studying gene families in either laboratory or industrial yeast strains.

An abnormal response of retinoblastoma cells (Y-79) to neurotrophins

PURPOSE

To clarify the expression of neurotrophins and their receptors in retinoblastoma (Rb) cells, to elucidate their potential role in the proliferation of neuroectodermal tumor cells, and to establish conditions for Rb cell differentiation.

METHODS

The Rb-derived cell line Y-79 was grown in serum-free suspension or monolayer culture. Proliferating and differentiated cells were isolated and submitted to semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis, immunostaining, and flow cytometry. The proliferation rate of the cells was estimated by 5-bromo-2'-deoxyuridine (BrdU) incorporation, and the effects of neurotrophins and laminin on BrdU-incorporation, process outgrowth, or immunostaining were determined.

RESULTS

In contrast to previously studied normal retinal precursor cells, Y-79 cells not only express nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and p75, but also the corresponding high affinity receptors TrkA, TrkB, and TrkC. Proliferation was stimulated by exogenous and endogenous neurotrophin receptor ligands. Inhibition of protein kinase phosphorylation with K252a blocked proliferation and promoted differentiation. The effect of K252a on differentiation was enhanced by the addition of soluble laminin. After 9 days of combined treatment, the fraction of differentiated cells amounted to 30%, differentiation being characterized by improved attachment, neurite outgrowth, expression of NF-68, and a loss of glial fibrillary acidic protein (GFAP) and parvalbumin immunoreactivity. These changes were accompanied by a downregulation of TrkB and TrkC, but not TrkA or p75. Differentiated cells were isolated and further grown in the absence of K252a. However, despite the high level of TrkA expression in differentiated cells, the addition of NGF had no effect on their survival.

CONCLUSIONS

A mitogenic action of neurotrophins could contribute to retinal tumor growth.

Application of yeast cells transformed with GFP expression constructs containing the RAD54 or RNR2 promoter as a test for the genotoxic potential of chemical substances

Yeast strains transformed with high copy number plasmids carrying the gene encoding a green fluorescent protein optimised for yeast (yEGFP3) under the control of the RAD54 or RNR2 promoter were used to investigate the activity of potentially DNA-damaging substances. The assays were performed on 96-well microtitre plates in the presence of different concentrations of the test substances. The synthesis of GFP protein was measured through the fluorescence signal and cell growth was monitored by absorption. Here, we demonstrate that this system can be used as a biosensor to assess the genotoxic potential of drugs and other chemical substances. The use of microtitre plates will enable full automation of the system and allows the inclusion of internal reference standards in each assay.

Transcript analysis of 250 novel yeast genes from chromosome XIV

The European Functional Analysis Network (EUROFAN) is systematically analysing the function of novel Saccharomyces cerevisiae genes revealed by genome sequencing. As part of this effort our consortium has performed a detailed transcript analysis for 250 novel ORFs on chromosome XIV. All transcripts were quantified by Northern analysis under three quasi-steady-state conditions (exponential growth on rich fermentative, rich non-fermentative, and minimal fermentative media) and eight transient conditions (glucose derepression, glucose upshift, stationary phase, nitrogen starvation, osmo-stress, heat-shock, and two control conditions). Transcripts were detected for 82% of the 250 ORFs, and only one ORF did not yield a transcript of the expected length (YNL285w). Transcripts ranged from low (62%), moderate (16%) to high abundance (2%) relative to the ACT1 mRNA. The levels of 73% of the 206 chromosome XIV transcripts detected fluctuated in response to the transient states tested. However, only a small number responded strongly to the transients: eight ORFs were induced upon glucose upshift; five were repressed by glucose; six were induced in response to nitrogen starvation; three were induced in stationary phase; five were induced by osmo-stress; four were induced by heat-shock. These data provide useful clues about the general function of these ORFs and add to our understanding of gene regulation on a genome-wide basis.

Conserved and divergent roles for members of the Snail family of transcription factors in the chick and mouse embryo

The members of the Snail family of zinc-finger transcription factors have been implicated in the formation of distinct tissues within the developing vertebrate and invertebrate embryo. Two members of this family have been described in higher vertebrates, Snail (Sna) and Slug (Slu), where they have been implicated in the formation of tissues such as the mesoderm and the neural crest. We have isolated the mouse homologue of the Slu gene enabling us to analyse and compare the amino acid sequences and the patterns of expression of both Sna and Slu in the chick and mouse. We have detected features in the sequences that allow the unequivocal ascription of any family member to the Sna or Slu subfamilies and we have observed that, during early stages of development, many of the sites of Slu and Sna expression in the mouse and chick embryo are swapped. Later in development, the sites of expression of Slu and Sna are conserved between these two species. These data, together with the data available in other species, lead us to propose that Slu and Sna arose as a duplication of an ancestor gene and that an extra duplication in the fish lineage has given rise to two Sna genes. Furthermore, several early sites of Slu and Sna expression have been swapped in the avian lineage. Our analysis of the Snail family may also shed new light on the origin of the neural crest.

Multiple roles of Eph-like kinases and their ligands during development

The Eph family of tyrosine kinase receptors and their ligands have aroused much attention over the last couple of years, because of the demonstration of their pivotal role in axon guidance and pathfinding in the developing vertebrate central nervous system. However, the first indications that these receptors may play important roles during development came from studies of segmentation in the early embryo. In this review, we discuss the two roles that have been attributed to Eph receptors and their ligands (regionalisation and axon guidance) with reference to the two systems in which they were originally described, viz., the hindbrain and the retina, respectively. Furthermore, we discuss evidence that these molecules fulfill both these functions in each of the systems analysed, the role played by members of these two families at any one time being dependent on the developmental stage at which they are expressed.

Novel expression gradients of Eph-like receptor tyrosine kinases in the developing chick retina

Eph-like receptor tyrosine kinases have recently been identified as critical components in the development of the retinotectal system. Complementary gradients of receptors and ligands in the retina and tectum, and within the retina itself, have previously been described. Here, we present a novel centroperipheral gradient of expression for one member of this family of receptors, Cek9, suggesting that retinal patterning and axon guidance during the establishment of retinotectal projections may involve coordinate mapping along three axes. Furthermore, we show matching gradients of two cytoplasmic kinases, compatible with their putative involvement in the intracellular signaling pathways used by these receptors in the retina. We also demonstrate a dorsal to ventral expression gradient for Cek11, an Eck-like receptor, the Eph subclass previously suggested to specify positional information along the temporonasal axis.

Slug, a zinc finger gene previously implicated in the early patterning of the mesoderm and the neural crest, is also involved in chick limb development

The great advances made over the last few years in the identification of signalling molecules that pattern the limb bud along the three axes make the limb an excellent model system with which to study developmental mechanisms in vertebrates. The understanding of the signalling networks and their mutual interactions during limb development requires the characterisation of the corresponding downstream genes. In this study we report the expression pattern of Slug, a zinc-finger-containing gene of the snail family, during the development of the limb, and its regulation by distinct axial signalling systems. Slug expression is highly dynamic, and at different stages of limb development can be correlated with the zone of polarizing activity, the progress zone and the interdigital areas. We show that the maintenance of its expression is dependent on signals from the apical ectodermal ridge and independent of Sonic Hedgehog. We also report that, in the interdigit, apoptotic cells lie outside of the domains of Slug expression. The correlation of Slug expression with areas of undifferentiated mesenchyme at stages of tissue differentiation is consistent with its role in early development, in maintaining the mesenchymal phenotype and repressing differentiation processes. We suggest that Slug is involved in the epithelial-mesenchymal interactions that lead to the maintenance of the progress zone.

Experimental manipulations of compaction and their effects on the phosphorylation of uvomorulin

Compaction of the eight-cell stage mouse embryo is a critical event in the generation of different cell types within the preimplantation embryo. Uvomorulin, a member of the cadherin family of cell adhesion molecules, is important during compaction and its phosphorylation increases early in the eight-cell stage, suggesting that this posttranslational modification may be important for compaction to proceed. We have assessed the importance of the phosphorylation of uvomorulin during compaction by preventing, reversing, or inducing adhesion prematurely. The only condition that affected the overall level of uvomorulin phosphorylation was the prevention of compaction through prolonged exposure of four-cell embryos to low Ca2+. This treatment reduced the level of uvomorulin phosphorylation in eight-cell embryos, and perturbed its localization to regions of cell-cell contact. Thus, whilst the phosphorylation of uvomorulin does not appear to regulate directly uvomorulin's adhesive function, it may be associated with the redistribution of uvomorulin during compaction.

Synthesis and phosphorylation of uvomorulin during mouse early development

The cell adhesion molecule, uvomorulin, is synthesised in both the 135 × 10(3) M(r) precursor and 120 × 10(3) M(r) mature forms on maternal mRNA templates in unfertilized and newly fertilized mouse oocytes. Synthesis on maternal message ceases during the 2-cell stage to resume later on mRNA encoded presumptively by the embryonic genome. Uvomorulin is detectable by immunoblotting at all stages upto the blastocyst stage, but shows variations in its total amount and processing with embryonic stage. Whilst only trace levels of phosphorylated uvomorulin are detectable in early and late 4-cell embryos, uvomorulin in 8-cell embryos is phosphorylated.