Neural crest induction in Xenopus: evidence for a two-signal model

We have investigated the molecular interactions underlying neural crest formation in Xenopus. Using chordin overexpression to antagonize endogenous BMP signaling in whole embryos and explants, we demonstrate that such inhibition alone is insufficient to account for neural crest induction in vivo. We find, however, that chordin-induced neural plate tissue can be induced to adopt neural crest fates by members of the FGF and Wnt families, growth factors that have previously been shown to posteriorize induced neural tissue. Overexpression of a dominant negative XWnt-8 inhibits the expression of neural crest markers, demonstrating the necessity for a Wnt signal during neural crest induction in vivo. The requirement for Wnt signaling during neural crest induction is shown to be direct, whereas FGF-mediated neural crest induction may be mediated by Wnt signals. Overexpression of the zinc finger transcription factor Slug, one of the earliest markers of neural crest formation, is insufficient for neural crest induction. Slug-expressing ectoderm will generate neural crest in the presence of Wnt or FGF-like signals, however, bypassing the need for BMP inhibition in this process. A two-step model for neural crest induction is proposed

Molecular mechanisms of neural crest formation

The neural crest is a transient population of multipotent precursor cells named for its site of origin at the crest of the closing neural folds in vertebrate embryos. Following neural tube closure, these cells become migratory and populate diverse regions throughout the embryo where they give rise to most of the neurons and support cells of the peripheral nervous system (PNS), pigment cells, smooth muscle, craniofacial cartilage, and bone. Because of its remarkable ability to generate such diverse derivatives, the neural crest has fascinated developmental biologists for over one hundred years. A great deal has been learned about the migratory pathways neural crest cells follow and the signals that may trigger their differentiation, but until recently comparatively little was known about earlier steps in neural crest development. In the past few years progress has been made in understanding these earlier events, including how the precursors of these multipotent cells are specified in the early embryo and the mechanisms by which they become migratory. In this review, we first examine the mechanisms underlying neural crest induction, paying particular attention to a number of growth factor and transcription factor families that have been implicated in this process. We also discuss when and how the fate of neural crest precursors may diverge from those of nearby neural and epidermal populations. Finally, we review recent advances in our understanding of how neural crest cells become migratory and address the process of neural crest diversification

Do community-driven development projects enhance social capital ? evidence from the Philippines

This paper explores the social capital impacts of a large-scale, community-driven development project in the Philippines in which communities competed for block grants for infrastructure investment. The analysis uses a unique data set of about 2,100 households collected before the project started (2003) and after one cycle of sub-project implementation (2006) in 66 treatment and 69 matched control communities. Participation in village assemblies, the frequency with which local officials meet with residents and trust towards strangers increased as a result of the project. However, there is a decline in group membership and participation in informal collective action activities. This may have been because households were time-constrained, so that in order to participate in project activities, they needed to temporarily reduce their participation in informal activities. An alternative explanation is that the project improved the efficiency of formal forms of social capital and thus households needed to rely less on informal forms. Finally, the results indicate that, in the short run, the project might have reduced the number of other investments.Housing&Human Habitats,Access to Finance,Social Accountability,Social Capital,Banks&Banking Reform

A road to trust

The authors explore the relationship between transaction costs and generalized trust. Using panel data from 2,100 households in 135 rural communities of the Philippines, the paper shows that where transaction costs are reduced (proxied by road construction), there is an increase in generalized trust. Consistent with the argument that generalized trust is built through repeated interactions, the authors find that the individuals most likely to engage in exchange exhibit an increase in trust after road construction. These results suggest that, rather than being an input to economic growth, trust might be a product of reduced transaction costs (which also favors growth).Post Conflict Reconstruction,Transport Economics Policy&Planning,Rural Roads&Transport,Social Capital,Corporate Law

The power of information : the impact of mobile phones on farmers'welfare in the Philippines

The authors explore the impact of access to information on poor farmers’ consumption. The analysis combines spatially coded data on mobile phone coverage with household panel data on farmers from some of the poorest areas of the Philippines. Both the ordinary least squares and instrumental variable estimates indicate that purchasing a mobile phone has a large, positive impact on the household-level growth rate of per capita consumption. Estimates range from 11 to 17 percent, depending on the sample and the specification chosen. The authors perform a range of reliability tests, the results of which all suggest that the instruments are valid. They also present evidence consistent with the argument that easier access to information allows farmers to strike better price deals within their existing trading relationships and to make better choices in terms of where they choose to sell their goods.E-Business,Access to Finance,Rural Poverty Reduction,Debt Markets,Poverty Lines

Conflict, Ideology and Foreign Aid

In this paper, we present a rent-seeking model of conflict, which highlights the role of ideology in determining whether the government or the rebels take the initiative. We use the model to interpret the impact of a large-scale Community-Driven Development project on civil conflict in the Philippines. The country is characterized by the presence of two rebel groups, the New People's Army (NPA) and the Moro Islamic Liberation Front (MILF), with two distinct ideologies. We use a unique geo-referenced panel dataset on the occurrence of conflicts in 2003 and 2006 gathered from local newspapers that we match with nationally representative household survey and budget data on all municipalities in the country. Consistent with our model's predictions, using a variety of estimation strategies, we find robust evidence that the project leads to a decline in MILF-related events and to an increase in NPA-related events.Civil Conflict;foreign aid;Rent Seeking;Community-Driven Development;philippines

Conflict, Ideology and Foreign Aid

In this paper, we present a rent-seeking model of conflict, which highlights the role of ideology in determining whether the government or the rebels take the initiative. We use the model to interpret the impact of a large-scale Community-Driven Development project on civil conflict in the Philippines. The country is characterized by the presence of two rebel groups, the New People's Army (NPA) and the Moro Islamic Liberation Front (MILF), with two distinct ideologies. We use a unique geo-referenced panel dataset on the occurrence of conflicts in 2003 and 2006 gathered from local newspapers that we match with nationally representative household survey and budget data on all municipalities in the country. Consistent with our model's predictions, using a variety of estimation strategies, we find robust evidence that the project leads to a decline in MILF-related events and to an increase in NPA-related events.Civil Conflict, foreign aid, Rent Seeking, Community-Driven Development, philippines