Kinetics of morphogen gradient formation     

Kicheva A  Pantazis P  Bollenbach T  Kalaidzidis Y  Bittig T  Jülicher F  González-Gaitán M 《Science (New York, N.Y.)》2007,315(5811):521-525

In the developing fly wing, secreted morphogens such as Decapentaplegic (Dpp) and Wingless (Wg) form gradients of concentration providing positional information. Dpp forms a longer-range gradient than Wg. To understand how the range is controlled, we measured the four key kinetic parameters governing morphogen spreading: the production rate, the effective diffusion coefficient, the degradation rate, and the immobile fraction. The four parameters had different values for Dpp versus Wg. In addition, Dynamin-dependent endocytosis was required for spreading of Dpp, but not Wg. Thus, the cellular mechanisms of Dpp and Wingless spreading are different: Dpp spreading requires endocytic, intracellular trafficking.  相似文献   

Role of histone H3 lysine 27 methylation in X inactivation   总被引：1，自引：0，他引：1  

Plath K  Fang J  Mlynarczyk-Evans SK  Cao R  Worringer KA  Wang H  de la Cruz CC  Otte AP  Panning B  Zhang Y 《Science (New York, N.Y.)》2003,300(5616):131-135

The Polycomb group (PcG) protein Eed is implicated in regulation of imprinted X-chromosome inactivation in extraembryonic cells but not of random X inactivation in embryonic cells. The Drosophila homolog of the Eed-Ezh2 PcG protein complex achieves gene silencing through methylation of histone H3 on lysine 27 (H3-K27), which suggests a role for H3-K27 methylation in imprinted X inactivation. Here we demonstrate that transient recruitment of the Eed-Ezh2 complex to the inactive X chromosome (Xi) occurs during initiation of X inactivation in both extraembryonic and embryonic cells and is accompanied by H3-K27 methylation. Recruitment of the complex and methylation on the Xi depend on Xist RNA but are independent of its silencing function. Together, our results suggest a role for Eed-Ezh2-mediated H3-K27 methylation during initiation of both imprinted and random X inactivation and demonstrate that H3-K27 methylation is not sufficient for silencing of the Xi.  相似文献   

French protests. Impasse continues, D-Day looms     

Casassus B 《Science (New York, N.Y.)》2004,303(5663):1446

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Planning the genome institute's future     

Uhlmann WR  Bennett R  Botkin JR  Botstein D  Boughman JA  Chakravarti A  Clayton EW  Kahn J  Koenig B  Murray TH  Olson MV  Rowley J  Terry S  Valle D 《Science (New York, N.Y.)》2003,299(5612):1515; author reply 1515

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Neurobiology. A glial spin on neurotrophins     

Hempstead BL  Salzer JL 《Science (New York, N.Y.)》2002,298(5596):1184-1186

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From the editor     

Harvey James 《Agriculture and Human Values》2007,24(3):275-279

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The political ecology of dietary transitions: Changing production and consumption patterns in the Kolli Hills,India     

Elizabeth Finnis 《Agriculture and Human Values》2007,24(3):343-353

Using a case study from the Kolli Hills, India, I suggest that political ecology provides a useful theoretical basis for considering localized dietary transitions in rural, agricultural communities in developing countries. By examining the reasons for the near-disappearance of local minor millets as staple foods in three small-farmer communities, I argue that an explicit, actor-oriented analysis allows for an integration of food issues with considerations of environmental circumstances, local aspirations, and labor concerns. That is, an agricultural shift that abandons minor millets as a food resource reflects environmental changes and household economic aspirations. Such an analysis has implications for the creation of practical food security projects through the recognition and incorporation of small-farmer experiences, voices, and priorities. This research was undertaken through ethnographic fieldwork, using semi-structured interviews and participant observation as the primary methods. Elizabeth Finnis obtained her PhD from McMaster University in Canada and is currently a post-doctoral fellow in the Department of Anthropology and the Centre for Society, Technology, and Development at McGill University.  相似文献   

Explaining disparities in food safety compliance by food stores: does community matter?     

Kameshwari Pothukuchi  Rayman Mohamed  David A. Gebben 《Agriculture and Human Values》2008,25(3):319-332

This paper provides a conceptual framework to explain why disparities may exist in food safety code compliance by food stores in different neighborhoods. Explanations include market dynamics, community characteristics, retailer attributes, inspector characteristics, and enforcement approaches, and interactions among the factors. A preliminary and limited empirical test of some of these relationships in Detroit, Michigan shows a higher rate of food safety violations by stores in poorer neighborhoods and in neighborhoods with higher concentrations of African-American residents. Stores inspected by female inspectors also scored higher numbers of critical violations, suggesting a need for greater examination of the social relations associated with enforcement interactions in food safety studies.

Kameshwari PothukuchiEmail:

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Kameshwari Pothukuchi   PhD, is Associate Professor of Urban Planning at Wayne State University. She conducts research on issues related to urban food security, including grocery stores, community gardens, and community and regional food planning. A policy guide on community and regional food planning, co-authored by her, was recently adopted by the American Planning Association (). Rayman Mohamed   PhD, is Assistant Professor of Urban Planning at Wayne State University. He conducts research on land use and environmental planning. His recent articles examine decision making by developers, the economics of conservation subdivisions, and the relationship between sprawl and the costs of infrastructure. David A. Gebben   is a graduate student of agricultural economics and a research assistant in the Global Urban Studies Program at Michigan State University.  相似文献   

Livelihood change,farming, and managing flood risk in the Lerma Valley,Mexico     

Hallie Eakin  Kirsten Appendini 《Agriculture and Human Values》2008,25(4):555-566

In face of rising flood losses globally, the approach of “living with floods,” rather than relying on structural measures for flood control and prevention, is acquiring greater resonance in diverse socioeconomic contexts. In the Lerma Valley in the state of Mexico, rapid industrialization, population growth, and the declining value of agricultural products are driving livelihood and land use change, exposing increasing numbers of people to flooding. However, data collected in two case studies of farm communities affected by flooding in 2003 illustrate that the concept of flood as agricultural “hazard” has been relatively recently constructed through public intervention in river management and disaster compensation. While farming still represents subsistence value to rural households, increasingly rural communities are relying on non-farm income and alternative livelihood strategies. In this context, defining flooding in rural areas as a private hazard for which individuals are entitled to public protection may be counterproductive. A different approach, in which farmers’ long acceptance of periodic flooding is combined with valuing agricultural land for ecoservices, may enable a more sustainable future for the region’s population.

Hallie EakinEmail:

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Hallie Eakin   received her doctorate in Geography and Regional Development from the University of Arizona in 2002. She is currently an assistant professor at the University of California, Santa Barbara. As a postdoctoral researcher at the Center of Atmospheric Sciences of the National Autonomous University of Mexico in Mexico City, she continued to work on issues related to economic globalization, agricultural change, and rural vulnerability to climate in the context of several comparative international projects involving case studies in Mexico, Argentina, Guatemala, and Honduras. Her articles on this research have been published in World Development, the Journal of Environment and Development, Climatic Change, Global Environmental Change and Physical Geography. Her book Weathering Risk in Rural Mexico, based on her research on agricultural adaptation to neoliberal reforms and climatic variability in central Mexico, was released by the University of Arizona Press in 2006. Kirsten Appendini   has a doctorate in Agricultural Economics from the National Autonomous University of Mexico (UNAM). She currently is a researcher and professor on the faculty of the Center for Economic Studies (Centro de Estudios Económicos) at the Colegio de México in Mexico City. She has published widely on issues of agrarian change, rural poverty, food security, and food policy in Mexico. Her book on Mexican maize policy, De la milpa a los tortibonos: La restructración de la política alimentaria en México (Colmex 2001) is now on its second edition. She has also served as a consultant to the UN Food and Agriculture Organization and several bilateral development agencies.  相似文献   

How farmers matter in shaping agricultural technologies: social and structural characteristics of wheat growers and wheat varieties     

Leland L. Glenna  Raymond A. JussaumeJr.  Julie C. Dawson 《Agriculture and Human Values》2011,28(2):213-224

Science and technology studies (STS) research challenges the concept of technological determinism by investigating how the end users of a technology influence that technology’s trajectory. STS critiques of determinism are needed in studies of agricultural technology. However, we contend that focusing on the agency of end users may mask the role of political-economic factors which influence technology developments and applications. This paper seeks to mesh STS insights with political-economic perspectives by accounting for relationships between availability of diverse technologies, variations in political-economic structures, and farmer interests and characteristics. We present the results of an analysis on the recent development of three wheat varieties: (a) a wheat variety that was modified genetically to tolerate the herbicide glyphosate, (b) wheat varieties with characteristics selected to serve specific markets, (c) and emerging research and development of perennial wheat varieties. Using data obtained through a survey of wheat growers in Washington State, we analyzed whether farmer interest in these three clusters of wheat varieties was associated with distinct individual characteristics and attitudes and whether those characteristics and attitudes are consistent with political economic structures. Although our analysis did not allow us to assess the degree of direct influence that farmers have on the technological development trajectory for these types of wheat, we were able to document variation in technological alternatives and farmer characteristics related to different political-economic trends.  相似文献