Actin remodeling is at the heart of the response of cells to external or internal stimuli, allowing a variety of membrane protrusions to form. Fifteen years ago, tunneling nanotubes (TNTs) were ...identified, bringing a novel addition to the family of actin-supported cellular protrusions. Their unique property as conduits for cargo transfer between distant cells emphasizes the unique nature of TNTs among other protrusions. While TNTs in different pathological and physiological scenarios have been described, the molecular basis of how TNTs form is not well understood. In this review, we discuss the role of several actin regulators in the formation of TNTs and suggest potential players based on their comparison with other actin-based protrusions. New perspectives for discovering a distinct TNT formation pathway would enable us to target them in treating the increasing number of TNT-involved pathologies.
Novel structures, known as tunneling nanotubes (TNTs), are membranous protrusions supported by filamentous actin that mediate continuity between remote cells by remaining open at both ends for cargo transport.The formation of morphologically similar protrusions, such as filopodia, microvilli, and immature dendritic spines, involves the processes of initiation, elongation, and stabilization; this includes many actin and membrane regulators, such as Rho GTPases, I-BAR proteins, actin nucleators, and actin bundlers, which likely participate in TNT formation.The unique length of TNTs implies the involvement of motor proteins able to efficiently transport the required components to the growing end, and likely a specific actin arrangement.Specificity in TNT biogenesis may arise from differences in the ability of common actin-regulating molecules to promote TNTs versus filopodia.
THE GLOBAL DISTRIBUTION OF ECONOMIC ACTIVITY Henderson, J. Vernon; Squires, Tim; Storeygard, Adam ...
The Quarterly journal of economics,
02/2018, Letnik:
133, Številka:
1
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We explore the role of natural characteristics in determining the worldwide spatial distribution of economic activity, as proxied by lights at night, observed across 240,000 grid cells. A ...parsimonious set of 24 physical geography attributes explains 47% of worldwide variation and 35% of within-country variation in lights. We divide geographic characteristics into two groups, those primarily important for agriculture and those primarily important for trade, and confront a puzzle. In examining within-country variation in lights, among countries that developed early, agricultural variables incrementally explain over 6 times as much variation in lights as do trade variables, while among late developing countries the ratio is only about 1.5, even though the latter group is far more dependent on agriculture. Correspondingly, the marginal effects of agricultural variables as a group on lights are larger in absolute value, and those for trade smaller, for early developers than for late developers. We show that this apparent puzzle is explained by persistence and the differential timing of technological shocks in the two sets of countries. For early developers, structural transformation due to rising agricultural productivity began when transport costs were still high, so cities were localized in agricultural regions. When transport costs fell, these agglomerations persisted. In late-developing countries, transport costs fell before structural transformation. To exploit urban scale economies, manufacturing agglomerated in relatively few, often coastal, locations. Consistent with this explanation, countries that developed earlier are more spatially equal in their distribution of education and economic activity than late developers.
Urbanization in the Developing World Henderson, J. Vernon; Turner, Matthew A.
The Journal of economic perspectives,
08/2020, Letnik:
34, Številka:
3
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We describe patterns of urbanization in the developing world and the extent to which they differ from the developed world. We consider the extent to which urbanization in the developing world can be ...explained by conventional models of spatial equilibrium. Despite their relative poverty, developing world cities are relatively highly productive and often provide good access to safe water, improved sanitation, schooling, and inoculations. In some parts of the world, they are home to a surprisingly small number of factory workers and a surprisingly large number of farmers. Developing world cities seem to do less well at protecting their residents from lifestyle diseases and crime, their female residents from domestic violence, and their children from illness. In thinking about these facts, we note that one strand of the literature focused on structural transformation has suggested that urbanization in the developing is occurring “too early,” while another strand argues that urbanization is occurring “too slow” to be consistent with conventional models of spatial equilibrium. Despite many differences between developing and developed world cities, our new results combined with those in the literature suggest that models of spatial equilibrium can be adapted as a useful guide to understanding the urbanization process in the developing world.
Measuring Economic Growth from Outer Space Henderson, J. Vernon; Storeygard, Adam; Weil, David N.
The American economic review,
04/2012, Letnik:
102, Številka:
2
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We develop a statistical framework to use satellite data on night lights to augment official income growth measures. For countries with poor national income accounts, the optimal estimate of growth ...is a composite with roughly equal weights on conventionally measured growth and growth predicted from lights. Our estimates differ from official data by up to three percentage points annually. Using lights, empirical analyses of growth need no longer use countries as the unit of analysis; we can measure growth for sub- and supranational regions. We show, for example, that coastal areas in sub-Saharan Africa are growing slower than the hinterland.
Summary
Problems with tracheal intubation are infrequent but are the most common cause of anaesthetic death or brain damage. The clinical situation is not always managed well. The Difficult Airway ...Society (DAS) has developed guidelines for management of the unanticipated difficult tracheal intubation in the non‐obstetric adult patient without upper airway obstruction. These guidelines have been developed by consensus and are based on evidence and experience. We have produced flow‐charts for three scenarios: routine induction; rapid sequence induction; and failed intubation, increasing hypoxaemia and difficult ventilation in the paralysed, anaesthetised patient. The flow‐charts are simple, clear and definitive. They can be fully implemented only when the necessary equipment and training are available. The guidelines received overwhelming support from the membership of the DAS.
Disclaimer: It is not intended that these guidelines should constitute a minimum standard of practice, nor are they to be regarded as a substitute for good clinical judgement.
Measuring urban economic density Henderson, J. Vernon; Nigmatulina, Dzhamilya; Kriticos, Sebastian
Journal of urban economics,
September 2021, 2021-09-00, Letnik:
125
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At the heart of urban economics are agglomeration economies, which drive the existence and extent of cities. This paper estimates urban agglomeration effects, exploring simple and very nuanced ...measures of economic density to explain household income and wage differences across cities in six Sub-Saharan African countries. A key aspect of the work is that we define cities consistently across space based on fine scale density measures, in order to gauge the economic extent of the city. The evidence suggests that more nuanced measures of density, which attempt to capture within-city differences in the extent of clustering, do no better than a simple density measure in explaining income differences across cities. However, total population is a poor measure. We find large wage gains to being in denser cities in Sub-Saharan Africa, generally larger than such estimates for other parts of the world. We also find extraordinary household income gains to density that are far greater than wage ones. Such gains help explain the pull forces driving rapid urbanization in the region.
We investigate how urban railroad and highway configurations have influenced urban form in Chinese cities since 1990. Each radial highway displaces 4% of central city population to surrounding ...regions, and ring roads displace about an additional 20%, with stronger effects in the richer coastal and central regions. Each radial railroad reduces central city industrial GDP by about 20%, with ring roads displacing an additional 50%. We provide evidence that radial highways decentralize service sector activity, radial railroads decentralize industrial activity, and ring roads decentralize both. Historical transportation infrastructure provides identifying variation in more recent measures of infrastructure.
Building functional cities Henderson, J. Vernon; Venables, Anthony J.; Regan, Tanner ...
Science,
05/2016, Letnik:
352, Številka:
6288
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The literature views many African cities as dysfunctional with a hodgepodge of land uses and poor "connectivity." One driver of inefficient land uses is construction decisions for highly durable ...buildings made under weak institutions. In a novel approach, we model the dynamics of urban land use with both formal and slum dwellings and ongoing urban redevelopment to higher building heights in the formal sector as a city grows. We analyze the evolution of Nairobi using a unique high–spatial resolution data set. The analysis suggests insufficient building volume through most of the city and large slum areas with low housing volumes near the center, where corrupted institutions deter conversion to formal sector usage.
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