Inhibition of netrin-mediated axon attraction by a receptor protein tyrosine phosphatase

During axon guidance, the ventral guidance of the Caenorhabditis elegans anterior ventral microtubule axon is controlled by two cues, the UNC-6/netrin attractant recognized by the UNC-40/DCC receptor and the SLT-1/slit repellent recognized by the SAX-3/robo receptor. We show here that loss-of-function mutations in clr-1 enhance netrin-dependent attraction, suppressing ventral guidance defects in slt-1 mutants. clr-1 encodes a transmembrane receptor protein tyrosine phosphatase (RPTP) that functions in AVM to inhibit signaling through the DCC family receptor UNC-40 and its effector, UNC-34/enabled. The known effects of other RPTPs in axon guidance could result from modulation of guidance receptors like UNC-40/DCC.     

Values and the agricultural crisis: Differential problems,solutions, and value constraints

Policies are set by governments in an attempt to bring about desired ends within a society. These ends are often vaguely put and phrased in terms of values. Agrarianism, as a value, has been used to justify current farm policy. Yet, that policy has also been used as a mechanism to solve a variety of problems for the United States: those of the rural sector, farmers themselves, and even the land upon which they farm. This paper tries to separate the problems that are part of the farm crisis and to show how policies designed to solve one of the problems for one set of actors, and frequently defended in the name of agrarianism, may actually exacerbate the problems for other actors. An overarching value, however, that may further inhibit problem solution and lead us further into an expensive and ineffectual farm program is the basic value that planning is somehow bad. Agrarianism and the value of spontaneity underlie some of the current decision-making or lack thereof in the farm program.     

Spatial distribution,architecture, and development of the root system of Pinus banksiana Lamb. in natural and planted stands

In the province of Québec, Canada, the majority of planted jack pine (Pinus banksiana Lamb.) seedlings are produced in rigid wall containers. More than 95% of them exhibit deformations of the root system which may induce stem instability. Studies of the root architecture of planted jack pine have been limited to a 30 cm radius from the stem, as barely any studies have been devoted to naturally regenerated stands. Moreover, only a few researches have focused on temporal evolution of root systems. The aim of the present study was to characterize the architectural, spatial, and temporal development of jack pine roots in natural and planted stands. Study sites were located in the continuous boreal forest of Quebec. The plantation was done in 1987, so that the trees were 15 years old at the time of sampling. Trees from natural stand had regenerated after a fire in 1983 and were 13–16 years old. The root systems of 14 jack pine trees per site were manually excavated up to a <5 mm diameter, without regard to their distance from the stem. The number, length, diameter, and the spatial and temporal development of roots were analyzed according to three scales of root architecture: the root system, axes, and segments. Overall, the numbers and lengths of roots were higher with planted pines. However, naturally regenerated trees displayed a better distribution of their roots around the stem and at depth, combined with more rapid length growth during the first years. In natural stands, all the trees had a taproot and 30% of the main roots originated at a depth of more than 20 cm, and they are regularly distributed around the stems. Planted trees did not present a taproot and 97% of the main roots originated in the first 20 cm beneath the soil surface. Moreover, 50% of root length was located in one-third of the area surrounding the stems, an area that corresponded to the furrow. Finally, the annual development of lateral roots in planted stand displayed a 5-year delay when compared with natural stand, which also affected maximum growth length and development of the branching pattern. Root distribution and temporal development are known to play a major role in the stability of aerial parts. Seedling production methods, container type, site preparation and planting techniques need to be examined in greater detail in order to assess their effect throughout the development of the root system. It is necessary to compare different sylvicultural practices and with natural/planted stands to gain a clearer understanding of this problem.     

Dynamics of 13C‐labeled mustard litter (Sinapis alba) in particle‐size and aggregate fractions in an agricultural cropland with high‐ and low‐yield areas

The application of ¹³C‐labeled litter enables to study decomposition processes as well as the allocation of litter‐derived carbon to different soil C pools. ¹³Carbon‐labeled mustard litter was used in order to compare decomposition processes in an agricultural cropland with high‐yield (HY) and low‐yield (LY) areas, the latter being characterized by a finer texture and a lower organic‐C (OC) content. After tracer application, ¹³C concentrations were monitored in topsoil samples in particulate organic matter (POM) and in fine mineral fractions (silt‐ and clay‐sized fractions). After 568 d, approximately 5% and 10% of the initial ¹³C amount were found in POM fractions of LY and HY areas, respectively. Higher amounts were found in POM occluded in aggregates than in free POM. Medium‐term (0.5–2 y) storage of the initial ¹³C in fine silt‐ and clay‐sized fractions amounts to 10% in HY and LY soils, with faster enrichment but also faster disappearance of the ¹³C signal from LY soils. Amounts of 80%–90% of the added ¹³C were mineralized or leached in the observed period. Decomposition of free POM was faster in HY than in LY areas during the first year, but the remaining ¹³C amounts in occluded‐POM fractions were higher in HY soils after 568 d. High‐yield and low‐yield areas showed different ¹³C dynamics in fine mineral fractions. In LY soils, ¹³C amounts and concentrations in mineral‐associated fractions increased within 160 d after application and decreased in the following time period. In HY areas, a significant increase in ¹³C amounts did not occur until after 568 d. The results indicate initially faster decomposition processes in HY than in LY areas due to different soil conditions, such as soil texture and water regime. The higher silt and clay contents of LY areas seem to promote a faster aggregate formation and turnover, leading to a closer contact between POM and mineral surfaces in this area. This favors the OC storage in fine mineral fractions in the medium term. Lower aggregate formation and turnover in the coarser textured HY soil leads to a delayed C stabilization in silt‐ and clay‐sized fractions.     

Eosinophilia in a cat with acute leukemia

A 4-year-old castrated male domestic shorthaired cat with a history of vomiting and anorexia was diagnosed with leukemia with marked hepatic and splenic infiltration and concurrent eosinophilia with marked tissue infiltration. Despite thorough immunocytochemical and immunohistochemical immunophenotyping, the cell lineage of the leukemia was not identified.     

Fingerprinting sediment sources in the outlet reservoir of a hilly cultivated catchment in Tunisia

Purpose

Approximately 74 % of agricultural soils in Tunisia are affected by water erosion, leading to the siltation of numerous human-made reservoirs and therefore a loss of water storage capacity. The objective of this study was to propose a methodology for estimating the relative contributions of gully/channel bank erosion and surface topsoil erosion to the sediment accumulated in small reservoirs.

Materials and methods

We tested an approach based on the sediment fingerprinting technique for sediments collected from a reservoir (which has been in operation since 1994) at the outlet of a catchment (Kamech, 2.63 km²). Sampling concentrated on the soil surface (in both cropland and grassland), gullies and channel banks. A total of 17 sediment cores were collected along a longitudinal transect of the Kamech reservoir to investigate the origin of the sediment throughout the reservoir. Radionuclides (particularly caesium-137, ¹³⁷Cs) and nutrients (total phosphorus, total nitrogen and total organic carbon (TOC)) were analysed as potential tracers.

Results and discussion

The applications of a mixing model with ¹³⁷Cs alone or ¹³⁷Cs and TOC provided very similar results: The dominant source of sediment was surface erosion, which was responsible for 80 % of the total erosion within the Kamech catchment. Additionally, we showed that the analysis of a single composite core provided information on the sediment origin that was consistent with the analysis of all sediment layers in the core. We demonstrated the importance of the core sampling location within the reservoir for obtaining reliable information regarding sediment sources and the dominant erosion processes.

Conclusions

The dominance of surface erosion processes indicates that conservation farming practices are required to mitigate erosion in the agricultural Kamech catchment. Based on the results from 17 sediment cores, guidelines regarding the number and location of sampling cores to be collected for sediment fingerprinting are proposed. We showed that the collection of two cores limited the sediment source apportionment uncertainty due to the core sampling scheme to <10 %.     

Social capital dimensions in household food security interventions: implications for rural Uganda

We demonstrate that social capital is associated with positive food security outcomes, using survey data from 378 households in rural Uganda. We measured food security with the Household Food Insecurity Access Scale. For social capital, we measured cognitive and structural indicators, with principal components analysis used to identify key factors of the concept for logistic regression analysis. Households with bridging and linking social capital, characterized by membership in groups, access to information from external institutions, and observance of norms in groups, tended to be more food secure. Households with cognitive social capital, characterized by observance of generalized norms and mutual trust, were also more food secure than others. However, we established that social capital is, by itself, insufficient. It needs to be complemented with human capital enhancement. We recommend that development interventions which focus on strengthening community associations and networks to enhance food security should support activities which enhance cognitive social capital and human capital skills. Such activities include mutual goal setting, trust building and clear communication among actors. Education efforts for community members, both formal and non-formal, should also be supported such that they potentially strengthen social capital to improve food security in rural Uganda.     

Efficient inhibition of the Alzheimer's disease beta-secretase by membrane targeting

beta-Secretase plays a critical role in beta-amyloid formation and thus provides a therapeutic target for Alzheimer's disease. Inhibitor design has usually focused on active-site binding, neglecting the subcellular localization of active enzyme. We have addressed this issue by synthesizing a membrane-anchored version of a beta-secretase transition-state inhibitor by linking it to a sterol moiety. Thus, we targeted the inhibitor to active beta-secretase found in endosomes and also reduced the dimensionality of the inhibitor, increasing its local membrane concentration. This inhibitor reduced enzyme activity much more efficiently than did the free inhibitor in cultured cells and in vivo. In addition to effectively targeting beta-secretase, this strategy could also be used in designing potent drugs against other membrane protein targets.