A maize thiamine auxotroph is defective in shoot meristem maintenance

Plant shoots undergo organogenesis throughout their life cycle via the perpetuation of stem cell pools called shoot apical meristems (SAMs). SAM maintenance requires the coordinated equilibrium between stem cell division and differentiation and is regulated by integrated networks of gene expression, hormonal signaling, and metabolite sensing. Here, we show that the maize (Zea mays) mutant bladekiller1-R (blk1-R) is defective in leaf blade development and meristem maintenance and exhibits a progressive reduction in SAM size that results in premature shoot abortion. Molecular markers for stem cell maintenance and organ initiation reveal that both of these meristematic functions are progressively compromised in blk1-R mutants, especially in the inflorescence and floral meristems. Positional cloning of blk1-R identified a predicted missense mutation in a highly conserved amino acid encoded by thiamine biosynthesis2 (thi2). Consistent with chromosome dosage studies suggesting that blk1-R is a null mutation, biochemical analyses confirm that the wild-type THI2 enzyme copurifies with a thiazole precursor to thiamine, whereas the mutant enzyme does not. Heterologous expression studies confirm that THI2 is targeted to chloroplasts. All blk1-R mutant phenotypes are rescued by exogenous thiamine supplementation, suggesting that blk1-R is a thiamine auxotroph. These results provide insight into the role of metabolic cofactors, such as thiamine, during the proliferation of stem and initial cell populations.     

Explaining Disparities in Use of Skilled Birth Attendants in Developing Countries: A Conceptual Framework

Despite World Health Organization recommendations that all women deliver with a skilled birth attendant (SBA), research continues to demonstrate large disparities in use of SBAs by socioeconomic status (SES). Yet few quantitative studies empirically examine the factors underlying these disparities, due in part to the fact that current models do not provide clear pathways—with measurable mediators—for how distal factors like SES may affect maternal health-seeking behaviors like delivering with SBAs. We propose the Disparities in Skilled Birth Attendance (DiSBA) framework for examining the determinants of use of SBAs. We posit that three proximal factors directly affect use of SBAs: perceived need, perceived accessibility of maternal health services, and perceived quality of care. Distal factors like SES affect use of SBAs indirectly through these proximal factors, and the effects can be measured. We test the assumptions of the DiSBA framework using data from the Ghana Maternal Health Survey. The analytic techniques we use include logistic regression with mediation analysis to examine the intervening effects. We find that our proxies for perceived access, perceived need, and perceived quality of care account for approximately 23% of the difference between women with no education and those with primary school education, and about 55% of the difference between women in the lowest wealth quintile and those in the middle wealth quintiles. This study suggests that proximal factors are worthy of increased attention in terms of measurement, data collection, analysis, programmatic efforts, and policy interventions, as these factors are potentially more amenable to change than the distal factors. The effects of proximal factors are also likely context specific, thus sufficient understanding in different contexts is essential to developing appropriate interventions.     

Design and synthesis of MMP inhibitors with appended fluorescent tags for imaging and visualization of matrix metalloproteinase enzymes

We describe the synthesis, MMP-2 and 9 potency, and in vitro evaluation of a series of α-sulfone hydroxmate MMP inhibitors conjugated to a series of dyes with different absorption/emission lamina maxima’s that can be used to visualize tumors.     

Patterns of characterization in folktales across geographic regions and levels of cultural complexity

Literary scholars are generally suspicious of the concept of universals: there are presently no candidates for literary universals that a high proportion of literary scholars would accept as valid. This paper reports results from a content analysis of patterns of characterization in folktales from 48 culture areas, aimed at identifying patterns of characterization that apply across regions of the world and levels of cultural complexity. The search for these patterns was guided by evolutionary theory and the findings are consistent with previous research on patterns of altruism, sex differences in mate preferences, sex differences in reproductive strategy, and differing emphases on male and female physical attractiveness. World literature, especially originally oral literature, represents a vast and neglected repository of information that researchers can use to more precisely map the contours of human nature. Jonathan Gottschall received his Ph.D. in English from Binghamton University and now teaches at St. Lawrence University in Canton, New York. His research focuses on integrating Darwinian approaches to human behavior and psychology with literary studies. The other authors are undergraduate students at St. Lawrence University.     

Protein-level fluctuation correlation at the microcolony level and its application to the Vibrio harveyi quorum-sensing circuit

Gene expression is stochastic, and noise that arises from the stochastic nature of biochemical reactions propagates through active regulatory links. Thus, correlations in gene-expression noise can provide information about regulatory links. We present what to our knowledge is a new approach to measure and interpret such correlated fluctuations at the level of single microcolonies, which derive from single cells. We demonstrated this approach mathematically using stochastic modeling, and applied it to experimental time-lapse fluorescence microscopy data. Specifically, we investigated the relationships among LuxO, LuxR, and the small regulatory RNA qrr4 in the model quorum-sensing bacterium Vibrio harveyi. Our results show that LuxR positively regulates the qrr4 promoter. Under our conditions, we find that qrr regulation weakly depends on total LuxO levels and that LuxO autorepression is saturated. We also find evidence that the fluctuations in LuxO levels are dominated by intrinsic noise. We furthermore propose LuxO and LuxR interact at all autoinducer levels via an unknown mechanism. Of importance, our new method of evaluating correlations at the microcolony level is unaffected by partition noise at cell division. Moreover, the method is first-order accurate and requires less effort for data analysis than single-cell-based approaches. This new correlation approach can be applied to other systems to aid analysis of gene regulatory circuits.     

Non-native ecosystem engineer alters estuarine communities

Many ecosystems are created by the presence of ecosystem engineers that play an important role in determining species' abundance and species composition. Additionally, a mosaic environment of engineered and non-engineered habitats has been shown to increase biodiversity. Non-native ecosystem engineers can be introduced into environments that do not contain or have lost species that form biogenic habitat, resulting in dramatic impacts upon native communities. Yet, little is known about how non-native ecosystem engineers interact with natives and other non-natives already present in the environment, specifically whether non-native ecosystem engineers facilitate other non-natives, and whether they increase habitat heterogeneity and alter the diversity, abundance, and distribution of benthic species. Through sampling and experimental removal of reefs, we examine the effects of a non-native reef-building tubeworm, Ficopomatus enigmaticus, on community composition in the central Californian estuary, Elkhorn Slough. Tubeworm reefs host significantly greater abundances of many non-native polychaetes and amphipods, particularly the amphipods Monocorophium insidiosum and Melita nitida, compared to nearby mudflats. Infaunal assemblages under F. enigmaticus reefs and around reef's edges show very low abundance and taxonomic diversity. Once reefs are removed, the newly exposed mudflat is colonized by opportunistic non-native species, such as M. insidiosum and the polychaete Streblospio benedicti, making removal of reefs a questionable strategy for control. These results show that provision of habitat by a non-native ecosystem engineer may be a mechanism for invasional meltdown in Elkhorn Slough, and that reefs increase spatial heterogeneity in the abundance and composition of benthic communities.     

The role of temporal generalization in a temporal discrimination task

Two experiments trained rats to discriminate two or three stimulus durations using a temporal discrimination task. A standard peak shift effect was observed when training was administered with short versus long signals in Experiment 1. Both discrimination accuracy scores and the generalization gradients revealed that shorter intervals were discriminated more accurately, which may be due to the scalar property of timing. In Experiment 2, three signals (short, medium, and long) were associated with three different responses, or two of the intervals were associated with one response (short and long or short and medium) and the other interval with a different response. Here, the short/medium versus long discrimination was learned most readily of the three tasks. The results of both experiments indicated a strong contribution of learning of individual durations combined with scalar generalization gradients, but Experiment 2 indicated that categorical encoding of durations may have also been operating.     

Cutting edge: a role for B lymphocyte stimulator in systemic lupus erythematosus

Increased levels of B lymphocyte stimulator (BLyS) are associated with systemic autoimmunity in animal models of spontaneous autoimmune disease, and transgenic animals expressing BLyS develop typical autoimmune disease. Here, we demonstrate significant elevations of BLyS in the patients with systemic lupus erythematosus (SLE). The BLyS isolated from the sera of SLE patients had the same m.w. as the natural soluble form and was able to stimulate B cell activation in vitro. Increased BLyS in SLE patients was partially associated with higher levels of anti-dsDNA Ab of the IgG, IgM, and IgA classes, but not associated with the disease activity. Our results suggest that BLyS may be a useful marker for early activation of an autoimmune diathesis and likely plays a critical role in triggering activation of self-Ag-driven autoimmune B cells in human SLE. BLyS may provide an effective therapeutic target in systemic autoimmunity.