Time-resolved fluorescence anisotropy for systems with lifetime and dynamic heterogeneity

The time dependence of the fluorescence anisotropy expected when a fluorophore exists in distinct environments having different fluorescence decay and motional behavior is illustrated by simulation calculations. A wide range of behavior is observed. The analysis of such decays in terms of the underlying physical parameters is also illustrated and discussed. In particular, the analysis of 'associated' heterogeneous behavior using a homogeneous environment model with complex motional behavior is evaluated. It is argued that anisotropy decays that exhibit a high initial anisotropy and that rise at long times must be due to a heterogeneous environment. Anisotropic rotor diffusion cannot give rise to behavior of this type. A similar conclusion is reached for anisotropies that exhibit downward curvature. On the other hand, anisotropy decays that are monotonically decreasing and have a positive second derivative at all times cannot be analyzed in a unique fashion and therefore an ambiguity exists in the interpretation of such data in terms of motional behavior.     

Host exclusion and coexistence in apparent and direct competition: An application of bifurcation theory.

Recent empirical studies have focused attention on the interplay in multi-host systems of parasite-mediated apparent competition and direct competition between hosts. However, theoretical investigation of such systems has been hindered by the onset of algebraic intractability with the increase in system dimensionality. In this paper we circumvent this problem by using a geometric approach in which arrays of bifurcation maps are constructed, each map being structured by the set of (bifurcation) points in parameter space at which qualitative changes in system behaviour take place. From these maps can be compiled a concise catalogue of the possible modes of system behaviour, enabling an investigation of the interaction of apparent and direct competitive forces to be carried out. Of importance is the identification of those situations where increasing one or both of these competitive forces leads to a change in the stability state. The maps provide an efficient way of determining whether, and, if so, under what conditions, specific modes of behaviour are allowed by the model. Two field phenomena of particular interest, discussed in the paper, are host invasion and dominance reversal resulting from the introduction of the pathogen into a directly competitive system.     

Cultural and instrumental approaches to ethnic nationalism

This article identifies a set of assumptions that underlie culturalist approaches to ethnic nationalism and it assesses these assumptions from a particular instrumentalist point of view ‐ collective‐choice theory. It is argued that cultural approaches are structuralist, leaving little room for intentional explanations and, when agent‐centred explanations are used, they are typically embedded within a moral economic theory of groups. In contrast, collective‐choice theory is intentionalist and political‐economic in orientation. From the perspective of these different approaches, the article examines a common dilemma of mobilization in nationalist movements ‐ how popular support can be mobilized by activists who, for entrepreneurial or ideological reasons, have formed a nationalist organization. Empirical illustrations are drawn from interwar Brittany and contemporary Quebec.     

Fighting by Kittens and Piglets during Suckling: What Does it Mean?

Newborn kittens and piglets show some notable similarities in suckling‐associated behaviours. Both develop a pattern of teat use in which each member of the litter predominantly occupies one or two particular nipples or teats, both show agonistic behaviour towards littermates during suckling, and both are born with ‘weapons’–kittens with sharp claws and piglets with sharp needle teeth. Traditionally, the differential use of nipples or teats has been thought to be due to differential quality of the mammary glands. However, neither our findings in kittens nor an examination of the literature on piglets support this view. As mammary glands usually are of equal quality and as there are normally more glands than young, there seems little reason for littermates to fight. Furthermore, there is also little evidence that individual performance in suckling contests or use of ‘weapons’ is related to weight gain or to dominance relations. Given the present lack of satisfying adaptive explanations for the seemingly aggressive behaviour and use of weapons by kittens and piglets, we suggest these to be epiphenomena of developmental processes anticipating the use of these behaviours and structures in later adaptive contexts.     

Submillisecond Elastic Recoil Reveals Molecular Origins of Fibrin Fiber Mechanics

Fibrin fibers form the structural scaffold of blood clots. Thus, their mechanical properties are of central importance to understanding hemostasis and thrombotic disease. Recent studies have revealed that fibrin fibers are elastomeric despite their high degree of molecular ordering. These results have inspired a variety of molecular models for fibrin’s elasticity, ranging from reversible protein unfolding to rubber-like elasticity. An important property that has not been explored is the timescale of elastic recoil, a parameter that is critical for fibrin’s mechanical function and places a temporal constraint on molecular models of fiber elasticity. Using high-frame-rate imaging and atomic force microscopy-based nanomanipulation, we measured the recoil dynamics of individual fibrin fibers and found that the recoil was orders of magnitude faster than anticipated from models involving protein refolding. We also performed steered discrete molecular-dynamics simulations to investigate the molecular origins of the observed recoil. Our results point to the unstructured αC regions of the otherwise structured fibrin molecule as being responsible for the elastic recoil of the fibers.     

β-Catenin-Driven Binary Fate Specification Segregates Germ Layers in Ascidian Embryos

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Highlights? β-catenin nuclear asymmetry after animal-vegetal-oriented cell divisions ? β-catenin nuclear asymmetry drives binary cell fate choices ? Combinatorial codes of nuclear β-catenin activation segregate ascidian germ layers ? Nuclear β-catenin ON-to-OFF activity is required for marginal mesoderm formation     

Proteomics of Breast Muscle Tissue Associated with the Phenotypic Expression of Feed Efficiency within a Pedigree Male Broiler Line: I. Highlight on Mitochondria

As feed represents 60 to 70% of the cost of raising an animal to market weight, feed efficiency (the amount of dry weight intake to amount of wet weight gain) remains an important genetic trait in animal agriculture. To gain greater understanding of cellular mechanisms of feed efficiency (FE), shotgun proteomics was conducted using in-gel trypsin digestion and tandem mass spectrometry on breast muscle samples obtained from pedigree male (PedM) broilers exhibiting high feed efficiency (FE) or low FE phenotypes (n = 4 per group). The high FE group had greater body weight gain (P = 0.004) but consumed the same amount of feed (P = 0.30) from 6 to 7 wk resulting in higher FE (P < 0.001). Over 1800 proteins were identified, of which 152 were different (P < 0.05) by at least 1.3 fold and ≤ 15 fold between the high and low FE phenotypes. Data were analyzed for a modified differential expression (DE) metric (Phenotypic Impact Factors or PIF) and interpretation of protein expression data facilitated using the Ingenuity Pathway Analysis (IPA) program. In the entire data set, 228 mitochondrial proteins were identified whose collective expression indicates a higher mitochondrial expression in the high FE phenotype (binomial probability P < 0.00001). Within the top up and down 5% PIF molecules in the dataset, there were 15 mitoproteome proteins up-regulated and only 5 down-regulated in the high FE phenotype. Pathway enrichment analysis also identified mitochondrial dysfunction and oxidative phosphorylation as the number 1 and 5 differentially expressed canonical pathways (up-regulated in high FE) in the proteomic dataset. Upstream analysis (based on DE of downstream molecules) predicted that insulin receptor, insulin like growth receptor 1, nuclear factor, erythroid 2-like 2, AMP activated protein kinase (α subunit), progesterone and triiodothyronine would be activated in the high FE phenotype whereas rapamycin independent companion of target of rapamycin, mitogen activated protein kinase 4, and serum response factor would be inhibited in the high FE phenotype. The results provide additional insight into the fundamental molecular landscape of feed efficiency in breast muscle of broilers as well as further support for a role of mitochondria in the phenotypic expression of FE.Funding provided by USDA-NIFA (#2013–01953), Arkansas Biosciences Institute (Little Rock, AR), McMaster Fellowship (AUS to WB) and the Agricultural Experiment Station (Univ. of Arkansas, Fayetteville).