Nonlinear scaling of foraging contacts with rodent population density

Density‐dependent shifts in population processes like territoriality, reproduction, dispersal, and parasite transmission are driven by changes in contacts between individuals. Despite this, surprisingly little is known about how contacts change with density, and thus the mechanisms driving density‐dependent processes. A simple linear contact–density function is often assumed, but this is not based on a sound basis of empirical data. We addressed this question using a replicated, semi‐natural experiment in which we measured contacts at feeding stations between multimammate mice, Mastomys natalensis, across ten distinct, linearly increasing densities between 10 and 272 animals/ha. Unexpectedly, unique contacts increased not linearly but sigmoidally with density, which we attribute to the species’ scramble competition mating system, small‐scale dominance/avoidance and absence of territoriality. These results provide new insights into how species’ characteristics can relate to density‐dependent changes in contacts, and the unexpected shape of the contact–density function warrants that density‐dependence in ecological models, such as parasite transmission models, must be parameterized with care.     

Comparative maps of motion and assembly of filamentous actin and myosin II in migrating cells

To understand the mechanism of cell migration, one needs to know how the parts of the motile machinery of the cell are assembled and how they move with respect to each other. Actin and myosin II are thought to be the major structural and force-generating components of this machinery (Mitchison and Cramer, 1996; Parent, 2004). The movement of myosin II along actin filaments is thought to generate contractile force contributing to cell translocation, but the relative motion of the two proteins has not been investigated. We use fluorescence speckle and conventional fluorescence microscopy, image analysis, and computer tracking techniques to generate comparative velocity and assembly maps of actin and myosin II over the entire cell in a simple model system of persistently migrating fish epidermal keratocytes. The results demonstrate contrasting polarized assembly patterns of the two components, indicate force generation at the lamellipodium-cell body transition zone, and suggest a mechanism of anisotropic network contraction via sliding of myosin II assemblies along divergent actin filaments.     

Over-expression and refolding of MAP kinase phosphatase 3

MAP kinase phosphatase 3 (MKP3, also known as DUSP6 and PYST1) is involved in extracellular signal receptor kinase (ERK) regulation and functions as a specific phosphatase to the activated (phosphorylated) forms of ERK1 and ERK2. MKP3 displays allosteric activation, which aids in tightly regulating its function to ERK substrates, but not other related MAPKs. Due to MKP3's specificity for the ERK signaling pathway, the development of specific activators or inhibitors to the enzyme have been suggested in order to expressly influence the ERK1 and ERK2 pathways. To produce the high yields of MKP3 protein necessary for physico-chemical characterization of MKP3 and for high throughput screening of its small-molecule activators and inhibitors, we have cloned, purified and, and identified refolding conditions suitable for producing full-length, human MKP3 from Escherichia coli inclusion bodies. Furthermore, we demonstrate the use of a 96-well plate format refolding assay in which the ERK-induced activity of MKP3 is simulated by 33% DMSO. The assay allowed for rapid detection of MKP3's function following a refolding screen in the absence of ERK and thus provides quick and inexpensive testing of MKP3 activity. Following screening, the refolded product was confirmed to be correctly folded by steady-state kinetic analysis and by the CD spectroscopy-determined secondary structure content. CD data were consistent with 36% helix and 14% sheet, which compared to an expected 32.9% helix and 12.4% sheet. These data indicated that MKP3 was properly folded, making it a suitable protein for use in functional studies.     

Bayesian multisensory integration and cross-modal spatial links.

Our perception of the word is the result of combining information between several senses, such as vision, audition and proprioception. These sensory modalities use widely different frames of reference to represent the properties and locations of object. Moreover, multisensory cues come with different degrees of reliability, and the reliability of a given cue can change in different contexts. The Bayesian framework--which we describe in this review--provides an optimal solution to deal with this issue of combining cues that are not equally reliable. However, this approach does not address the issue of frames of references. We show that this problem can be solved by creating cross-modal spatial links in basis function networks. Finally, we show how the basis function approach can be combined with the Bayesian framework to yield networks that can perform optimal multisensory combination. On the basis of this theory, we argue that multisensory integration is a dialogue between sensory modalities rather that the convergence of all sensory information onto a supra-modal area.     

Genome sequence of the probiotic strain Bifidobacterium animalis subsp. lactis CNCM I-2494

Bifidobacterium animalis subsp. lactis CNCM I-2494 is part of a commercialized fermented dairy product with documented health benefits revealed by multiple randomized placebo-controlled clinical trials. Here we report the complete genome sequence of this strain, which has a circular genome of 1,943,113 bp with 1,660 open reading frames and 4 ribosomal operons.     

No short‐ or long‐term effects of geolocator attachment detected in Pied Flycatchers Ficedula hypoleuca

Tracking small passerines using miniaturized location tags is a rapidly expanding field of study. In a 1‐year study, we tested whether there were any short‐ or longer‐term effects of fitting geolocators weighing 3% of body mass on male Pied Flycatchers Ficedula hypoleuca. In the deployment year, we compared adult provisioning rates to nestlings, nestling growth and nest success between nesting attempts in which adult males were fitted with a geolocator, with control nests where males had the same capture history but were not tagged. We found no difference between treatments in provisioning effort by males or their associated female 2 days after geolocator fitting, in terms of nestling growth, subsequent brood reduction or nest success. Return rate, arrival date on territories, nest timing and breeding parameters were compared between tagged and untagged males in the following breeding season. We found no difference in return rate or arrival date, and no difference in nest timing, fecundity or outcome. Our study suggests that fitting lightweight tags to small passerines need not affect behaviour, breeding or apparent between‐year survival. However, tagging new species should still require assessment and comparison with well‐matched control cohorts, and it should be recognized that tag effects could vary between years and populations, mediated by environmental conditions.     

Notch1 is essential for postnatal hair follicle development and homeostasis

Notch genes encode evolutionarily conserved large, single transmembrane receptors, which regulate many cell fate decisions and differentiation processes during fetal and postnatal life. Multiple Notch receptors and ligands are expressed in both developing and adult epidermis and hair follicles. Proliferation and differentiation of these two ectodermal-derived structures have been proposed to be controlled in part by the Notch pathway. Whether Notch signaling is involved in postnatal hair homeostasis is currently unknown. Here, we investigate and compare the role of the Notch1 receptor during embryonic hair follicle development and postnatal hair homeostasis using Cre-loxP based tissue specific and inducible loss-of-function approaches. During embryonic development, tissue-specific ablation of Notch1 does not perturb formation and patterning of hair follicle placodes. However, Notch1 deficient hair follicles invaginate prematurely into the dermis. Embryonic as well as postnatal inactivation of Notch1 shortly after birth or in adult mice results in almost complete hair loss followed by cyst formation. The first hair cycle of Notch1 deficient mice is characterized by shortened anagen and a premature entry into catagen. These data show that Notch1 is essential for late stages of hair follicle development during embryogenesis as well as for post-natal hair follicle development and hair homeostasis.     

Proteomic analysis of nuclear proteins from proliferative and differentiated human colonic intestinal epithelial cells

Self-renewing tissues such as the intestine contain progenitor proliferating cells which subsequently differentiate. Cell proliferation and differentiation involve gene regulation processes which take place in the nucleus. A human intestinal epithelial cell line model (Caco2/TC7) which reproduces these dynamic processes has been used to perform proteomic studies on nuclear proteins. Nuclei from Caco2/TC7 cells at proliferative and differentiated stages were purified by subcellular fractionation. After two-dimensional gel electrophoresis separation and ruthenium staining, 400 protein spots were detected by image analysis. Eighty-five spots corresponding to 60 different proteins were identified by matrix-assisted laser desorption/ionization mass spectrometry in nuclei from proliferative cells. Comparison of nuclear proteomes from proliferative or differentiated cells by differential display resulted in the identification of differentially expressed proteins such as nucleolin, hnRNP A2/B1 and hnRNP A1. By using Western blot analysis, we found that the expression and number of specific isoforms of these nuclear proteins decreased in differentiated cells. Immunocytochemistry experiments also showed that in proliferative cells nucleolin was distributed in nucleoli-like bodies. In contrast, hnRNPs A2/B1 and A1 were dispersed throughout the nucleus. This study of the nuclear proteome from intestinal epithelial cells represents the first step towards the establishment of a protein database which will be a valuable resource in future studies on the differential expression of nuclear proteins in response to physiological, pharmacological and pathological modulations.