Hydrodynamic attraction of swimming microorganisms by surfaces

Cells swimming in confined environments are attracted by surfaces. We measure the steady-state distribution of smooth-swimming bacteria (Escherichia coli) between two glass plates. In agreement with earlier studies, we find a strong increase of the cell concentration at the boundaries. We demonstrate theoretically that hydrodynamic interactions of the swimming cells with solid surfaces lead to their re-orientation in the direction parallel to the surfaces, as well as their attraction by the closest wall. A model is derived for the steady-state distribution of swimming cells, which compares favorably with our measurements. We exploit our data to estimate the flagellar propulsive force in swimming E. coli

Role of a Ubiquitously Expressed Receptor in the Vertebrate Olfactory System

Odorant cues are recognized by receptors expressed on olfactory sensory neurons, the primary sensory neurons of the olfactory epithelium. Odorant receptors typically obey the “one receptor, one neuron” rule, in which the receptive field of the olfactory neuron is determined by the singular odorant receptor that it expresses. Odor-evoked receptor activity across the population of olfactory neurons is then interpreted by the brain to identify the molecular nature of the odorant stimulus. In the present study, we characterized the properties of a C family G-protein-coupled receptor that, unlike most other odorant receptors, is expressed in a large population of microvillous sensory neurons in the zebrafish olfactory epithelium and the mouse vomeronasal organ. We found that this receptor, OlfCc1 in zebrafish and its murine ortholog Vmn2r1, is a calcium-dependent, low-sensitivity receptor specific for the hydrophobic amino acids isoleucine, leucine, and valine. Loss-of-function experiments in zebrafish embryos demonstrate that OlfCc1 is required for olfactory responses to a diverse mixture of polar, nonpolar, acidic, and basic amino acids. OlfCc1 was also found to promote localization of other OlfC receptor family members to the plasma membrane in heterologous cells. Together, these results suggest that the broadly expressed OlfCc1 is required for amino acid detection by the olfactory system and suggest that it plays a role in the function and/or intracellular trafficking of other olfactory and vomeronasal receptors with which it is coexpressed

Role of a Ubiquitously Expressed Receptor in the Vertebrate Olfactory System

Odorant cues are recognized by receptors expressed on olfactory sensory neurons, the primary sensory neurons of the olfactory epithelium. Odorant receptors typically obey the "one receptor, one neuron" rule, in which the receptive field of the olfactory neuron is determined by the singular odorant receptor that it expresses. Odor-evoked receptor activity across the population of olfactory neurons is then interpreted by the brain to identify the molecular nature of the odorant stimulus. In the present study, we characterized the properties of a C family G-protein-coupled receptor that, unlike most other odorant receptors, is expressed in a large population of microvillous sensory neurons in the zebrafish olfactory epithelium and the mouse vomeronasal organ. We found that this receptor, OlfCc1 in zebrafish and its murine ortholog Vmn2r1, is a calcium-dependent, low-sensitivity receptor specific for the hydrophobic amino acids isoleucine, leucine, and valine. Loss-of-function experiments in zebrafish embryos demonstrate that OlfCc1 is required for olfactory responses to a diverse mixture of polar, nonpolar, acidic, and basic amino acids. OlfCc1 was also found to promote localization of other OlfC receptor family members to the plasma membrane in heterologous cells. Together, these results suggest that the broadly expressed OlfCc1 is required for amino acid detection by the olfactory system and suggest that it plays a role in the function and/or intracellular trafficking of other olfactory and vomeronasal receptors with which it is coexpressed

Wild-Derived Inbred Mice Have a Novel Basis of Susceptibility to Polyomavirus-Induced Tumors

Polyomavirus induces a broad array of tumors when introduced into newborn mice of certain standard inbred strains, notably those bearing the H-2(k) haplotype. Susceptibility in these mice is conferred by an endogenous mouse mammary tumor virus superantigen (Mtv-7 sag) that acts to delete T cells required for polyomavirus-induced tumor immunosurveillance. In the present study we show that mice of two wild-derived inbred strains, PERA/Ei (PE) and CZECH II/Ei (CZ), are highly susceptible to polyomavirus but carry no detectable Mtv sag-related sequences and show no evidence of Vβ deletion. C57BR/cdJ (BR) mice, which are H-2(k) but lack the endogenous Mtv-7, are highly resistant based on an effective anti-polyomavirus tumor immune response. When crossed with BR, both PE and CZ mice transmit their susceptibility in a dominant fashion, indicating a mechanism(s) that overrides the immune response of BR. Susceptibility in PE and CZ mice is not based on interference with antigen processing or presentation since cytotoxic T cells from BR can efficiently kill F(1)-derived tumor cells in vitro. The expected precursors of polyomavirus-specific cytotoxic T cells are present in both the wild inbred animals and their F(1) progeny. These findings indicate a novel basis of susceptibility that operates independently of endogenous superantigen and prevents the development of tumor immunity

Neighborhood Social Resources and Depressive Symptoms: Longitudinal Results from the Multi-Ethnic Study of Atherosclerosis

The ways in which a neighborhood environment may affect depression and depressive symptoms have not been thoroughly explored. This study used longitudinal data from 5475 adults in the Multi-Ethnic Study of Atherosclerosis to investigate associations of time-varying depressive symptoms between 2000 and 2012 (measured using the 20-item Center for Epidemiologic Studies Depression Scale (CES-D)) with survey-based measures of neighborhood safety and social cohesion (both individual-level perceptions and neighborhood-level aggregates) and densities of social engagement destinations. Linear mixed models were used to examine associations of baseline cross-sectional associations and cumulative exposures with changes over time in CES-D. Econometric fixed effects models were utilized to investigate associations of within-person changes in neighborhood exposures with within-person changes in CES-D. Adjusting for relevant covariates, higher safety and social cohesion and greater density of social engagement destinations were associated with lower CES-D at baseline. Greater cumulative exposure to these features was not associated with progression of CES-D over 10 years. Within-person increases in safety and in social cohesion were associated with decreases in CES-D, although associations with cohesion were not statistically significant. Social elements of neighborhoods should be considered by community planners and public health practitioners to achieve optimal mental health