68 research outputs found
Boundaries can steer active Janus spheres
The advent of autonomous self-propulsion has instigated research towards making colloidal machines that can deliver mechanical work in the form of transport, and other functions such as sensing and cleaning. While much progress has been made in the last 10 years on various mechanisms to generate self-propulsion, the ability to steer self-propelled colloidal devices has so far been much more limited. A critical barrier in increasing the impact of such motors is in directing their motion against the Brownian rotation, which randomizes particle orientations. In this context, here we report directed motion of a specific class of catalytic motors when moving in close proximity to solid surfaces. This is achieved through active quenching of their Brownian rotation by constraining it in a rotational well, caused not by equilibrium, but by hydrodynamic effects. We demonstrate how combining these geometric constraints can be utilized to steer these active colloids along arbitrary trajectories
Evolutionary factors affecting Lactate dehydrogenase A and B variation in the Daphnia pulex species complex
Background: Evidence for historical, demographic and selective factors affecting enzyme evolution can be
obtained by examining nucleotide sequence variation in candidate genes such as Lactate dehydrogenase (Ldh). Two
closely related Daphnia species can be distinguished by their electrophoretic Ldh genotype and habitat. Daphnia
pulex populations are fixed for the S allele and inhabit temporary ponds, while D. pulicaria populations are fixed for
the F allele and inhabit large stratified lakes. One locus is detected in most allozyme surveys, but genome
sequencing has revealed two genes, LdhA and LdhB.
Results: We sequenced both Ldh genes from 70 isolates of these two species from North America to determine if
the association between Ldh genotype and habitat shows evidence for selection, and to elucidate the evolutionary
history of the two genes. We found that alleles in the pond-dwelling D. pulex and in the lake-dwelling D. pulicaria
form distinct groups at both loci, and the substitution of Glutamine (S) for Glutamic acid (F) at amino acid 229
likely causes the electrophoretic mobility shift in the LDHA protein. Nucleotide diversity in both Ldh genes is much
lower in D. pulicaria than in D. pulex. Moreover, the lack of spatial structuring of the variation in both genes over a
wide geographic area is consistent with a recent demographic expansion of lake populations. Neutrality tests
indicate that both genes are under purifying selection, but the intensity is much stronger on LdhA.
Conclusions: Although lake-dwelling D. pulicaria hybridizes with the other lineages in the pulex species complex,
it remains distinct ecologically and genetically. This ecological divergence, coupled with the intensity of purifying
selection on LdhA and the strong association between its genotype and habitat, suggests that experimental
studies would be useful to determine if variation in molecular function provides evidence that LDHA variants are
adaptive
Stem rust resistance in wheat is suppressed by a subunit of the mediator complex
Stem rust is an important disease of wheat that can be controlled using resistance genes. The gene SuSr-D1 identified in cultivar 'Canthatch' suppresses stem rust resistance. SuSr-D1 mutants are resistant to several races of stem rust that are virulent on wild-type plants. Here we identify SuSr-D1 by sequencing flow-sorted chromosomes, mutagenesis, and map-based cloning. The gene encodes Med15, a subunit of the Mediator Complex, a conserved protein complex in eukaryotes that regulates expression of protein-coding genes. Nonsense mutations in Med15b.D result in expression of stem rust resistance. Time-course RNAseq analysis show a significant reduction or complete loss of differential gene expression at 24h post inoculation in med15b.D mutants, suggesting that transcriptional reprogramming at this time point is not required for immunity to stem rust. Suppression is a common phenomenon and this study provides novel insight into suppression of rust resistance in wheat. Stem rust is an important disease of wheat and resistance present in some cultivars can be suppressed by the SuSr-D1 locus. Here the authors show that SuSr-D1 encodes a subunit of the Mediator Complex and that nonsense mutations are sufficient to abolish suppression and confer stem rust resistance
Effects of Heart Rate Variability Biofeedback in Subjects with Stress-Related Chronic Neck Pain: A Pilot Study
Climate change in arid lands and Native American socioeconomic vulnerability: The case of the Pyramid Lake Paiute Tribe
Heart Rate Variability Biofeedback Intervention for Reduction of Psychological Stress During the Early Postpartum Period
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