454 research outputs found
Keratins and protein synthesis: the plot thickens
In addition to protecting epithelial cells from mechanical stress, keratins regulate cytoarchitecture, cell growth, proliferation, apoptosis, and organelle transport. In this issue, Vijayaraj et al. (2009. J. Cell Biol. doi:10.1083/jcb.200906094) expand our understanding of how keratin proteins participate in the regulation of protein synthesis through their analysis of mice lacking the entire type II keratin gene cluster
The Mass-Loss Induced Eccentric Kozai Mechanism: A New Channel for the Production of Close Compact Object-Stellar Binaries
Over a broad range of initial inclinations and eccentricities an appreciable
fraction of hierarchical triple star systems with similar masses are
essentially unaffected by the Kozai-Lidov mechanism (KM) until the primary in
the central binary evolves into a compact object. Once it does, it may be much
less massive than the other components in the ternary, enabling the "eccentric
Kozai mechanism (EKM):" the mutual inclination between the inner and outer
binary can flip signs driving the inner binary to very high eccentricity,
leading to a close binary or collision. We demonstrate this "Mass-loss Induced
Eccentric Kozai" (MIEK) mechanism by considering an example system and defining
an ad-hoc minimal separation between the inner two members at which tidal
affects become important. For fixed initial masses and semi-major axes, but
uniform distributions of eccentricity and cosine of the mutual inclination,
~10% of systems interact tidally or collide while the primary is on the MS due
to the KM or EKM. Those affected by the EKM are not captured by earlier
quadrupole-order secular calculations. We show that fully ~30% of systems
interact tidally or collide for the first time as the primary swells to AU
scales, mostly as a result of the KM. Finally, ~2% of systems interact tidally
or collide for the first time after the primary sheds most of its mass and
becomes a WD, mostly as a result of the MIEK mechanism. These findings motivate
a more detailed study of mass-loss in triple systems and the formation of close
NS/WD-MS and NS/WD-NS/WD binaries without an initial common envelope phase.Comment: 12 pages, 6 figures, 1 table. Accepted for publication in ApJ. For a
brief video explaining this paper, see http://youtu.be/4CdTOF17q5
Comparing process-based and constraint-based approaches for modeling macroecological patterns
Ecological patterns arise from the interplay of many different processes, and
yet the emergence of consistent phenomena across a diverse range of ecological
systems suggests that many patterns may in part be determined by statistical or
numerical constraints. Differentiating the extent to which patterns in a given
system are determined statistically, and where it requires explicit ecological
processes, has been difficult. We tackled this challenge by directly comparing
models from a constraint-based theory, the Maximum Entropy Theory of Ecology
(METE) and models from a process-based theory, the size-structured neutral
theory (SSNT). Models from both theories were capable of characterizing the
distribution of individuals among species and the distribution of body size
among individuals across 76 forest communities. However, the SSNT models
consistently yielded higher overall likelihood, as well as more realistic
characterizations of the relationship between species abundance and average
body size of conspecific individuals. This suggests that the details of the
biological processes contain additional information for understanding community
structure that are not fully captured by the METE constraints in these systems.
Our approach provides a first step towards differentiating between process- and
constraint-based models of ecological systems and a general methodology for
comparing ecological models that make predictions for multiple patterns.Comment: 45 pages, 3 main figures, 3 tables, 2 appendices. arXiv admin note:
text overlap with arXiv:1308.073
Metastudies for Robust Tests of Theory
We describe and demonstrate an empirical strategy useful for discovering and replicating empirical effects in psychological science. The method involves the design of a metastudy, in which many independent experimental variables—that may be moderators of an empirical effect—are indiscriminately randomized. Radical randomization yields rich datasets that can be used to test the robustness of an empirical claim to some of the vagaries and idiosyncrasies of experimental protocols and enhances the generalizability of these claims. The strategy is made feasible by advances in hierarchical Bayesian modeling that allow for the pooling of information across unlike experiments and designs and is proposed here as a gold standard for replication research and exploratory research. The practical feasibility of the strategy is demonstrated with a replication of a study on subliminal priming
Decreased levels of keratin 8 sensitize mice to streptozotocin-induced diabetes
AimDiabetes is a result of an interplay between genetic, environmental and lifestyle factors. Keratin intermediate filaments are stress proteins in epithelial cells, and keratin mutations predispose to several human diseases. However, the involvement of keratins in diabetes is not well known. K8 and its partner K18 are the main ?-cell keratins, and knockout of K8 (K8?/?) in mice causes mislocalization of glucose transporter 2, mitochondrial defects, reduced insulin content and altered systemic glucose/insulin control. We hypothesize that K8/K18 offer protection during ?-cell stress and that decreased K8 levels contribute to diabetes susceptibility.MethodsK8-heterozygous knockout (K8+/?) and wild-type (K8+/+) mice were used to evaluate the influence of keratin levels on endocrine pancreatic function and diabetes development under basal conditions and after T1D streptozotocin (STZ)-induced ?-cell stress and T2D high-fat diet (HFD).ResultsMurine K8+/? endocrine islets express ~50% less K8/K18 compared with K8+/+. The decreased keratin levels have little impact on basal systemic glucose/insulin regulation, ?-cell health or insulin levels. Diabetes incidence and blood glucose levels are significantly higher in K8+/? mice after low-dose/chronic STZ treatment, and STZ causes more ?-cell damage and polyuria in K8+/? compared with K8+/+. K8 appears upregulated 5 weeks after STZ treatment in K8+/+ islets but not in K8+/?. K8+/? mice showed no major susceptibility risk to HFD compared to K8+/+.ConclusionPartial K8 deficiency reduces ?-cell stress tolerance and aggravates diabetes development in response to STZ, while there is no major susceptibility to HFD
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