Are populations like a circuit? Comparing isolation by resistance to a new coalescent‐based method

A number of methods commonly used in landscape genetics use an analogy to electrical resistance on a network to describe and fit barriers to movement across the landscape using genetic distance data. These are motivated by a mathematical equivalence between electrical resistance between two nodes of a network and the ‘commute time’, which is the mean time for a random walk on that network to leave one node, visit the other, and return. However, genetic data are more accurately modelled by a different quantity, the coalescence time. Here, we describe the differences between resistance distance and coalescence time, and explore the consequences for inference. We implemented a Bayesian method to infer effective movement rates and population sizes under both these models, and found that inference using commute times could produce misleading results in the presence of biased gene flow. We then used forwards‐time simulation with continuous geography to demonstrate that coalescence‐based inference remains more accurate than resistance‐based methods on realistic data, but difficulties highlight the need for methods that explicitly model continuous, heterogeneous geography.     

The augmentation of human natural killer cell activity by interferon-gamma is not associated with the induction of the interferon-alpha-inducible proteins

Treatment of partly purified large granular lymphocytes (LGL) with either IFN-alpha or IFN-gamma for 2 hr augmented their NK cell activity. This augmentation was completely inhibited by the addition of 10 micrograms/ml of cycloheximide. In contrast, when the effects of IFN-gamma on the synthesis of specific proteins in these cells was directly studied by use of two-dimensional gel electrophoresis, we found that IFN-gamma was unable to induce any of the earlier detected, IFN-alpha/IFN-beta-inducible proteins within 18 hr of incubation. No additional, IFN-gamma-induced proteins were detected in either the partly purified LGL or purified T cells. In contrast, the effects of the two factors were comparable in the glioma cell line 251 MG. This shows i) that the effects of IFN-alpha and IFN-gamma are dependent on the responder cell type, ii) that there exists at least one mechanism that can augment NK cell activity that is not dependent on the increased synthesis of the IFN-alpha-inducible proteins, and iii) that either the nine IFN-alpha-inducible proteins are not involved in any leukocyte function that is augmentable by both IFN-alpha and IFN-gamma, or that the two factors exert their actions in leukocyte through different mechanisms.     

Ion gradients between dental enamel matrix and region of Tomes processes. A secondary ion mass spectrometry analysis in rats

During the ameloblast differentiation stages, variations in the composition of different elements in the enamel matrix occur. The stages are characterized by a certain composition of elements being transported to, or from, the sites of calcification, forming a number of elemental gradients between hard and soft tissues. Sprague--Dawley rat incisor fragments, harbouring secretory ameloblasts, were frozen in liquid nitrogen, dried by sublimation, embedded, ground cut and subjected to quantitative secondary ion mass spectrometry. In addition, rats were perfused with an aldehyde, after which the maxillary incisors were extracted, embedded, ground cut and subjected to secondary ion mass spectrometry imaging. The ion gradients of 12C, 19F, 23Na, 35Cl and 44Ca in the Tomes processes region--enamel matrix interface were mapped. The results showed steep elemental gradients between the Tomes processes region and the enamel matrix, demonstrating preserved barrier functions after fixation. The gradients of 12C, 19F, 23Na and 44Ca were maintained close to, or within, the Tomes processes. The data are in favour of a theory that the Tomes processes region--enamel matrix interface acts as a selectively permeable barrier. © 1998 Chapman & Hall