TonB or not TonB: is that the question?

Bacteria are able to survive in low-iron environments by sequestering this metal ion from iron-containing proteins and other biomolecules such as transferrin, lactoferrin, heme, hemoglobin, or other heme-containing proteins. In addition, many bacteria secrete specific low molecular weight iron chelators termed siderophores. These iron sources are transported into the Gram-negative bacterial cell through an outer membrane receptor, a periplasmic binding protein (PBP), and an inner membrane ATP-binding cassette (ABC) transporter. In different strains the outer membrane receptors can bind and transport ferric siderophores, heme, or Fe3+ as well as vitamin B12, nickel complexes, and carbohydrates. The energy that is required for the active transport of these substrates through the outer membrane receptor is provided by the TonB/ExbB/ExbD complex, which is located in the cytoplasmic membrane. In this minireview, we will briefly examine the three-dimensional structure of TonB and the current models for the mechanism of TonB-dependent energy transduction. Additionally, the role of TonB in colicin transport will be discussed.     

Xenografts: are the risks so great that we should not proceed?

Animal organs could save patients needing transplants, but further research is necessary to resolve remaining problems with organ rejection. Furthermore, xenotransplantation risks transmitting animal pathogens to patients and to the general population. It would be unethical to proceed with clinical trials before principles and procedures for dealing with this risk are in place.     

Autism: not interested or not 'tuned-in'?

Recent studies of perceptual adaptation to faces have revolutionised our understanding of neural mechanisms that support face recognition. A new study has applied this approach to autistic spectrum disorders, revealing severe deficits in such adaptation.     

Pannexin: to gap or not to gap, is that a question?

Vertebrates express two families of gap junction proteins: the well characterized connexins and the recently discovered pannexins. The latter are related to invertebrate innexins. Here we present the hypothesis that pannexins, rather than providing a redundant system to gap junctions formed by connexins, exert a physiological role as nonjunctional membrane channels. Specifically, we propose that pannexins can serve as ATP release channels. This function presumptively is also performed by innexins in invertebrates, in addition to their traditional gap junction role.     

Summer mastitis: vector transmission or not?

Summer mastitis is on acute, suppurative infection of cattle with considerable importance to European agriculture. The causative bacteria are thought to be transmitted by the fly Hydrotaea irritans (L.) but evidence for this remains circumstantial. In this article, Eric Hillerton presents a working hypothesis to explain the transmission mechanism.     

Monozygotic twins: genes are not the destiny?

Monozygotic twins are considered to be genetically identical, yet can show high discordance in their phenotypes and disease susceptibility. Several studies have emphasized the influence of external factors and the role of epigenetic polymorphism in conferring this variability. However, some recent high-resolution studies on DNA methylation show contradicting evidence, which poses questions on the extent of epigenetic variability between twins. The advent of next-generation sequencing technologies now allow us to interrogate multiple epigenomes on a massive scale and understand the role of epigenetic modification, especially DNA methylation, in regulating complex traits. This article briefly discusses the recent key findings, unsolved questions in the area, and speculates on the future directions in the field.     

Density dependence tests,are they?

A large number of time series of abundances of insects and birds from a variety of data sets were submitted to a new density dependence test. The results varied enormously between data sets, but the relation between the frequency of statistically significant density dependence (SSDD) and the length of the series was similar to that of the power curve of the test, making the results consistent with the hypothesis of the density-dependent model being universally applicable throughout the data used. Pest and non-pest species did not differ in the incidence of SSDD. The more sampling error present in the data, the higher the percentages of SSDD. This was expected given that the power of the test increases with increasing sampling error in the data. Many of the data used here, as well as in the literature, clearly violate the basic assumption of the test that the organism concerned should be univoltine and semelparous. Yet the incidence of SSDD was the same in univoltine as in bi/polyvoltine species and the same in semelparous organisms as in birds that are reproductively active in more than one year. The seasonal migrant Autographa gamma in Britain and Czechoslovakia and even rainfall data were found to have SSDD. Statistical significance, however, does not automatically lead to the conclusion of density-dependent regulation. Any series of random variables which are in a stochastic equilibrium, such as a series of independent, identically distributed, random variables, is typically described better by the alternative (density-dependent) model than by the null (density-independent) model. Significant test results were often obtained with sloppy data, with data that clearly violate the basic assumptions of the test and with other data where an interpretation of the results in terms of densitydependent regulation was absurd. Given the fact that other explanations have to be found for significant test results for all these cases, mechanisms other than regulation may very well be applicable too where the data are entirely appropriate for the test. The test is simply a data-based choice between a model without and one with a stochastic equilibrium. A time series as such does not contain any information about the causes of the fluctuation pattern, so that one cannot expect statistics to produce such information from that time series. A significant test result using suitable data is entirely consistent with the hypothesis of density-dependent regulation, but also with any other suitable hypotheses. Because the test results were generally consistent with the hypothesis of a universal applicability of the density-dependence model, a negative test result may only mean that the time series was not long enough for the density dependence that was present to become statistically significant. Positive results are difficult to interpret, but so are negative results. A final decision needs to be based not so much on the test result as on much detailed information about the population concerned. Because the density-dependence test does not test for the presence of the mechanism of density-dependent regulation and because of the loaded, multiple meanings of the term density-dependence, calling the test a test of statistical density dependence may be preferable.     

TPX or not TPX?

An Aurora A regulatory module has been identified in two different proteins: TPX2 in Xenopus laevis and TPXL-1 in C. elegans. The diverse roles of these two proteins in spindle assembly leave us to beckon the true C. elegans TPX2 ortholog to center stage.