Formation of stable epialleles and their paramutation-like interaction in tetraploid Arabidopsis thaliana

Polyploidization is found frequently in plants, and species previously considered to be diploid may show remnants of earlier polyploidization events on closer inspection of their genomes. The success of polyploids may lie in increased genetic redundancy supporting subsequent genetic diversification. Although doubling the genome does not generate diversity per se, recent studies show that rapid genomic rearrangements and changes in DNA modification and gene expression patterns are associated with polyploid formation. But recessive modifications will not become phenotypically apparent in early polyploid generations. Here we show that epialleles in tetraploid plants (but not in diploids) interact in trans and lead to heritable gene silencing persisting after segregation from the inactivating allele. This mechanism, resembling paramutation, leads to the establishment of functional epigenetic homozygosity and, thus, to conversion of new recessive alleles into traits expressed in early polyploid generations. Such interactions probably contribute to rapid adaptation and evolution of polyploid plant species.     

Hypomagnesemia with secondary hypocalcemia is caused by mutations in TRPM6, a new member of the TRPM gene family

Magnesium is an essential ion involved in many biochemical and physiological processes. Homeostasis of magnesium levels is tightly regulated and depends on the balance between intestinal absorption and renal excretion. However, little is known about specific proteins mediating transepithelial magnesium transport. Using a positional candidate gene approach, we identified mutations in TRPM6 (also known as CHAK2), encoding TRPM6, in autosomal-recessive hypomagnesemia with secondary hypocalcemia (HSH, OMIM 602014), previously mapped to chromosome 9q22 (ref. 3). The TRPM6 protein is a new member of the long transient receptor potential channel (TRPM) family and is highly similar to TRPM7 (also known as TRP-PLIK), a bifunctional protein that combines calcium- and magnesium-permeable cation channel properties with protein kinase activity. TRPM6 is expressed in intestinal epithelia and kidney tubules. These findings indicate that TRPM6 is crucial for magnesium homeostasis and implicate a TRPM family member in human disease.     

Characterization of murine interleukin B by a monoclonal antibody

Interleukin B (IL-B), formerly termed BEF (B-cell-derived enhancing factor) or IL-B4, was originally described as a non-immunoglobulin regulatory factor spontaneously produced by B lymphocytes and B-cell lines that enhances the in vitro antigen-driven antibody response of unfractionated spleen cells stimulated by thymus-dependent antigens. Since then we have examined the function of interleukin B in a number of immune reactions, both in vitro and in vivo, and found that it inhibits the activation of suppressor T lymphocytes. We report here the production of two monoclonal antibodies (mAb) that specifically inhibit interleukin B activity. The use of these mAb in the purification and characterization of IL-B is described. IL-B from both normal and transformed B cells consists of two subunits of similar size and amino-acid composition. The structure of interleukin B and its specific behaviour in biological assay distinguish it from many other known lymphokines.     

Levi-Civitasche Parallelverschiebung,affiner Zusammenhang, Übertragungsprinzip: 1916/17–1922/23

Zusammenfassung Der Riemannschen Geometrie fehlte lange Zeit ein zentraler Begriff, nämlich der des Parallelismus. Als Einstein 1916 seiner allgemeinen Relativitätstheorie die Riemannsche Geometrie in Form des damaligen Tensorkalküls (Ricci-Kalkül) zugrunde legte, war dieser ein rein formaler Kalkül ohne geometrische Interpretationen. Diesen Mangel an Geometrie behob die Einführung der Parallelverschiebung, die darüber hinaus auch eine anschaulichere, geometrische Erklärung des Krümmungstensors ermöglichte.Ausgehend von der Levi-Civitaschen Parallelverschiebung schuf Weyl 1918 den für die zukünftige Entwicklung so bedeutenden Begriff des affinen Zusammenhangs, den Schouten 1922 zum Übertragungsprinzip erweiterte. Aus den alten Christoffelsymbolen wurden die neuen , die in Zukunft sowohl in der Relativitätstheorie (Feldtheorie) als auch in der Differentialgeometrie eine fundamentale Rolle spielten. Aus der Differentialgeometrie wurden die (verschiedenen Arten von) Differentialgeometrien, die durch die vorgegebenen Übertragungen definiert waren.Zum 50. Todestag von Tullio Levi-Civita (29. 3. 1873–20. 12. 1941)     

Tools, Objects, and Chimeras: Connes on the Role of Hyperreals in Mathematics

We examine some of Connes’ criticisms of Robinson’s infinitesimals starting in 1995. Connes sought to exploit the Solovay model ${\mathcal{S}}$ as ammunition against non-standard analysis, but the model tends to boomerang, undercutting Connes’ own earlier work in functional analysis. Connes described the hyperreals as both a “virtual theory” and a “chimera”, yet acknowledged that his argument relies on the transfer principle. We analyze Connes’ “dart-throwing” thought experiment, but reach an opposite conclusion. In ${\mathcal{S}}$ , all definable sets of reals are Lebesgue measurable, suggesting that Connes views a theory as being “virtual” if it is not definable in a suitable model of ZFC. If so, Connes’ claim that a theory of the hyperreals is “virtual” is refuted by the existence of a definable model of the hyperreal field due to Kanovei and Shelah. Free ultrafilters aren’t definable, yet Connes exploited such ultrafilters both in his own earlier work on the classification of factors in the 1970s and 80s, and in Noncommutative Geometry, raising the question whether the latter may not be vulnerable to Connes’ criticism of virtuality. We analyze the philosophical underpinnings of Connes’ argument based on Gödel’s incompleteness theorem, and detect an apparent circularity in Connes’ logic. We document the reliance on non-constructive foundational material, and specifically on the Dixmier trace ${-\hskip-9pt\int}$ (featured on the front cover of Connes’ magnum opus) and the Hahn–Banach theorem, in Connes’ own framework. We also note an inaccuracy in Machover’s critique of infinitesimal-based pedagogy.