From Mediterranean shores to central Saharan mountains: key phylogeographical insights from the genus Myrtus

Aim The Mediterranean region is often regarded as a crossroads where species of various origins meet. However, the biogeographical relationships between this region and contiguous Saharan, Macaronesian and Irano‐Turanian regions have not been investigated in detail. The aim of this study was to characterize the phylogeography of the circum‐Mediterranean species Myrtus communis and to investigate the origin of isolated central Saharan populations of Myrtus nivellei. Location The distribution ranges of M. communis from Macaronesia to the Irano‐Turanian region (173 sampled populations) and of M. nivellei in the mountains (Hoggar, Tassili n’Ajjer, Immidir, Tibesti) of the central Sahara (23 populations). Methods Nuclear ribosomal DNA (nrDNA) sequences of Myrtaceae were used to root the phylogeny of Myrtus, and to date its crown node, according to a detailed review of the palaeobotanical records used for multiple fossil calibration. Chloroplast DNA (cpDNA) sequences were analysed through the determination of genetic diversity indices and by statistical phylogeography. Results Both cpDNA and nrDNA markers indicated east–west genetic differentiation within M. communis. During the late Miocene, a key vicariance event affected the previous circum‐Mediterranean distribution of Myrtus, leading to the isolation of eastern populations. During the late Miocene or early Pliocene, two clades diverged: one is now scattered in the Mediterranean Basin and adjacent regions, whereas the other evolved in the western Mediterranean region. The differentiation of lineages during the Plio‐Pleistocene occurred mainly in the western part of the Mediterranean Basin, which has been at the origin of migrations towards Macaronesian islands and Saharan mountains. This is one of the first plant phylogeographical studies to report migrations from the Mediterranean to the Sahara. Main conclusions The genus Myrtus has persisted in the Mediterranean region since at least the Neogene and its biogeography reflects the cumulation of the species’ responses to successive palaeoenvironmental changes. The current distribution of the genus Myrtus in the Mediterranean Basin and in isolated areas, such as the Macaronesian islands and Saharan mountains, can be explained by the striking ability of this plant not only to persist locally in various refugia, but also to migrate.     

The genus Pyrus L. (Rosaceae) in south-west Europe and North Afkica

A multivariate morphometric study of the genus Pyrus in south-west Europe and North Africa shows that five species may be recognized in the area: P. bourgaeana Decne., P. communis L., P. cordata Dew., P. spinosa Forssk, and P. nivalis Jacq. Some valuable characters for identification of these species are proposed. In particular the width of fruit peduncle, petal size, leaf width and petiole length served to discriminate the taxa. Several names such as P. gharbiona Trab., P. cossonii Rehder (|M= P. longipes Balansa ex Coss. & Durieu) and P. boisseriana Buhse, are regarded as synonyms of P. cordata , while P. marnormis Trab. of P. bourgaeana. Consequently a check-list and a key to these species are provided.     

Association of the DNMT3B -579G>T Polymorphism with Risk of Thymomas in Patients with Myasthenia Gravis

Increasing evidence suggests a contribution of epigenetic processes in promoting cancer and autoimmunity. Myasthenia gravis (MG) is an autoimmune disease mediated, in approximately 80% of the patients, by antibodies against the nicotinic acetylcholine receptor (AChR+). Moreover, epithelial tumours (thymomas) are present in about 10-20% of the patients, and there is indication that changes in DNA methylation might contribute to the risk and progression of thymomas. However, the role of epigenetics in MG is still not completely clarified. In the present study we investigated if a common polymorphism (-579G>T: rs1569686) in the promoter of the DNMT3B gene coding for the DNA methyltransferase 3B, an enzyme that mediates DNA methylation, increases the risk to develop MG or MG-associated thymomas. The study polymorphism was selected based on recent reports and a literature meta-analysis suggesting association with increased risk of various types of cancer. We screened 324 AChR+ MG patients (140 males and 184 females, mean age 56.0 ± 16.5 years) and 735 healthy matched controls (294 males and 441 females, mean age 57.3 ± 15.6 years). 94 of the total MG patients had a thymoma. While there was no association with the whole cohort of MG patients, we found a statistically significant association of the DNMT3B-579T allele (OR = 1.51; 95% CI=1.1-2.1, P = 0.01) and the TT homozygous genotype (OR = 2.59; 95% CI=1.4-4.9, P = 0.006) with the risk of thymoma. No association was observed in MG patients without thymoma, even after stratification into clinical subtypes. Present results suggest that the DNMT3B-579T allele might contribute to the risk of developing thymoma in MG patients, particularly in homozygous TT subjects.     

Biomolecular-Solvent Stereodynamic Coupling Probed by Deuteration

Abstract

Thermodynamic interpretation of experiments with isotopically perturbed solvent supports the view that solvent stereodynamics is directly relevant to thermodynamic stability of biomolecules. According with the current understanding of the structure of the aqueous solvent, in any stereodynamic configuration of the latter, connectivity pathways are identifiable for their topologie and order properties. Perturbing the solvent by isotopie substitution or, e.g., by addition of co-solvents, can therefore be viewed as reinforcing or otherwise perturbing these topologie structures.

This microscopic model readily visualizes thermodynamic interpretation. In conclusion, the topologie stereodynamic structures of connectivity pathways in the solvent, as modified by interaction with solutes, acquire a specific thermodynamic and biological significance, and the problem of thermodynamic and functional stability of biomolecules is seen in its full pertinent phase space.     

Dendritic action potentials connect distributed dendrodendritic microcircuits

Lateral inhibition of cells surrounding an excited area is a key property of sensory systems, sharpening the preferential tuning of individual cells in the presence of closely related input signals. In the olfactory pathway, a dendrodendritic synaptic microcircuit between mitral and granule cells in the olfactory bulb has been proposed to mediate this type of interaction through granule cell inhibition of surrounding mitral cells. However, it is becoming evident that odor inputs result in broad activation of the olfactory bulb with interactions that go beyond neighboring cells. Using a realistic modeling approach we show how backpropagating action potentials in the long lateral dendrites of mitral cells, together with granule cell actions on mitral cells within narrow columns forming glomerular units, can provide a mechanism to activate strong local inhibition between arbitrarily distant mitral cells. The simulations predict a new role for the dendrodendritic synapses in the multicolumnar organization of the granule cells. This new paradigm gives insight into the functional significance of the patterns of connectivity revealed by recent viral tracing studies. Together they suggest a functional wiring of the olfactory bulb that could greatly expand the computational roles of the mitral-granule cell network.     

ModelDB: A Database to Support Computational Neuroscience

Wider dissemination and testing of computational models are crucial to the field of computational neuroscience. Databases are being developed to meet this need. ModelDB is a web-accessible database for convenient entry, retrieval, and running of published models on different platforms. This article provides a guide to entering a new model into ModelDB.