The origin and early evolution of mitochondria

Complete sequences of numerous mitochondrial, many prokaryotic, and several nuclear genomes are now available. These data confirm that the mitochondrial genome originated from a eubacterial (specifically α-proteobacterial) ancestor but raise questions about the evolutionary antecedents of the mitochondrial proteome.     

The Influence of Whole Grain Products and Red Meat on Intestinal Microbiota Composition in Normal Weight Adults: A Randomized Crossover Intervention Trial

Intestinal microbiota is related to obesity and serum lipid levels, both risk factors for chronic diseases constituting a challenge for public health. We investigated how a diet rich in whole grain (WG) products and red meat (RM) influences microbiota. During a 10-week crossover intervention study, 20 healthy adults consumed two isocaloric diets, one rich in WG products and one high in RM. Repeatedly data on microbiota were assessed by 16S rRNA based denaturing gradient gel electrophoresis (DGGE). A blood sample and anthropometric data were collected. Mixed models and logistic regression were used to investigate effects. Microbiota showed interindividual variability. However, dietary interventions modified microbiota appearance: 8 bands changed in at least 4 participants during the interventions. One of the bands appearing after WG and one increasing after RM remained significant in regression models and were identified as Collinsella aerofaciens and Clostridium sp. The WG intervention lowered obesity parameters, while the RM diet increased serum levels of uric acid and creatinine. The study showed that diet is a component of major relevance regarding its influence on intestinal microbiota and that WG has an important role for health. The results could guide investigations of diet and microbiota in observational prospective cohort studies.

Trial registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT01449383","term_id":"NCT01449383"}}NCT01449383     

Vertebrate anteroposterior patterning: the Xenopus neurectoderm as a paradigm

This review discusses formation of the vertebrate anteroposterior (AP) axis, focusing on the dorsal ectoderm, which gives rise to the nervous system, using the frog Xenopus as a model. After summarizing classical models of AP neural patterning, we describe recent molecular studies that are encouraging re-examination of these models. Such studies have shown that AP ectodermal patterning occurs by the onset of gastrulation, much earlier than previously thought. The identity of tissues that determine AP pattern is discussed, and the definition of the Organizer is reconsidered. The activity of factors secreted by inducing tissues in early patterning decisions is assessed and formulated into a revised model for Xenopus AP neural patterning. Finally, AP ectodermal patterning in Xenopus dorsal ectoderm is compared to that of other germ layers, and to other vertebrates.     

Monophyly of primary photosynthetic eukaryotes: green plants, red algae, and glaucophytes

Between 1 and 1.5 billion years ago, eukaryotic organisms acquired the ability to convert light into chemical energy through endosymbiosis with a Cyanobacterium (e.g.,). This event gave rise to "primary" plastids, which are present in green plants, red algae, and glaucophytes ("Plantae" sensu Cavalier-Smith). The widely accepted view that primary plastids arose only once implies two predictions: (1) all plastids form a monophyletic group, as do (2) primary photosynthetic eukaryotes. Nonetheless, unequivocal support for both predictions is lacking (e.g.,). In this report, we present two phylogenomic analyses, with 50 genes from 16 plastid and 15 cyanobacterial genomes and with 143 nuclear genes from 34 eukaryotic species, respectively. The nuclear dataset includes new sequences from glaucophytes, the less-studied group of primary photosynthetic eukaryotes. We find significant support for both predictions. Taken together, our analyses provide the first strong support for a single endosymbiotic event that gave rise to primary photosynthetic eukaryotes, the Plantae. Because our dataset does not cover the entire eukaryotic diversity (but only four of six major groups in), further testing of the monophyly of Plantae should include representatives from eukaryotic lineages for which currently insufficient sequence information is available.     

Open and closed conformation of the E. coli purine nucleoside phosphorylase active center and implications for the catalytic mechanism.

The crystal structure of the ternary complex of hexameric purine nucleoside phosphorylase (PNP) from Escherichia coli with formycin A derivatives and phosphate or sulphate ions is determined at 2.0 A resolution. The hexamer is found as a trimer of unsymmetric dimers, which are formed by pairs of monomers with active sites in different conformations. The conformational difference stems from a flexible helix (H8: 214-236), which is continuous in one conformer, and segmented in the other. With the continuous helix, the entry into the active site pocket is wide open, and the ligands are bound only loosely ("open" or "loose binding" conformation). By segmentation of the helix (H8: 214-219 and H8': 223-236, separated by a gamma-turn), the entry into the active site is partially closed, the pocket is narrowed and the ligands are bound much more tightly ("closed" or "tight binding" conformation). Furthermore, the side-chain of Arg217 is carried by the moving helix into the active site. This residue, conserved in all homologous PNPs, plays an important role in the proposed catalytic mechanism. In this mechanism, substrate binding takes place in the open, and and the catalytic action occurs in the closed conformation. Catalytic action involves protonation of the purine base at position N7 by the side-chain of Asp204, which is initially in the acid form. The proton transfer is triggered by the Arg217 side-chain which is moved by the conformation change into hydrogen bond distance to Asp204. The mechanism explains the broad specificity of E. coli PNP, which allows 6-amino as well as 6-oxo-nucleosides as substrates. The observation of two kinds of binding sites is fully in line with solution experiments which independently observe strong and weak binding sites for phosphate as well as for the nucleoside inhibitor.     

Early anteroposterior division of the presumptive neurectoderm in Xenopus

We analyze the timing of neural patterning in Xenopus and the mechanism by which the early pattern is generated. With regard to timing, we show that by early gastrula, two domains of the anteroposterior (A/P) pattern exist in the presumptive neurectoderm, since the opl gene is expressed throughout the future neural plate, while the fkh5 gene is expressed only in more posterior ectoderm. By mid-gastrula, this pattern has become more elaborate, with an anterior domain defined by expression of opl and otx2, a middle domain defined by expression of opl and fkh5, and a posterior domain defined by expression of opl, fkh5 and HoxD1. Explant assays indicate that the late blastula dorsal ectoderm is specified as the anterior domain, but is not yet specified as middle or posterior domains. With regard to the mechanism by which the A/P pattern is generated, gain and loss of function assays indicate that quantitatively and qualitatively different factors may be involved in inducing the early A/P neural pattern. These data show that neural patterning occurs early in Xenopus and suggest a molecular basis for initiating this pattern.     

Chromatin,Chromosomen, Gene

Ohne Zusammenfassung     

Die Feinstruktur des Protonephridialsystems von Turbanella cornuta Remane,einem marinen Gastrotrich der Ordnung Macrodasyoidea

Zusammenfassung Die Protonephridien des marinen Gastrotrichs Turbanella cornuta Remane werden elektronenmikroskopisch untersucht. Die Terminalapparate der Macrodasyoidea sind Cyrtocyten. Ein Reusenröhrchen besteht aus acht Längsstäben mit netzartigen Zwischenwänden aus dünnen Fibrillen. Im Lumen des Röhrchens schwingt eine Geißel. Die Wand eines Terminalbechers bildet ein zusätzliches Reusensystem, das mit Poren und Schlitzen versehen ist. Die drei bis vier Cyrtocyten eines Protonephridiums münden in eine Sammelzelle ein. Von dieser geht ein Exkretionsröhrchen mit Treibwimperflamme aus, welches von einer Ausleitungszelle gebildet wird. Die Cyrtocyten der beiden Gastrotrichenordnungen (Chaetonotoidea u. Macrodasyoidea) grenzen sich strukturell gegenüber bisher bekannten Formen dieses Zelltyps ab.

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The fine structure of the protonephridial system of Turbanella cornuta remane, a marine gastrotrich of the order macrodasyoidea

Summary The protonephridial system of the marine gastrotrich Turbanella cornuta Remane was studied with the electron microscope. The terminal cells of the Macrodasyoidea are Cyrtocytes. Each tube for filtration consists of eight longitudinal rods with a net of fine fibrils between them; it contains a single whip. The wall of a terminal cup with its pores and slits is an additional system for filtration. Three or four filtration tubes are ending in a collecting cell. From this cell an excretory channel with one whip formed by an outlet cell arises. The filtration tubes of Macrodasyoidea are similar to those of Chaetonotoidea and differ from other forms of this cell-type.