Multiple origins of the cortical γ rhythm

Gamma rhythms (30-80 Hz) are a near-ubiquitous feature of neuronal population activity in mammalian cortices. Their dynamic properties permit the synchronization of neuronal responses to sensory input within spatially distributed networks, transient formation of local neuronal "cell assemblies," and coherent response patterns essential for intercortical regional communication. Each of these phenomena form part of a working hypothesis for cognitive function in cortex. All forms of physiological gamma rhythm are inhibition based, being characterized by rhythmic trains of inhibitory postsynaptic potentials in populations of principal neurons. It is these repeating periods of relative enhancement and attenuation of the responsivity of major cell groups in cortex that provides a temporal structure shared across many millions of neurons. However, when considering the origins of these repeating trains of inhibitory events considerable divergence is seen depending on cortical region studied and mode of activation of gamma rhythm generating networks. Here, we review the evidence for involvement of multiple subtypes of interneuron and focus on different modes of activation of these cells. We conclude that most massively parallel brain regions have different mechanisms of gamma rhythm generation, that different mechanisms have distinct functional correlates, and that switching between different local modes of gamma generation may be an effective way to direct cortical communication streams. Finally, we suggest that developmental disruption of the endophenotype for certain subsets of gamma-generating interneuron may underlie cognitive deficit in psychiatric illness.     

Characterization and Phylogenetic Relationships of Photorhabdus luminescens subsp. sonorensis (γ-Proteobacteria: Enterobacteriaceae), the Bacterial Symbiont of the Entomopathogenic Nematode Heterorhabditis sonorensis (Nematoda: Heterorhabditidae)

Photorhabdus are motile Gram-negative bacteria that have a mutualistic association with Heterorhabditis nematodes (Heterorhabditidae). These bacteria possess peculiar biochemical characteristics such as inability to reduce nitrates, and the capacity to ferment only a limited number of carbohydrates. Heterorhabditis nematodes vector the bacteria from one insect host to another and also provide shelter to the bacteria from soil stressors and antagonists. Once inside the insect host, the bacterial symbionts are released and produce toxins and secondary metabolites and broad-spectrum antibiotics, which kill the host by septicemia within 48 h. At present, three Photorhabdus spp. have been identified: P. luminescens, P. temperata, and P. asymbiotica, and many subspecies have also been described. Characterization of new species and subspecies has been based on sequence data, mostly of the 16S rDNA, and also of a selection of protein coding genes. In addition to this, phenotypic traits including temperature growth, colony morphology, color, light production, carbohydrate response, and assimilation, among others, have been considered. In this study, we characterize the bacterial symbiont of Heterorbabditis sonorensis, a recently discovered entomopathogenic nematode species form the Sonoran desert in Arizona, USA. A selection of classic biochemical and molecular methods including sequence data of six genes: 16s rDNA, and four protein coding genes: gyrB, recA, gltX, and dnaN were considered. Evolutionary relationships of this new Photorhabdus subsp. were inferred considering maximum parsimony and Bayesian analyses.     

Comparative anatomy of the heart–glomerulus complex of Cephalodiscus gracilis (Pterobranchia): structure,function, and phylogenetic implications

Cephalodiscus gracilis Harmer, 1905 is a semi-sessile deuterostome that shares with fish-like chordates pharyngeal gill slits and a dorsally situated brain. In order to reveal structures potentially homologous among deuterostomes and to infer their functional roles, we investigated the axial complex, associated blood vessels and structures of C. gracilis using transmission electron microscopy, light microscopy, and digital 3D reconstructions. We describe the smooth, bipartite cephalic shield retractor muscles that originate as solid compact muscles and fan out to traverse the protocoel as individual muscle cells. The axial complex consists of a cap-shaped coelomic sac, the pericardium that surrounds the central heart. The pericardium is constituted of myoepithelial cells, with the cells facing the heart being thicker and richer in myofilaments. A prominent dorsal median blood vessel opens into the heart, which gives rise to a short median ventral vessel that opens into the paired glomeruli connected to the ventral side of the stomochord. The tip of the curved stomochord rests precisely above the connection of the dorsal median vessel with the heart, a position that would allow the stomochord to function as a valve facilitating unidirectional blood flow. Glomeruli are lined by podocytes of the spacious protocoel and are considered to be the site of ultrafiltration. Two pairs of blood vessels enter the median dorsal blood vessel from the tentacles. The median dorsal blood vessel is separated from the brain by a thin basement membrane. This arrangement is consistent with the hypothesis that blood vessels in the tentacles increase oxygen supply for the brain. Based on detailed similarities, the heart–glomerulus complex of C. gracilis is considered homologous with the heart–glomerulus complex in Rhabdopleura spp., and Enteropneusta, and the axial complex in Echinodermata. In addition, we hypothesize homology to the excretory complex including Hatschek’s nephridium in Cephalochordata. Thus, the heart–glomerulus complex does not support a sister-group relationship between Echinodermata and Hemichordata, whereas the organization of the cephalic shield retractor muscles is consistent with the evolution of pterobranchs within enteropneusts.     

An ‘open’ structure of the RecOR complex supports ssDNA binding within the core of the complex

Efficient DNA repair is critical for cell survival and the maintenance of genome integrity. The homologous recombination pathway is responsible for the repair of DNA double-strand breaks within cells. Initiation of this pathway in bacteria can be carried out by either the RecBCD or the RecFOR proteins. An important regulatory player within the RecFOR pathway is the RecOR complex that facilitates RecA loading onto DNA. Here we report new data regarding the assembly of Deinococcus radiodurans RecOR and its interaction with DNA, providing novel mechanistic insight into the mode of action of RecOR in homologous recombination. We present a higher resolution crystal structure of RecOR in an ‘open’ conformation in which the tetrameric RecR ring flanked by two RecO molecules is accessible for DNA binding. We show using small-angle neutron scattering and mutagenesis studies that DNA binding does indeed occur within the RecR ring. Binding of single-stranded DNA occurs without any major conformational changes of the RecOR complex while structural rearrangements are observed on double-stranded DNA binding. Finally, our molecular dynamics simulations, supported by our biochemical data, provide a detailed picture of the DNA binding motif of RecOR and reveal that single-stranded DNA is sandwiched between the two facing oligonucleotide binding domains of RecO within the RecR ring.     

(Multiple) Isotope probing approaches to trace the fate of environmental chemicals and the formation of non-extractable ‘bound’ residues

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Tissue engineering: Dentin – pulp complex regeneration approaches (A review)

Dental pulp is a highly specialized tissue that preserves teeth. It is important to maintain the capabilities of dental pulp before a pulpectomy by creating a local restoration of the dentin-pulp complex from residual dental pulp. The articles identified were selected by two reviewers based on entry and exit criteria. All relevant articles indexed in PubMed, Springer, Science Direct, and Scopus with no limitations from 1961 to 2016 were searched. Factors investigated in the selected articles included the following key words: Dentin-Pulp Complex, Regeneration, Tissue Engineering, Scaffold, Stem Cell, and Growth Factors. Of the 233 abstracts retrieved, the papers which were selected had evaluated the clinical aspects of the application of dentin-pulp regeneration. Generally, this study has introduced a new approach to provoke the regeneration of the dentin-pulp complex after a pulpectomy, so that exogenous growth factors and the scaffold are able to induce cells and blood vessels from the residual dental pulp in the tooth root canal. This study further presents a new strategy for local regeneration therapy of the dentin-pulp complex. This review summarizes the current knowledge of the potential beneficial effects derived from the interaction of dental materials with the dentin-pulp complex as well as potential future developments in this exciting field.     

Mandibular remains of Procardiomys martinoi Pascual, 1961 (Hystricognathi,Cavioidea) from the Arroyo Chasicó Formation (early late Miocene) of Argentina: anatomy and the phylogenetic position of the genus within Caviidae

Hydrochoerinae is a clade of caviomorph rodents broadly distributed in South America, which includes the maximum body size recorded among extant rodent taxa. The most basal forms of this group are an assemblage of small to medium body size extinct taxa with a plesiomorphic dentition, traditionally clustered in the group cardiomyines. One of the oldest known cardiomyine is Procardiomys martinoi (Chasicoan South American Land Mammal Age SALMA; early late Miocene), which was known only from the holotype, a fragmentary palate with the left and right molar series. New mandibular remains from the Arroyo Chasicó Formation (Chasicoan SALMA) are described and identified here as belonging to P. martinoi because they share a unique combination of characters (as well matching in size) with the upper dentition of the holotype. These materials help in critically reviewing the taxonomic identification of the mandibular remains previously assigned to Procardiomys and allow testing the phylogenetic affinities of this taxon within Caviidae. P. martinoi is depicted as one of the most basal forms of Hydrochoerinae, placed basally on the lineage leading to extant capybaras after the split between the common ancestor of Kerodon and Hydrochoerus.

http://zoobank.org/F60356E0-CB8E-48C2-BF86-429E347A9579     

Distribution of NRPS gene families within the Neotyphodium/Epichloë complex

Neotyphodium and Epichloë spp are closely related asexual and sexual endophytic fungi, respectively, that form mutualistic associations with cool season grasses of the subfamily Pooideae. The endophytes confer a number of advantages to their hosts, but also can cause animal toxicoses and these effects are, in many cases, due to the production of fungal secondary metabolites. In filamentous fungi, secondary metabolite genes are commonly clustered and, for those pathways involved in non-ribosomal peptide synthesis, a non-ribosomal peptide synthetase (NRPS) gene is always found as a key component of the cluster. Members of this gene family encode large multifunctional enzymes that synthesize a diverse range of bioactive compounds and in numerous cases have been shown to serve as pathogenicity or virulence factors, in addition to suggested roles in niche adaptation. We have used a degenerate PCR approach to identify members of the NRPS gene family from symbiotic fungi of the Neotyphodium/Epichloë complex, and have shown that collectively, at least 12 NRPS genes exist within the genomes examined. This suggests that secondary metabolites are important during the life cycles of these fungi with their hosts. Indeed, both the ergovaline and peramine biosynthetic pathways, which confer competitive abilities to Neotyphodium and Epichloë symbioses, contain NRPS genes at their core. The distribution of these genes among different Neotyphodium/Epichloë lineages suggests that a common ancestor contributed most of the complement of NRPS genes, which have been either retained or lost during the evolution of these fungi.     

The α2(XI) collagen gene lies within 8 kb of Pb in the proximal portion of the murine major histocompatibility complex

A number of serious hereditary disorders are now known to be associated with defective expression of collagen genes, and these findings have underscored the important and varied roles that the collagen family of genes must play during normal mammalian development. Although the activities of genes encoding the quantitatively major types of collagen are fairly well characterized, functions of the many minor types of collagen remain a matter of speculation. As a first step toward a functional analysis of type XI collagen, a member of this class of poorly understand minor collagen proteins which is expressed primarily in hyaline cartilage, we have used human probes for the gene encoding the protein's 2-subunit (COL11A2) to isolate and map homologous murine DNA sequences. Our results demonstrate that Col11a-2 is embedded within the major histocompatibility complex (MHC), within 8.4 kb of the class II pseudogene locus, Pb, and confirm that human and murine 2(XI) collagen genes are located in very similar genomic environments. The conserved location of these genes raises the possibility that type XI collagen genes may contribute to one or more of the diverse hereditary disorders known to be linked to the MHC in mouse and human.     

Len Muscatine (1932–2007) and his contributions to the understanding of algal-invertebrate endosymbiosis

The late Leonard (Len) Muscatine (1932–2007) played a key role in the development of the understanding of algal-invertebrate symbioses. For over 40 years (1958–2005), Professor Muscatine was an inspirational mentor and leader in this field, guiding both the ideas and lives of generations of scientists, many of whom are still active in this research area. His scientific contributions were instrumental in crafting the understanding of a fundamentally important part of our world; that of endosymbiosis, where two or more independent organisms live together in a cellular harmony that belies a complex set of molecular and evolutionary interactions. Muscatine’s research career was defined by investigations aimed at unraveling these interactions, particularly the specificity, metabolism, regulation, and disintegration of algal-invertebrate symbiosis. His gentle interrogation of his students and colleagues as to “What is the question?” led more than often to the focused research that yielded the insightful answers that still resonate today as the most current in the field.     

Interactions of quinone with the iron-sulfur protein of the bc(1) complex: is the mechanism spring-loaded?

Since available structures of native bc(1) complexes show a vacant Q(o)-site, occupancy by substrate and product must be investigated by kinetic and spectroscopic approaches. In this brief review, we discuss recent advances using these approaches that throw new light on the mechanism. The rate-limiting reaction is the first electron transfer after formation of the enzyme-substrate complex at the Q(o)-site. This is formed by binding of both ubiquinol (QH(2)) and the dissociated oxidized iron-sulfur protein (ISP(ox)). A binding constant of approximately 14 can be estimated from the displacement of E(m) or pK for quinone or ISP(ox), respectively. The binding likely involves a hydrogen bond, through which a proton-coupled electron transfer occurs. An enzyme-product complex is also formed at the Q(o)-site, in which ubiquinone (Q) hydrogen bonds with the reduced ISP (ISPH). The complex has been characterized in ESEEM experiments, which detect a histidine ligand, likely His-161 of ISP (in mitochondrial numbering), with a configuration similar to that in the complex of ISPH with stigmatellin. This special configuration is lost on binding of myxothiazol. Formation of the H-bond has been explored through the redox dependence of cytochrome c oxidation. We confirm previous reports of a decrease in E(m) of ISP on addition of myxothiazol, and show that this change can be detected kinetically. We suggest that the myxothiazol-induced change reflects loss of the interaction of ISPH with Q, and that the change in E(m) reflects a binding constant of approximately 4. We discuss previous data in the light of this new hypothesis, and suggest that the native structure might involve a less than optimal configuration that lowers the binding energy of complexes formed at the Q(o)-site so as to favor dissociation. We also discuss recent results from studies of the bypass reactions at the site, which lead to superoxide (SO) production under aerobic conditions, and provide additional information about intermediate states.     

Cryptic species and systematics of the hynobiid salamanders of the Liua–Pseudohynobius complex: Molecular and phylogenetic perspectives

Using mitochondrial DNA sequencing and allozyme electrophoresis, we examined 18 populations of the Liua–Pseudohynobius complex, endemic to China. Based on their phylogenetic affiliation and exhibited fixed allelic differences, the complex comprises at least six species, two of which are previously unknown cryptic species. The complex is clearly divided into two groups, genus Liua including Liua shihi and Liua tsinpaensis, and genus Pseudohynobius including Pseudohynobius flavomaculatus, Pseudohynobius shuichengensis and the two new species. The previously often used genus name Ranodon is inappropriate, because the type species of the genus, Ranodon sibricus, is distantly related to this complex. The species diversity among Chinese hynobiid salamanders are far from being recognized and further effort should be directed at extensive field collection in central and western China.     

The complete mitochondrial genomes of two octopods of the eastern Pacific Ocean: Octopus mimus and ‘Octopus’ fitchi (Cephalopoda: Octopodidae) and their phylogenetic position within Octopoda

Molecular Biology Reports - The complete mitochondrial genomes of two important octopus species from the eastern Pacific were sequenced, obtaining their complete nucleotide sequences. Octopus mimus...     

Plicatamide: A lead to the biosynthetic origins of the tunichromes?

Plicatamide is a modified octapeptide from the ascidian Styela plicata having the structure Phe-Phe-His-Leu-His-Phe-His-decarboxyDeltaDOPA (where decarboxyDeltaDOPA = decarboxy-(E)-alpha,beta-dehydro-3, 4-dihydroxyphenylalanine). Edman sequencing, tandem mass spectrometry, and proton NMR have been used to characterize 100 microg of the compound. Plicatamide represents an important link between two classes of biomolecules: the tunichromes which share an oxidatively decarboxylated C-terminus and higher molecular weight DOPA-polypeptides. The 8-residue sequence provides the first opportunity to investigate the biosynthetic origins of the tunichrome family by molecular biological techniques.     

Detection of a restriction site polymorphism within the human α-globin gene complex

Summary A mutant RsaI restriction endonuclease site of high frequency has been identified in individuals of German, Greek, Italian, and Turkish origin. The mutation was found within the -globin gene complex and is located 0.7 kb 5 to the -globin gene. In individuals of central European origin 34 out of 58 chromosomes exhibited the -gene linkage to the presence of the polymorphic site, and thus a preliminary estimate of the gene frequency for this allele would be 0.59. DNA analysis data of individuals derived from Mediterranean populations indicate a distribution of this polymorphic marker in similar frequencies.     

Mitochondria: One of the origins for autophagosomal membranes?

Macroautophagy is a transport pathway to the lysosome/vacuole that contributes to the degradation of numerous intracellular components. Despite the recent advances achieved in the understanding of the molecular mechanism underlying macroautophagy, the membrane origin of autophagosomes, the hallmark of this process is still a mystery. It has been suggested that mitochondria may be one of the lipid sources for autophagosome formation and that possibly this organelle provides the phosphatidylethanolamine (PE) that covalently links to the members of the ubiquitin-like Atg8/microtubule-associated protein 1 light chain 3 (LC3) protein family. These lipidated proteins are inserted into the outer and inner surface of autophagosomes and are essential for the biogenesis of these large double-membrane vesicles. However, because PE is an integral component of all cellular membranes, designing appropriate experiments to determine the origin of the autophagosomal PE is not easy. In this review, we discuss the idea that mitochondria provide the pool of PE necessary for the autophagosome biogenesis and we propose some possible experimental approaches aimed to explore this possibility.     

Astyanax hastatus Myers, 1928 (Teleostei,Characidae): A new species complex within the genus Astyanax?

Four populations of Astyanax hastatus Myers 1928 from the Guapimirim River basin (Rio de Janeiro State) were analyzed and three distinct cytotypes identified. These cytotypes presented 2n = 50 chromosomes, with 4M+8SM+10ST+28A (Cytotype A), 8M+10SM+14ST+18A (Cytotype B), 6M+8SM+4ST+32A (Cytotype C) and scanty heterochromatin, mainly located throughout pericentromeric regions of several chromosomal pairs. No homologies with the As-51 satellite DNA were observed in the three cytotypes, although all of them presented multiple 18S rDNA sites, as detected by both silver nitrate staining and FISH (fluorescent in situ hybridization). The application of the term "species complex" in Astyanax is discussed from a cytotaxonomic viewpoint.     

Ultrastructure of the stomochord and the heart–glomerulus complex in<Emphasis Type="Italic"> Rhabdopleura compacta</Emphasis> (Pterobranchia): phylogenetic implications

Pterobranchia and Enteropneusta traditionally form the highest ranking sister taxa within the Hemichordata. The most prominent feature of all representatives of the Hemichordata is the stomochord, which is associated with an anterior excretory complex. The stomochord has been homologized with the notochord of the Chordata species, though this hypothesis is still under debate. Recently, even the validity and position of the Pterobranchia and the Hemichordata has been doubted. These uncertainties are along with a lack of information on the Rhabdopleurida, one of the highest ranking taxa within the Pterobranchia. This study analyzes the stomochord and the heart–glomerulus complex of Rhabdopleura compacta on the ultrastructural level. The data confirm that a glomerulus exists in representatives of the Rhabdopleurida, which previously was only known from the Cephalodiscida, the second highest ranking Pterobranchia taxon. The heart–glomerulus complex is, as expected, associated with the stomochord. Consisting of monociliated, non-vacuolated cells that form a monolayered epithelium of presumed ectodermal origin in R. compacta, the stomochord belongs to the ground pattern of the Pterobranchia and Enteropneusta. Information that would support a homology hypothesis of the chordate notochord and the hemichordate stomochord was not found. Furthermore, there is some evidence that the stomochord might represent a glandular organ. Thus, differences concerning the possible ontogenetic origin, morphology, and function are assumed to result from an independent evolution of the stomochord and the notochord.